4 HP on 115v??

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Al Reid responds:

Yeah, well Marathon is said to be among the best--and with the 3600 rpm 1-1/2 HP unit listing for $320, they should be!
Charlie Self "Character is much easier kept than recovered." Thomas Paine
http://hometown.aol.com/charliediy/myhomepage/business.html
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My point was to show that motors are still rated in output HP from reputable vendors. Delta, for example, list their saws in traditional HP whale others list input amps or that fictitious peak HP baloney.
Having worked with AC motors and machinery for almost 25 years, I understand how one arrives at the BHP and torque requirements for a machine and tow to match a motor to the application. Again, the only thing that is meaningful is the HP and Torque at the output shaft. With that you can do a reasonable comparison.
The other interesting thing is that when these ratings are used, there is no easy way to compare. Just look at how many different Peak HP figures there are for 115v 15A input devices. Saws at 4.4HP, compressors at 6HP.
-- 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

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A motor _should_ be rated by the HP it can deliver continuously. Additional ratings are often given for various duty cycle such as a 1 hour rate (normally 10 to 20 % higher than continuous) at which the motor can be loaded for 1 hour without overheating. Most AC induction motors can develop two to four times their continuous rating for a short time. This has nothing to do with stall condifiton since with a stalled rotor, not power is being developed - although a lot of power is going in and being turned to heat.
The current rating of a motor should be the current it draws at rated voltage when developing rated continuous power.
As to efficiency - it depends on many things. It varies with the motor constuction which can provide in excess of 90% maximum efficency to less than 60% for a lousy motor at peak effciency. It also depends on load. Peak efficiency normally occurs under light load and drops as the motor is loaded to its continuous rating (whick can still be over 80% efficiency) and continues down as the motor is loaded closer to its peak rating.
If you will note, most of these inflated power ratings have the words peak or maximum. This peak can be reached momentarily either by a fused circuit for a brief time as the fuse becomes overloaded and then reacts to the overload, or by a circuit (just for testing) that can supply whatever current the motor asks for.
The best lies are 99% true. I'll bet these inflated ratings can be backed up by actual data. What isn't said is that these test conditions can't be approached in ordinary use.
Allen
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