cwah said:
But the top part of the Fet is in metal and the screw are in metal too. So weather there is a plastic washer or not it would short it, if short is possible isn't it?
No. the plastic "tophat" washers prevent the screw from touching the FET's tab. Look at the washers you took out with the original FETs, or if you don't have thsoe anymore, look at one from one of the still-isntalled originals. You'll see a lip that extends down into the FET's tab moutning hole to keep the screw from touching it.
The gray (sometimes yellow) material behind the FETs prevents them from directly touching the metal heatsink bar.
That's why both of those are very important and why they install them in the first place. For reducing heat (and cost), it would be better not to install them, but they are required, so they do.
What surprise me is that all the new FETs I installed were killed from the moment I plugged my controller.
Depending on what path the short circuit thru the heatsink bar provides, they may well not be blown, but simply appear shorted because of the short htru the bar itself. Once unscrewd from the bar they may not be shorted anymore. If they are either shroted or blown open, then that means the short circuit path was one that allowed power to flow thru them direclty from battery+ batteyr- probably, whcih is usually very bad, and is called a Shoot-thru or Pass-thru event when it happens during motor operation.
I think I can throw my controller away...? Maybe only keep the 6 remaining fets that are still alive?
Depending on what happened you can probably still fix it by replacing the FETs again, only this time using the original mounting hardware and thermal pads (or equivalent replacments). Couldn't say without further troubleshooting, or just trying it by replacing those FETs.
It is possible that other thigns fried, too, like gate driver transistors, but you'd have to do further tests to determine that. I haven't read thru the rest of your thread so perhaps you have already done that part before, and already know how--if not, and you want to know, someone should be able to walk you thru it at least by pointing to posts where others have done the same thing before (I don't have a link handy).
If you do decide to replace the FETs again, I recommend installing the original mounting hardware first, to ensure they're bolted properly to the heatsink bar, then test for continuity from FET tab to taht bar, there should be none. Then solder them into the PCB and retest continuity/etc.
