What voltage FETS for a 72V (nominal) ebike?

[4LivesPerGallon]

Seeing so many controller problems.

So, if I don't want blown MOSFETS in a 72V ebike, what is the highest voltage or lowest voltage spec that you suggest, for a long-term electric bike?

Thank you.

 

[bowlofsalad]

There is no correct general answer for various unknown random controllers. Some might guess 90v, but the right answer is it's wholly dependent upon components like the mosfets and capacitors used within the controller. They have a voltage thresh hold, exceed it and the component breaks. Someone could sell you a controller for your 48v pack but the controller might be capable of handling 100v. Perhaps your best bet is to ask the person who sells you this controller exactly what the maximum input voltage is. If you want, you might try to open a controller and look at the components to learn some of this yourself, but chances are you'll probably want to ask.

It's hard to speak on the subject of controller reliability. Sometimes heat or moisture might be the culprit, sometimes a lot of rough riding or user error could be the fault. A lot of controller failure might be solved by using a temperature sensor and potting the controller. A controller like the [img=http://www.ebikes.ca/shop/ebike-parts/controllers/c-phaserunner.html]phase runner[/img] comes to mind. Chalo once suggested an alterative to potting might be bees wax as the wax would also potentially act as an excellent phase change thermal transfer material. If the controller needed to be repaired, all you'd need to do is heat up the box and the controller would be able to be pulled out, I have no idea if this is viable, blah blah, just throwing thoughts out there. Food for thought.

 

[BSATOM]

For 72v use a 100v FET like a IRFB4110 or IRFP4468. Do not try to use a 75V or 80V FET, those will blow because of reverse voltage spikes from the motor eventually, if not sooner.
There are several reasons why so many controllers blow. It's the same as audio amps.... people overpower them, wire them wrong during setup, the output cables get shorted together under power load conditions, heat build up, fate, destiny, freewill, shit happening, etc.
Make sure all of those possibilities are addressed and/or eliminated and you will have a long and reliable controller life.