12 FET Controller blown?

[turbojo]

Hi, all this is my first post so please bear with me!
I think its probably best I retell the whole story so as not to leave anything out.
I was running a EM3EV 12Fet 4110 controller on a 72V SLA pack on a EGO scooter, I also have a cheap chinese amp/volt meter which plays up sometimes and flashes and can't make up its mind how many volts ect are to be displayed. Easy fix is to switch off and start again.
It was raining hard the other night and didn't want to stop so I switched it off whilst still doing 10mph. As soon as I switched off there was a loud drumming noise and I came to an abrupt halt. The motor was obviously shorted as it was nearly impossible to push so I suspected some blown FET's which after a hard push home at barely a walking pace it turned out to be the first two from the wiring end (A-).
Seeing as I wished to up the voltage to 84V I purchased 12 4115's and began to solder them in. When I checked it all to be ok I plumbed it up and turned the throttle, the motor turned about 3 degrees and the whole lot then shut down. This time FET 7 and 8 (again from the wiring end) which is phase 'B+' had shorted. The wheel was once again hard to turn.
I bought two more, soldered them in and it was exactly the same, wheel free until the throttle was twisted then the 3deg of wheel movement and wheel hard to turn thereafter.
I've checked the resistance between each of the phase wires on the motor and they are all 1.8ohm according to my meter so I don't suspect a short there.
When FET 7 - 8 blow the gate to source resistance drops to 50 ohm and the source/drain are shorted completely. This is testing after I've removed them.
I'm stumped and have spent £60 in 4115's.
Help!

 

[e-beach]

Hey turbojo! Sounds like you got a short someplace. But before we get into it first thing first. Follow the directions below.



OK, now that that is done lets see if someone around here can help you figure out your problem.

With all phase wires disconnected from the controller does your motor spin freely?

With all your wires connected properly and the power on, did your motor spin freely before you fried the controller again? (I think that is what you hinted to in your OP.)

Have you carefully checked your wiring harness to see that their is no short in the wiring? If you have no short in your motor but the wires inside your harness are melted together under insulation, that could also be a source of shorts.

Is your controller a 12 fet IRFB4110 Infineon Controller like this one?
http://em3ev.com/store/index.php?route=product/product&path=38&product_id=82

Can you post some very clear pictures of both sides of the pc board of your controller? Just keep the file sizes under 500kb so you can post them on ES

Edit: BTW, what are the caps in that controller rated for?

Lets start with the above and see if someone can help figure it out.

 

[turbojo]

Hi, hopefully this answers all your questions. I've also attached a couple of pics.
Please excuse my dicky soldering, I was beginning to loose my patience! There are however no shorts in it.
With the two FET's missing the bike runs - abiet not very well.
Thanks.

Hey turbojo! Sounds like you got a short someplace. But before we get into it first thing first. Follow the directions below.
With all phase wires disconnected from the controller does your motor spin freely? Yes
With all your wires connected properly and the power on, did your motor spin freely before you fried the controller again? (I think that is what you hinted to in your OP.) Yes
Have you carefully checked your wiring harness to see that their is no short in the wiring? If you have no short in your motor but the wires inside your harness are melted together under insulation, that could also be a source of shorts. 1.8ohm across all three phases measured with the controller disconnected but at the plug
Is your controller a 12 fet IRFB4110 Infineon Controller like this one? http://em3ev.com/store/index.php?route=product/product&path=38&product_id=82 Yes
Edit: BTW, what are the caps in that controller rated for? 100V - but still running on a 72V pack at the mo.
Lets start with the above and see if someone can help figure it out.