More Heater Woes

I have good news and bad news.

Good news #1 is that I know that I can drive for at least 25 minutes withOUT the DC-DCs running into my 9AH 12V battery. In the daytime anyway.

Good new #2 is that I now also know that the NS syle BS88 16A offset blade industrial fuses that feed +300V and -300V into the Heater and DC-DC, simultaneuously blow and safely disconnect the 600VDC from both the afore-mentioned. When replaced with 20A (that's all I had) they safely blew again. (I crushed one in a vise after it blew and the sand had nicely fused to break the Arc).

The bad news.
My heater stopped again rather dramatically. It had worked for about 3 days then one morning last week - no heat. After about 12 minutes of driving I decided that the 12V turn indicators were a fraction slow and pulled over to check the 12V battery - 12.0 volts - not good. There was no power to the DC-DCs. Neither +300V or -300V - which surprised me.

So I went back home because I wasn't carrying spares or even a screwdriver.

I disconnected the heater (funny that), replaced the fuses and DC-DC was back again. 13.6V on 12V battery.

While live (car on) I reconnected the heater -300V all OK, then +300V SPLAT - BUUMPH! Both 20A fuses blew at once.

So I have the heater controller out again. The IGBT AND the Fast recovery diode across the Ceramic element have shorted. It also blew a bit of track off my PCB.

Is PWM controlling a ceramic heater element that hard?
The bottom of my control board. I have circled the missing bit of track. The missing track used to connect the fast recovery diode across the heater element.

After a heap of discussion on the AEVA forums we have finally concluded that ceramic heater elements have very high capacitance. That's why they are not suited to PWM control. The power IGBT is switching into something close to a short circuit at normal switching rates.

In other news, somewhere last week the Vogue passed 1100kM as an electric vehicle.
I'm not driving it this week (or late last week) due to 1 degree C temperatures on Melbourne mornings.