dnmun wrote:each phase has mosfets between the B+ of the battery and the phase wire so current can flow into the phase wire. these are called the hiside mosfets.
between the phase wire and ground there are mosfets to drain the current from the phase wire to the ground, or B- of the battery. these are called the loside mosfets.
the mosfet has three legs, gate, drain, source legs when looking from the front, left to right.
the mosfet has an internal diode. if you connect positive to the source, and negative to the drain then current will flow through the mosfet, as it does through a diode. you can measure that forward voltage bias with the diode function on your meter.
the hiside mosfet is installed so the battery plus is applied to the drain and the source is connected to the phase wire. so this prevents the current from leaking through the body diode of the mosfet because it is now 'reverse biased'. it will appear open circuit.
the loside mosfet has the drain attached to the phase wire and the source leg to the battery B-. same thing as with hiside, phase wire is positive to the battery B- so it is reverse biased too and should be open circuit to your meter.
you should be able to see that when you examine how the traces run on the underside of the pcb.
test each of the mosfet body diodes with your meter. they should all be identical except the ones that shorted.
when the mosfets are connected in parallel, if just one is shorted the adjacent ones in parallel will appear shorted also whether they are or not. replace all three in each bank that is shorted.
dnmun..... don't you ever sleep? lol I'm glad you are here..... really!
I'm an amateur radio op and was comms/electronics in the Canadian Military for 22 years. Mostly the Comms side and decided to self teach myself
electronics as much as possible, but I'm only "dangerous" to say the least... lol My gift is understanding other experts and being able to apply
what I learn
I noticed that the 3 fets in bank "C" were paralleled therefore all showing shorts
But from your explanation, I now can see the Hi/lo sides
The 3 FET's in question on Bank "C: are on the Bat + HiSide.
I'm leery to apply voltage to the FET's in question as I'm not sure how this is done. Do I fire up the power to the controller?
Also leery to do this as the traces/Solder dams are very close together.
Have I determined the bad FET's already and just need to replace the 3 in Bank "C" hiside?
What a mess this will be. I wish they had just used heavy copper traces instead of solder.
Tommy L sends....