Generator - Blowing the Start Compacitor of an Air Compressor? - Power Equipment Forum : Power Equipment Forums
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post #1 of 2 (permalink) Old 12-14-2017, 11:28 PM Thread Starter
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Generator - Blowing the Start Compacitor of an Air Compressor?

Good evening,

I can use some help and knowledge to try and fix a problem I've been having with my air compressors. I'm trying to convert a 40' bus into a tiny home and can use the insight from some good electricians (I've been talking with my old military electricians and they are stumped as am I).

I have a 7500 watt generator that I have been using to power my air compressors. It worked great for awhile, every now and then I would notice a little smoke coming from one of the electric motors (I know not the best), until recently. I hooked the generator up to one compressor and the ended up cause the start compacitor to leak fluid and no longer work. Ohm tested the start compacitor and it read as an open circuit (I believe open is the correct term for it to no read any MFD or the ohms to no fluctuate at all). I checked the voltage coming from the 240v outlet on the generator and it read roughly 275v. I pulled the back casing off the generator and turned down the AVR to as low as it would go, and it now reads 253v coming from my 240v outlet without a load. Silly me, I installed a new start compacitor, the compressor started up for all of 5 seconds before the circuit popped, the electric motor started smoking probably due to the start compacitor failing and leaking the oil from within.

So I am wondering is this due to my voltage regulator being bad and maybe giving too much voltage under load? Is there a good way to check this without ruining anything else? The start compacitor is 227-293 mfd 250v (they used to work alright) which is why my thought goes to the generator.
Could this be something that is bad inside my electric motor of the compressor?
Could there be something else wrong within the generator...more so what would cause a start compactior to almost instantly leak fluid?

I am very grateful for your time and help. I was a jet mechanic in the Navy so with the right help and guidance I would like to troubleshoot this properly to prevent having to spend more time and money to try and keep these compressors running to work on my bus.

Thank you!
1974Crownbus is offline  
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post #2 of 2 (permalink) Old 12-19-2017, 12:05 PM
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Al Caps operate on peak voltage not RMS (meter reading)voltage. 275 phase to phase (meter reading is about 389+ an 389 - which is 778 peak to peak. The high voltage is what is damaging your caps. Your AVR could be bad, but if the engine speed is too high, that will drive up your voltage (depending unit) to the point the AVR can be turned all the way down but the voltage is still high. If you have a hertz meter at no load you should be reading a max of 63 hertz an at full load it should be 60 hertz. I normally set small units with a 5% governor droop to 62.5 no load which will give you 59.5 at full load.
If your hertz is correct at no load an full load, an the voltage is still high you could have a bad AVR that is compounding when the load hits it. Rule out the engine speed(hertz) first before you go to the next step on the diagnosis chain.
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