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FET Voltage ratings of 84V versus 67 volt wheels?


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5 hours ago, DaveThomasPilot said:

Maybe this belongs in the "Mods, Repairs, & DIY" forum, but I thought I'd start here.

I'm going to get either a 16s or a Tesla.  I really like the idea of the higher voltage--assuming the control board designer knows what he's doing and used FETS with a sufficiently higher voltage specification.

I worry, since there have been reports of FET failures.  Could it be they are using the same FETS as in 67 volt boards?

A higher voltage breakdown specification means either a higher Rdson ( on resistance), or a bigger (and more expensive) die.  Bigger die have higher gate capacitance, and are harder to drive.  Higher switching losses could result if the gate driver isn't scaled appropriately.

 Inexperienced power conversion designers sometimes chase low RDSon to minimize conduction losses in the FETS, and compromise reliability with a insufficient voltage margin. 

Has anyone seen a P/N on the FETs when their wheel was apart?   It would be nice to check the specs on the FETS they are using.

Otherwise, I'll go with the KingSong and avoid the higher voltage wheels until they have proven reliability.    Failures should be in parts per million, not in the low percentage points.  Otherwise, the problem is likely a design issue.

I'll leave the technical discussion to others. I can say that over 1500-miles on five different 84-volt Gotway wheels, I have had no MOSFET failure. Anecdotal I know, but there you have it. In my opinion the 84-volt wheels have been proven reliable. Hell, it's kind of old news now. Were you aware that the new KingSong 18L is an 84-volt wheel?

All the 84-volt wheels have more oomph (very technical term) than any 67-volt wheel that I've ridden.

Join the club, you'll have a blast - maybe that was a poor choice of words :facepalm:

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