Thanks very much for your ideas how to unscrewe this controller, I will try to fabricate my own triangular screwdriver:-)
Was the regen more effective with the windings switched to Delta or Wye configuration?
I didn't notice any difference in braking effect in delta or wye, I rode without cycle analyst, so I can not tell difference between those two modes in order to regen amps, but feeling of braking effect was more or less the same.
But now I realize, that I was switching from delta to wye during regen braking (accident) and because I am using 3x SPDT relay for switching, so perhaps that was the cause of failure. Relays perhaps didn't switch in exact same time and shorted phases together. In ES forum was several times mentioned that if you switching with this kind of relays you need to have zero throttle (logically regen as well) in that moment so that current is not flowing through those relays. Could that blew mosfets out?
Thanks again for your considerations,
Lubos
It just occured to me the other day that besides relays shorting when swapping from Y(Star) to Delta, there is also the another possibility, being an industrial electrician, I had to go to a job to replace a blown up 415v 15kw Star/Delta starter on a sawdust extraction fan (the motor was around 800mm by 400 diameter), it was only a week old, I replaced it with an identical unit and noticed the supply fuses to it were way overrated for the starter, so put the correct size fuses in hooked up my ammeter and gave it a go with an extended Star time.
The fan started and ran fine for the 3 seconds before Star, then died completely on Delta with my clamp ammeter going off the scale, had a look and fuses were blown, one of the guys came up and said he just got sawdust blown all over his bench so I must have had it in reverse. Now I suspected what was wrong, having done a lot of Star/Delta stuff over the years, I always thought this was possible and had been careful to avoid doing it, but had never seen it done before.
The Electrician who replaced the old Star Delta with the unit that blew up was a younger less experienced guy, what was happening was it was starting in Star reverse and about a second later just as it got to full speed it was thrown into Delta forward direction, so he just put bigger fuses in, it got away with one start each morning for 5 days. It's lucky it hadn't thrown the fan blades off or sheared the main shaft.
Maybe there's the possibility you could be doing the same with this motor on regenerative braking. It also stands to reason that the one with half the amps of current is also probably doubling the output voltage.
The timers for Start/Delta motor starters all have a 1/4 second delay between the 2 steps, and normally the contactors are interlocked through auxillary contacts so the second contactor can only power up and close when the first one has actually opened.
