Hi,

I know there's a lot of ambiguity about horsepower in electric
motors, and maybe I shouldn't even go there. So I'll get right to the
application.

I should be done next weekend with my KMG clone, a 2X72" grinder.
I'm told that I'll want 2-3hp running it, I believe it.

I may have found a freebee motor off of an ancient-looking machine.
I haven't run it, but looks in good shape. The specs a

1160 rpm
110/220V & 9.2/8.6 amp
..5 HP

it is something a little over a foot in diameter. At least by hobbyist
woodworking standards, I consider it quite a large motor. It is
labeled 1/2 hp, but is bigger than my 2hp bandsaw at home, and far
bigger than my "2hp" hand-held router.

Is this just a matter of semantics? And this motor might be powerful
enough to run my grinder just fine?

Or, someone at a used machinery dealership once told me that such
motors ARE in fact merely as powerful as their faceplate says, no
stronger, but that because of their massive construction they'll just
never burn out whereas those hand-held routers eventually do?



thanks!
-Bernard Arnest

"Bernard Arnest" wrote in message
oups.com...
Hi,

I know there's a lot of ambiguity about horsepower in electric
motors, and maybe I shouldn't even go there. So I'll get right to the
application.

I should be done next weekend with my KMG clone, a 2X72" grinder.
I'm told that I'll want 2-3hp running it, I believe it.

I may have found a freebee motor off of an ancient-looking machine.
I haven't run it, but looks in good shape. The specs a

1160 rpm
110/220V & 9.2/8.6 amp
.5 HP

it is something a little over a foot in diameter. At least by hobbyist
woodworking standards, I consider it quite a large motor. It is
labeled 1/2 hp, but is bigger than my 2hp bandsaw at home, and far
bigger than my "2hp" hand-held router.

Is this just a matter of semantics? And this motor might be powerful
enough to run my grinder just fine?

The specs seem inconsistent. It's drawing a lot of amps for a 1/2 HP motor,
and should draw about half the amps at 220 that it does at 110. WRT the
other question about motor ratings, some small tool and vacuum motors are
deceptively rated at peak power output.

If it says half horse then that is what you've got. Many high speed
motors such as routers and shop vacs claim 5 and 6 developed hp. but this is
not true horse power as they soon loose rpms with any load. It takes nearly
15 amps of 115 V current to develop 1 hp.

--
Richard H. Neighbors
Building and repairing fine billiard cues for real pool players at
affordable prices.
Over 35 years exp. Located in Cincinnati OH
ph.# 513 233-7499
e-mail
web site http://www.dickiecues.com
"Bernard Arnest" wrote in message
oups.com...
Hi,

I know there's a lot of ambiguity about horsepower in electric
motors, and maybe I shouldn't even go there. So I'll get right to the
application.

I should be done next weekend with my KMG clone, a 2X72" grinder.
I'm told that I'll want 2-3hp running it, I believe it.

I may have found a freebee motor off of an ancient-looking machine.
I haven't run it, but looks in good shape. The specs a

1160 rpm
110/220V & 9.2/8.6 amp
.5 HP

it is something a little over a foot in diameter. At least by hobbyist
woodworking standards, I consider it quite a large motor. It is
labeled 1/2 hp, but is bigger than my 2hp bandsaw at home, and far
bigger than my "2hp" hand-held router.

Is this just a matter of semantics? And this motor might be powerful
enough to run my grinder just fine?

Or, someone at a used machinery dealership once told me that such
motors ARE in fact merely as powerful as their faceplate says, no
stronger, but that because of their massive construction they'll just
never burn out whereas those hand-held routers eventually do?



thanks!
-Bernard Arnest

Hi,

Oh, sorry; the 8.6 is a typo. I believe it was half of the 9.2.

Why the enormous size then? Does it just have a larger casing, or
are even 1750/3500 rpm motors of more realistic size also going to lose
rpms under load compared to this half horse that looks like a 5 horse
in size?

Even assuming that the 9.2/8.6 amps is really 9.2/4.6 amps, the specs
seem to be out of whack. That works out to 1012 watts at full current
draw. 1 hp is 746watts plus add some for various losses so that motor
should put out well more than 1/2 hp or else it will be getting very HOT!

Old motors were always much larger than newer ones. On top of the design
issues, this one is an 1160 rpm motor which means it is a 6 pole motor
compared to the usual 4 pole (1750 rpm) or 2 pole (3450 rpm)

This motor will have a big torque curve as well a huge reserve capacity
when you try to bog it down. Downside is that you will likely want to
use a belt drive to increase the rpm at the sander head. Get you surface
speed right and try it out.

Bernard Arnest wrote:
Hi,

I know there's a lot of ambiguity about horsepower in electric
motors, and maybe I shouldn't even go there. So I'll get right to the
application.

I should be done next weekend with my KMG clone, a 2X72" grinder.
I'm told that I'll want 2-3hp running it, I believe it.

I may have found a freebee motor off of an ancient-looking machine.
I haven't run it, but looks in good shape. The specs a

1160 rpm
110/220V & 9.2/8.6 amp
.5 HP

it is something a little over a foot in diameter. At least by hobbyist
woodworking standards, I consider it quite a large motor. It is
labeled 1/2 hp, but is bigger than my 2hp bandsaw at home, and far
bigger than my "2hp" hand-held router.

Is this just a matter of semantics? And this motor might be powerful
enough to run my grinder just fine?

Or, someone at a used machinery dealership once told me that such
motors ARE in fact merely as powerful as their faceplate says, no
stronger, but that because of their massive construction they'll just
never burn out whereas those hand-held routers eventually do?



thanks!
-Bernard Arnest

From direct experience: I have a VERY old 20" bandsaw with a motor about
that size. It is rated at 800 RPM. and the lower wheel is driven directly
off the motor shaft. It takes about 30 seconds to come up to speed, and I
can slow it down easily by forcing the wood into the blade.

There are a couple of reasons your motor is so large: 1.) It is old 2.)
It is low RPM.

Routers use brush (AC/DC) motors, and turn at very high RPM. Power is the
product of RPM and torque. Your motor turns slow, and has lots of torque.
Routers turn fast and have low torque.

You can try, but I am afraid that if you use a belt/pulleys to get the RPM
up, you will be able to stall it when you grind.

Bernard Arnest wrote:

it is something a little over a foot in diameter. At least by
hobbyist woodworking standards, I consider it quite a large motor.
It is labeled 1/2 hp, but is bigger than my 2hp bandsaw at home, and
far bigger than my "2hp" hand-held router.


I'm not a motor expert by any means, but I can relate my recent experience
in replacing the huge 1140RPM motor off my '33 South Bend (the original and
rated at 1/2 HP) with a modern motor/VFD rated at 1HP that is less than half
the size and weight of the original.

The new motor is clearly more powerful. The original motor weighed 100
pounds easy, but the new motor, while smaller and not nearly as cool looking
is way stronger. I posted about this subject while I was going through the
process of deciding whether I should replace or rebuild, and the responses I
got might be interesting reading for you. Try a Google search.

Peter

"Bernard Arnest" wrote in message
ups.com...
Hi,

So do you think, even being 1/2 HP, that it would work for this
grinder? I was planning on a belt drive anyway, so that's no big deal
at all. Are 2hp only needed because of the load the grinder puts on it
anyway, so with the reserve capacity I could get away with it?



thanks!
-Bernard

A large part of the size difference is because of the allowable temperature
rise. Old motors used insulating materials that would not stand very high
temperatures. They had to be larger to dissipate the power losses without
getting too hot. Newer motors use high temperature rated insulations and can
safely run hotter, so can be smaller. The old motors tend to have more
losses which also requires them to be bigger.

Because of the larger thermal mass, an old motor would take longer to
overheat when overloaded but motors are basically rated for their maximum
continuous power within allowable temperature rise. I do not think that an
old 1/2HP motor should be expected to be satisfactory for an application
needing 2HP to be available.
Don Young

Bernard Arnest wrote:

I know there's a lot of ambiguity about horsepower in electric
motors, and maybe I shouldn't even go there.

It perhaps isn't quite so much of a minefield as you think. Most decent
industrial quality motors are honestly and unambiguously rated. Many
motors on consumer goods, cheap power tools, cheap compressors etc. are
not. Two of the most common ways to boost a motor's rating for marketing
purposes are to (i) quote the input power rating instead of the output
power, or (ii) quote an intermittent power rating, which the motor
cannot sustain continuously. There are also no doubt less scientific
methods which verge on sheer lies.

As people have mentioned, there are a few reasons why your 1/2 hp motor
is so large. Firstly it's old. Old motors run cooler and operate at a
lower magnetic flux density than modern motors. In order for them to run
cooler they require a larger surface area to conduct their lost power to
the atmosphere, which requires the motor to be physically larger. They
also require a larger diameter rotor in order to generate the same
torque in a field of lower magnetic flux density. Lastly, it's a slow
running, six pole motor. Old or new, a slow running motor will be larger
than a fast running motor of the same horsepower rating because it needs
to produce more torque.

Old motors do have the advantage of greater thermal capacity, which
means that they may be capable of withstanding short term overloads
better. I have a 3/4 hp motor (probably dates from the 1950s and weighs
about 40-50 lbs) which has seen quite a lot of abuse during experiments.
I remember noticing that after being stalled repeatedly over the course
of about 10 minutes it was barely warm. Old motors are also inherently
nicer in their construction and appearance - you don't get problems with
fins breaking off, cracked fan cowlings, etc. - but there's some luck in
the draw. Some ancient, scrounged motors run perfectly and seem almost
indestructable, but others will need a rewind.

There's no harm in trying your motor out to see if it will run your
machine. Set it up to give the correct grinding speed and see if it
provides adequate torque. If it does, run the machine hard for a few
minutes and see how hot the motor gets. Touching it with your hand is a
pretty poor way of telling if the motor is too hot, but if you quickly
disconnect it from the electricity supply you can measure the change in
winding resistance and from that calculate the temperature rise. If it's
of interest I can scan a page from one of my books which explains the
procedure.

Give it a go (I'm a great enthusiast for old motors).

Chris

Pulling those currents, it's around half a horse. If it's old enough,
it's probably got woven cotton or maybe silk insulation, those are very
bulky compared with the insulation coatings we have today, they needed
a lot of space for the same number of turns of wire. The magnetic
materials were less efficient than what we have today and the allowable
running temperatures were lower, too. As others have said, it's a
low-speed motor, more poles so it's bigger. Might be something other
than a capacitor-start split-phase unit, too, there were some other,
less-common, starting technologies in the past. I don't think you're
going to be happy replacing a 2 HP unit with it. If it's free, give it
a whirl, though.

Router units are high-speed series AC-DC motors with brushes, they're
MADE to wear out. Regular single phase motors will last as long as the
starter switch contacts, bearings and insulation hold out, decades for
most.

Stan

Hi,

Thanks for the answers! They helped a lot. I'll keep on
looking, then, for a 2-horse, but might as well pick this one up. I'll
always have a use for another decent motor; many things can run off of
1/2 hp.

One more question out of curiosity: If 3500 rpm motors can be
smaller than 1750 rpm motors, isn't it cheaper to exclusively
manufacture 3500 rpm motors and then always use a belt to slow it down
to 1750 if that's what you wanted? Often I want a belt even if there
is no rpm change; it is more forgiving than direct drive to set up, and
if I overload it the belt can slip, which is safer for the motor's
health.

So long, of course, as the bearings aren't too likely to wear out
much faster on the faster motor. Naturally I wouldn't find a 2hp
router off ebay and then gear it down to run my bandsaw, even if it
actually does have the horse power I think I'd just wear it out too
quickly :-)




-Bernard

Christopher Tidy wrote:
Bernard Arnest wrote:

snip

One more question out of curiosity: If 3500 rpm motors can be
smaller than 1750 rpm motors, isn't it cheaper to exclusively
manufacture 3500 rpm motors and then always use a belt to slow it down
to 1750 if that's what you wanted?


I've seen it done on a few cheap machine tools, but I don't think it
gives the advantage you might expect. Both 2-pole (3500 rpm in the US)
and 4-pole (1750 rpm) motors are pretty cheap. Using a faster motor may
well require an additional belt drive stage, which adds to the cost and
reduces efficiency. Faster motors are also noisier and wear out more
quickly, so they have significant disadvantages in a quality machine
tool. Where it is more common is when an output speed of a few hundred
rpm is required. Rather than buy (or build) a bulky and expensive 8-,
12- or 16-pole motor, a 4-pole motor will usually be used and the speed
reduced using a belt drive or gear train.

Each shaft/sheave combination absorbs some energy, and adds cost. It isn't
always true that faster motors are noisier, though. I have a 3450 rpm 3-phase
motor which has sleeve bearings which runs quietly.

GWE

Bernard Arnest wrote:

snip

One more question out of curiosity: If 3500 rpm motors can be
smaller than 1750 rpm motors, isn't it cheaper to exclusively
manufacture 3500 rpm motors and then always use a belt to slow it down
to 1750 if that's what you wanted?

I've seen it done on a few cheap machine tools, but I don't think it
gives the advantage you might expect. Both 2-pole (3500 rpm in the US)
and 4-pole (1750 rpm) motors are pretty cheap. Using a faster motor may
well require an additional belt drive stage, which adds to the cost and
reduces efficiency. Faster motors are also noisier and wear out more
quickly, so they have significant disadvantages in a quality machine
tool. Where it is more common is when an output speed of a few hundred
rpm is required. Rather than buy (or build) a bulky and expensive 8-,
12- or 16-pole motor, a 4-pole motor will usually be used and the speed
reduced using a belt drive or gear train.

Best wishes,

Chris

On 17 Apr 2006 13:16:53 -0700, "Bernard Arnest"
wrote:

Hi,

Thanks for the answers! They helped a lot. I'll keep on
looking, then, for a 2-horse, but might as well pick this one up. I'll
always have a use for another decent motor; many things can run off of
1/2 hp.

One more question out of curiosity: If 3500 rpm motors can be
smaller than 1750 rpm motors, isn't it cheaper to exclusively
manufacture 3500 rpm motors and then always use a belt to slow it down
to 1750 if that's what you wanted? Often I want a belt even if there
is no rpm change; it is more forgiving than direct drive to set up, and
if I overload it the belt can slip, which is safer for the motor's
health.

So long, of course, as the bearings aren't too likely to wear out
much faster on the faster motor. Naturally I wouldn't find a 2hp
router off ebay and then gear it down to run my bandsaw, even if it
actually does have the horse power I think I'd just wear it out too
quickly :-)




-Bernard
SOME of the big motors have repulsion start, which gives more STARTING
power than the smaller cap start motor, which gives more starting
power than a split phase or shaded pole. There are applications where
a repulsion start 1/2 horse will start a bigger load than a 1 or 2 hp
capstart, and the bigger motor(1 or 2 HP) is only used because the
start load is too big for today's common cap starts.

We had a 2HP repulsion start Leyland motor on a bale elevator - took a
5HP cap-start to start with the same load. Could likely have RUN the
elevator on 1HP if you never started it under load. We used it for
bale threshing, so it OFTEN started with a full load.
*** Posted via a free Usenet account from http://www.teranews.com ***

clare at snyder.on.ca wrote in message
...
On 17 Apr 2006 13:16:53 -0700, "Bernard Arnest"
wrote:

Hi,

Thanks for the answers! They helped a lot. I'll keep on
looking, then, for a 2-horse, but might as well pick this one up. I'll
always have a use for another decent motor; many things can run off of
1/2 hp.

One more question out of curiosity: If 3500 rpm motors can be
smaller than 1750 rpm motors, isn't it cheaper to exclusively
manufacture 3500 rpm motors and then always use a belt to slow it down
to 1750 if that's what you wanted? Often I want a belt even if there
is no rpm change; it is more forgiving than direct drive to set up, and
if I overload it the belt can slip, which is safer for the motor's
health.

So long, of course, as the bearings aren't too likely to wear out
much faster on the faster motor. Naturally I wouldn't find a 2hp
router off ebay and then gear it down to run my bandsaw, even if it
actually does have the horse power I think I'd just wear it out too
quickly :-)




-Bernard
SOME of the big motors have repulsion start, which gives more STARTING
power than the smaller cap start motor, which gives more starting
power than a split phase or shaded pole. There are applications where
a repulsion start 1/2 horse will start a bigger load than a 1 or 2 hp
capstart, and the bigger motor(1 or 2 HP) is only used because the
start load is too big for today's common cap starts.

We had a 2HP repulsion start Leyland motor on a bale elevator - took a
5HP cap-start to start with the same load. Could likely have RUN the
elevator on 1HP if you never started it under load. We used it for
bale threshing, so it OFTEN started with a full load.

My old Wells 8M band saw has a repulsion start motor.