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 self-destruct.

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.

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