I am trying to find a BLDC servo motor for a pump. I have calculated the required speed, but while the manufacturer was good in getting back to me with the torque requirements, they did not give much detail. So, I only have a ballpark figure for worst-case the torque.
My instinct is to pick a motor with a much higher rated torque than quoted. My thinking goes that the higher torque rating basically means higher current carrying capacity, which means larger windings. If the motor is used up to its limits, it will work OK because its rated for them. If used well below its limits, the larger body will dissipate heat more efficiently, and the windings will have a lower resistance – so if anything it will use less power a smaller one operating at its limits.
So, rather than try to estimate the torque, I should just buy the largest motor that fits with my other constraints.
Have I assessed this correctly? Are there any downsides to oversizing a BLDC motor?
Related: Aside from cost, is there any disadvantage to using thicker wire than required?
Best Answer
BLDC with higher torque rating will differ in the size, thus it will have larger inertia, making the motor less prone to the fast dynamic change of speed, position.
If your driver can fed the motor with less than rated current the overall torque will be smaller than rated. The only constraint is the match between driver and motor - the driver has to have the capabilty to drive the motor within the range of winding inductance.