Battery capacity drop

trex

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May 15, 2011
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prismatic cells are used in rectangular packs like inside rack batteries or behind seat post batteries.
 
D

Deleted member 4366

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Most ebike batteries these days have 18650 cells regardless of size, shape or position of the battery. Prismatic cells are more or less obsolete. Pouch cells are still used in some, but they're often glued together, which makes servicing difficult. The only easy to service batteries are ones with Headway cells, but they're relatively large and heavy for their capacity.

Bottle batteries are the hardest to repair because they're welded after assembly to the cell-holders, so you can't get the cells out. In the pod type batteries that I indicated above, the cells are welded in a block, so it's not quite so difficult. If you get a battery with branded cells, it'll probably last for years.
 

Khumarahn

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Feb 4, 2014
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Many thanks to everybody for help! I wouldn't be able to do anything without your advice. I decided to try to fix the battery, and maybe buy a new one if I fail, or other cells go bad, or I need a new bms. I bought four of these: http://www.ebay.co.uk/itm/360939737464 . It will take some time for the delivery, and then I plan to spend two weeks in Russia, but when I get everything and start working on it, I will let you know how it goes.
 

Khumarahn

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Feb 4, 2014
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I have disassembled the battery. I noticed that it smelled sort of burned, but I was not sure. I found some defects around 10-th cell (but not only), see my photos below:
IMG_2584.JPG IMG_2585.JPG IMG_2586.JPG

This is frustrating...

This may have happened this way: some time ago on my way to work the battery fell off on the road. The little plastic plate that holds the lock on the attachment of the battery cracked:2014-08-13 12.22.00.jpg

and probably some vibrations helped the battery out. It was a dangerous moment, because I was on a speed of around 24mph and in traffic, and a car behind me had to do an emergency break. But the battery didn't fall high, and it rolled to a stop.

Maybe this battery design is not reliable enough for the vibrations of the road bike?

Anyway, I will try to solder cells and assemble the battery back, we'll see what it gives.
 

Khumarahn

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Feb 4, 2014
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Some things on the battery look strange:
IMG_2588.JPG

How could that small peace break? Why is there solder on a cell?
 

awol

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Sep 4, 2013
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I think each section will be continuity checked/stress tested and any rejects will be soldered up before final assembly into the battery.
 
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Deleted member 4366

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Are not those soldered joints the power wires from one section to the next?
 

Khumarahn

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Feb 4, 2014
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yes, that too. But the big blob joins broken tab, this is not very clear on my photo, but that is so.

I am soldering all over by your method, will try to reassemble the battery now.
 

Khumarahn

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Feb 4, 2014
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Finished measuring battery capacity at 3-4 amp load, results are 10.2 Ah, 385 Wh. Not very precise, since I use hall sensor based current sensor.

I didn't need any new cells, only had to fix connections...

Will try to sleep before morning.
 
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trex

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May 15, 2011
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good pictures.
you've got the patience of a saint!
and I admire your systematic approach too.
 

JohnCade

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May 16, 2014
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This may have happened this way: some time ago on my way to work the battery fell off on the road.

and probably some vibrations helped the battery out. It was a dangerous moment, because I was on a speed of around 24mph and in traffic, and a car behind me had to do an emergency break. But the battery didn't fall high, and it rolled to a stop.

Maybe this battery design is not reliable enough for the vibrations of the road bike?
I had a bottle battery before and it didn't seem very secure to me. It rattled even when the lock was properly adjusted. I kept it tight and safer with a strip of velcro around it and the down tube.
 
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Deleted member 4366

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An excellent result. Much neater than my repair. Let's hope the BMS works now.
 

Khumarahn

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Feb 4, 2014
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What wire did you use?
A piece of 1.35 copper wire, taken from the household mains cable, something like 80p per meter in Wilko.

I had a bottle battery before and it didn't seem very secure to me. It rattled even when the lock was properly adjusted. I kept it tight and safer with a strip of velcro around it and the down tube.
I have been fighting rattling with soft pads between the battery and the frame, and battery and battery holder. After battery fell out, I use velcro strip too.

I complained to bmsbattery about battery falling out and later about capacity drop. They normally just do not reply to my messages, but after several attempts they got back to me. For $15 (shipping cost) they sent me a replacement for the broken plastic part. For the battery - they offered a 10% discount if I buy a new one. This is less than I would expect, but better than nothing :)

Thank you again for the support! I had zero knowledge about how these batteries are made, and how bms works, until I started this thread.
 

awol

Esteemed Pedelecer
Sep 4, 2013
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A piece of 1.35 copper wire, taken from the household mains cable, something like 80p per meter in Wilko.
Thanks for the info, it's given me an idea to join a couple 18650 cells to fix a 4-cell light battery pack where 2 are ok and 2 are dud.
So I strip out a small length of the bendy copper single strand from that heavy main cable, then tin a length first, then tin the cell ends, cut a piece of the already tinned copper strand to size then melt all together?
Does that sound about right?
Any other tips. Thanks.
 

awol

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Sep 4, 2013
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Couldn't get the solder to stick to that piece of single copper wire even using flux also tried a flame torch, so plan-B will be to use normal type wire and try to solder along that.
Is really showed me how difficult it really is to make such a good job like Khumarahn made.
 

Alan Quay

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Dec 4, 2012
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I've made up loads of 18650 packs. For what it's worth, here's my method:

1. Tin the wire first.
2. Now apply a liitle flux to the battery, and get it clamped.
3. Get a blob of solder to flow onto the battery. Make sure it flows.
4. Place the tinned wire on top of the battery terminal, apply iron, and again ensure solder flows.

Never failed me yet.