RY40511: a few notes

Monday, October 27, 2014

Stuff to note for other tinkerers out there:

• The entire controller gets extremely hot at 50A with the stock transistors, probably too hot for continuous duty without a fan. However, the limit is probably purely thermal - I did most of my initial testing with a 50A max current setpoint with the motor coupled to a second chainsaw motor driving a dead short, and both the current loop and short-term behavior of the controller seemed reasonable.
• Likewise, the motor is not good for 50A under stall or near-stall conditions; everything gets rather hot. However, at reasonable RPM it is probably actually a 2KW motor thanks to the integrated fan.
• Without some further connection on the blue "COMM" wire coming out of the battery, the integrated BMS shuts off at 25A. Charles has gotten 65A out of the battery, so presumably reconnecting this wire will enable high current operation; given the lack of thermal protection on both controller and motor some adaptive current limiting will probably be necessary to keep temperatures down.
• If you want to upgrade the MOSFETs, go for the lowest Rds,on FETs you can afford - gate charge doesn't really matter given the 10nF parallel capacitor on the gate. Furthermore, only 1/6 of the FETs are switching at any one time, and only at 8KHz, so switching losses are negligible. In fact, switching too fast will result in nasty transients and FET failures (don't use logic level FETs!).
• The 40V voltage limit is pretty hard with the board in its stock state; the high-side gate drive BJTs see 55V and are rated to 65V. Likewise, the LVPS assembly is not going to appreciate any sort of significant overdrive. Replacing the BJTs with 100V parts might allow it to operate at a 48V nominal pack voltage.
• Post-PRS Detroit update: confirmed that the time to failure of the stock chainsaw without fan is 15 minutes with a 40A current limit under vehicular load, so a fan is definitely needed for continuous operation at high power. The sensors on the motor are also phased so that reverse performance is extremely poor.