# Controller upgrade with bigger Mosfets?



## frodus (Apr 12, 2008)

not very likely it'd work at all, you'd need multiple larger ones in parallel and make sure that they gate at the same time. Higher currents cause EMF that can effect a controller that is not designed for it.

The current sense is not likely going to work, same thing for the voltage sense and internal circuitry that is designed to run off 12V.

Its not "simple", and you'd spend less time and money getting it working than you would just buying the controller.


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## Amberwolf (May 29, 2009)

Theoretically it's possible, but you'd be designing and building a whole new power section board for it, in order to put the other parts on there you'd need (capacitors, probably gate drivers, etc). 

THen if there is feedback from the power section, voltage-wise, to the control section, you need to work out a way to scale that down to the range it used to be in, so the controller responds the same.

Then you need to work out a way to either entirely defeat any current limiting it has, or scale the sensor input so that it "thinks" the higher max current is the same as what it would have been for it's original limit. That part is probably easier than designing the power section.

Then you probably also need to work out a low-voltage regulator to replace whatever is in the controller that runs all the non-power section stuff, since it likely won't run on the higher pack voltage without cutting it down to the original max input voltage. 

By the time you get the bugs worked out of all of that, you may have spent enough money to have bought a better controller to start with. 


FWIW, I've done this with one ScootNGo controller that I used on my ebike, going from 24V to 36V, and while it wasn't much of an effort to do it, I did have wierd things happen because of my insufficient mods. All I did was ensure it had basic zener protection against the higher voltage for the control section (because 36V is over the limit for the LM339 in it, especially since SLAs fully charged are *much* more than that), replaced the tiny transistor gate drivers with bigger JFETs, and used NTY100N10's in place of the dinky MOSFETs it started with. I also used a much heftier flyback diode pack, out of a large PC power supply, I think it was.

Since those were all much larger than the originals, and I was too lazy to build a PCB for them (and didn't have the money or materials), I just bolted the drivers, diode pack, and MOSFETs on a large heatsink that was then bolted to the ~1.5 square foot 1/4" thick metal plate the motors were mounted to, and ran individual wires from the pins back to the PCB. 

It did work, but it was always quirky, and I doubt it performed like it should have. Under the much higher power levels of a car, I doubt that my style of modification would have worked, or if it did, not reliably or for very long. 

FWIW, eventually various control section parts died, and the last straw was the LM339, which is what pushed me into using a 2QD (better design, long-proven in the field since the current revision has been around successfully since 1998, and others for years before that! Heck, it's so good that even though the manufacturer tried to discontinue it, they still get enough quantity orders for it to keep making it!). 


So, yeah, you could do it, but I'm not sure I'd trust it if all you do is literally replace the MOSFETs with higher voltage and current rated ones, without doing all the other modifications necessary.
________
How To Roll A Blunt


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