On 12/2/2011 7:02 AM, harry wrote:
On Dec 1, 11:57 pm, The Daring
wrote:
On 11/30/2011 9:01 AM, bud-- wrote:





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.

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- Hide quoted text -

- Show quoted text -

I think most of the motor rewind places over here have closed down.
Cheaper to junk them and replace.
A lot of the new ones can't b erewound.

My first job out of college was working for an electrical supply company
that also had an electric motor repair and rewind shop.
The company supplied industry throughout that area of the state.
Repair and rewinding of electric motors is still a big business
around here.

TDD