Horsepower of electric motor V/S Size of motor

I have a 1/2HP electric motor on a power saw, and that motor is fairly large. I just bought a portable pump for transferring water from items such as a flooded washing machine, bathtub with clogged drain, etc. That motor is only about 35% of the size of the motor on my power saw, yet the tag says it's a 1/2HP motor.
How can one 1/2HP motor less than half the size of another 1/2HP motor produce the same horsepower? Is there another factor to take into account besides the HP? Is it torque, or some other factor? Somehow I cant see how this small pump motor could power my saw....
Thanks
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snipped-for-privacy@myplace.com wrote in

1. Skimpy design. 2. The waterpump may be cooled a bit by the pumped water. 3. The designer might have counted on short runs with enough cooling down in between. All that allowes a smaller motor.
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I think that the water cooling may be a big part of it. Heat buildup is part of the reason regular continuous-duty electrical motors are so large - for example, an automotive starter motor develops more power than likely anything in your workshop but is relatively small - because it's not designed for continuous usage, so heat buildup is pretty much neglected as a design consideration. But try to use one under load for more than a couple minutes at a time, and see what happens...
nate
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Ever notice the HP ratings on shop vacuums?
I saw one that said 6 HP yet it had a 16 gauge power cord on it.
Since 1 HP = 746 watts, that cord was passing 4476 watts or 37.3 amps.
WTF? How could that be? It seems as though someone is stretching the HP rating a bit.
Didn't the small gas engine companies get busted for lying about their HP?
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From:
http://machinedesign.com/article/green-technology-more-efficient-motors-0619
<<Six factors account for most of the energy lost in an ordinary induction motor: iron-core losses, stator resistance, rotor resistance, windage and friction, and stray load losses. NEMA Premium motors minimize these factors in a variety of ways, usually through use of high-grade steel and increased use of active materials. For example, high-grade steel in the rotor lets manufacturers use thicker laminations that take less time to manufacture, but which still reduce ironcore losses caused by circulating currents. Similarly, manufacturers reduce stator resistance by boosting the amount of copper in the stator windings.>>
--
Bobby G.




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one thing for certain newer motors, ones produced in the last 10 years are physically smaller.....
they are welded or glued together, lack heavy steel cases, and no doubt cant last as long as older ones, no service needed, typical cheap modern design. toss and replace when it has a problem...
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On 11/30/2011 3:46 AM, harry wrote:

Adding to that, motor design was pushed closer to the electrical design edge to make cheaper motors. (Some of that has been reversed in high efficiency motors.) Many years ago the standard 'frame size' was reduced a couple times if I remember right. If the saw has a motor that is quite old it may be larger than an equivalent motor made now.
Some motors have a "service factor" rating (maybe 1.15). That means the motor can be operated beyond its rated HP with a somewhat shorter life but not drastically shorter life. I never looked, but motors with a SF rating may be larger.
Motors have a nameplate "duty" rating, usually "continuous". Sjouke suggests the pump may have an intermittent rating.
Then there is the deliberate misrating of motors, as was done for instance by compressor manufacturers.

In case that isn't clear, lower RPM motors are likely larger for the same HP.
<...>

There are limits, like saturating the magnetic material.
--
bud--

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On 11/30/2011 9:01 AM, bud-- wrote:

I go through a lot of electric motors at times and air handlers in some of the older commercial buildings will have these huge 1/2 to 1hp cast iron frame motors that are infinitely rebuildable as long as the casting isn't cracked or wallowed out. The motor rewind shops I deal with usually keep a few already rewound in stock. Some years back, I had to remove for rewinding, a 60hp 444S frame motor from a 60 ton open drive air conditioner compressor and the old 60 horse was the same size as a modern 100hp electric motor. I actually found the guy who had rewound the motor 20 years before, he remembered it and rewound it again. ^_^
TDD
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Without even going into considerations of efficiency, torque characteristics, or type of moter (induction, series/universal, etc.) one common way is simply to increase the operating RPM. A 1 HP motor operating at 3600 rpm can be significantly smaller than one operating at 1800 rpm.
--
There are no stupid questions, but there are lots of stupid answers.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
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On Tue, 29 Nov 2011 23:03:30 -0600, snipped-for-privacy@myplace.com wrote:

I am surprised in all of the answers, nobody mentioned there are different types of motors. There are smaller motors like the one on a hand drill that create a lot more horsepower in a small package than the induction motor on your saw. They are not as efficient. and they won't last as long tho. Perhaps that is where you should start. what kind of motor is it?
Of course there are also a lot of out right lies in motor ratings, particularly when the motor is built in and you don't have a regular NEMA nameplate.
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On Nov 30, 12:03am, snipped-for-privacy@myplace.com wrote:

There is no standard ratings system for tool and appliance motors, and manufacturers use fuzzy math to make their products look more powerful than they really are.
Just look at vacuum cleaners. You go to Kmart and pick up some cheap plastic Hoover that boasts "2.5 HP" or some such... Plug it into the WattsUp meter at home and it might draw 7 Amps when it's trying to inhale the fringe throw rug.
7 Amps at 120V is nowhere near 2.5 HP. You couldn't put 2.5 HP worth of power through the 15A electrical circuit you have it plugged into.
They rated the motor by how many Amps it is drawing just before it stalls and burns out.
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