Adjusting an overload properly

Ignoramus16649 · 2009-03-04T13:23:27+00:00

I have been cleaning up this Quincy install by properly tucking cablesinto conduits, wiring things correctly, using crimped terminals whereappropriate, etc.My Quincy compressor comes with a nice old Size 2 electrical control.The nice thing about it is that overloads are adjustable by turninglittle knobs, so I do not have to buy overload heaters. At 220v, it israted at up to 15 HP. The motor I have on the compressor right now, is10 HP.The compressor was wired for 440 volts originally and had a 7.5 HPmotor (much bigger than my current 10 HP motor). So the overload settingthat it had set, obviously would not match. For for the first fewweeks I did not use overloads by bypassing them, but now I want to setthem properly.The question is what is "properly".My thinking is that in this context, it means that the compressor canreliably restart at the restarting pressure (100 PSI or so), but atthe same time, overloads should pop in a second or so if the motor isstalled. I can reproduce a stalled motor very easily, by stopping thecompressor when there is pressure in the tank, and restarting within aminute, before unloaders bleed enough air. (I hope that it is not anindication that something is wrong with unloaders, a separate topic)I already set the overloads, apparently high enough so that they donot pop when the motor is running regularly. So, therefore, to me theprocedure now would be to turn them down, to the point when theyreliably pop on a stalled motor, but when compressor still startswell.Am I missing something and is that too unscientific?

Mar 04, 2009 22 Replies

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RogerN 17 years ago

Normally I just set the overloads to the full load amps of the motor. They should be designed to allow over current for starting but pop before the motor gets hot enough to damage it.

RogerN

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Wes 17 years ago

His is a far more complex unloader system than most. Nice touches though!

Wes

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Buerste 17 years ago

I'm reminded of all the times I've bypassed heaters. They usually were replaced in a day or two, but production comes first!

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