Bricked Controller
Well after attempting a firmware upgrade on my Kelly KHB 72701 controller, the master FW failed to program and the controller was frozen. The team at Kelly offered to reflash my controller if I sent it to them. I used USPS Global Express service, I was able to send the dead controller to Kelly and it arrived in about 4 business days. Global Express is a partnership with FedEx so the box moved by USPS across the ocean but was then handed off to FedEx for the local delivery in China. Full tracking information from both USPS and FedEx was available online. The team at Kelly, reflashed the unit and shipped it back (2 day service from China) to me for no charge, which is quite generous since the unit is over 2 years old and a year out of warranty. The controller arrived in great shape and came right up. I wish all companies had this level of customer service.
Noise on the Ground
Well the new controller highlighted a problem I had with my timing advance circuit. I'm not sure if some wiring clean-up exposed this or the new firmware has slightly different timing for the phase signals from the motor. Either way, my timing advance system stopped working and started causing the controller to report either a non-spinning motor or a hall-phase error. Bypassing the timing advance board cleared the problem, so it was obvious where the problem was centered.
After some sniffing around with a scope, I found there was a lot of noise on the phase sensor signals from the motor. I could see the phase signal but a high-frequency 2V noise was riding on top of the low-frequency motor phase signals when the motor was spinning. Looked a lot like the high-voltage PWM from the controller, though I never measured the frequency to confirm.
Two realizations:
- The case of the controller is tied to the high-voltage motor signals through large resistors to drain residual charge once the controller is turned off. The team at Kelly suggested that if the case was tied to chassis ground, it could be introducing some noise on the 12V ground. Isolating the controllers case from chassis ground (with a rubber mat) improved the noise quite a bit, but there was still an issue with phase signals.
- More digging revealed a wiring issue. Originally, I had used the ground signals (RTN) from controller as the ground for the hall sensor in the motor. I suspect the controller was passing some noise through the ground lines to the hall sensor. Switching the hall sensor ground to be the sourced from the timing advance system (a good chassis ground) provided a significant reduction in the noise on the hall sensor signals. I suspect the Kelly Controller is more tolerant of noise or has some high frequency input filters which my timing advance circuit does not.
