Kawasaki eliminator 125cc cruiser build

[MX-215]

I'm doing a build on a Kawasaki Eliminator (aka bn125), a small 125cc cruiser-style bike. I'm using this bike simply because I have it already.

I've been back and forth on hub vs mid-drive; I am pretty sure I'll do mid-drive using the qs138 v3 with gearbox. It seems like the easier way to go, with less fab needed and so on.

I'm stuck on the battery - to build or buy, what specs needed, etc? The goal is primarily to use this as a learning excercise, but at the end I'd like a bike that performs as close to the gas version as possible. It's not a fast or quick bike, with a 125cc ~16hp engine it tops out at about 50mph (downhill tailwind etc).

Advice?

 

[MDG]

That’ll be cool! I’d get the motor mounted first then figure out battery size. I recommend Amorge batteries if you buy one. They can make custom sizes and amp outputs. All 3 of mine have been awesome. Highly recommend the 138 as well. Nice running close to stock sized sprockets!

 

[amberwolf]

I recommend checking the advice I've given in other MC build threads, regarding the job you need it to do under the riding style and conditions you have to find out hte power needed to do that job. That will tell you how much battery you need for a given range and speed, etc.

If you just want to duplicate the original range, speed, etc., you can use calculators or simulators like the one at ebikes.ca to guesstimate the power required to do that, and then use that to see how much motor, controller, and battery you'll need for this.

Or you can look up what wh/mile people report that various e-motorcyles already take for that speed, and work it that way.


At a guess you'll probably need a battery that can supply at least 200A, and has at least 4-8kWh, depending on the acceleration and range you're after.


If you build a battery, I recommend used EV modules, that use large-format cells; places like Batteryhookup often have these. They'll almsot certainly behave better than those built from 18650s or other small-capacity cells which will also not be well-matched like the EV cells almost certainly will.

 

[MX-215]

Thanks for the tips - I'm very much in the beginning of this journey! The motor kit came, and I'm starting to work on the mounting process while I figure out battery options. In the meantime, is there a way that people benchtest these using a power supply or something else? I'd love to be able to turn it on!

I'm using the EM200-2 controller, which calls for 57V-72V

 

[SlowCo]

Nice conversion project!
I love builds like this and hope you will update this thread with much photos for us to follow your progress.

 

[MDG]

Yes, you’ll need your battery, controller, motor, an on/off switch and the wiring all put together to bench test it.

What motor did you get? I’m gonna guess you’ll need a 72V power supply for it to turn on.

 

[MX-215]

Yes, you’ll need your battery, controller, motor, an on/off switch and the wiring all put together to bench test it.

What motor did you get? I’m gonna guess you’ll need a 72V power supply for it to turn on.

Yes, I know. I have all but the power source (battery or power supply) - is there a decent inexpensive benchtop supply that people use for testing? I have a qs138 90h v3 and a votol em200-2 controller.

 

[amberwolf]

What kind of testing do you want to do? If it's very low current (no load) testing, which is usually less than 10A, you could use a CC/CV PSU or LED PSU, or even a battery charger (if it doens't require the battery to be connected to provide output), so...you could buy the charger you want to use on your battery, and use that. (the PSU can be used as a charger, if it's one of those two types).

You could use two Meanwell HLG-600H-48A (or 54A) LED PSUs in series for up to 11-12A of current, and they could be set to the right voltage to charge a 72v battery (84v full). They are solid, fanless, potted, weatherproof and vibrationproof, so you can even mount them on the bike for charging wherever you go; they'll take 115v or 230v so you can use them on EV charging stations (with the right plug). At a guess it'll be about $400 for two of them brand new, so not cheap but reliable. (I have had one mounted on the bottom of the SB Cruiser trike for years, and it's been submerged in flash flood waters more than once while riding home from work).


If you need to do any loaded testing, youre better off to just get your battery first, because a power supply that could handle high currents is likely to cost enough to buy a good battery.

 

[dominik h]

Problem while testing with power supplies is that they do not accept any current coming backwards from the motor/controller. If that happens the supply voltage raises quickly and the controller can die if the voltage gets to high.

 

[amberwolf]

So could the PSU.

That's a good point I didn't think of while posting previously.

 

[MX-215]

That’s great advice thanks! Yes I’m thinking of no-load testing, just to make sure that I’m putting things right as I go. Documentation on the motor controller etc is sparse to say the least! It sounds like I really just need to move on the battery.