the Confusion about DC Motor HP Ratings
By: J. McNamara & D. L. Davis
a popular question in the electric golf car
motor business. As the leading distributor
for General Electric® (GE) golf car motors,
the staff at one of our manufacturers, hears
it often. "Why is your D380 motor, rated
at a mere 5.5 horsepower (HP), faster and more
powerful than a competitor's motor rated at
11 or 16 HP?" Though the answer may not
be simple, we can clear up some of the confusion.
main source of confusion is the result of companies
rating their motors at or near peak outputs.
Though there is nothing wrong with this practice,
it is quite misleading. The thing to keep in
mind is that peak horsepower output of a direct
current (DC) motor cannot be sustained for
more than a second or two. If a motor was forced
to operate at peak performance for any longer,
it would self-destruct.
manufacturer has worked with GE's engineers
to determine the true sustainable HP rating
of our motors. Our ratings are the result of
rigorous testing, both at GE's plant, as well
as our own. Once the rating has been determined,
we label our motors indicating the horsepower
at or near the true sustainable output in actual
factor to consider with horsepower is line/battery
resistance. The true output of a DC golf car
motor drops even further when the golf car
system resistance is factored into the equation.
Even the length and diameter of battery cables
will affect the output of a motor.
following chart gives examples of ratings and
how they are affected by amperage and resistance,
such as the D380 which is rated as high as
36 HP at 48V and 700 amps. As previously mentioned,
these are peak ratings, not sustainable ratings
which indicate the actual horsepower of the
motor. We rate our motors based on output during
actual use so you know what you are getting.
next time you are deciding which motor to use
to upgrade a golf car and the salesman is telling
you his motor, rated at 11, 16 or whatever
horsepower, is better than our 5.5 HP motor
(D380), youll know that labels dont
tell the whole story. The proof is in the performance
and HT Electrics motors, built by GE,
outperform any comparable motor on the market.
you buy a motor based solely on label information,
ask the salesman if it is rated at "peak" or "sustained" performance.
Also ask if line/battery resistance was factored
into the calculation. You will surprise him
with your knowledge and help clear the confusion
about HP ratings for DC motors.