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Mattlikesbikes

E-Cruiser - Li Battery repair

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Neighbor knows I am the bike guy, so she gave me her R Martin Cruiser (Circa 2011 per the battery). A step through with a 7spd rear hub motor. She thought the battery was in great shape as she connected it recently. Best guess it is toast, as it charges for 4 seconds then the green light comes on. But when on the bike it shows low power. It's a 36v 14ah top tube mounted battery pack. 

I'd love to get this thing working for my disabled SIL, as the hills by her place are too much for her to ride, but she would love getting around more. But I don't know that I want to throw a bunch of cash at having the battery rebuilt commercially (non original packs won't mount up in the same spot as easily, though I could rewire it to a back rack battery). 

Anyone have experiece opening these things up to check cells? After reading up, I know there is a decent chance the Li batteries are toast from not being used, but also might be salvageable if I can get around the BMS to force charge them (BMS seems to think they are charged). 

 

Alternatively, if this battery pack is toast, I may start experimenting with a bike for me. Move the 26" disc 7spd hub motor to a donor frame and build a shredder for out at the ranch. 

 

Who wants to tinker?

 

 

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4 hours ago, Mattlikesbikes said:

Neighbor knows I am the bike guy, so she gave me her R Martin Cruiser (Circa 2011 per the battery). A step through with a 7spd rear hub motor. She thought the battery was in great shape as she connected it recently. Best guess it is toast, as it charges for 4 seconds then the green light comes on. But when on the bike it shows low power. It's a 36v 14ah top tube mounted battery pack. 

I'd love to get this thing working for my disabled SIL, as the hills by her place are too much for her to ride, but she would love getting around more. But I don't know that I want to throw a bunch of cash at having the battery rebuilt commercially (non original packs won't mount up in the same spot as easily, though I could rewire it to a back rack battery). 

Anyone have experiece opening these things up to check cells? After reading up, I know there is a decent chance the Li batteries are toast from not being used, but also might be salvageable if I can get around the BMS to force charge them (BMS seems to think they are charged). 

 

Alternatively, if this battery pack is toast, I may start experimenting with a bike for me. Move the 26" disc 7spd hub motor to a donor frame and build a shredder for out at the ranch. 

 

Who wants to tinker?

 

 

I'd love to have the time to tinker with it, but I don't right now.  I don't know anything about the charger or what it's doing to detect when a pack is charged. My experience is with NiCd or NiMH and what you are describing sounds like a false peak probably due to a cell that is now at high impedance.   With RC packs, we have fancy chargers that will allow us to tweak stuff like charging rate and peak detection and re-conditioning cycles for packs.  If we got to the point where we had an obvious bad cell we'd take the pack apart, find the bad cell, then characterize all the cells and match them to make new packs.   Looking at prices for the cells, they are really not that expensive.  I'd shoot for matching the same types in order to match to the existing charger and motor.  The question for me would be:  is the charger good?  

What does the pack look like?  Sealed in a plastic pack that's glued together?

@TheX has more experience with Lithium batteries than me I think but not sure if he's messing with pack builds/rebuilds.

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If the pack can be safely opened, it can be rebuilt more than likely. They all contain the same basic cells.

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You can definitely crack this one open. Has a little glue, but mostly bolts and some do not tamper stickers holding it together. 

 

I'll open it up. Is there a way to test individual cells once they are welded together into series? Seems like you could get the reading on a block, but maybe not the whole.

 

 

 

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If there's even a partial charge, you can measure across each cell with a voltmeter to see if there's one reading low.

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So watching more videos on how much power you need, I may hobble something together for her to try it, but I suspect this 500W setup isn't going to be enough. my SIL is a bit overweight, lives off Far West and would want to get down to Anderson and Burnet, so up and down the far west pedestrian bridge. A bit of a hill and maybe too much for 500W pedal assist.

 

In that case the 500W wheel goes to me. So I maybe on the look out for a beater 26" frame (or better a Stinky or similar). Something to hoon at the ranch.

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I found a local battery rebuilder who is going to rebuild some of my Kobalt lawn equipment batteries. He quoted me $140 to rebuild the 36v 14ah pack on the ebike. While I am not sure if the bike is powerful enough, if all I sink into it is $140, I am sure I can resell it working for more than that.

 

 

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7 minutes ago, Mattlikesbikes said:

I found a local battery rebuilder who is going to rebuild some of my Kobalt lawn equipment batteries. He quoted me $140 to rebuild the 36v 14ah pack on the ebike. While I am not sure if the bike is powerful enough, if all I sink into it is $140, I am sure I can resell it working for more than that.

The demand for such knowledge and services is already here. for people who have a mastery of electronics, there's a service they can provide for $$.

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6 minutes ago, mack_turtle said:

The demand for such knowledge and services is already here. for people who have a mastery of electronics, there's a service they can provide for $$.

For sure. Battery pack work is super straight forward, but it takes the gear (spot welder, and supplies) and if you are doing anything other than rebuilds, lots of experience with pack design. If this guy does good work, I'll let folks know. I'm already looking around the garage at all the battery junk that I could have rebuilt instead of throwing away (looking at you NiteRider HID setup).

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