Mains LED

[Stuart]

Need a bit of help adding LEDs to an existing circuit...

I have a mains driven clock, and I want to add 4 LED's to it (3.3v
20mA). There are no low voltages available, just a bridge rectifier for
~230V DC.

I was going to use a capacitor inline with the LEDs and some diodes,
like in this circuit http://www.marcspages.co.uk/tech/6103.htm but since
there is already a DC supply, I wondered if there was a simpler way?

Stuart.

 

As there is a bridge rectifier involved on 230VAC (nom.) mains, there
will
be significantly more than 230VDC.

How much more? The peak will be 1.414 *230 = 325, but the RMS will
still be 230, and the resistor will still be 230/.02 for RMS current of
20 mA.

-Bill

 

[Mark]

Consider using a series capacitor to limit the current and connect the
LEDs two in sereis and another two in series back to back with the
first two. Each pair will limit the reverse voltage for the other
pair. The cap will limit the forward current. Use a cap
conservativley rated, if the cap should fail short, the LEDs will
disappear in a flash of smoke. I'd add a small resistor 100 Ohms and
fuse in series with the cap just to limit the fault and high frequency
surge current.

Maybe for more saftey use two caps, one on each power lead.

The total reactance of the caps should be on the order of (you figure
out the exact value) 5kohms which is about 0.47 uF.

Mark

 

[Ken Taylor]

"Mac" <foo@bar.net> wrote in message
newsan.2005.02.16.04.24.14.847669@bar.net...

On Mon, 14 Feb 2005 21:11:51 +1300, Ken Taylor wrote:

OP is from UK, blessed as it is with a mains voltage
suitable for domestic purposes, unlike your quaint, paler imitation.

Cheers.

Ken

I suppose you're right. Here in the states, many houses are forced to run
in a special 220 VAC circuit for things like air conditioners, electric
heaters or clothes dryers, and electric ovens or ranges.

It probably would be a bit easier if we just used 220 for everything.

But you have to admit that 60 Hz is vastly better than 50 Hz. ;-)

--Mac

Yeah, I just don't know how we manage with 10 less than you guys. Still, we

go for quality, not quantity, with everything.

Ken

 

[R.Lewis]

"Ken Taylor" <ken123@xtra.co.nz> wrote in message
news:37hikkF5bp0feU1@individual.net...

"Mac" <foo@bar.net> wrote in message
newsan.2005.02.16.04.24.14.847669@bar.net...
On Mon, 14 Feb 2005 21:11:51 +1300, Ken Taylor wrote:

OP is from UK, blessed as it is with a mains voltage
suitable for domestic purposes, unlike your quaint, paler imitation.


Cheers.

Ken

I suppose you're right. Here in the states, many houses are forced to
run
in a special 220 VAC circuit for things like air conditioners, electric
heaters or clothes dryers, and electric ovens or ranges.

It probably would be a bit easier if we just used 220 for everything.

But you have to admit that 60 Hz is vastly better than 50 Hz. ;-)

--Mac

Yeah, I just don't know how we manage with 10 less than you guys. Still,
we
go for quality, not quantity, with everything.

Perhaps one of the reasons for not knowing how to cope with 10 less than a

proper supply is the fact that it is 20 less.

 

[Mark]

OK thats a good point about the turn on surge, lets make it just a bit
more complicated then......


How about a series cap feeding a beey zener at about 10 volts that can
take the surge current. Then you can rectify and filter the output
from the zener so that you also solve the strobe problem.

Mark

 

[HKJ]

"Mark" <makolber@yahoo.com> wrote in message
news:1108749612.412474.305450@g14g2000cwa.googlegroups.com...

OK thats a good point about the turn on surge, lets make it just a bit
more complicated then......


How about a series cap feeding a beey zener at about 10 volts that can
take the surge current. Then you can rectify and filter the output
from the zener so that you also solve the strobe problem.

Just download and use:
http://hjem.get2net.dk/hkj/miscelLeds.html

There your can select between multiple LED circuits for AC and it will also
do all calculations for you.

 

[HKJ]

"Pig Bladder" <pigbladder@neodruid.net> wrote in message
newsan.2005.02.21.09.25.55.201646@neodruid.net...

So Do The Fucking Demonstration and Report Back.

Have been there and jumped (It was a few hundrede uF at 200 volts).

 

[Rich Grise]

On Thu, 17 Feb 2005 18:19:06 +0000, R.Lewis wrote:

"Ken Taylor" <ken123@xtra.co.nz> wrote in message
news:37hikkF5bp0feU1@individual.net...
"Mac" <foo@bar.net> wrote in message
newsan.2005.02.16.04.24.14.847669@bar.net...
On Mon, 14 Feb 2005 21:11:51 +1300, Ken Taylor wrote:

OP is from UK, blessed as it is with a mains voltage
suitable for domestic purposes, unlike your quaint, paler imitation.


Cheers.

Ken

I suppose you're right. Here in the states, many houses are forced to
run
in a special 220 VAC circuit for things like air conditioners, electric
heaters or clothes dryers, and electric ovens or ranges.

It probably would be a bit easier if we just used 220 for everything.

But you have to admit that 60 Hz is vastly better than 50 Hz. ;-)

--Mac

Yeah, I just don't know how we manage with 10 less than you guys. Still,
we
go for quality, not quantity, with everything.

Perhaps one of the reasons for not knowing how to cope with 10 less than a
proper supply is the fact that it is 20 less.

He was talking about Hertz.

And you don't need to "run in a sepcial 220 VAC circuit" to run dryers and
water heaters and stoves. It comes in 120-0-120, you just use opposite
legs. Some call these "phases," but that's wrong. They're simply opposite
polarity - they come from a center-tapped transformer, so really the whole
household system is 240, with a convenient, grounded center-tap so that we
can run lamps and radios and stuff off a saner, less lethal voltage. ;-p

Cheers!
Rich

 

[Rich Grise]

On Mon, 21 Feb 2005 06:59:50 +0100, HKJ wrote:

"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:37soaoF5g32sjU1@individual.net...

Just because you keep repeating that a few uF is not dangerous doesn't
make
it so.
Why don' you bother to find out about something before ranting on with
such
rubbish?

Your starting saying it was deadly, why dont your some information about how
many people has die'ed from touching a few uF.

They don't die from microfarads. They die from milliamperes, which are
pushed through the resistance of the body by way of the heart, which
interrupts its regular rhythm, which causea arrhythmia, fibrillation,
and/orcardiac arrest, not necessarily in that order.

The capacitive reactance of "a few microfarads" at 50 or 60 Hz, and
mains voltage, in series with the resistance of your body's meat, will
allow lethal current to flow.

To put this in perspective: It takes 20 mA to light a(an?) LED to spec.
It takes 15 mA to kill a healthy adult human.

You do the math.

Don't poke around with the mains if you don't know absolutely what you're
doing.

Good Luck!
Rich