On Wed, 20 Jun 2007 14:17:58 -0700, "RST Engineering"
wrote:

Good Lord, starting current of 64 amps at 115 volts? Most 15 amp breakers
would pop in half a second at 400% overload; how do these little one horse
compressors plug into a 15 amp circuit and start so easily? It is just when
you don't have nearly infinite current available from house mains and you
start fooling with generators that the situation becomes sticky.

If you go to Baldor's website and look at this motor (and the 3600RPM
is different), you'll note that this 1HP will acutally supply 2HP and
not stall ...

Lessee now, lets go to the 100% (one horse) column and we find at 115 volts
a PF of 79, 66% efficiency, and 15.4 line amps. One horse is 750 watts and
at the one horse level this rascal is sucking 1770 watts, or an efficiency
of 42%. But the table shows a 66% efficiency.

that's 1770 VA, not watts ... watts will be that times PF (already the
cos of phase angle applied) gives 1400 watts ... which my pea brain
shows as a hair under 54% ... not the 66% they show.

I work with 3 phase motors, and have found the calculations to be
better ... wonder where the extra power is?

Hmmm ... cos (79°) = .2 but
that factor of out of phase isn't going to get me into the ballpark, nor is
the sin at .98 going to get me anywhere either.

0.79 is cos(38 degrees)

Hmmmm ...

Jim

I agree that the data doesn't fit itself ... but it was a copy/paste,
not hand entered, so I didn't check carefully.

If you got a store bought 1HP compressor, I'd bet ti would have a more
accurately defined 0.5HP unit ... see following ... at 100% the
numbers check out ... 3.9A*230V*0.69*0.607=375W ...

Product Nameplate Data :
Rated Output .5 HP Hertz 60 NEMA Nom. Eff. 57
Volts 115/230 Phase 1 Power Factor 71
Full Load Amps 7.4/3.7 NEMA Design Code N Service
Factor 1.25
Speed 3450 LR KVA Code K Rating - Duty 40C AMB-CONT

(Typical performance - Not guaranteed values)
General Characterstics at 230 V, 60 Hz, 0.5 HP
Full Load Torque 0.75 LB-FT Starting Current 18.5
Amps
Start Configuration DOL No-Load Current 2.95 Amps
Break Down Torque 2 LB-FT Line-line Resistance @ 25° C
4.72 Ohms
Pull-Up Torque 1.6 LB-FT Temperature Rise, C @ FL (in deg) 78
Locked-Roter Torque 3 LB-FT Temp. Rise @ S.F. Load (in
deg) 92
Load Characteristics at 230 V, 60 Hz , 0.5 HP
% of Rated Load 25 50 75 100 125 150
S.F.
Power Factor 39 49 61 69 74 78 74
Efficiency 38.3 49.7 57.4 60.7 60.9 59.8 60.9
Speed (rpm) 3530 3490 3450 3420 3380 3340 3380
Line Amperes 3 3.2 3.5 3.9 4.4 4.95 4.4