On Tue, 19 Jun 2007 21:09:51 -0700, "RST Engineering"
wrote:

Simple question. One horse compressor motor. How much peak
amperage/wattage to start it zero PSI in the tank, how much to keep it
running to max PSI of (say) 100 psi, and how much to REstart it when the
pressure drops to 80 psi.

Jim

You don't have full information there, but I went to Baldor's site and
picked a 1HP single phase general purpose motor, their L1310 for some
numbers.

Starting, 32A @ 230V (will be roughly double on 115). If less is
available, starting will take longer. No load current is 4.8A. NOTE
that power consumption at idel is not 4.8x230; idle PF will be less
than 0.1, I'd guess.

Following are 230V numbers, double currents for 115

Load Characteristics at 230 V, 60 Hz , 1 HP
% of Rated Load 25 50 75 100 125 150
S.F.
Power Factor 37 52 64 72 79 83 76
Efficiency 43.4 58.2 64 66 65.8 63.7 65.9
Speed (rpm) 1782 1766 1749 1729 1706 1676 1715
Line Amperes 4.9 5.3 5.9 6.7 7.7 9.1 7.3

ASSUMING 100 psi is 90% load, mayne 6.5A on 230. Restart at 80psi, if
compressor is properly designed, will be no worse than 0 psi start,
ie, it starts briefly unloaded. (It won't draw any more current in
any event, but the starting time would be extended)