500A controller troubleshooting II

[Piotrsko]

I could be wrong but I think on failed mosfets the gate shorts to the drain.

[thingstodo]

The Drain and Source appear to be directly connected, perhaps by small bits of metal that melted through the FET part?

Resistance is the same whether from Drain to Source or Source to Drain.

The resistors that connect to Gate SHOULD conduct all of the time, but don't appear to get overly warm. If they did get warm, I could tell which were failed!

[thingstodo]

I've been messing with the Cougar controller today. I have an accurate resistance measurement tool - a Micro Ohmeter, or Ductor - and have checked the resistance of each leg of the MOSFETs to the B- busbar and to the M- busbar.

The results are confusing for me.

I had assumed that one leg of each MOSFET was connected to the M- and the other leg was connected to the B- copper bars. When M- is connected to B- through the MOSFETs, current flows from the battery pack + to B+ to Motor+, through the motor, to motor -, to M-, through the MOSFETs to B-, and on to the battery pack -

I have MOSFETs that during one set of measurements appear to have a poor connection to B-, but the same MOSFET has to good connetion to M-.

Table of measurements below. MOSFETs 1 and 3 have had their leads cut - scorch marks were a good hint that they had failed. But not just them!
Resistances are listed in milli-ohms

Measure resistance from B- to MOSFETs
MOSFET	Middle	Right
1		dead	dead
2		>200	14.7
3		dead	dead
4		3.9	10.1
5		8.4	0.7
6		3.8	2.6
7		3.7	9.6
8		3.7	22.7
9		2.8	1.7
10		3.8	16.4

Measure resistance from M- to MOSFETs
MOSFET	Middle	Right
1		dead	dead
2		>200	>200
3		dead	dead
4		2.4	9.3
5		7.0	4.6
6		0.6	50.0
7		0.5	6.4
8		0.5	19
9		0.5	1.7
10		0.5	13.0

I'm not sure what I was expecting. But whatever THAT was - THIS does not match it!

I took the Cougar out to my battery pack, put a resistor in series with it, then connected it first across 4V, then 8V, 12V, 16V and on up until I ran out of batteries. There was no current measured except for charging the caps. I was expecting current to flow somewhere. 12V was not connected to the Cougar at the time.

I disconnected the pack and just connected 12V to the controller. I checked for heat on each resistor. Nothing. I checked for voltage across the resistors that drive the MOSFETs. Nothing.

Paul - what am I doing wrong here?

[thingstodo]

Update for Dec 21.

After doing some AC controller testing I connected the Cougar to a 24V pack. All OK. To avoid turning any of the MOSFETs on, I left the throttle off and did not power up the controller with 12V. All seems fine.

I then turned off power and connected the Warp 9 motor. When I powered up the precharge resistor gets *HOT* ... 6.7 ohm 20W resistor.

I then pulled in the contactor and let some smoke out

2 of the resistors driving the MOSFETs actually caught FIRE! It appears that most of the MOSFETs were actually failed on. There are 3 resistors that have not turned black or burned. I left the controller that way until the smoke stopped and the current dropped. Any MOSFET that was failed stayed on until it *HOPEFULLY* melted.

I have video but I think I lost the audio track. I will post when I get it edited. I hope to get the Cougar connected to a small test blower and a small test pack in my basement to see if anything still works.

So far, I have cut off 2 MOSFETs that were obviously damaged, the controller sends the power up message but will not respond to text commands, or even echo the characters. I have re-soldered the serial header and made a new serial connector - no response. And lastly I cooked several of the MOSFETs and the resistors that drive them ON as described above.

I'm still hopeful that I have a couple of operational MOSFETs ... but hope is dwindling ...

My education is EXPENSIVE ... because I BLOW **** UP!

[Piotrsko]

I got a quarter that says all your mosfets are toasted by now. 20 watt resistor got hot? hmmm sounds like a lot more than 10 amps current flowing. What does your motor need to idle? My Kostov takes 30 amps @ 12 volts.

[thingstodo]

Originally Posted by Piotrsko

I got a quarter that says all your mosfets are toasted by now.

I've got to agree - but I'll check anyway

20 watt resistor got hot? hmmm sounds like a lot more than 10 amps current flowing. What does your motor need to idle? My Kostov takes 30 amps @ 12 volts.

At 24V, spinning unloaded at 3600 rpm, the warp 9 takes about 40 amps. To accelerate to that speed it starts out over 100 amps.

I think I tried 12V in the past but I didn't write down what it takes to make it spin.

If any MOSFETs are left undamaged, I don't think the output current will be much. 10 pairs of MOSFETs to start, only 3 resistors left that are not visibly failed means a max of 6 MOSFETs. If 20 MOSFETs can do 500 amps, 6 can only do 150?

[MPaulHolmes]

Actually there are 10 mosfets and 10 diodes. So 6 unfailed mosfets would be 300amp.

[thingstodo]

Originally Posted by MPaulHolmes

Actually there are 10 mosfets and 10 diodes. So 6 unfailed mosfets would be 300amp.

Uh-oh. The ones on the inside, where you can't really see them, are diodes? Connected to the heat spreader ... sorry about that! And thanks for the correction.

I guess I'll just have to try them out and see which ones still work.

I might get some time between family stuff in this next week ... but that would be a bonus.

[MPaulHolmes]

Yes the inside ones are diodes. I've never seen a diode failure. Are any of them bad?

[thingstodo]

Last of the video updates from Dec 21

The Cougar controller has failed MOSFETs - I just can't figure out which ones. Put power on the controller (B+ and B-, not 12V to the controller) and see what happens.

https://youtu.be/soV_Voq2bmM