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Old 01-31-2020, 09:11 PM
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itsid itsid is offline
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No no.. the MosFETS do not need to be swapped out I bet!

Do you see the pattern?
++xx ++xx ++xx

Now your BLDC is a three phase motor (three leads right?)
each set of four MosFets power one of those phases
in your pic from left to right namely Green, Blue and Yellow

And now comes the interesting bit.. a Mosfet is unidirectional,
it can only forward current in ONE specific direction!
your motor phases however need a polydirectional powersource
(the wires swap between being positive and negative back and forth)
And that's where the second set of MosFets comes in!
Source and Drain are swapped

Take a close look at your pcb and you'll see
here's an example of what the underside of your PCB would look like:
(cut to one phase but I think it's even the same controller)
Click image for larger version

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every three pin set is one Mosfet,
they're all facing the same way (tab facing towards the bottom edge)
the left most pin in that view is the gate pin (in your pic as well)
the center pin is the drain and the rightmost the source (for future reference)

Now, the straight bus bars you see soldered above and below within the box are tied to the battery
the P+ just above the box and to the left is where the upper rail is wired to (your Red battery wire)
and the P- on the righthand side is where the lower rail connects to (your Black battery wire)

The center Island blob is where the phase wire is connected to
Anyhow see how the Mosfets are differently connected

the two left ones' drain pin is connected to P+
(on second one the connection is on the other side of the PCB so you can't really see that)
but you see the source pin being connected to the phase wire.

on the rightmost two you see how the source pin is connected to the P- bar
and the drain pin is connected to the phase wire, right?

So when you measured every other pair of MosFets as faulty,
chances are it's because you did it incorrectly indeed.

I hope you measured in diode test mode and under no power..
otherwise there's a chance they are indeed faulty by now.
since you can short them out and pop the diode inside.

'sid

PS hm frankly I may suffer from a brain fart but
P+ and P- in my pic should be swapped *headscratch* .. nevermind...
important is they are connected in opposite direction in pairs of two!
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