1) hope the motor powers from some multiple of 6 or 12 volts.
2) lacking the above, build one MAN of a DC supply.
3) take it to a good motor shop
It would cost you more than it's worth to figure out if the torque, speed,
and stall current are within spec, if you had to build or buy the equipment.
Assuming that such a motor has a wound field rather than permanent
1) estimate rated field current by seeing what current results in a
steadystate temperature rise of about 20C with armature not excited.
2) With that field current applied, energize the armature with rated
voltage. Measure no-load speed and stall torque. (do the later
test quickly!) Measure armature current while stalled.
These tests are sufficient to determine the constants for the DC motor
equations describing speed and torque as fns of armature voltage,
armature current and field current.
it needs 80 amps at 250 V DC to run at rated load. Probably much less
without load, except at startup.
If you have a suitably rated rectifier, and a good electrical
subpanel, you can rectify your 220V AC.
If your motor is a permanent magnet design, it can function as a
generator. You can try spinning the shaft with anything and measuring
voltage across leads. If it spins and produces voltage, it is probably
There are much better experts than me, so let's see what they say.
A bit difficult to second guess the field rating and this is a
problem because it has such a major effect on motor performance. Field
dissipation of 5% of rated power or 20 deg C rise is a good starting
point but a this assumption may be well removed from the manufacturers
intended rating. I would have expected a motor of this size to carry
more nameplate information.
At rated voltage, the stalled armature current of a motor of
this size is little short of spectacular! I think it would be safer
to settle for a measurement of stalled torque per amp at close to
rated full load amps together with a measurement of back EMF per
Proper evaluation of a motor of this size needs pretty
substantial ancilliary equipment and a good understanding of it's
operation and limitations. For anything more than a rough test to see
if it's a dud motor it's not a task to be taken lightly. The light
hearted uncertainty on whether it's a 12 volt or 360 volt machine
doesn't engender a lot of confidence!
Or if he has a dynamometer, hold speed constant and record a change in
torque vs a change in armature current. For the EMF constant spin the
motor with field current applied and measure the generated open circuit
voltage at the armature terminals. He should post all of the
information on the namplate as a start.
As you say, a lot depends on the equipment available...
This is not a job to be undertaken by someone who has to ask such basic
questions in a METALworking group.
It is proper engineering job for an experienced consulting engineer with
experience in this type of indstallation.
Not sure what you mean by bench testing. Do you want to determine the
characteristics or just see if it runs?
Don explained some of the methods for determining motor constants.
Depending on your use, and since it's a big motor, you may also want
to measure friction and the armature inertia
Other parameters would be armature resistance and inductance to
complete the full set of parameters.
Then you can model the DC motor...
Of course, he could calculate counter emf at various points too, by
running the motor (if he knew the armature resistance) by measuring
armature current and applied voltage
How do you suppose engineers become trained to do such consulting?
That's why schools have labs.
I'm glad there are still students working with real machines in a real
laboratory rather than with 'puter sims. You can't simulate the
experience of a 50 HP DC motor drawing a gazillion amps of armature
current at stall, or if the field comes loose. Ya gotta see it in
person, after duly noting the motor bits still embedded in the bricks
from previous oopsies.
Unscheduled experiment: how fast can a twit lab TA dive under a
bench? Open field on big DC motor running with rated armature
voltage, time the twit when he hears it accelerating rapidly toward
kaboom. (Do close the field pretty quick. Forget about killing
armature current at that point; opening the switch results in a big
The show is well worth the ensuing loud lecture endured with
simulated contrite humility. Your grade may partly depend on the
quality of your simulation....