There is a Craftsman 14a 1hp motor locally for very little. I would like to
try to use it to replace the 10a 1hp motor on my Delta 14" bandsaw.
The craftsman would have to be really really inefficient to only product 1hp
on 14a. I am thinking they are more conservative than delta on their
Does this seem like a reasonable try, or would I just be wasting money on a
really really inefficient motor?
True to a point. Some older motors were very inefficant.
If you need a replacement motor it probably will work fine, but don't be
surprsed it you see little or no power improvement. If you are replaceing it
just for the power gains I would save my money for a motor that you are
certain of the power, say a new 1-1/2 HP.
Motor designs and efficiencies haven't changed significantly in the last 90
years, so I would be more willing to believe that the labeling on the
Craftsman motor is incorrect. It could be that the motor was originally part
of a tool and the label showed the whole tool's power requirements rather
than just the motor. Without measuring the current draw of each motor under
an equal load and comparing them it will be difficult to know for sure. A 1
horsepower single phase 115 volt induction type motor will normally draw 6.4
amperes at full load, so neither label actually shows the rated current for
a typical 1 hp motor.
Are the motors physically the same size? Is the motor label clear (maybe you
are mis-reading it)? If it's significantly larger in size than your motor,
maybe it's a 2 hp motor. If it is larger, maybe it's worth the gamble to buy
it and find out.
"Wade Lippman" < email@example.com> wrote in message
While basic design of electric motors is the same as it was 90 years ago
there _have_ been significant changes in the execution of those designs.
And some types of motor, e.g. repulsion start/induction run, have not been
manufactured in perhaps 50 years or so. The motors made today are, in
general, more efficient than those produced 90 years ago. And there isn't
an electric motor made that will draw only 6.4 amps while producing a
Often wrong, never in doubt.
Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
Part of the problem lies in sensationalizing the motor claims. The current
rating might be a "peak inrush current" this number is obtained just before
the motor stalled. I really wish there was a requirement to state if the
values (either HP or current) were from continuous duty (What the motor
would be doing under normal operation But they tend to put the peak values
just to make the motor seems more powerful. in plan terms BS.
Power ratings on electric motors are "variable". As the mechanical load
on the motor increases the motor will draw more juice to carry the load.
The only thing that prevents the motor from developing near infinite
amounts of power is heat. The more juice the motor pulls, the hotter it
gets. When it gets hot enough the winding solder joints melt and the
electrical insulation cooks.
Physically bigger motors have more surface area to dump heat into
the air. For continuous duty (say turning a pump) a bigger motor has
more power than a smaller one, because the bigger one has more surface
area to exchange heat with the air. For intermittant duty (like
starting a car engine) we can extract quite a bit more power, because we
will turn the motor off before it overheats.
The same motor might be able to develop many horsepower for a short
period of time, but only a fraction of a horsepower for continuous duty.
For instance you can overheat your starter motor by hanging on t he key
and grinding away on a cold morning. The maker's marketing dept likes
to sell the product by giving it the highest horsepower rating they
dare, and they dare more and more as the years go by.
Rule of thumb, electric motors of the same size and weight are good
for the same amount of horsepower in real service (as opposed to
Motor current rating is usually concerned with fuse blowing. The
motor draws its max current under "infinite" load, i.e. with the rotor
Some loads, (for instance table saws) can load the motor enough to stall
it. The current rating is the the stall current rating. The 14 amp
stall current will twist harder (produce more stall torque) than the 10
amp will. This is acheived by using a lower resistance (thicker wire)
Electric motors are better than 90% efficient. 100% efficient motors
use 745 electrical watts to produce a mechanical horsepower. 90%
efficient motors use 827 watts to produce a horsepower. 827 Watts is
6.89 amps on a 120 volt circuit.
So, go with the 14 amp Craftsman if it is a deal. It will run just
as cool as the original motor, and perhaps have a little more starting
torque (which is a good thing). Or it might simply have a more
marketing driven stall current rating. If they are the same size
(aprox) then they will produce the same amount of useable mechanical power.
The National Electric Manufacturers Association (NEMA) controls the
rating of "standalone" motors, and NEMA requires a continuous duty
rating for motor power. Tools with built in, cannot-be-sold-by-them
-selves, motors like shop vacs and radial arm saws are not NEMA rated
and the maker usually gives an optomistic peak power rating.
Your post is accurate as I see it with only a couple of small nits to
pick about only" heat limiting power".
All it needs is the stipulation that the motor stays in synch with
Power factor and pole-slippage also limits what one gets to test at
Induction motors' biggest problem, aside from weight, is their limited
To get the tip speed on small diameter components to a usable
velocity, such as small router bits in edgebanders, for instance, one
has to increase the frequency of the supply...IF one wants to deal
with induction motors. Induction motors are preferred in those
applications, simply because when they're held withing their operating
range, the rotation speed is constant.
7 amps for a 1 HP induction motor at 120 volts is a reasonable
Sears has never been known for being conservative in their claims of motor HP;
quite the opposite, in fact.
Make sure you're comparing apples to apples, and not oranges: if the 10A
rating on the Delta motor is continuous-duty current, but the 14A rating on
the Craftsman motor is (as I suspect) locked-rotor current, you're better off
with the Delta.
Doug Miller (alphageek at milmac dot com)
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