8iowa wrote:A/C induction motors are rated a certain HP at a maximum continuous temperature rise. This is done in a dynomometer lab with thermocouples in a lot of places on the motor. This does not result in haphazard ratings from one manufacturer to the next, because the HP, frame size, and temperature rise (55 degrees C) of induction motors is standardized by the National Electrical Manufacturer's Association (NEMA). One of the characteristics of single phase and three phase induction motors is that the speed torque curve is very flat. Thus the motor can be overloaded, almost to the point of breakdown, without very much drop in speed. Thus a 1 HP motor can withstand brief overloads of say 1 1/3 HP, but of course would eventually burn up with this overload in continuous operation. Perhaps this is where the "developed HP" term comes from, but this term is not used by NEMA. Some motors, built with higher temperature insulation are rated 1.15 service factor, and this would be so indicated on the nameplate. Induction motors are wound around a certain even number of poles, which gives the motor a set speed at 60HZ, ie: 3600 rpm - 2 pole, 1800 rpm - 4 pole, 900 rpm - 6 pole, ect. The actual full load speed will slightly less due to slippage between the field and the rotor, thus nameplate full load speeds are usually around 3450 rpm - 2 pole, 1750 rpm - 4 pole, 870 rpm - 6 pole.
A great many universal type electrical motors and now being used to power stationary power tools. This of course is a cheaper power source than a NEMA induction motor. Universal motors can be made to operate on A/C or direct current. They have brushes and commutators and operate at very high speeds, 10,000 to 20,000 rpm being very common. There are no standards, NEMA or otherwise for universal motors. They are electrically less efficient than induction motors and characteristically they have a much higher noise level. They also have a much shorter life span. Since HP is basically a formula involving speed and torque, universal motors get their HP essentially from speed rather than torque. Quite often now-a-days, universal motors are rated in amps, a rating whose only useful purpose is to help you ascertain if your circuit is adequate. For the user, the actual HP would be largely a guess
8Iowa
What you said is basically correct but fact is most woodworking tool manufactures don't used NEMA rated motors. Most in fact are sparsely labeled motors from over seas. The only real concern they have is frame size and what hype they can use in their ads. The main concern of most non industrial tool manufactures is obtaining the UL sticker which limits their input amperage by voltage.
Nonetheless the fact is two motors turning basically the same speed drawing basically the same amperage produce nearly the horsepower, certainly not the differences some manufacture claims of 2 and 3 horse power.
I agree while amperage is a fairly nebulous term the fact remains you don't get something for nothing. Wiser men than me have decided that 745.69982 watts of electrical energy eguals one horsepower of mechanical energy and proven science tells us 745.6992 units of energy measured in watts
absolutely/B] can not/will not produce more than 745.69982 watts of energy output. Also knowing that friction causes some input energy to be lost in heat the productive or useful output must always be less than input. No exceptions!
Now if people want to play games and make believe they have discovered perpetual motion or magically multiplication of power by listing ridiculous horsepower claims fine. But the fact is they MUST use terms like developed or realized horsepower and that should alert everyone that they are playing games.
Again the government has jumped on more than one manufacture over this very issue. New truth in labeling laws that are being enacted and class action suits have made most horsepower ratings without an additional adjective a thing of the past for consumer products.
