Over volting and current limiting an electric motor.

BrainFog

Joined Jan 24, 2011
122
This is another one of my "out of curiosity" threads.

Quite some time ago I remember reading a short mention that it is good to power a DC motor with 10 or 20 times the rated voltage and current limit it.

Firstly: did this person know what they were talking about?

Secondly: I can see the logic in using higher voltage and lower current however how would this current limiting be achieved? I doubt a PWM would be what they were referring to.

Thirdly: voltage, I would have imagined that if you go that far out the specs you may have trouble with using such a high voltage on windings that were not built for it. What kind of voltage can the thin enamel on magnet wire stand? I would also suspect that other problems may occur.

kubeek

Joined Sep 20, 2005
5,772
AFIK this is recommended for stepper motors where it enhances torque at high RPM. I don´t know how fast are the transients on the commutator of a DC motor, but I suspect the current source would need to have pretty high slew rate for it to have any benefit.

Another problem is that curent limting is linear and cant really be done with PWM, so you waste 10 to 20 times the motor power in the constant current source.

GetDeviceInfo

Joined Jun 7, 2009
2,095
Secondly: I can see the logic in using higher voltage and lower current however how would this current limiting be achieved? I doubt a PWM would be what they were referring to
that's the only way I could see it happening. Your motor is basically an L filter, smoothing out the current from the input voltage. A current sense resistor is common, feeding to your PWM for current control. We routinely megger motors at 1KVolt that are nameplated in the range of 120-480. A 12 vdc motor should be able to withstand upwards of 200volts, but that will be manufacturer specific.

Smoke_Maker

Joined Sep 24, 2007
126
Quite some time ago I remember reading a short mention that it is good to power a DC motor with 10 or 20 times the rated voltage and current limit it.

Define DC motor ????

I have over-volted a series wound DC motor by 3 times and the motor lived, some of them did not live long because the part between the motor and load broke.

SgtWookie

Joined Jul 17, 2007
22,226
It's mostly done with stepper motors. Feeding the motor a higher voltage gets the current flowing through the windings much more quickly, but it's important to limit the maximum current to keep it within the motors' specifications.

A simple way to do this with steppers is to use a resistive load, or a light bulb. A more sophisticated method is a so-called "chopper driver", which is a form of PWM that controls the maximum current. Once the limit is reached, the driver will chop off the current for a fixed amount of time, and then turn it back on until the limit is again reached.