Low voltage mystery

Thread Starter

radman2020

Joined Jan 29, 2023
10
I have undercabinet lights that are low voltage. They work xenon pucks just fine. I want to convert to low voltage LEDS. Supposedly these are 12V DC but when I hook 12V DC LED pucks up, they don't work.

There is a switch to turn these on that is 120 volts. Somewhere buried behind the wall is a 120 to 12VDC converter. I can't access it. I am assuming there is too much current to the lights so the LEDs won't work... maybe more than the 12V. I bought a multimeter but it doesn't show any voltage. I put the wires together and I get a spark so I know there is power. Maybe I am using the multimeter wrong? I put the probes to each end of the wire. I also put it to one end of the wire and to a ground. Nothing.

In the end, I want the LED's to light up but they don't seem to want to respond to the power getting to them. Is there anything I can do??
 

nsaspook

Joined Aug 27, 2009
12,998
Maybe the xenon undercabinet lights are low voltage AC. Switch the meter to measure AC voltage. If you get the correct reading then you need LED pucks that accept a low voltage AC supply.
 

Thread Starter

radman2020

Joined Jan 29, 2023
10
Maybe the xenon undercabinet lights are low voltage AC. Switch the meter to measure AC voltage. If you get the correct reading then you need LED pucks that accept a low voltage AC supply.
The meter only reads in the setting I have here. Is that AC? But .4 is so low.....20230129_223451.jpg
 

sghioto

Joined Dec 31, 2017
5,370
You are on the 200 volt ac scale.
Turn the dial to the left to the 20 volt dc setting.
Try reconnecting the xenon lamps to verify power.
 
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Thread Starter

radman2020

Joined Jan 29, 2023
10
It reads zero on that setting. I know there is power because I get a spark when I put the wires together. My xenon bulb are now all burnt out.
 

sghioto

Joined Dec 31, 2017
5,370
Also, check the meter leads by turning the dial to the 200 ohm setting at the 6 o'clock position of the dial.
Touch the meter leads together, should read close to zero ohms.
 

Thread Starter

radman2020

Joined Jan 29, 2023
10
When I put it to 200 ohms, it also reads 0.4. When I touch the leads together at that point, I get a spark and the number jumps up (but I don't want to short it so I don't wait) to see the number it jumps to.
 

sghioto

Joined Dec 31, 2017
5,370
When I put it to 200 ohms, it also reads 0.4. When I touch the leads together at that point, I get a spark and the number jumps up (but I don't want to short it so I don't wait) to see the number it jumps to.
Just touch the meters leads together not to the wires.
 

sghioto

Joined Dec 31, 2017
5,370
That tells me the leads and at least the ohm section of the meter are good.
Have you tried testing each LED assembly separately from another 12 volt supply? How many LED lights are going to be on the system?
 

Ian0

Joined Aug 7, 2020
9,620
Did you get the polarity reversed? It appears to have two white wires, but I assume that one of them has an identification stripe.
Does the black stripe represent positive or negative?
Did you destroy the LED by connecting it with reversed polarity?
 

Ya’akov

Joined Jan 27, 2019
9,044
Did you get the polarity reversed? It appears to have two white wires, but I assume that one of them has an identification stripe.
Does the black stripe represent positive or negative?
Did you destroy the LED by connecting it with reversed polarity?
Looks like one of the leads has a black stripe. I would normally assume that was the negative, but…

In any case, it does seem likely that the output of the power supply is AC since there is no point in supplying the Xe lamps with DC and a transformer is the usual deal for such arrangements. I would expect, though, that the LEDs would have at least lit momentarily if not with a half-wave flicker (if they could handle the reverse bias).
 

Ian0

Joined Aug 7, 2020
9,620
Looks like one of the leads has a black stripe. I would normally assume that was the negative, but…
. . . speaker leads are often white with a black tracer, and the tracer generally indicates the signal, and non-tracer is ground. From there it’s easy to get to “tracer=power non-tracer=ground“, and soon we have ended up with the black tracer on the positive supply.
 

Thread Starter

radman2020

Joined Jan 29, 2023
10
Looks like one of the leads has a black stripe. I would normally assume that was the negative, but…

In any case, it does seem likely that the output of the power supply is AC since there is no point in supplying the Xe lamps with DC and a transformer is the usual deal for such arrangements. I would expect, though, that the LEDs would have at least lit momentarily if not with a half-wave flicker (if they could handle the reverse bias).
Why can't I figure that out with the multimeter?
 

MisterBill2

Joined Jan 23, 2018
18,061
First of all it seems that the TS is not very familiar with using the meter. I suggest a study of the instructions that came with the meter before any more measurements.
Xenon incandescent lights will certainly be AC powered, and certainly AC power is not suitable for LED lights unless they are marked as using AC power, which most of them ARE NOT FOR AC POWER.
Next, with low voltage AC wiring polarity is seldom considered and so the black stripe on the white wire is not to be trusted as meaning anything. Most two conductor pairs are marked so they can be identified, no mater what the application will be. That is the way wire cables are made.
To power the LED lights a DC power supply will be needed that is for the correct voltage and rated for adequate current, which will be at least the total of the current markings on all of the LED lights to be installed. I recommend an at least 10% safety margin in the LED power supply rating.
 

Thread Starter

radman2020

Joined Jan 29, 2023
10
1st. You are correct- I am not a pro with the multimeter. That's why I am asking here. The directions are horrible so it doesn't help. The only reading I get is 0.4 when I set it as above. I believe that is the AC measurement and it seems very low.

2nd, I replaced all my halogen lights (low voltage ceiling lights with 2 pins) with LEDs and it worked great. Are you saying that xenons are different? I think these were originally halogens and switched them for xenons... and they worked fine.

I would just get new xenons if I could, even though they use more energy and get very hot. The pucks are now gone.
I can't get to (or even find) the transformer and these are all hard wired in behind tile... can't really get to the wiring.
 

Ian0

Joined Aug 7, 2020
9,620
I’m not sure what xenon lamps really are. I very much doubt that they are xenon gas-discharge tubes (as in photo-flash). I think it is marketing hype for something or other.
 
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