My line voltage alarm went off while sitting in my trailer today, I was taking a rest, from a small welding project I did. I checked the alarm and it showed 137 volts, my inverter circuit had kicked in protecting my TV and computer, but the Norcold fridge is on the circuit and a few other things. I heard a pop and a hiss, and white smoke started filling the trailer, I have heard the pop hiss before working in electronics, and the smell was reminiscent of fried capacitors and/or transformers, I ran around flipping off circuit breakers and the main battery switch, the smoke continued filling the trailer and forcing me outside. I unplugged the trailer and waited for the smoke to disperse, rushing in to open my electric area, and rushing back out when throat and eyes started burning. My fans wouldn't work (I had turned off the 12v power.) Since I could not see flames nor smell burning wood, I waited a bit with extinguisher in hand. The smoke cleared and I could see my autoformer was smoking and had left some goo splattered around. I pulled the autoformer out, still hot and smoking and took it outside.
I pulled the autoformer apart, and checked the wiring and circuitry, I am unhappy, there were no MOV's in the unit, it appears they were not installed. MOV's are small self sacrificing components to protect from over-voltage and voltage spikes. Instead the autoformer sacrificed itself to protect the trailer. The goo is the transformer potting material that was heated into liquid goo and smoke.
The autoformer got hot enough to melt the vinyl flooring making it stick to the autoformer, the wood underneath is not burnt but has some goo on it.
If I had a Surge-guard inline this would not have happened, or if the autoformer had overvoltage/undervoltage protection. I have been very happy with my Hughes Autoformer and undervoltage problems up till this point, it seems it was an older unit that did not have the MOV surge/overvoltage protection. After my research it seems that Franks RV voltage booster has under/over voltage protection built in.
Also see I'm tired of RV resort excuses for Voltage
