Can I safely operate a DC motor at 40% higher voltage than nominal?

Question

I'm aware that you can power a wound motor (DC or even stepper) if you limit the current inside the coils. You cannot just apply a higher DC voltage to them.

I'm using a DRV8871 to control a VN-C1 pump (that comes with a 12V DC motor).

At 12V the pump will draw slightly more than 800 mA. My circuit is powered by a 4S LiPo battery that reaches 16.8V when fully charged - and that is 40% more than the nominal voltage of the motor.

I'm going to set the current limit of the DRV8871 to 800 mA (or even less) and connect the Vmotor directly to the battery pack. I'm trying to avoid the use of a "large" current (> 1A) step-down converter.

I wasn't able to find a proper datasheet for the VN-C1 pump and every request sent to several vendors was ignored. I'm pretty sure the windings can withstand such a voltage and I might set up a long-running test and a stress-test to find out the real limits.

But my question is related to certifications (CE marking): I'm afraid using a device outside its operating range won't be accepted.

Question: can I "safely" (in the certification meaning) operate a DC motor at 40% higher voltage than nominal?

Answer 1

If you use the correct battery type for the application, you will not have a problem. 4S LFP is a drop-in replacement for 12-volt systems, so the problem will be avoided.

Lipos are mainly used for drones and RC aircraft, requiring insane discharge rates over 30C and as high as 100C. The biggest mistake amateurs and consumers make is using the wrong lithium chemistry.

You would not get your device certified by any testing agency UL would not even consider it.

Answer 2

For an ideal motor, the voltage controls the speed, and the current controls the torque. Limiting the current only incidentally affects the speed if the load happens to have a suitable torque/speed curve.

Running a motor at a higher voltage will ideally make it go at a higher speed. As the mechanical forces tending to burst the rotor rise as the square of the speed, there is not much leeway in how much faster you can run the motor. One algorithm to find the highest voltage you can use is to increase the voltage until the rotor bursts, then back off a bit, which only works if you have a lot of motors.

A pump would be an ideal load for limiting the current to actually limit the speed, as it's likely to have a fairly repeatable speed/torque curve. However, if it's a pump for liquid, and it ever runs dry, the torque required will drop dramatically, and the speed will rise to that dictated by the voltage.

At your voltages, you are unlikely to run into a wire insulation problem. Commutator sparking is a different matter however, which could increase wear.