Do CIM elevator motors overheat?

[AdamHeard]

Originally Posted by MrForbes

Are you sure about the voltage thing? I don't really understand the whole voltage/current/percent power relationship with speed controllers...but my guess is you're providing it quite a bit more than 1.2 volts if you're commanding 10% power, using PWM.

Yes, absolutely.

Model motor as a resistor, you can get it's resistance from the spec voltage of 12V and spec stall current of 133 Amps. V=IR gets you R = .09 Ohms.

Kt is torque/Amp, and therefore stall torque scales with voltage. So, at 10% of spec voltage, you have 10% current draw, which means 10% of spec stall torque.

Stalling a motor in no way leads to failure on it's own. Putting too high of a continuous current into a motor (whether that's at stall, or while rotating) is what fails it (due to heat building up wrecking insulation).

Originally Posted by Thad House

Exactly. If you calculate it so you only need 10% of your stall torque to hold the object up, you only need 10% of the motors stall current to do so. Which you get if you input 10% of the nominal voltage. That becomes 13 amps at 1.2 volts, which is only 16 watts. A CIM can easily dissipate that much wattage, and will have no trouble doing that for the entire match.

You can extrapolate this a tad further and do a BS calc where you say .2 or so of the motors mass is the armature weight in copper, and then do Q = m*C*deltaT, but change Q to Power input and deltaT to deltaT/sec. This lets you get an approximate temp rise per second that's pretty conservative as it neglects ALL heat transfer paths out of the motor.