Low voltage lighting transformers going bad way to fast

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I'm helping a friend out with some low voltage lights he has, they are 120 to 12 v transformers operating MR16 bulbs on an electronic dimmer, each circuit has 6 lights on it and he has 6 circuits, all in the same configuration.

The problem is he had a couple lights go bad after only being there a couple of years. When I checked it out I wasn't getting any voltage from the transformer, tested line side and was getting about 120v. I ordered him 2 new transformers, the same exact ones actually (all the reviews i read on them were good so i decided to stick with em).

I put them in and tested them, worked fine... A couple weeks later he had a couple more PLUS one I had just replaced go out.

I can't figure out what's making the transformers go out so quickly, line voltage is fine. I have a feeling it may be because they are installed on a dimmer but the transformers claim to be dimmable... I'm not very familiar with low voltage stuff though which is why I came here, if anyone can help me out it would be greatly appreciated!

The transformers are WAC HR801's btw and the dimmers are Lutron electronic dimmers with MR16 50w bulbs and the transformers are rated for 60w.

Thanks!
 

Dennis Alwon

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Location
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Retired Electrical Contractor
What is the wattage of the transformer. You have 6- 50 watt bulbs-- that is 300 watts and you won't find a single transformer that is over 300 watts. Personally I would use a magnetic transformer as they are the bulldogs, IMO.

Also are the dimmers electronic low voltage dimmers or just electronic dimmers?
 

Electric-Light

Senior Member
Are you using a dimmer specifically compatible with transformer load and suitable for type of transformer (magnetic or electronic) you're using?

I can't tell if you mean touchpad/push button type or electronic transformer rated by "electronic dimmer".

Only three ways...
incorrect dimmer
overload
line voltage in excess of 126v for an extended period of time.
 

TNBaer

Senior Member
Location
Oregon
Only three ways...
incorrect dimmer
overload
line voltage in excess of 126v for an extended period of time.

Lemme add one to this: Excessive Heat.

I had a customer with MR16s in tiny 3" or 4" cans and the transformers just baked. I mentioned this in another thread recently, but I cannot stress enough how poorly Halogen performs in those types of conditions.
 
Each fixture has its own transformer, and it's quite possible heat is the issue here, the fixtures are in the ceiling and, therefore, are in the attic of the house.

But the insulation is clear of all the fixtures, and these fixtures do have sensors that are supposed to cut off the light if they over heat.

And the dimmers are Lutron Maestro dimmers, s/p, and there's a separate switch for each circuit. Specs claim to work with low voltage lighting.

I am beginning to think heat is the culprit here though, that attic gets unbelievably hot and the sun bakes the roof most of the day, and these fixtures do have heat sensors to shut off the bulb if they overheat, but they are before the bulb, not the transformer...
 

mauk

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Location
NY
Occupation
Electrical Engineer
And the dimmers are Lutron Maestro dimmers, s/p, and there's a separate switch for each circuit. Specs claim to work with low voltage lighting.
some of the lutron devices i have used have different models for electronic and magnetic low-voltage transformers....does your dimmer match your transformer type?
 

TNBaer

Senior Member
Location
Oregon
I am beginning to think heat is the culprit here though, that attic gets unbelievably hot and the sun bakes the roof most of the day, and these fixtures do have heat sensors to shut off the bulb if they overheat, but they are before the bulb, not the transformer...

An attic in the summer, core temp is prolly 115+. A halogen can is 300 - 400 degrees Fahrenheit. That's not a lot of room to breath and nothing externally working to cool down the can. Electronics don't like heat, that's why computers got that little fan. My money is on heat.

From Universal Ballast's website:
Ballast Heat: Electronic ballasts are designed to operate in ambient temperatures less than 105 degrees F. The inside or core temperature of the ballast is not to exceed 75 degrees C. Magnetic ballasts have a maximum core temperature of 90 degrees C. It is important to remember that electronic ballasts are more heat sensitive than magnetic ballasts as indicated by the lower maximum core temperature.

And this link seems to suggest the same thing saying:
But Markey says electronic [transformers] are sensitive to heat, so if you put them in a metal fixture or in a fixture with a canopy and the fixture gets hotter than its recommended temperature, the transformer's lifespan will be cut short. In fact, for every five degrees Celsius it gets over its recommended temperature, the transformer's lifespan is cut in half. Since they only have about a five- to six-year lifespan when operating properly, this means their realistic lifespan is even shorter.

I got 20 bucks on a heat issue.
 
An attic in the summer, core temp is prolly 115+. A halogen can is 300 - 400 degrees Fahrenheit. That's not a lot of room to breath and nothing externally working to cool down the can. Electronics don't like heat, that's why computers got that little fan. My money is on heat.

From Universal Ballast's website:

And this link seems to suggest the same thing saying:

I got 20 bucks on a heat issue.

After talking with you guys and looking over it again my moneys on heat too... Not quite sure how to resolve this issue though, far to many lights to simply replace (money wise that is), but I'll figure it out now that I know what was making them go bad.

Thanks a lot for your help!
 

TNBaer

Senior Member
Location
Oregon
Last edited:

Electric-Light

Senior Member
I've posted here before my dislike of LEDs....might be worth a shot.

As posted here, Halogen kills bunnies. Watch at your own risk. :)

An appeal to fear marketing. There are MR16s with dichroic filters that reflects IR off the front, then pass them out the back, so majority of IR is prevented from leaving with the light beam and they're directed out the rear, but this would actually make it worse as far as the heat at the fixture
 

TNBaer

Senior Member
Location
Oregon
An appeal to fear marketing. There are MR16s with dichroic filters that reflects IR off the front, then pass them out the back, so majority of IR is prevented from leaving with the light beam and they're directed out the rear, but this would actually make it worse as far as the heat at the fixture

Good call. In all fairness, you pay a premium for those lamps, and in the end, probably a higher cost of ownership on the commodity side than LEDs. For real small can lights in this type of application the ideal solution would be fiber optics. No heat, remote location. But...well, fiber. How realistic is that? Integrated CFLs may have the same issue the customer is currently experiencing, and you'll be upgrading can diameter. LEDs have too much glare for my liking. You could go 120v halogen with, say, a PAR16 lamp. That'd solve the problem and keep can size, but the energy saving facist in me hates mentioning such a thing. :D
 
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