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VIDGuide
06-08-2008, 11:01 PM
Hi guys,
this is just a basic electronics query, is it possible to operate regular, off the shelf LEDs from an AC power source, and if so, how?

Googling this topic finds plenty of people operating LEDs from 110v AC or 240v AC directly via a few components, but nothing in regards to low voltages.

For example, I have 7VAC and 10VAC handy, and a system that is currently all incandescent bulbs. Obviously this won't be changing at once, so SSR's to operate these will be AC, since they are a) cheaper, and b) the system is already up and running in AC.

however, I do plan to change these to LEDs at some point in the future, and would like to know, is it at all possible to operate regular LEDs from this same AC with only a few simple/cheap components added, or would I have to change both, the power source & SSRs?

Thanks in advance!

VIDGuide
06-08-2008, 11:39 PM
Ok, doing some follow up research, I may have answered my own question, but if an expert here could confirm it would be great! :)

From reading, along with the appropriate resistor, I would also need to fit a 1N4001 or similar AFTER the LED, to prevent the reverse wave exceeding the LED's reverse limit, is this correct? Otherwise, the LED will light fine, and the ripple at 50hz would be un-noticeable in a fixed position LED, correct?

Thanks for your help guys! :)

maffeirw
06-09-2008, 02:13 AM
Ok, doing some follow up research, I may have answered my own question, but if an expert here could confirm it would be great! :)

From reading, along with the appropriate resistor, I would also need to fit a 1N4001 or similar AFTER the LED, to prevent the reverse wave exceeding the LED's reverse limit, is this correct? Otherwise, the LED will light fine, and the ripple at 50hz would be un-noticeable in a fixed position LED, correct?

Thanks for your help guys! :)


I’m far from an expert but I’ve been running a couple of LED’s in the middle of my 12v AC landscape lighting system for a couple of weeks now without trouble. I calculated the resistance needed to provide the appropriate forward voltage & current to the LED using one of the LED calculators I found in Reference Depot forum. I am assuming that none of the LED’s will have a lower reverse voltage that forward voltage (at least I haven’t seen any LED specs which showed that as yet). So the resistor should take care of maintaining the voltage below critical levels without the need for an additional diode. I have run both multiple LED’s in series with a single resistor 3 (30ma 3.4v) as well as a single higher powered LED (100ma warm white) and matching resistor with the 12v AC supply without any problems even while other incandescent bulbs burn on the same circuit. See attached pictures. LED on left in the first picture.
I’ve also put together a tester using the another 12v AC supply for testing the Ren16 I am building (16 single LED’s with corresponding resistors) which also is working fine.

For info on the tester see:
http://www.doityourselfchristmas.com/forums/showthread.php?p=30954#post30954

Hope this helps :)

ppohlman
06-09-2008, 10:08 AM
VIDGuide-
I too am not an expert but I've been dabbling around with building a 4x color LED AC light (120VAC) that can be controlled by Vixen. One thing I'm doing is installing all LEDs in pairs. With LEDs installed in an opposing fashion, you wouldn't need to extra diode. This would also help to "remove" the semi-visible 50/60Hz flicker if the LEDs are right next to each other.

I've already built the LED portion of the light and have tested it on a test setup and it works great. I'm just trying to figure out how to make a nice overall package that I'm going to screw it into my lamp post.

maffeirw
06-09-2008, 11:26 AM
VIDGuide-
I too am not an expert but I've been dabbling around with building a 4x color LED AC light (120VAC) that can be controlled by Vixen. One thing I'm doing is installing all LEDs in pairs. With LEDs installed in an opposing fashion, you wouldn't need to extra diode. This would also help to "remove" the semi-visible 50/60Hz flicker if the LEDs are right next to each other.

I've already built the LED portion of the light and have tested it on a test setup and it works great. I'm just trying to figure out how to make a nice overall package that I'm going to screw it into my lamp post.

That's a great idea, if you don't mind I'll use it on my deck lights. I was going to add a second LED anyway, now I can just put them in parallel using the same resistor. Brighter and less flicker great combination. Thanks :D

ppohlman
06-09-2008, 11:32 AM
Not a problem. I'm glad I could help.

It wasn't my idea, though. I just got different ideas from the web and put them together for my project.

omzig
06-09-2008, 11:47 AM
I don't see what the big deal is with using a few standard rectifiers when you can get 1N4001-1N4004's from Mouser for 3¢ or less. Even if you use 4 of them for full-wave, you're still only talking 12¢! I bought 100 1N4004's from Mouser for $2.50.

I used some surplus white LED's for night lighting on my pool deck. I just used 4 1N4004's in bridge fashion for full-wave rectification. I heat shrunk them and put them in the landscape transformer enclosure that I'm using.

dmcole
06-09-2008, 11:48 AM
FWIW, here's my little primer on using LEDs in a garden-lighting environment (i.e.: 12v AC):

http://www.45mm.com/lighting/leds.html

\dmc

VIDGuide
06-10-2008, 01:36 AM
Thanks for the info guys, you have all been extremely helpful. The idea of doubling them in reverse is perfect, and even if I have to put a proper diode in there, its not expensive, thats great! Thanks again guys!