How can I wire up an LED puck light to an AC power source?

[DaveC426913]

OK, here's what I'm doing:

I currently have a single 20 watt halogen puck:
[PLAIN]http://www.lightingfx.com/media/images/product_category/ro29.jpg
powered through a rectifier from AC.

The reason I've done this is because I need the interrupt the AC with a light timer switch.

I want to toss out the 20watt halogen puck and substitute an LED puck light (IKEA, INREDA). So I'll be keeping the rectifier.


The new light from IKEA does not seem to be listed yet. (I remember when you could go to Ikea and trust that what you bought last time was still there.)

There are four pucks in a pack, each puck can be seen to have 18 LEDs. I only need 1 puck.
The power supply is listed as:
DC12V, max 500mA, 0.5-6W
DC700mA, max 8.5V.

I want to figure out how to wire this up in place of my halogen puck light. I know i'll need a resistor in series with the LEDs but does the fact that there are 18 of them change how I calculate it?

 

[vk6kro]

Those power supply figures don't make much sense.

In any case, you would need to use a transformer to get about 6 or 12 volts, then rectify the AC.

I did a Google search for "120 V puck LEDs" and it came up with a lot of them.

Here is one:
http://shop.hardwaresolutions2001.com/Super-Bright-LED-Under-Cabinet-Puck-Light-512003.htm

It looks as if you just apply 120 V AC and it works.

 

[DaveC426913]

In any case, you would need to use a transformer to get about 6 or 12 volts, then rectify the AC.

Did I not make it clear that I already have the 12V and the rectified DC?

 

[sparkey]

well, you need some information about the LEDs to make a proper calculation. the voltage drop across each LED, max current through each would be a good place to start.**edit**here are good pages for you to reference
http://www.kpsec.freeuk.com/components/led.htm#calculate
http://led.linear1.org/led.wiz

 

[vk6kro]

Did I not make it clear that I already have the 12V and the rectified DC?

No, you didn't.

It looks like that transformer will give 12 volts at up to 500 mA load and 8.5 volts at 700 mA load.

I have some devices like that LED puck which already include 3 "AA" batteries and built-in current limiting. If you already have one, you could check if this is the case with yours.
One of mine came from Ikea. It uses about 30 mA at 4.5 volts.
This one turns on when you push the front of the device and another turns on with a switch at the side.

Either of these would be OK if you just connected the transformer and a series resistor, to drop the voltage to 4.5 volts, instead of the batteries.

 

[cjameshuff]

Did I not make it clear that I already have the 12V and the rectified DC?

You mentioned the power supply, but it wasn't clear if it was something you had or something you needed.

To summarize, you have:
12VDC@500mA/8.5VDC@700mA power supply, from the halogen light
20 watt halogen puck, to be replaced
LED puck, to replace it

Do the LED pucks not have any sort of voltage or current ratings on them? And is that really the power supply for the 20 W halogen? It certainly won't be putting out 20 watts...unless that's the power supply requirements for the LED pucks, in which case what are you powering the halogen with?

 

[sophiecentaur]

Are you sure your PSU has a rectifier? Halogen bulbs don't insist on DC so I wouldn't expect one on a domestic system - just a transformer.
If your PSU really is DC out then you should be able to use it directly for your LEDs. Their power consumption is bound to be less than the halogen supply can give you. If it's not DC, then you can put in your own rectifier. You may need a capacitor to reduce / eliminate flicker? Halogen filaments smooth out the 50Hz but LEDs won't.
I'm assuming your LED lamp is 12V, of course.