Troubleshooting Puck-Light Dimmers

Cabinetmakers consider what might be making low-voltage lighting dimmers malfunction. May 7, 2007

Iíve installed four 20 watt low voltage puck lights by Westek. Iíve done this several times before with no problems. Now Iím going through dimmers. I canít explain it Ė a recent customer has gone thruogh three in 2 months. 2 out of the 3 worked when I left the house, only to be called the next day to say they donít work anymore.

What could be causing dimmer to stop working? Iíve checked the connections and Iíve called Westek (they said I must have sent the wrong one Ė although Iím sure it wasnít). Could there be an electrical problem in the house? I usually take off the pad and wire direct to a hinge.

For the last dimmer I replaced it and I left the pad on, only to be called again 3 weeks later. Tonight I checked it out and although the lights work on high when the dimmer is plugged in, the lights have no other levels. Itís very weird. If the dimmer is shot, I would think the lights would not work at all unless you bypass the dimmer. Does anyone have any thoughts? Iíve actually switched suppliers thinking I got a bad batch. What could I be doing wrong?

Forum Responses
(Cabinetmaking Forum)
From contributor J:
This is a shot in the dark, but have you tried changing the transformer? I'm wondering whether a problem with it could affect the dimmers.

From the original questioner:
I guess I could try that. Itís weird - the first dimmer that went bad would not allow the lights to go on at all. The 2nd dimmer that went bad kept the lights on at 100% and nothing else. Iíve triple checked what I bought and everything is right on. I can only do so much. I mean, these things worked when I left the house. I showed the customer this. What could possibly happen to them?

From contributor D:

Dimmers are basically variable resistors. Resistors limit the flow of electricity in a circuit. They can be damaged by two things, too high of voltage or too much current. I would replace the transformer as Jon suggested and check the input voltage from the supply line. The transformer is used to step down the voltage to a usable level. If it is defective or shorted it could be producing too high of voltage. If the supply voltage is off it could cause either a voltage or a current problem.

From contributor K:
This could be static discharge. Try wiring an MOV (metal oxide varistor) from the touch plate to ground. Any good electronic supply should have what you need. Radio Shack might have them also. This is just a slightly educated guess but it's not expensive and worth a try.

From contributor K:
Here is what I know about power control. Modern dimmers are a phase fired triac circuit not a variable resistor a variable resistor sometimes is used to control the triac circuit. The touch type is a little different. A variable resistor large enough to work for a dimmer of that wattage would be around 6 inches in diameter 2 inches thick and weigh about 5 pounds.

If you have only full on then the triac is shorted or the control circuit is bad. No light means the triac is open or the control circuit is bad. Phase fired triac or SCR circuits need to be designed to drive a transformer load or it may not work very well or long.

In short, dimmers need to be designed for a transformer load and transformers need to be designed to be driven from a dimmer. A 1000 watt dimmer can drive a 1000 watt light bulb forever but a 1000 watt dimmer driving a transformer driving a 1000 watts of light bulbs, unless designed for it, will only go maybe 2 weeks to 2 months, then one or the other will fail.

From contributor L:
I assume you are using the recommended amount of wattage or less for the rating of the dimmer. If you overload the dimmer it will fail.

From contributor F:
I ran into the same problem a while back. I re-worked the lights and transformer several times. It would usually work at first, then stop or become erratic in operation. During the third installation, her cordless phone that was in the room rang and the lights went nuts. The radio frequency was screwing things up somehow. The vendor sent me a new dimmer that was shielded more against that and I have not been back since. Itís worth a look.