Low Resistance BLDC Motor

Hello all,
is it possible to run a motor with low resistance such as:

with the SimpleFOC shield? The documentation says that the shield should be used with >10 Ohm motors. I would like to use them for a pretty large 3d printer and I am unsure what type of controller I need.

Thanks

I read, that I could use a current limiting power supply. In this case the motor is rated for 5.9A. Would I need to set the limit to this value or something lower? Would limiting the current flow limit the motor in it’s total power output? Is the power limit functionality from a lab power supply enough or do I need to watch out for something?

Thanks

Hi @Knicklicht,

The SimpleFOC shield can handle about 5A before it’s over-current protection kicks in and shuts it off. But to handle > 2A on a continuous basis you will need to add a heat-sink.

To run lower resistance motors, you have two options:

  • set a low voltage limit - this will prevent the currents getting too high, but will limit the motors performance.
  • use current sensing (works with the right MCU) to directly control the current, allowing for higher voltages to be used, and utilising the max torque you can get out of the motor/driver/PSU combination.

I would recommend trying with voltage limits first, and then moving to current sensing once things are working in a simpler setup.

Using the PSU’s current limit is probably not enough by itself. This will be a hard limit for the system, but there can be a number of problems. If SimpleFOC doesn’t know about the limit, and tries to use more current than the PSU can deliver, then you have to see what happens - many PSU just “brown out” i.e. they deliver their max current and the voltage begins to drop. Other PSUs switch off.

In any case the motor’s 5.9A are beyond what the SimpleFOC driver can do, so you’d have to use a bit less than that. Also, most motor data sheets are somewhat “aspirational”, so actually running 5.9A through your motor will probably burn it up unless it has a good cooling system.

It’s really best to use a good PSU which can handle the maximum intended current + a bit extra as margin, and then to use the software and driver limits to make sure things stay in range.
The PSU’s current limiting can then be viewed as an additional safety feature…