OVERVOLTING LIMITS

[m303625]

This is for all you tech heads and tinkerers out there
Can someone give me some advice?
I have a small chinese controller for my brushless bafang motor, it uses only 2 fets per phase rated at 60v 60a, originally designed for 36v 15a. I have been able to use 44.4v lipos at 16amps peak current draw reliably (the pack fresh off the charger is just on 50v). I have tried it at 13s pack (55v off charger) which works but have not wanted to risk it so close to it's limits.
My question is "Has anyone tried voltages at or above the fets specified limits with any success?" as I suspect these devices may have some overhead built in.
I would like to try 15s pack nominal voltage 55.5v but off the charger would be more like 65v
before anyone suggests this I have tried 100v 57A fets (IRF3710) in place of the ST 60v 60A fets (65NFO6) but they only worked for a short time (few seconds) before triggering some form of controller shutdown??? I assume thermal related, which given a few seconds would reset the controller & I have modified the feed voltage to the lm317 voltage controller so the 12v & 5v rail is ok.
Still do not understand why the 100v fets didn't work as the triggering voltages according to the data sheets are the same along with the Drain Source resistance
any advice appreciated
thanks Mike

 

[Anonymous]

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[gmouchawar]

The IRF3710 has an internal resistance of 23 miliohms. The ST part P6N06 has an intenal resistance of <16 milliohms.
Although the IR part has a higher voltage rating it is 50% worst on current carrying capability. If you are taking the trouble
to replace the FETs why not use the famous IRF4110. That should give you plenty of both voltage rating and current carrying
capability. The resistance of the 4110 is 4 milliohms. You are likely to be limited by the wiring and not the FET is you use it.

BTW watch out for the capacitors. They need to be properly rated also. A rule of thumb is atleast 20% headroom from the rating.

 

[m303625]

Guys, thanks for the quick reply
I have upgraded the 50v filter caps with 63v on the controller I am playing with ( have been running the 50v caps for several weeks now using 50v lipos with no problem)
I was unaware of the 4110 fets and did not think the Rds resistance was that critical, but that would explain the problems I was having with the replacement fets!
I will check the specs on the 4110 and see if I can source some to try
thanks
Mike

 

[Anonymous]

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[wrobinson0413]

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