TurboWelderMonkey said:
I know the sabvoton won't run sensorless so that still leads me to believe there is another FET or 2 that are damaged, would that be safe to assume?
Probably that or the gate drive on the repaired phase.
I had a controller I was experimenting with that something happened and my hand on throttle moved and the motor jerked and caused the board to land on a metal tool, and it damaged the controller in a way that even after replacing blown FETs left it "working", but not like it used to.
https://endless-sphere.com/forums/viewtopic.php?f=4&t=21830&p=320682#p514878
https://endless-sphere.com/forums/viewtopic.php?p=515777#p515777
I never got around to completely fixing it as it wasn't that great anyway, though I still have it and sometimes think about using an oscilloscope to check out the gate drive of each phase relative to each other to see if that's the cause...but I never have enough time/energy for even the stuff that's critical.... It coud also be that the FETs used were different in characteristics. There's video and scope pics and stuff if you're interested, in the last link.
My buddy says they cannot be tested in circuit so ill have to pull them all.
They can be tested in circuit as a group (whole top or bottom of each phase), but not individually. So for instance you wouldn't know if just one was causing a problem, or not working at all, just if the whole paralleled set was wonky.
I'm also wondering if there's any specific way to tell that the driver is bad or if i should just order those as well since they are pretty cheap?
To test them, you'd probably need an oscilloscope to see the waveforms, since you already know they are driving the FETs, just that something is not happening as it is supposed to. You'd probalby see something differentn between the undamaged phases and the damaged ones.
It probably won't hurt to just replace the gate drivers of the damaged phase before doing the FETs in all the phases, just to see if it makes any difference. But if you want to see wha'ts going on and learn even more, and have access to even the most basic oscilloscope (there are cheap "front ends" available online that connect to your phone using OTG/USB, for instance, though I've never used any of them; also cheap old standard benchtop used ones on ebay and the like), you could see the waveforms and even post pics of the results.
My buddy also looked at the data sheet for the FETs we got and said I shouldn't have any compatibility issues replacing the whole phase, he actually picked the replacements. He said it may just handle the load a little better even. (This is just his opinion, im not saying anyone is right I just like to hear different opinions.)
Most likely the different FETs aren't teh cause of the problem--it's usually only if the Qg (gate charge) or RDSon is significantly different from the others taht you get different behavior enough to cause a problem. Usually it doesn't matter...but there are a lot of different kinds of characteristics of a FET, and sometimes certain ones are needed for certain applications...I am not expert enough to help with those, but you can read about them in various custom motor controller and powerstage design threads by those that are.
A big enough difference in gate charge means the FET may turn on or off with enough difference in timing to the others that it creates problems, or that it takes more than the gate driver can provide (especially if it's already damaged).
I also showed him a reply that you (I think, maybe one of the other Forum Daddy's here.) posted to someone who had sent you a blown Sabvoton to take apart and you were telling about how they are just clones now with way too little capacitance and very weak FETs and other components, he said it was bound to fail even if my cable didn't short out, so I'm not opposed to doing more surgery on this big heat sink of a board!
Was probably someone else; I don't think I've had a sabvoton here yet, but there have certainly been enough blown ones posted about.