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Air Compressor power question


Jan 6, 2007
Please excuse me I haven’t read all the replies my iPad seems to be acting up.
It sounds like the unloader valve isn’t doing the job and the motor has to fight the partially full cylinder of air, you can hear that, you want that compressor up to speed before it gets to do any squeezing air, I’d check it
I fitted a bigger unloader pressure switch to my cheap air pumper, it really made a difference, the one on it was a tiny tube.
I’ve done a manual unload with a 1/2” ball valve inserted in a tee between the head and non return valve ( cheap ones usually leak air between the receiver and the cylinder)


Hot Rolled
Feb 24, 2013
Santa Cruz
When I first started my shop I had a single phase 7.5hp IR reciprocating compressor. Every time it started my lights would dim and my CNC's would error.

This was with 200 amp service and #2 wire. I was stumped.

One of the big issues and people here have alluded to it was that I had a 10kva transformer on the pole out front connected to my shop with #2 wires.

Power company replaced that with a 50kva transformer and 4/0 wires and I never had power drop issues again. Might need to look upstream of your place.

BT Fabrication

Nov 3, 2019
We have a 1200A 208V 3 phase service at our shop. What they don't say is that if you draw 1200A the voltage will drop to 183 volts.

In some areas they'll refuse to upgrade your service capacity, not because of the capacity of the wires, but because the resistance is so high you won't have enough voltage left.

yep, even a 400A service is only rated at 340A continuous i believe