Mixer here, PowerFlex 525, 30hp, 480VAC. The panel builder put a contactor between the drive output and the motor, and the safety relay drops that contactor on e-stop. Every e-stop under load the drive faults, F012 hardware overcurrent most times, once it was F021 output phase loss. We e-stop that mixer a couple of times a shift, so it's a reset and a restart from cold every time and the operators are sick of it.
Read somewhere the contactor was probably too small for it, so we went up a frame size and got exactly the same faults. Meggered the motor after that and went over the leads, all fine. The drive is the smallest frame that fits the motor, so is it just weak? Anyone run an output contactor on a 525 without this? Or is dropping that contactor with the drive still driving into it never going to end any other way, because I'm out of ideas on the drive side?
What's the e-stop meant to do here, take power off the motor or just stop it? Does the drive have its STO wired, S1 and S2 to the relay, or is the relay only dropping that contactor?
Relay only drops the contactor. S1 and S2 are jumpered from S+. Builder said opening the output was the safe way to do it and STO was "too clever". Its not my panel, I've just been stuck resetting it since.
The drive is still switching when that contactor opens under load. Current interrupted mid cycle, then the contacts bounce and the motor reconnects with its own back EMF against the drive's PWM. That's the spike, F012. I reckon the F021 was the bounce too. A bigger contactor opens the same way. The drive isn't weak, it's protecting its IGBTs.
Don't break the output under load, that's the rule. Wire the relay's two outputs to S1 and S2, jumper out, and torque goes away without a fault. Keep the contactor if the risk assessment wants an air gap, but sequence it: STO first, contactor a second later off a delayed output. Or move the contactor to the drive's input side.
Keep the contactor's NC aux in the relay's feedback loop whichever way you go. And once the stopping job moves from the contactor to STO you have changed the safety function, so it gets proved again and signed off before it runs production. Ours wants the risk assessment looked at again for a change like that.