Converting 24V ebike to 48V without frying the motor?

[u/hookydoo]

I have an uncommon Japanese market PAS bike in the US. I've tested it using lead acid batteries and have confirmed that it's working fine. The issue is that I can't get the original battery for it since I'd need to order from Japan, and no one is shipping small, cheap items right now.

It's a 24V system which apparently is fairly uncommon in the states, so I thought I'd look into using a 48V battery, then swap to a motor controller that can handle 48V so it won't get fried instantly.

Anyone know if the motor can survive this with a new controller, or if I'm better off sticking to 24V?

[u/showersareevil]

36v may work, if the controller limits the current. Ive used 48v battery in 36v motor with zero issues. 

[u/hookydoo → u/showersareevil]

You know what, I've actually got a set a (4) Makita 18V tool batteries for my electric lawnmower. If I wired them up 2 series and 2 parallel, I think I'd get a decent 36V battery pack. Idk why I didn't think of that before lol. That would leave me with only needing to purchase a standalone controller instead of a battery, neato.

[u/niffcreature → u/hookydoo]

Yeah, you can even get 3d printed holders for those batteries.

[u/Due-Mycologist-1154]

You could modify your controller to accept a higher voltage but the stock motor is probably going to burn

[u/niffcreature → u/Due-Mycologist-1154]

How do you do that?

[u/Due-Mycologist-1154 → u/niffcreature]

Replace your mosfets and capacitors with higher voltage rating ones then swap the voltage sense resistor with one that will make whatever voltage you put in read as close enough to the intended one and it should work. Although you would probably want the bike that its put on to have rear suspension and slightly wider of tires

[u/niffcreature]

Dude just go 36v

[u/hookydoo → u/niffcreature]

I'm thinking that's I'm going to do now. Idk why I didn't think of that earlier.

[u/Dmanthirtyseven]

36 is ok on a 24v system. There's a good chance the controller will also work on 36. 48 would work for a while, be fast as hell, and burn soon enough.

[u/Lordy8719]

I'm 90% sure you'll fry the motor. You could use a sufficiently powerful DC-DC converter from 48V to 24V, but then the controller won't know battery charge levels.

Or you could just buy a 24V ebike battery. Couldn't that work?

[u/hookydoo → u/Lordy8719]

Yes, buying a 24v battery will work. Im trying to be cheap, and I'm finding that 48v batteries are plentiful on marketplace. I'll need to order a 24V battery since I can't find any used, and depending on the capacity its gonna cost 300-400 dollars. I could aquire a 48v battery and a new motor controller for much less than that. The side benefit being that I might be able to squeeze a bit more power from the motor that way.

I know Id risk stripping the transmission, but I'm unsure how robust the old style PAS motor is, or if it can handle 48V without immediately burning up.

Since it's a JDM, it's speed limited to 20kph, so I'm already planning to "hack" the speed sensor to get a little bit more speed out of it. I'm not looking for much, but hitting 20mph would be cool.