LED AC vs DC

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Old 11-03-08, 11:05 AM
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LED AC vs DC

I just can't seem to find an answer to this/these question(s).

I have the typical 12VAC pathway lights. To save a few energy pennies and replacement pennies I decide to replace the 4W incadescent lamps with LED lamps. OK, so there are like 2 color options available for the 12VAC replacements. So I got some samples of 12VDC LED's with more color options. They will operate in the AC circuit. Question one, how will the life of the 12VDC LED's be affected in the AC circuit? Second question, is there a small rectifier available for purchase that I can put in the AC circuit to convert it to DC? Currently circuit is used for 20 fixtures. That may well grow over time so amperage draw is minimal. Sorry, I dont have readings for actuals.

Anyone that can help with these basic questions I'd greatly appreciate the help,

Thanks,

Charlie
 
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Old 11-03-08, 03:00 PM
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Don't confuse LED lamps that are designed to run on AC with raw LEDs.

All LEDs are DC semiconductors. Raw LEDs can run on AC, but most will fail quickly unless you install a reverse-biased standard diode in parallel. They also will require a series resistor to limit the current. The lamps have this circuitry inside, but raw LED components do not.

You can certainly install a rectifier in the circuit to change the AC to DC. Make sure it's rated to handle the total current load of all the LEDs.

DC low-voltage circuits are notorious for dropping voltage over the distance of a wire run, though, so you also have to take that into account: One bridge rectifier near the transformer will cause voltage drop at the far end of the line, whereas multiple parallel reverse-biased diodes at each LED will allow the length of wires to be AC, thus minimizing the affects of voltage drop.

Either way, each raw LED will still need a series resistor to limit the current. The value of the resistor (in ohms) is determined by the voltage and operating current of the LED, so you'll need to look at the spec sheet for the LEDs you'll be using.

That's a cool project. Please let us know what you decide to do.
 
 

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