On 11/30/2011 3:46 AM, harry wrote:
On Nov 30, 5:03 am, wrote:
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

The technology of motor has has improved vastly over the years.
Better, more heat resistant/thinner insulation, better magnetic
matrials, better design, Smaller clearance between stator and rotor.

Result, smaller and cheaper motor.

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.


HP equivalent to Watts.
HP =speed of motor X torque x a conversion factor

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

...


An electric motor size is limited only by heat losses and ability to
disperse them.

There are limits, like saturating the magnetic material.

--
bud--