Making a 36V controller into a 72V.

[OpAmp]

I own the C3635SI (36V 35A) controller that is sold by e-bikes.ca. Is there anything else other then changing the FET’s that needs to be done to allow this controller to run at 72 volts without frying something?

 

[Link]

You need to replace the caps and the diodes, too.

 

[OpAmp]

I believe you're talking about the 3 large electrolytic caps, but which diodes need replacing?

 

[Dr. Shock]

I don't know that controller, but there are usually some Schottky diodes either interspersed with the FETs or near them. Sometimes you don't need to change them because they are already rated for higher voltage. That was the case with a YiYun LB-37 controller I modded. You have to find the diode (usually the outer two pins will be soldered to the same bus) and read the model code printed on them. Then pull a datasheet from Digi-key or elsewhere and figure out what voltage they're rated for. If you need something bigger, then replace them.

On the controllers I've modded, I had to replace the power resistor feeding the control circuitry. These usually were about 1K ohms and I had to replace them with 1.6 or 1.7 K ohms to keep the input to the voltage regulator in spec.

Don't forget the precharge resistor.

 

[OpAmp]

I sent ebikes an email and it turns out that all I have to do is put the fets in and it will be able to operate at 72v. I know that just because someone says it will work, doesn't mean it will work in spec.

I’ll be using the IRFB4110. Once I get the controller open, I’ll check the parts you guys mentioned and get some voltage readings to make sure everything will be operating in spec. Most likely I won’t be putting more then 66V on it. Sure sucks that you have to slide the board out, in order to see what parts are in there or to get any readings.

 

[lazarus2405]

Dr Shock, you're thinking of brushed controllers. :wink:

Just the FETS and perhaps the caps. Those big electrolytic things, and in a 36v unit they are most likely rated for 63v. To run at 72v, you'd be wise to upgrade them to 100v rated ones of at least the same capacitance.

 

[Dr. Shock]

Yes, quite right, Laz. I didn't realize the brushless were also diodeless.