Flickering LED supply

T

Tough Guy no. 1265

Guest
https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week it began flickering badly. 240V AC in on the right. The circuit outputs 75V DC on the left, with a 3.5V AC ripple on it (with the 100uF capacitor included, which I verified is ok). With a 680uF capacitor in its place, there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger capacitor?
 
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com> wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week it began flickering badly. 240V AC in on the right. The circuit outputs 75V DC on the left, with a 3.5V AC ripple on it (with the 100uF capacitor included, which I verified is ok). With a 680uF capacitor in its place, there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger capacitor?
Click to expand...

Forgot to add, I checked the voltage and current output with the larger capacitor, and it was virtually identical.
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week it
began flickering badly. 240V AC in on the right. The circuit outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF capacitor
included, which I verified is ok). With a 680uF capacitor in its place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger capacitor?

Forgot to add, I checked the voltage and current output with the larger
capacitor, and it was virtually identical.
Click to expand...

When you first switch on, the fully discharged capacitor looks like a dead
short for the split second it takes to charge up. The bigger capacitor will
cause the turn on surge to last nearly 7x longer.

If the circuit has a NTC thermistor inrush limiter, you're probably OK.
I usually look for them in any equipment I scrap, when I still used filament
bulbs - one of those added behind the switch plate makes the bulb last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm diameter, they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

Cut a track in the AC live side and bridge it with the thermistor.

If the donor equipment also includes an MOV surge arrestor, that's also
worth adding to your kit.

Similar physical description, but they're usually beige colour or black and
most often shiny.

Its easy to tell the difference - the NTC will show continuity at low
voltage, the MOV should stand normal mains without conducting.
 
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week it
began flickering badly. 240V AC in on the right. The circuit outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF capacitor
included, which I verified is ok). With a 680uF capacitor in its place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger capacitor?

Forgot to add, I checked the voltage and current output with the larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a dead
short for the split second it takes to charge up. The bigger capacitor will
cause the turn on surge to last nearly 7x longer.
Click to expand...

The LEDs light up very slowly with the bigger capacitor (for half to one second perhaps), so I think it's being limited. Also, when I turn it off, won't the capacitor stay charged to the voltage just below what's required to make the LEDs conduct, so it's not going to be empty at the next startup?

If the circuit has a NTC thermistor inrush limiter, you're probably OK.
I usually look for them in any equipment I scrap, when I still used filament
bulbs - one of those added behind the switch plate makes the bulb last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm diameter, they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.
Click to expand...

I can't see one. There's a resistor connected directly to neutral on the bottom right of the photo. In series with that resistor are the two capacitors (blue and yellow), going across to live. Connected across those two capacitors is the input to the bridge rectifier made up of four diodes (under the blue capacitor). The red capacitor is across the output of the bridge. I can't easily make out what's connected to what for the rest of it, but there's a microchip, and the current going to the LEDs is very constant no matter what capacitor I put on it, so I'm guessing good regulation. These are also the only LEDs I've ever bought which stay the same brightness when I change the input mains voltage by 20 volts (which is what my UPS does when the voltage reaches 250 - I've got a very crap mains supply here since they changed the substation and they won't do anything about it as it's "within legal parameters", so my lighting circuit goes though the UPS).

Cut a track in the AC live side and bridge it with the thermistor.

If the donor equipment also includes an MOV surge arrestor, that's also
worth adding to your kit.

Similar physical description, but they're usually beige colour or black and
most often shiny.

Its easy to tell the difference - the NTC will show continuity at low
voltage, the MOV should stand normal mains without conducting.
Click to expand...

--
Women do not snore, burp, sweat, or fart.
Therefore, they must "bitch" or they will blow up.
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week it
began flickering badly. 240V AC in on the right. The circuit outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger capacitor?

Forgot to add, I checked the voltage and current output with the larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a
dead
short for the split second it takes to charge up. The bigger capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to one
second perhaps), so I think it's being limited. Also, when I turn it off,
won't the capacitor stay charged to the voltage just below what's required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm diameter,
they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral on the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.
Click to expand...

Post a photo.
 
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week it
began flickering badly. 240V AC in on the right. The circuit outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger capacitor?

Forgot to add, I checked the voltage and current output with the larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a
dead
short for the split second it takes to charge up. The bigger capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to one
second perhaps), so I think it's being limited. Also, when I turn it off,
won't the capacitor stay charged to the voltage just below what's required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm diameter,
they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral on the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.
Click to expand...

The link is at the top of this post, you must have missed it.

--
What comes after 69?
Mouthwash.
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a
dead
short for the split second it takes to charge up. The bigger capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to one
second perhaps), so I think it's being limited. Also, when I turn it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm diameter,
they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral on
the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.
Click to expand...

Can't see anything that looks like an NTC, or a MOV, adding them wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing anything to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU circuit
would try to even out the voltage regardless - if it has overcurrent trip;
too big a capacitor would keep tripping it every time it started up again.
But it might eventually get going.
 
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1 week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a
dead
short for the split second it takes to charge up. The bigger capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to one
second perhaps), so I think it's being limited. Also, when I turn it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm diameter,
they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral on
the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing anything to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU circuit
would try to even out the voltage regardless - if it has overcurrent trip;
too big a capacitor would keep tripping it every time it started up again.
But it might eventually get going.
Click to expand...

It appears to be current limited. It takes some time to charge the larger capacitor. The LEDs gradually brighten.

--
ADULT: A person who has stopped growing at both ends and is now growing in the middle.
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1
week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to
one
second perhaps), so I think it's being limited. Also, when I turn it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably
OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral on
the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing anything to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the larger
capacitor. The LEDs gradually brighten.
Click to expand...

A constant voltage supply driving LEDs would let the magic smoke out.
 
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265 <no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1
week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to
one
second perhaps), so I think it's being limited. Also, when I turn it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably
OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as compared to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral on
the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing anything to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.
Click to expand...

Well most of the LED lamps I've got change brightness depending on the mains voltage. So they can't be that constant current. Maybe they just have a voltage as a fraction of the mains, then rely on a resistor to limit the current?

--
Why didn't Noah swat those two mosquitoes?
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1
week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to
one
second perhaps), so I think it's being limited. Also, when I turn
it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably
OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral
on
the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing anything
to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.

Well most of the LED lamps I've got change brightness depending on the
mains voltage. So they can't be that constant current. Maybe they just
have a voltage as a fraction of the mains, then rely on a resistor to
limit the current?
Click to expand...

I bought various LED lamps from a discount store just to crack open and see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a single
1.5V cell called a "Joule thief" its basically a flyback converter with no
regulation, but the LED only conducts on the flyback peaks so there is a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in series
with the mains so capacitive reactance is large compared to the dynamic
resistance of the LED load, with large Xc, current doesn't change much with
varying mains - some commercial LED bulbs use it.
 
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1
week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half to
one
second perhaps), so I think it's being limited. Also, when I turn
it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the next
startup?

If the circuit has a NTC thermistor inrush limiter, you're probably
OK.
I usually look for them in any equipment I scrap, when I still used
filament
bulbs - one of those added behind the switch plate makes the bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral
on
the
bottom right of the photo. In series with that resistor are the two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing anything
to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.

Well most of the LED lamps I've got change brightness depending on the
mains voltage. So they can't be that constant current. Maybe they just
have a voltage as a fraction of the mains, then rely on a resistor to
limit the current?

I bought various LED lamps from a discount store just to crack open and see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a single
1.5V cell called a "Joule thief" its basically a flyback converter with no
regulation, but the LED only conducts on the flyback peaks so there is a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in series
with the mains so capacitive reactance is large compared to the dynamic
resistance of the LED load, with large Xc, current doesn't change much with
varying mains - some commercial LED bulbs use it.
Click to expand...

I was going to make something using a wattless dropper once. I think it was just to power an indicator LED from 240VAC instead of fitting a neon. Something made me decide it wasn't as good as it was made out to be.

--
Arriving home unexpectedly early from a business trip, the tired executive was shocked to discover his wife in bed with his next door neighbour.
"Since you are in bed with my wife," the furious man shouted, "I'm going over to sleep with yours!"
"Go right ahead," was the reply. "The rest will do you good."
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1
week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks
like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half
to
one
second perhaps), so I think it's being limited. Also, when I turn
it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I still
used
filament
bulbs - one of those added behind the switch plate makes the bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral
on
the
bottom right of the photo. In series with that resistor are the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.

Well most of the LED lamps I've got change brightness depending on the
mains voltage. So they can't be that constant current. Maybe they just
have a voltage as a fraction of the mains, then rely on a resistor to
limit the current?

I bought various LED lamps from a discount store just to crack open and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a
single
1.5V cell called a "Joule thief" its basically a flyback converter with
no
regulation, but the LED only conducts on the flyback peaks so there is a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in series
with the mains so capacitive reactance is large compared to the dynamic
resistance of the LED load, with large Xc, current doesn't change much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I think it
was just to power an indicator LED from 240VAC instead of fitting a neon.
Something made me decide it wasn't as good as it was made out to be.
Click to expand...

You have to include a resistor in series, the current peaks during the
highest rate of change of the voltage waveform. Any spikes on the mains need
to be attenuated too.
 
On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After 1
week
it
began flickering badly. 240V AC in on the right. The circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the 100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks
like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for half
to
one
second perhaps), so I think it's being limited. Also, when I turn
it
off,
won't the capacitor stay charged to the voltage just below what's
required
to make the LEDs conduct, so it's not going to be empty at the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I still
used
filament
bulbs - one of those added behind the switch plate makes the bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to neutral
on
the
bottom right of the photo. In series with that resistor are the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.

Well most of the LED lamps I've got change brightness depending on the
mains voltage. So they can't be that constant current. Maybe they just
have a voltage as a fraction of the mains, then rely on a resistor to
limit the current?

I bought various LED lamps from a discount store just to crack open and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a
single
1.5V cell called a "Joule thief" its basically a flyback converter with
no
regulation, but the LED only conducts on the flyback peaks so there is a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in series
with the mains so capacitive reactance is large compared to the dynamic
resistance of the LED load, with large Xc, current doesn't change much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I think it
was just to power an indicator LED from 240VAC instead of fitting a neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during the
highest rate of change of the voltage waveform. Any spikes on the mains need
to be attenuated too.
Click to expand...

I probably gave up on the idea because of how much limiting resistor I'd still need, and decided a neon would use no more power, although would eventually expire.

--
Isn't it a bit unnerving that doctors call what they do "practice?"
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7caf7itcpfvgl@red.lan...
On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After
1
week
it
began flickering badly. 240V AC in on the right. The
circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the
100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with
the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks
like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for
half
to
one
second perhaps), so I think it's being limited. Also, when I
turn
it
off,
won't the capacitor stay charged to the voltage just below
what's
required
to make the LEDs conduct, so it's not going to be empty at the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I still
used
filament
bulbs - one of those added behind the switch plate makes the
bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as
compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to
neutral
on
the
bottom right of the photo. In series with that resistor are the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the
bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has
overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.

Well most of the LED lamps I've got change brightness depending on the
mains voltage. So they can't be that constant current. Maybe they
just
have a voltage as a fraction of the mains, then rely on a resistor to
limit the current?

I bought various LED lamps from a discount store just to crack open and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a
single
1.5V cell called a "Joule thief" its basically a flyback converter with
no
regulation, but the LED only conducts on the flyback peaks so there is
a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in
series
with the mains so capacitive reactance is large compared to the dynamic
resistance of the LED load, with large Xc, current doesn't change much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I think it
was just to power an indicator LED from 240VAC instead of fitting a
neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during the
highest rate of change of the voltage waveform. Any spikes on the mains
need
to be attenuated too.

I probably gave up on the idea because of how much limiting resistor I'd
still need, and decided a neon would use no more power, although would
eventually expire.
Click to expand...

The only neons I've ever seen expire, was ones I was experimenting on.
 
On Fri, 30 Oct 2015 22:10:47 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7caf7itcpfvgl@red.lan...
On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs. After
1
week
it
began flickering badly. 240V AC in on the right. The
circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the
100uF
capacitor
included, which I verified is ok). With a 680uF capacitor in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the larger
capacitor?

Forgot to add, I checked the voltage and current output with
the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor looks
like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for
half
to
one
second perhaps), so I think it's being limited. Also, when I
turn
it
off,
won't the capacitor stay charged to the voltage just below
what's
required
to make the LEDs conduct, so it's not going to be empty at the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I still
used
filament
bulbs - one of those added behind the switch plate makes the
bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as
compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to
neutral
on
the
bottom right of the photo. In series with that resistor are the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the
bridge
rectifier.

If the electrolytic capacitor on the left was too small, the SMPSU
circuit
would try to even out the voltage regardless - if it has
overcurrent
trip;
too big a capacitor would keep tripping it every time it started up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke out.

Well most of the LED lamps I've got change brightness depending on the
mains voltage. So they can't be that constant current. Maybe they
just
have a voltage as a fraction of the mains, then rely on a resistor to
limit the current?

I bought various LED lamps from a discount store just to crack open and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a
single
1.5V cell called a "Joule thief" its basically a flyback converter with
no
regulation, but the LED only conducts on the flyback peaks so there is
a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in
series
with the mains so capacitive reactance is large compared to the dynamic
resistance of the LED load, with large Xc, current doesn't change much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I think it
was just to power an indicator LED from 240VAC instead of fitting a
neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during the
highest rate of change of the voltage waveform. Any spikes on the mains
need
to be attenuated too.

I probably gave up on the idea because of how much limiting resistor I'd
still need, and decided a neon would use no more power, although would
eventually expire.

The only neons I've ever seen expire, was ones I was experimenting on.
Click to expand...

You know those big old cooker switches with a socket on them, both with a neon? My parents' left the cooker switch on all the time. The neon got dimmer and flickerier over time.

--
I had some words with my wife, and she had some paragraphs with me.
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7cbnpf9cpfvgl@red.lan...
On Fri, 30 Oct 2015 22:10:47 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7caf7itcpfvgl@red.lan...
On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs.
After
1
week
it
began flickering badly. 240V AC in on the right. The
circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the
100uF
capacitor
included, which I verified is ok). With a 680uF capacitor
in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the
larger
capacitor?

Forgot to add, I checked the voltage and current output with
the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor
looks
like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for
half
to
one
second perhaps), so I think it's being limited. Also, when I
turn
it
off,
won't the capacitor stay charged to the voltage just below
what's
required
to make the LEDs conduct, so it's not going to be empty at the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I
still
used
filament
bulbs - one of those added behind the switch plate makes the
bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as
compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to
neutral
on
the
bottom right of the photo. In series with that resistor are
the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the
bridge
rectifier.

If the electrolytic capacitor on the left was too small, the
SMPSU
circuit
would try to even out the voltage regardless - if it has
overcurrent
trip;
too big a capacitor would keep tripping it every time it started
up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge
the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke
out.

Well most of the LED lamps I've got change brightness depending on
the
mains voltage. So they can't be that constant current. Maybe they
just
have a voltage as a fraction of the mains, then rely on a resistor
to
limit the current?

I bought various LED lamps from a discount store just to crack open
and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a
single
1.5V cell called a "Joule thief" its basically a flyback converter
with
no
regulation, but the LED only conducts on the flyback peaks so there
is
a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in
series
with the mains so capacitive reactance is large compared to the
dynamic
resistance of the LED load, with large Xc, current doesn't change
much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I think
it
was just to power an indicator LED from 240VAC instead of fitting a
neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during the
highest rate of change of the voltage waveform. Any spikes on the mains
need
to be attenuated too.

I probably gave up on the idea because of how much limiting resistor I'd
still need, and decided a neon would use no more power, although would
eventually expire.

The only neons I've ever seen expire, was ones I was experimenting on.

You know those big old cooker switches with a socket on them, both with a
neon? My parents' left the cooker switch on all the time. The neon got
dimmer and flickerier over time.
Click to expand...

It just occurred to me; that electrolytic capacitor on the end of the board
may not be such a good idea!

Depending on how it regulates current and exactly where the capacitor is
connected, if you get an intermittent connection to the LEDs, the capacitor
ceases to be clamped and the voltage rises - discharge that into the LEDs
and you've got a problem.

The SMPSU section should be running at least 15kHz, so flicker would be due
to something on the primary side. If you needed any smoothing for the LEDs,
about 0.22uF or 0.47uF would be sufficient.

With a typical 20W CFL, the mains rectifier reservoir capacitor can be as
small as 4.7uF - its not that difficult to find non-electrolytic types with
adequate voltage rating, a few manufacturers do that because electrolytics
are a reliability black-spot.
 
On Sat, 31 Oct 2015 18:14:15 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7cbnpf9cpfvgl@red.lan...
On Fri, 30 Oct 2015 22:10:47 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7caf7itcpfvgl@red.lan...
On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs.
After
1
week
it
began flickering badly. 240V AC in on the right. The
circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the
100uF
capacitor
included, which I verified is ok). With a 680uF capacitor
in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the
larger
capacitor?

Forgot to add, I checked the voltage and current output with
the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor
looks
like
a
dead
short for the split second it takes to charge up. The bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for
half
to
one
second perhaps), so I think it's being limited. Also, when I
turn
it
off,
won't the capacitor stay charged to the voltage just below
what's
required
to make the LEDs conduct, so it's not going to be empty at the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I
still
used
filament
bulbs - one of those added behind the switch plate makes the
bulb
last
years.

They look similar to a disc ceramic capacitor about 10 - 15mm
diameter,
they
tend to be dull green or black and have a matt finish as
compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to
neutral
on
the
bottom right of the photo. In series with that resistor are
the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the
bridge
rectifier.

If the electrolytic capacitor on the left was too small, the
SMPSU
circuit
would try to even out the voltage regardless - if it has
overcurrent
trip;
too big a capacitor would keep tripping it every time it started
up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge
the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke
out.

Well most of the LED lamps I've got change brightness depending on
the
mains voltage. So they can't be that constant current. Maybe they
just
have a voltage as a fraction of the mains, then rely on a resistor
to
limit the current?

I bought various LED lamps from a discount store just to crack open
and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires, I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from a
single
1.5V cell called a "Joule thief" its basically a flyback converter
with
no
regulation, but the LED only conducts on the flyback peaks so there
is
a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in
series
with the mains so capacitive reactance is large compared to the
dynamic
resistance of the LED load, with large Xc, current doesn't change
much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I think
it
was just to power an indicator LED from 240VAC instead of fitting a
neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during the
highest rate of change of the voltage waveform. Any spikes on the mains
need
to be attenuated too.

I probably gave up on the idea because of how much limiting resistor I'd
still need, and decided a neon would use no more power, although would
eventually expire.

The only neons I've ever seen expire, was ones I was experimenting on.

You know those big old cooker switches with a socket on them, both with a
neon? My parents' left the cooker switch on all the time. The neon got
dimmer and flickerier over time.

It just occurred to me; that electrolytic capacitor on the end of the board
may not be such a good idea!

Depending on how it regulates current and exactly where the capacitor is
connected, if you get an intermittent connection to the LEDs, the capacitor
ceases to be clamped and the voltage rises - discharge that into the LEDs
and you've got a problem.
Click to expand...

I don't foresee an intermittent connection to the LEDs. The original capacitor is connected on the circuit board across the wires which lead to the LEDs. My bigger one will be external to the unit as it's physically larger, and most easily connected at the other end of the LED strip (which has soldering points at both ends for + and -_.

The SMPSU section should be running at least 15kHz, so flicker would be due
to something on the primary side.
Click to expand...

The flicker is about 25Hz at a guess. Or maybe 50. Perhaps the full wave rectification is broken and it's getting half wave?

If you needed any smoothing for the LEDs,
about 0.22uF or 0.47uF would be sufficient.
Click to expand...

Well they used 100uF. And I need 680uF to smooth it with the unknown fault.

With a typical 20W CFL, the mains rectifier reservoir capacitor can be as
small as 4.7uF - its not that difficult to find non-electrolytic types with
adequate voltage rating, a few manufacturers do that because electrolytics
are a reliability black-spot.
Click to expand...

I rarely find broken electrolytics unless there's a design flaw and they were too hot.

--
Peter is listening to "Aerosmith - Living on the edge"
 
"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7dvhipwcpfvgl@red.lan...
On Sat, 31 Oct 2015 18:14:15 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7cbnpf9cpfvgl@red.lan...
On Fri, 30 Oct 2015 22:10:47 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7caf7itcpfvgl@red.lan...
On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b8xtyjcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b6clejcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:30:40 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b5hg2jcpfvgl@red.lan...
On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b187f2cpfvgl@red.lan...
On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7b1nus5cpfvgl@red.lan...
On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7bwoyr4cpfvgl@red.lan...
On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs.
After
1
week
it
began flickering badly. 240V AC in on the right. The
circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the
100uF
capacitor
included, which I verified is ok). With a 680uF
capacitor
in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the
larger
capacitor?

Forgot to add, I checked the voltage and current output
with
the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor
looks
like
a
dead
short for the split second it takes to charge up. The
bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for
half
to
one
second perhaps), so I think it's being limited. Also, when
I
turn
it
off,
won't the capacitor stay charged to the voltage just below
what's
required
to make the LEDs conduct, so it's not going to be empty at
the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I
still
used
filament
bulbs - one of those added behind the switch plate makes
the
bulb
last
years.

They look similar to a disc ceramic capacitor about 10 -
15mm
diameter,
they
tend to be dull green or black and have a matt finish as
compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to
neutral
on
the
bottom right of the photo. In series with that resistor are
the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding
them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the
bridge
rectifier.

If the electrolytic capacitor on the left was too small, the
SMPSU
circuit
would try to even out the voltage regardless - if it has
overcurrent
trip;
too big a capacitor would keep tripping it every time it
started
up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge
the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke
out.

Well most of the LED lamps I've got change brightness depending on
the
mains voltage. So they can't be that constant current. Maybe
they
just
have a voltage as a fraction of the mains, then rely on a resistor
to
limit the current?

I bought various LED lamps from a discount store just to crack open
and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires,
I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from
a
single
1.5V cell called a "Joule thief" its basically a flyback converter
with
no
regulation, but the LED only conducts on the flyback peaks so there
is
a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in
series
with the mains so capacitive reactance is large compared to the
dynamic
resistance of the LED load, with large Xc, current doesn't change
much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I
think
it
was just to power an indicator LED from 240VAC instead of fitting a
neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during
the
highest rate of change of the voltage waveform. Any spikes on the
mains
need
to be attenuated too.

I probably gave up on the idea because of how much limiting resistor
I'd
still need, and decided a neon would use no more power, although would
eventually expire.

The only neons I've ever seen expire, was ones I was experimenting on.

You know those big old cooker switches with a socket on them, both with
a
neon? My parents' left the cooker switch on all the time. The neon got
dimmer and flickerier over time.

It just occurred to me; that electrolytic capacitor on the end of the
board
may not be such a good idea!

Depending on how it regulates current and exactly where the capacitor is
connected, if you get an intermittent connection to the LEDs, the
capacitor
ceases to be clamped and the voltage rises - discharge that into the LEDs
and you've got a problem.

I don't foresee an intermittent connection to the LEDs. The original
capacitor is connected on the circuit board across the wires which lead to
the LEDs. My bigger one will be external to the unit as it's physically
larger, and most easily connected at the other end of the LED strip (which
has soldering points at both ends for + and -_.

The SMPSU section should be running at least 15kHz, so flicker would be
due
to something on the primary side.

The flicker is about 25Hz at a guess. Or maybe 50. Perhaps the full wave
rectification is broken and it's getting half wave?

If you needed any smoothing for the LEDs,
about 0.22uF or 0.47uF would be sufficient.

Well they used 100uF. And I need 680uF to smooth it with the unknown
fault.

With a typical 20W CFL, the mains rectifier reservoir capacitor can be as
small as 4.7uF - its not that difficult to find non-electrolytic types
with
adequate voltage rating, a few manufacturers do that because
electrolytics
are a reliability black-spot.

I rarely find broken electrolytics unless there's a design flaw and they
were too hot.
Click to expand...

About a decade ago there was a plague of dodgy electrolytics - mostly on PC
motherboards.

Industrial espionage gone wrong - one firm broke into a competitor's office
and nicked their electrolyte formula, and then found out the formula was
incomplete.

Its the single biggest cause of ATX PSU failures - which may or may not
destroy the MOBO.

I've spent a fair bit of money on capacitor test instruments because
capacitors are responsible for such a large proportion of faults.
 
On Sat, 31 Oct 2015 19:10:36 -0000, Ian Field <gangprobing.alien@ntlworld.com> wrote:

"Tough Guy no. 1265" <no@spam.com> wrote in message
news:eek:p.x7dvhipwcpfvgl@red.lan...
On Sat, 31 Oct 2015 18:14:15 -0000, Ian Field
gangprobing.alien@ntlworld.com> wrote:



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On Fri, 30 Oct 2015 22:10:47 -0000, Ian Field
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On Fri, 30 Oct 2015 21:53:16 -0000, Ian Field
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On Fri, 30 Oct 2015 20:52:55 -0000, Ian Field
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On Fri, 30 Oct 2015 20:06:02 -0000, Ian Field
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On Fri, 30 Oct 2015 19:04:07 -0000, Ian Field
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On Fri, 30 Oct 2015 18:48:26 -0000, Ian Field
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On Fri, 30 Oct 2015 17:10:19 -0000, Tough Guy no. 1265
no@spam.com
wrote:

https://www.dropbox.com/s/fy5xm8lmd3g2vdt/Circuit.jpg?dl=0&s=sl

This supply came with a 2 foot 9W strip light of LEDs.
After
1
week
it
began flickering badly. 240V AC in on the right. The
circuit
outputs
75V DC on the left, with a 3.5V AC ripple on it (with the
100uF
capacitor
included, which I verified is ok). With a 680uF
capacitor
in
its
place,
there is no visible flicker.

What's likely to have broken in this circuit?

What's the chances of it lasting if I run it with the
larger
capacitor?

Forgot to add, I checked the voltage and current output
with
the
larger
capacitor, and it was virtually identical.

When you first switch on, the fully discharged capacitor
looks
like
a
dead
short for the split second it takes to charge up. The
bigger
capacitor
will
cause the turn on surge to last nearly 7x longer.

The LEDs light up very slowly with the bigger capacitor (for
half
to
one
second perhaps), so I think it's being limited. Also, when
I
turn
it
off,
won't the capacitor stay charged to the voltage just below
what's
required
to make the LEDs conduct, so it's not going to be empty at
the
next
startup?

If the circuit has a NTC thermistor inrush limiter, you're
probably
OK.
I usually look for them in any equipment I scrap, when I
still
used
filament
bulbs - one of those added behind the switch plate makes
the
bulb
last
years.

They look similar to a disc ceramic capacitor about 10 -
15mm
diameter,
they
tend to be dull green or black and have a matt finish as
compared
to
capacitors that are usually shiny finish.

I can't see one. There's a resistor connected directly to
neutral
on
the
bottom right of the photo. In series with that resistor are
the
two
capacitors (blue and yellow), going across to live.

Post a photo.

The link is at the top of this post, you must have missed it.

Can't see anything that looks like an NTC, or a MOV, adding
them
wouldn't
hurt.

The NTC can be spliced into the mains live feed without doing
anything
to
the board, the MOV should be added across the AC input to the
bridge
rectifier.

If the electrolytic capacitor on the left was too small, the
SMPSU
circuit
would try to even out the voltage regardless - if it has
overcurrent
trip;
too big a capacitor would keep tripping it every time it
started
up
again.
But it might eventually get going.

It appears to be current limited. It takes some time to charge
the
larger
capacitor. The LEDs gradually brighten.

A constant voltage supply driving LEDs would let the magic smoke
out.

Well most of the LED lamps I've got change brightness depending on
the
mains voltage. So they can't be that constant current. Maybe
they
just
have a voltage as a fraction of the mains, then rely on a resistor
to
limit the current?

I bought various LED lamps from a discount store just to crack open
and
see
what's in them.

One had a 4 terminal component close to the pads for the LED wires,
I
couldn't identify the part but it probably has to do with current
regulation.

Among hobbyists, there is a circuit for powering regular LEDs from
a
single
1.5V cell called a "Joule thief" its basically a flyback converter
with
no
regulation, but the LED only conducts on the flyback peaks so there
is
a
sort of limiting.

Another trick is the so called "wattless dropper" - a capacitor in
series
with the mains so capacitive reactance is large compared to the
dynamic
resistance of the LED load, with large Xc, current doesn't change
much
with
varying mains - some commercial LED bulbs use it.

I was going to make something using a wattless dropper once. I
think
it
was just to power an indicator LED from 240VAC instead of fitting a
neon.
Something made me decide it wasn't as good as it was made out to be.

You have to include a resistor in series, the current peaks during
the
highest rate of change of the voltage waveform. Any spikes on the
mains
need
to be attenuated too.

I probably gave up on the idea because of how much limiting resistor
I'd
still need, and decided a neon would use no more power, although would
eventually expire.

The only neons I've ever seen expire, was ones I was experimenting on.

You know those big old cooker switches with a socket on them, both with
a
neon? My parents' left the cooker switch on all the time. The neon got
dimmer and flickerier over time.

It just occurred to me; that electrolytic capacitor on the end of the
board
may not be such a good idea!

Depending on how it regulates current and exactly where the capacitor is
connected, if you get an intermittent connection to the LEDs, the
capacitor
ceases to be clamped and the voltage rises - discharge that into the LEDs
and you've got a problem.

I don't foresee an intermittent connection to the LEDs. The original
capacitor is connected on the circuit board across the wires which lead to
the LEDs. My bigger one will be external to the unit as it's physically
larger, and most easily connected at the other end of the LED strip (which
has soldering points at both ends for + and -_.

The SMPSU section should be running at least 15kHz, so flicker would be
due
to something on the primary side.

The flicker is about 25Hz at a guess. Or maybe 50. Perhaps the full wave
rectification is broken and it's getting half wave?

If you needed any smoothing for the LEDs,
about 0.22uF or 0.47uF would be sufficient.

Well they used 100uF. And I need 680uF to smooth it with the unknown
fault.

With a typical 20W CFL, the mains rectifier reservoir capacitor can be as
small as 4.7uF - its not that difficult to find non-electrolytic types
with
adequate voltage rating, a few manufacturers do that because
electrolytics
are a reliability black-spot.

I rarely find broken electrolytics unless there's a design flaw and they
were too hot.

About a decade ago there was a plague of dodgy electrolytics - mostly on PC
motherboards.
Click to expand...

You mean the Dell motherboards? Yes, I replaced 150 of those. Some I got a new board under warranty, some I bought 2nd hand on Ebay, then I started replacing the caps and ended up with loads of free boards.

Industrial espionage gone wrong - one firm broke into a competitor's office
and nicked their electrolyte formula, and then found out the formula was
incomplete.

Its the single biggest cause of ATX PSU failures - which may or may not
destroy the MOBO.
Click to expand...

The only failures I've seen with ATX PSUs is when they're overloaded, because cheap ones simply cannot give out more than half the current they're rated at. And it's never the cap, usually several things melt.

> I've spent a fair bit of money on capacitor test instruments because

My multimeter tests up to 20uF.

> capacitors are responsible for such a large proportion of faults.

Aren't broken caps usually vented so obvious to look at?

--
Never have I seen a word as accurate as politics.
Poly meaning many, and tic being a blood-sucking thing.
 
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