burned up fixture transformers

[fisherelectric]

We are replacing existing switches and receptacles in a residence with new Adorne devices made by Legrand (http://www.legrand.us/adorne.aspx#.VEvMPOduAXk). We are using their "Tru-Universal" dimmer which is capable of dimming LED, CFL, Mag Low Volt, Electronic Low Voltage in forward and reverse phase, Incan, and halogen loads. The recessed fixtures we are dimming are magnetic low voltage with dimmable LED MR16 lamps. We had a situation where after installing a dimmer, within a few minutes the breaker tripped and we discovered that the 5 fixtures controlled all had fried transformers.
My electrician did not inadvertently hook 240volts up to these lights.
My question is, is it possible that this dimmer somehow caused these 5 transformers to burn up?
The dimmer no longer dimmed. We installed many of these dimmers and this is the only problem we've had.

Thanks in advance for any thoughts on this

 

[gar]

141025-1302 EDT

Since you say the transformer burned up I assume this means the primary overheated and is now an open circuit. Verify this.

Next find our the nature of the failure within the dimmer.

Report back.

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[starbolin]

Thanks in advance for any thoughts on this

I have seen certain lighting loads misbehave when, in parallel, on dimmers. We usually solve this by making at least one of the loads on the dimmer an incandescent. I'm thinking this may be related. In other words, it's not the dimmer per-se but the lamp drivers interacting with each other when driven by the non-sinusoidal waveform of the dimmers.

 

[gar]

141025-2132 EDT

starbolin:

If a dimmer is a three wire dimmer (this will be the case if the dimmer requires a neutral), then for a delay to trigger type of scr switch the turn on point is strictly controlled by the dimmer. Turn off is determined by when load current thru the scr switch goes thru zero. This should produce a very consistent waveform from no load to full load. Two wire dimmers do not have this waveform consistency, and may not even produce output under light load.

For no average DC in the output current the two halves of the cycle must be balanced.

If the dimmer goes into half cycle operation, then there is a large average DC current. This likely would cause a transformer to burn out. In half wave operation the RMS current needs to be determined and whether this would burn out the transformer primary.

.

 

[gar]

141025-2342 EDT

An experiment with a diode in series with the primary of a 170 VA 120 V transformer and no load on secondary.

The approximate nominal full load RMS current to this transformer is 170/120 = 1.4 A.

I don't have an instrumrent to measure the RMS value of a current with a combination of DC and AC current. However, the combination RMS current will not be less than the average DC current.

I adjusted the input AC voltage to the diode transformer primary series circuit to obtain an average DC current of 1.4 A. The input voltage was about 65 V. Clearly the current would be very much higher with a 120 V AC input, and the transformer primary would burn out.

.

 

[starbolin]

Thanks gar. I hadn't thought of that. You blew my mind.