Bionx Bike Defective Battery+Dead Motor - Seeking Advice

Hello all,

Someone gave me a Trek bike with a Bionx motor and battery (Model 7200+).

The battery has been sitting for years and it's dead. Won't charge, even after replacing the fuse that had been blown inside the battery. Voltage is zero. Charger seems to be functional.

I tried to ride the bike without a battery. The motor is "resisting", which makes me think that something's shorted inside, most likely the power MosFETs. I assume that the MosFETs blew the fuse. Yay.

At this point I'm considering buying new 18650 elements to rebuild the battery, AND dismantling the motor to fix the control board.

Is it fair to assume that's everything that's broken/defective?

Can anyone think of a better alternative that won't cost a lot more?

I also considered buying a different battery, gutting the motor and using a non-Bionx controller. Is that a reasonable alternative? Or is it too much work and way more expensive?

Thanks in advance for any answers!

The motor is probably good. Bionix is a DD motor. It is normal that it has some resistance when spinning it.

tude647 said:

Is it fair to assume that's everything that's broken/defective?

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Can you ask the former owner how it was working before the battery died? My experience with the BionX battery is that it has interior logic that bricks the battery if the voltage level falls below their programmed LVC, presumably to prohibit the user to charge and use a battery that has had its cells discharged down into the danger zone (avoiding the possible explosions/fires).

I bought a used 48V BionX ebike last year, similar condition to your story. Battery would not accept charge. Owner had left it alone in the garage several years and the BMS slowly drained the battery beyond its resuscitation point, so it bricked the battery. Found a great battery rebuilder in Michigan who was experienced in the BionX quirks and repopulated the battery with fresh 30Q cells and reset the logic board. Going on a year and it's working great!

tude647 said:

ICan anyone think of a better alternative that won't cost a lot more?

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Which battery is it? The 48V model? How much is "a lot more?" What is your skill set?

tude647 said:

I also considered buying a different battery, gutting the motor and using a non-Bionx controller. Is that a reasonable alternative? Or is it too much work and way more expensive?

Click to expand...

Only you can answer that. Are you set up for that job? Proper tools? Soldering skills? Available time?

Can you ask the former owner how it was working before the battery died? My experience with the BionX battery is that it has interior logic that bricks the battery if the voltage level falls below their programmed LVC, presumably to prohibit the user to charge and use a battery that has had its cells discharged down into the danger zone (avoiding the possible explosions/fires).

Click to expand...

The previous owner said that the bike worked great until the battery died all the sudden. I think this is what happened: the motor shorted out, and blew the fuse on the battery, which led him to believe that the battery was the only component that had failed.

I bought a used 48V BionX ebike last year, similar condition to your story. Battery would not accept charge. Owner had left it alone in the garage several years and the BMS slowly drained the battery beyond its resuscitation point, so it bricked the battery. Found a great battery rebuilder in Michigan who was experienced in the BionX quirks and repopulated the battery with fresh 30Q cells and reset the logic board. Going on a year and it's working great!

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I might buy cells and repopulate this battery as well, but I'll try to revive it first by charging it (slowly).

Which battery is it? The 48V model? How much is "a lot more?" What is your skill set?

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It's a 11S3P configuration, so I guess it's 40V. Doesn't sound like a common model, but that's what it is. The charger label says "for 40.7V battery".

Only you can answer that. Are you set up for that job? Proper tools? Soldering skills? Available time?

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I have the skills and some of the equipment, but I don't have the time. So I don't think I can afford to switch to a non-Bionx controller.

So I guess the plan looks like this:
Attempt to revive the original cells. If that fails, buy new cells, rebuild battery.
Buy transistors and fix the motor control board
Cross fingers and test.

Thanks so much for taking the time to answer all my questions!

MadRhino said:

The motor is probably good. Bionix is a DD motor. It is normal that it has some resistance when spinning it.

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I think I misspoke when i said that the motor is resisting.
The actual resistance is BRUTAL once I gain any amount of speed. I can't pedal for more than 1 minute without my legs burning and running out of breath, even on the lowest gear, so I'm assuming the control board is shorted.

This is symptomatic of shorted phases, most of the time outside of the motor at the axle channel. When phases are shorted, a DD hub becomes very hard to spin. This is used in some controllers as a thief security, and some defective controllers are shorting 2 phases by internal damage. Easy to test.

This is symptomatic of shorted phases, most of the time outside of the motor at the axle channel. When phases are shorted, a DD hub becomes very hard to spin. This is used in some controllers as a thief security, and some defective controllers are shorting 2 phases by internal damage. Easy to test.

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Is that something I can measure without opening it? There are only 2 cables that come out of the motor: one with 2 thick wires, which goes straight to the battery port, and a control cable with a bunch of wires. I disconnected both and the motor still drags when I try to ride the bike.
I guess it'll be hard to diagnose without opening it first.

[youtube]Wc8OJtFRUng[/youtube]

MadRhino said:

[youtube]Wc8OJtFRUng[/youtube]

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Looks like an awesome project, probably more than I can handle right now. Thank you for sharing.

So, I revived my battery, re-assembled it, plugged it into the bike, the little control unit lit up as soon as I pressed the ON button.

I moved the bike a little and then poof! the fuse blew. So I'm almost 100% I have some MosFETs to replace. It's not an ideal situation, but it's manageable.

Thank you all for your help so far!