Burning up motors?

[Dr.Love]

What causes a motor to burn up? I have burnt up two with in the last 6 months. I think the first one was due to high speeds. No idea on the 2nd one. I have been taking it easy on it. Could weak batteries cause one to burn up?
Thanks

[JohnnieB]

Originally Posted by Dr.Love

What causes a motor to burn up? I have burnt up two with in the last 6 months. I think the first one was due to high speeds. No idea on the 2nd one. I have been taking it easy on it. Could weak batteries cause one to burn up?
Thanks

Obviously, heat causes motors to burn up, so the real question is: What causes motors to get hot?

An electric motor is an energy conversion device. It converts electrical energy into either motion or heat. Ideally, most of the energy is converted into motion and not much into heat, but the way electric motors are used in golf carts is often less than ideal.

A stalled motor (0RPM) will convert 100% of the amps flowing through it into heat. The formula is W=I²R. W is Watts of heat I is Amps (quantity is squared) and R is the resistance (or impedance) of the motor.

As the magnetic field generated by the Armature (or rotor) of an electric motor spins within the magnetic field generated by the Stator (or Field) windings, and electromotive force is generated whose polarity is the opposite of the voltage being applied to the motor (called Back EMF), effectively increasing the impedance of the motor and reducing current flow through the motor.

Without mechanical drag, the motor's RPM will increase until the Back EMF equals the Applied voltage. At that point, 100% of the electrical energy is being converted to motion.

In real life there is always mechanical drag, so some of the electrical energy is always being converted to heat.

Accelerating from a standstill, climbing hills, turning tall tires (or high speed gears), pulling/carrying heavy loads and driving at low speeds in general, produce more heat than cruising along at mid to maximum speed on a hard, level surface.

My motor(s) get hotter driving around my 2 acres of bumpy, but mostly level, land at less than 6-10 MPH than driving at max speed for 10 miles.

Running at high RPM may explode a motor (I did) or seize a bad bearing, but it shouldn't overheat the motor unless the motor is undersized for the mechanical load it is attached to.

Since you are burning out motors, you might want to monitor your motor temperature. Attached are pictures of how I do it.

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Weak batteries (Low voltage) may be a contributing factor, but the way the cart is set up and driving style are more likely the cause.

[sportcoupe]

Excellent explanation Johnnie.

Another way to monitor temp is an inferred temp gun. Cheap at harbor freight.

What setup and mods do you have? All stock?

[yurtle]

Originally Posted by JohnnieB

In real life there is always mechanical drag,

That's called matrimony

Though I'll admit, without any coercion, my "mechanical drag" has been a positive influence in my life.