After the usual headless chicken routine I powered everything off then back on with the inverter disconnected looking for a smoking gun but I couldn't find anything. There are no shorts in the HV system so the positive contactor must have triggered before precharge had happened.
As I was tired I decided to sleep on it and as often happens woke this morning at 5am with a theory.
I have a Gen 1 Nissan Leaf VCU from Damien which has outputs to mitigate against this happening and I believe I have it connected correctly as the precharge is controlled by output 1, the main positive contactor by output 2 and the inverter by output 3. The VCU is not supposed to enable output 2 until after the inverter reports seeing pack voltage over 330V.
During all the testing I had done trying to get a reliable startup sequence I ended up connecting all of the timer relays to the ignition Pos 2 so they all powered on together, the Negative contactor triggers every time with the ignition Pos 1. I also had turned all the timers to 0 seconds as I was trusting the VCU to control precharge. I'm only using them as relays to drive the contactors.
After the issue while testing with the inverter disconnected, output 1 triggered but output 2 did not which is correct as the inverter could not see HV.
So if the VCU is operating correctly then how could the main positive contactor come on before the precharge has finished?
This is my theory and I'm hoping someone can advise if it is plausible.
Over the last few weeks I have seen the VCU hang at various times. I had put it down to being the laptop USB connection plugged in but wasn't sure as it seemed to happen randomly. Last night I had plugged in the laptop to see what voltage the inverter was reporting so this is definitely possible. Thinking back there were clues to what might happen that I didn't pick up at the time but on reflection it gives me a possible cause for the fuse blowing.
The first couple of times the VCU hung with the ignition on while I was testing. On these occasions I realised the motor had stopped spinning, turned the ignition off and on again and although the contactors all triggered as normal (I thought) I still didn't get motor spin until I reset the VCU.
A couple of times after this the VCU hung with the ignition off and I got no contactors turning on when I turned on the ignition. Resetting the VCU put everything back to normal. Mmmmmm
So it is possible the VCU was freezing with the outputs locked either on or off, depending on the state it was in when it froze and in this state when I turned the ignition off and on again all the timer relays would either trigger at the same moment or not at all. This would have the following results.
If it froze:-
1. With the ignition on, when I turned it off and on again reasonably quickly nothing bad would happen because the inverter would still be charged.
2. With the ignition off nothing would happen because the timer relays did not trigger.
3. With the ignition on when I turned the ignition off left it for 30 mins or so then back on all the timer relays triggered together and blew the fuse.
I haven't reconnected the inverter yet so don't know if more harm was done but now I have a plausible theory as to what happened will give it a try later today. Wish me luck.
So what are the take aways here?
1. It's good to have fuses
2. Do not have a single point of failure, nothing is fool proof. Had I turned up the timer for the Positive contactor even just a couple of seconds it would have been OK.
3. When something unusual happens investigate a bit more thoroughly than I did.
4. When Damien did his best to make his VCU idiot proof the world just went out and created a better idiot.
Any thoughts from others?
Is it unusual for connecting a laptop to mess up the VCU? Does it make a difference if the laptop is plugged in.
