I started off with the goal of replacing the controller for my (supposedly) 1000W Lathe motor. The current controller runs with hall sensors and is very jerky at low speeds. There is little hope of tuning the existing controller. I was able to run a prototype with simpleFOC on my bench with a small motor, STM32 board with current sensing. I got a DRV8302 driver board with the intent to drive the larger motor. Now when I started trying to reverse engineer the Lathe controller (yes, I should have done this first!) to get some specs and re-use the existing motor power supply, it seems it runs at +/-150V or so when I probed the 6 drive transistors. This is far higher than the DRV8302 is capable of, so I will need a new board. I would like to learn a bit about how the voltage is chosen for a BLDC motor, but I seem to find little literature. The resistance between any two of the 3 pins is about 6ohms (so 3ohms per coil?). Can someone point me in the right direction?
One last ditch effort is for me to find the pins driving PWM off the original controller (NEC D79F9211) and bypass those with STM32 SimpleFOC outputs. Attached a picture of the generic controller which can be found for purchase, though those sites warn that I am better off purchasing the motor and controller together as the programming is specific to the motor.
Say you have a motor for 100V and the wire in the coils goes around the stator 100 times. Then you could cut the winding in two parts and put the two 50 turn parts in parallel. You now have a motor for twice the Amps and 50V.
You could also buy thinner wire, about half the copper cross section and wind 200 turns on each part of the stator. You now have a motor for 200V and half the amps…
So for example for a gimbal motor, the RPM never needs to be more than say 10RPM. So it doesn’t matter that you would need a 3600V for 3000 RPM. So they aim for 10RPM at 12V, which gives the lowest current-per-torque figure possible for that motor.
There are some disadvantages to a low voltage, high current motor: The wires from powersource (bateries) to the controller and from the controller to the motor need to be bigger.
So for a lathe I’d expect them to just rectify and smoothen the line voltage to get about 160V, and then use that. (I’m guessing you’re in north america where line voltage is about 115V. In europe the motor would be configured for 320V as opposed to your 160V. The controller would then require higher voltage-capable mosfets, but only half the current).
Your question surrounding how to choose the voltage is an interesting one. Typically the voltage is chosen based on what supply is available. AC120, AC240, DC48. Once the supply is factored in, then the power (speed, torque) required can be factored, motor technology selected, then sizing equations can ensue.
Electrical safety regulations can play a role in what voltage you choose. Electrical safety is about risk of fire and people being exposed to electrical shock. It means risk of death and damage to property. If a product you are responsible for may have caused such things, insurance companies put layers on you, and they may not cover you. If you can keep the voltage at 24 V or below, the rules are not that severe and you got more room for experiments.
