Clearing the Confusion about DC
Motor HP Ratings
By: John McNamara & Debra L. Davis
It's a popular question in the electric golf car
motor business. As the leading distributor for General Electric®
(GE) golf car motors, the staff at HT Electric, Inc., in Tucson, Arizona
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, HT
Electric can clear up some of the confusion.
The 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
At HT Electric, we have 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 use.
Another 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.
The 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. At HT Electric, we rate our motors based
on output during actual use so you know what you are getting.
The 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), you’ll know that labels don’t tell the whole story. The
proof is in the performance and HT Electric’s motors, built by GE,
outperform any comparable motor on the market.
Before 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.