After several posts asking about Motor Horsepower, I found the simplest explanation on this website.
- posted
20 years ago
After several posts asking about Motor Horsepower, I found the simplest explanation on this website.
Thanks Dave...good reference.
Bob S.
Yep, great link. I just found out my TS motor has 54% efficiency... Time to go shopping?
Using the HP equation:
hp = v * i * eff / 746
Plug in my values:
1.5hp = 115V * 18A * eff / 746Do a little algebra:
eff = (1.5hp * 746) / (115V * 18A)
Therefore:
eff = 0.54 = 54%
We aim to please!
Dave
gabriel,
What is the service factor on the nameplate? 1.0, 1.15, etc.
-- Al Reid
Hmm... have to check, I'm not in front of the saw right now... What's a service factor?
Service Factor (SF) indicates how much above the nameplate rating a motor can be loaded without causing serious degradation. On high service factor motors (1.3 - 1.5) I have seen the nameplate amps shown at SF rather than at rated HP. If the amps are at SF the efficiency is not as bad as you may think.
My Delta contractor saw has a 1.5HP, 3450RPM, 1.15SF, 115/230V motor with
12.8FLA. That works out to be a 76% efficiency.On the other hand, my pool pump is a 3/4HP, 1.5SP 115/230V motor that is rated at 9.3 Amp (at SF). If I run the calculation assuming that it is
9.8FLA the efficiency is 52%. However, if I adjust for the fact that the current is at SF (1.125 HP) the efficiency works out to be about 78%.-- Al Reid
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain
Thanks. You are right, the efficiency seems awful and it appears that it really is. 18 amps is pretty high for a 1.5 hp motor. The motor on my jet saw says 1 3/4 hp, 12 amps at 115 volt. Jet puts pretty good motors on their equipment.
Bob
NEMA defines service factor as:
"The service factor of a general-purpose motor is a multiplier which, when applied to the rated horsepower, indicates a permissible horsepower rating loading which may be carried under the conditions specified for the service factor."
For a 2-pole, 1/2 through 1 HP motor the SF is 1.25;
1/6 - 1/3 HP it's 1.35; 1/20 - 1/8 HP it's 1.4.RB
gabriel wrote:
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