Main contactors dropping out when motor rotating, regen.

[Peter]

Hi Forum. I had an interesting development last evening where my 12v battery dipped under load and caused my main contactors to drop out when braking. Consequently thus generated power (??) from the Tesla had no where to go and destroyed (dramatically) the TVS I had fitted. I sorted the issue with 12v supply but was wondering if there was a way to prevent the generated power from destroying anything should the 12v be lost or contactors fail. As this is a situation where the power would be generating/regen (??) should I fit reverse biased power diodes across the contactors so the power can in fact still be fed back to batteries, is that an idea worth persuing as the voltage must have been very high, TVS rated at well over 450v and my batteries are 330v. Peter

[ZooKeeper]

Normally there is a DC-DC converter in the HV circuit that would prevent this.

[Isaac96]

Hi Forum. I had an interesting development last evening where my 12v battery dipped under load and caused my main contactors to drop out when braking. Consequently thus generated power (??) from the Tesla had no where to go and destroyed (dramatically) the TVS I had fitted. I sorted the issue with 12v supply but was wondering if there was a way to prevent the generated power from destroying anything should the 12v be lost or contactors fail. As this is a situation where the power would be generating/regen (??) should I fit reverse biased power diodes across the contactors so the power can in fact still be fed back to batteries, is that an idea worth persuing as the voltage must have been very high, TVS rated at well over 450v and my batteries are 330v. Peter

Damn good thing you had that TVS attached! Usually a contactor dropout results in a dead inverter!

There shouldn't be an issue with reverse biased diodes. But you should of course try to avoid 12v dropouts in the first case. Do we know what the OEMs do? I haven't seen anything of the sort in Leaf packs for example.

[ZooKeeper]

From what I can tell, the Prius and Leaf relays are ECU controlled, so if the ECU loses power, so will the relays.

[celeron55]

Maybe monitoring the 12V would be a good idea and disabling regen if it's apparent the dc-dc is having problems. Isn't the OI hardware already capable of this, just add a bit of code?

[Peter]

Lets assume the 12v is lost completely so the inverter has no control 12v so regen is not activated.
However the vehicle is coasting to a stop and the motor is spinning, does the SDU still act as a generator and put power to the DC bus?

[arber333]

Lets assume the 12v is lost completely so the inverter has no control 12v so regen is not activated.
However the vehicle is coasting to a stop and the motor is spinning, does the SDU still act as a generator and put power to the DC bus?

If SDU is ACIM then there should be no excitation on rotor. You should be good.
In real life there is quite some energy left in reverse diodes that can damage the power section. I would advise DC contactor to be connected in latching circuit and notaus button controling the pwm only.

[muehlpower]

Is there a possibility to use the battery or cabin heater to avoid excessive link circuit voltages after a blown fuse or an open main contactor?

[Peter]

I am now looking at using TVS in series with a high wattage resistor. Alternatively a crowbar circuit, zener switching a thyristor to dump the power into a resistor.