save electricity with compressor

I think your original premise was correct, even if your numbers were not. As for ac motors being inefficient at low loads, that's not really true. Obviously it doesn't make sense to use a 10 hp motor to drive a 1/2 hp load, but the losses are not that great. Putting a lot of oversize induction motors on a circuit is going to drive down the power factor, which will cause volt-amps to go up. But you pay for power, not volt-amps.

Charles

The volume of air I refer to is SCFM or standard cubic feet per minute of air. This maeans a cubic foor of UNPRESSURIZED air.

Your compressor is rather unusual in its amp draw. I have run mine with an clamp on amp meter on it and usually see no more than one amp of increase with pressure. Mines a 7.5 hp that draws about 32 amps. You must be running a ten hp or better unit.

Charles

It most certainly requires more energy to raise the tank pressure to a higher pressure. A lot of the energy is converted into heat, which is subsequently radiated through the tank wall and lost. So the most efficient way to operate an air compressor is to raise the pressure no higher than required to maintain regulated pressure.

True, your compressor draws a lot of current at startup, but that current spike does not necessarily translate to a lot of energy. Even assuming that current=power (it doesn't, by the way), a one-second startup would only consume a small percentage of the power in a two-minute run.

Whether or not you would save any significant money by running your compressor at a lower pressure is hard to say, but it makes no sense to operate the compressor at a higher pressure than is required. Higher pressure means more heat, and heat is what will kill your compressor.

Line losses and tool working efficiencies however are two reasons why setting the cutout pressure down to 120 psig might not be a great idea. But it depends on the actual installation, usage profile and acceptability of tools working at a lower performance than they are capable of. Grinders and sanders are particularly dependent on throttle pressures for good performance. For most home shops, I doubt the savings would be significant enough to warrant the costs in money and time to install the switches. You might not even be able to even notice the savings as they would likely be low enough to get lost in the normal variability of a home electric bill. Now if you were to install a KWH meter on just the compressor (additional $$$) you could eventually determine how much money you are saving (or already lost).

MAY GOD BLESS THE USA

Charles

Although startup current can be quite high, the duration is very short and little extra energy is consumed during startup. Unless you are paying for peak demand current startup peaks make little difference in power cost.

Regards
Gary