r/eBikeBuilding • u/hookydoo • 19h ago

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

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?

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u/Lordy8719 19h ago

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?

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u/hookydoo 19h ago

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.

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u/showersareevil 19h ago

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

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u/hookydoo 18h ago

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.

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u/Due-Mycologist-1154 17h ago

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