Running LED from Mains power

[Charlie+]

Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend for
running a (blue 25 to 40mA) LED at near its maximum output but from mains
power - 230V ac in my case?
Thanks

 

[Tom Biasi]

"Charlie+" <charlie@xxx.net> wrote in message
news1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com...

Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend
for
running a (blue 25 to 40mA) LED at near its maximum output but from mains
power - 230V ac in my case?
Thanks

Problems with AC mains is the voltage varies a lot and spikes are common.

The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

Tom

 

[Charlie+]

On Mon, 13 Jul 2009 05:20:25 -0400, "Tom Biasi" <tombiasi@optonline.net>
wrote as underneath my scribble :

"Charlie+" <charlie@xxx.net> wrote in message
news1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com...
Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend
for
running a (blue 25 to 40mA) LED at near its maximum output but from mains
power - 230V ac in my case?
Thanks

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

Tom
Thanks Tom!

 

[Phil Allison]

"Tom Biasi is a Fuckwit "

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

** The 230 volt version is dangerously bad design.

C1 is not rated for use with continuous, high AC voltage and will soon fail
short and destroy the rest of the circuit.

You are giving razor blades for babies to play with

- you fucking IDIOT !!



....... Phil

 

[Tom Biasi]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:7c0l12F264jgcU1@mid.individual.net...

"Tom Biasi is a Fuckwit "

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm


** The 230 volt version is dangerously bad design.

C1 is not rated for use with continuous, high AC voltage and will soon
fail short and destroy the rest of the circuit.

You are giving razor blades for babies to play with

- you fucking IDIOT !!



...... Phil

Take your medicine.

 

[Phil Allison]

"Tom Biasi is a Fuckwit "

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

** The 230 volt version is dangerously bad design.

C1 is not rated for use with continuous, high AC voltage and will soon fail
short and destroy the rest of the circuit.

You are giving razor blades for babies to play with

- you fucking IDIOT !!

Piss OFF !!!!



....... Phil

 

[Tom Biasi]

"Charlie+" <charlie@xxx.net> wrote in message
news:f37m55p6cv4dc8jp6com8ie16oma481lnm@4ax.com...

On Mon, 13 Jul 2009 05:20:25 -0400, "Tom Biasi" <tombiasi@optonline.net
wrote as underneath my scribble :


"Charlie+" <charlie@xxx.net> wrote in message
news1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com...
Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend
for
running a (blue 25 to 40mA) LED at near its maximum output but from
mains
power - 230V ac in my case?
Thanks

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

Tom
Thanks Tom!

Just wanted you to see how someone else did it.
I like Don's idea about the wall wart.
Some cell phone chargers have smart circuitry, you just want the voltage.

Tom

 

[Don Klipstein]

In article <p1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com>, Charlie+ wrote:

Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend for
running a (blue 25 to 40mA) LED at near its maximum output but from mains
power - 230V ac in my case?

Probably easiest is to use a "wall wart" type power supply, such as a
cellphone charger. Add an appropriate resistor. In my experience,
many modern cellphone chargers are good at minimizing power consumption
when lightly loaded or unloaded, so power consumption may be less than
half a watt.

To run an LED more directly from the mains, feed the LED with the output
of a bridge rectifier, put some impedance in series with one of the AC
leads of the bridge rectifier, then connect the AC.

If this impedance is a resistor, to pass 20 mA average current with
average voltage across it being about 205 volts, the resistance would be
10.2 K-ohms. The nearest common value is 10K ohms.
The RMS voltage across the resistor would be close to 225 volts. (230
minus the voltage drop of the LED ad two diodes in the bridge rectifier)
225 squared divided by 10,000 is 5.06 watts. Given tolerances in LED
voltage drop, resistor value and line voltage, the minimum wattage rating
of the resistor should be 10 watts. Keep in mind that a 10 watt resistor,
even with 5 watts going into it, can get egg-frying hot.

To reduce losses, use a capacitor instead of a resistor. If capacitive
reactance is 10K ohms at 50 Hz, capacitance is 1/ (2 * pi * F * Xc) or
..318 microfarad. The nearest common value is .33 microfarad. The
capacitor needs an actual AC voltage rating of at least 250 volts.

(Capacitors rated 400 or even 600 volts DC but lacking an AC voltage
rating, during prolonged use with AC, are likely to go KABLOOEY. I have
had a few 600 volt capacitors and even an 800 volt capacitor blow up from
use with 240 volts AC during my more reckless youth. Some of those
capacitor failures were spectacular. One sprayed the ceiling with hot oil
as it failed, leaving a very tough stain.)

If you use a capacitor, you should have some resistance in series with
it to limit the peak current that occurs when power is applied. If the
resistance is low enough to allow a peak current that is safe for
switches, etc. but unsafe for the LED, you need another capacitor across
the LED to smooth that out to something safe for the LED. The second
capacitor may need to be somewhat large unless a bit of resistance is
added in series with the LED.

If you use a capacitor, you also need to add a resistor to bleed it down
after power is shut off. If it is possible to touch the input connections
to this LED product after shutdown (such as by unplugging it), then the
bleeder resistor will have to discharge the capacitor to a safe voltage in
eyeblink time (.2-.25 second). Worst case peak capacitor voltage is peak
line voltage, about 325 volts. To discharge that down to say, 18 volts,
requires almost 3 time constants (natural logt of 325/18). So, one time
constant should be say, .07 second. Divide that by .00000033 farad, and
the bleeder resistor should be 212 K-ohms. The nearest common value is
220 K-ohms, though to err on the side of safety I would make it 180 or 150
K-ohms. A 150K resistor with 225 volts RMS AC aross it will dissipate
about 1/3 of a watt - use a 1/2 watt one minimum. It may dissipate more
power than a lightly loaded good modern cellphone charger does.

If you use a capacitor, you also need a fuse and anything else to ensure
that the LED product can only fail safely. If you have a second capacitor
across the LED, it should operate safely (or fail safely) if the LED
should fail open. (I have seen them do that, and I have seen solder
joints "crystalize" with age.) The product needs to not become unsafe if
any one component fails open or fails short (it may be a good idea to have
the bleeder resistor be two in parallel in case one fails, breaks, or a
solder joint fails).

You probably want to use a cellphone charger or other "wall wart"
power supply to power your LED.

- Don Klipstein (don@misty.com)

 

[Don Klipstein]

In article <4a5afc56$0$5936$607ed4bc@cv.net>, Tom Biasi wrote in part:

Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

I find some insufficiencies of this circuit:

1. The bleeder resistor provides a time constant of .33-.47 second. This
is safe for those who know what they are doing, but a child who is quick
to plug this into his mouth after unplugging it from the wall may get
shocked.

(This is not a concern if this circuit is in parallel with something
else that will discharge it quickly.)

2. The capacitor to limit AC current is shown with a DC voltage rating
and not an AC one. I have actual experience with capacitors lacking an AC
rating and used with AC of RMS voltage as low as 30% of the DC rating
failing - sometimes loudly and with spewing out some of their contents.

- Don Klipstein (don@misty.com)

 

[David L. Jones]

Tom Biasi wrote:

"Charlie+" <charlie@xxx.net> wrote in message
news1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com...
Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can
recommend for
running a (blue 25 to 40mA) LED at near its maximum output but from
mains power - 230V ac in my case?
Thanks

Problems with AC mains is the voltage varies a lot and spikes are
common. The drop needed is large compared to the LED voltage.
Take a look at this circuit:
http://www.turbokeu.com/myprojects/acled.htm

As others have said, that needs a proper mains class rated cap, not just a
any old cap with a high enough voltage rating as stated on that web page.
Also, if a constant known brightness is important to you, then you really
should drive LEDs with a constant current source instead of just a series
resistance. An LM317 in constant current mode will do the trick. e.g:
http://users.telenet.be/davshomepage/current-source.htm
once you've dropped the mains to a suitable level of course.

As always, be careful, direct mains powered devices are dangerous, and an
LM317 provides a nice big exposed metal tab you don't want to be touching.

Dave.

--
---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/

 

[David Eather]

Charlie+ wrote:

On Mon, 13 Jul 2009 05:20:25 -0400, "Tom Biasi" <tombiasi@optonline.net
wrote as underneath my scribble :

"Charlie+" <charlie@xxx.net> wrote in message
news1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com...
Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend
for
running a (blue 25 to 40mA) LED at near its maximum output but from mains
power - 230V ac in my case?
Thanks

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

Tom
Thanks Tom!

*A safety warning!* The specification for the capacitor in the above
link is incorrect. A non-mains rated capacitor is a fire hazard no
matter what it's voltage rating. Capacitors used on mains circuits need
to also have the property of "self healing", that is, if a mains spike
causes a puncture in the capacitor's plate-plate insulation it does not
cause a cascade effect ending with the capacitors destruction and a
fire. Only a mains rated capacitor is safe.


http://www.jaycar.com.au/productView.asp?ID=RG5238&CATID=51&form=CAT&SUBCATID=866

is a workable solution from Jaycar (220nf a bit small). RS, Farnell and
many others will sell you the exact component.

 

[Phil Allison]

"David L. Jerkoff"

As others have said, that needs a proper mains class rated cap, not just a
any old cap with a high enough voltage rating as stated on that web page.

** No-one has mentioned that the LED will have serious visible flicker too.

Cos it is being fed with 50 Hz pulses of current.

Also, if a constant known brightness is important to you, then you really
should drive LEDs with a constant current source instead of just a series
resistance.

** What do you think that series cap is ???



...... Phil

 

[Phil Allison]

"Don Klipstein"

The capacitor needs an actual AC voltage rating of at least 250 volts.

** This is very misleading.

A cap needs to be labelled with " X1 " or " X2 " to qualify as AC mains
voltage, continuously rated.

Such caps are internally quite different to standard, DC rated film caps -
see FYI.

(Capacitors rated 400 or even 600 volts DC but lacking an AC voltage
rating, during prolonged use with AC, are likely to go KABLOOEY.

** See above.

Many film cap makers mischievesly apply AC voltage ratings to all their DC
rated caps.

( Egs 100V poly cap = 63V AC and 400V poly cap = 200V AC etc. )

These ratings are supplied without any defined meaning.

Beware, continuous application of AC voltages above 150V rms will destroy
standard poly caps.

FYI:

Class X1 and X2 film caps are made with dual windings ( therefore two caps
in series) or are dual di-electric paper/film types impregnated with oil or
wax under vacuum and so free of all air inclusions.


..... Phil

 

[Tom Biasi]

"Charlie+" <charlie@xxx.net> wrote in message
news:f37m55p6cv4dc8jp6com8ie16oma481lnm@4ax.com...

On Mon, 13 Jul 2009 05:20:25 -0400, "Tom Biasi" <tombiasi@optonline.net
wrote as underneath my scribble :


"Charlie+" <charlie@xxx.net> wrote in message
news1ol55l50rrt1usq529janj5vht8ipp6dv@4ax.com...
Reading the thread on battery power with interest...
Is there a minimal and cheap junk box circuit that anyone can recommend
for
running a (blue 25 to 40mA) LED at near its maximum output but from
mains
power - 230V ac in my case?
Thanks

Problems with AC mains is the voltage varies a lot and spikes are common.
The drop needed is large compared to the LED voltage.
Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

Tom
Thanks Tom!

As others are pointing out, don't go into consumer production with your
circuit.
Tom

 

[Don Klipstein]

In article <7c20d4F25r6s4U1@mid.individual.net>, Phil Allison wrote:

"David L. Jerkoff"

As others have said, that needs a proper mains class rated cap, not just a
any old cap with a high enough voltage rating as stated on that web page.


** No-one has mentioned that the LED will have serious visible flicker too.

Cos it is being fed with 50 Hz pulses of current.

A minor change will fix that. Instead of two antiparallel LEDs, use one
LED and a bridge rectifier. The flicker rate then becomes 100 Hz (120 Hz
in North America).

- Don Klipstein (don@misty.com)

 

[Jasen Betts]

On 2009-07-14, Phil Allison <phil_a@tpg.com.au> wrote:

"David L. Jerkoff"

As others have said, that needs a proper mains class rated cap, not just a
any old cap with a high enough voltage rating as stated on that web page.


** No-one has mentioned that the LED will have serious visible flicker too.

Cos it is being fed with 50 Hz pulses of current.


Also, if a constant known brightness is important to you, then you really
should drive LEDs with a constant current source instead of just a series
resistance.

** What do you think that series cap is ???

Immaginary series resistance.

current will still change with supply voltage (i.e. not a whole lot).

 

[Phil Allison]

"Jasen Betts"
Phil Allison

"David L. Jerkoff"

As others have said, that needs a proper mains class rated cap, not just
a
any old cap with a high enough voltage rating as stated on that web
page.


** No-one has mentioned that the LED will have serious visible flicker
too.

Cos it is being fed with 50 Hz pulses of current.


Also, if a constant known brightness is important to you, then you
really
should drive LEDs with a constant current source instead of just a
series
resistance.

** What do you think that series cap is ???

Immaginary series resistance.

** Just add up with that * much lower value* real one in series.

current will still change with supply voltage (i.e. not a whole lot).

** Few apps would be so sensitive to a few percent change in light output
over the period of a day.



..... Phil

 

[greg]

What is this LED going to be used for?

If it's just a power indicator for a piece of mains
equipment, it may be easier and safer to use a
neon bulb and series resistor. You can get these as
a pre-made unit designed for exactly that application.

--
Greg

 

[default]

On Mon, 13 Jul 2009 18:52:41 +0000 (UTC), don@manx.misty.com (Don
Klipstein) wrote:

In article <4a5afc56$0$5936$607ed4bc@cv.net>, Tom Biasi wrote in part:

Take a look at this circuit: http://www.turbokeu.com/myprojects/acled.htm

I find some insufficiencies of this circuit:

1. The bleeder resistor provides a time constant of .33-.47 second. This
is safe for those who know what they are doing, but a child who is quick
to plug this into his mouth after unplugging it from the wall may get
shocked.

(This is not a concern if this circuit is in parallel with something
else that will discharge it quickly.)

I have built the circuit for the 120 VAC 60 Hz version but with a FWB

rectifier. The circuit was one recommended for AC ops in a Fairchild
application note. They use a 100 ohm 1/4 watt resistor - to fuse and
limit inrush current.

I accidentally shorted the cap while fooling with it - the 100 ohm
carbon film 5% resistor opened without singeing the paint. No flash
of light or smoke (that I noticed). A "flame proof" resistor might
be a better choice.

Unplugging it and putting it across my hand, the led lights but
there's no shock or any sensation. (with no 1M bleeder resistor) I
have no plans on putting it across my tongue to test that theory
though . . .

Mine has been in operation as a night light for close to 30 years with
one change of the 3 series leds (they dimmed with age running 24/7).

2. The capacitor to limit AC current is shown with a DC voltage rating
and not an AC one. I have actual experience with capacitors lacking an AC
rating and used with AC of RMS voltage as low as 30% of the DC rating
failing - sometimes loudly and with spewing out some of their contents.

- Don Klipstein (don@misty.com)

Agreed, a good rule of thumb is 3X or more the DC rating, non polar
film cap. An AC rated, polypropylene dielectric, cap would be my
first choice.
--

 

[default]

On Mon, 13 Jul 2009 18:52:41 +0000 (UTC), don@manx.misty.com (Don
Klipstein) wrote:

I lied. The AC circuit is from Siemens Optoelectronics data book 1990

I'll try putting the page up on alt.binaries.schematics.electronic
--