# Homebrew Batteries?



## Sheffield_Tiger (22 Mar 2019)

Just browsing eBay and came across this

https://www.ebay.co.uk/itm/unfinish...057740?hash=item340704d98c:g:D5cAAOSw78xck5xD

I like stuff like this: "battery is made up of 49 salvaged laptop cells (LG and Samsung, all re-sleeved) "

Liking the resourcefulness and makes sense given that the battery can be the most expensive part of an e-bike conversion - anyone else make their own batteries from reclaimed cells?

I'd have concerns about mix and match cells....


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## Edwardoka (23 Mar 2019)

Sheffield_Tiger said:


> I'd have concerns about mix and match cells....


You'd be right to. This is a catastrophically bad idea.

They would all charge and discharge at different rates and have different charge/recharge profiles.

Some cells would become deep discharged during use and therefore be prone to reverse charging (although this effect can be mitigated with a battery protection circuit on each bank of cells). If wired in parallel they'd be constantly fighting each other while trying to equalise charge. 

When charging, some cells would become overcharged while others were still charging.
All in, this is a terrible idea.


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## cheys03 (23 Mar 2019)

I disagree with @Edwardoka and speak from experience.
There are indeed all sorts of risks with second hand cells. The key is not to blindly wire cells together but to test them and ensure that the ones salvaged are no riskier than new cells. You do this with repeated charge/discharge cycles and leakage tests. Mapping the capacity of each cell accurately is crucial and allows matched banks to be built.

Is this example, 49 cells are used and the controller/motor is 24v. The battery will have cells in a 7series 7parallel arrangement. There’s nothing to suggest the mix of cells from different manufacturers is done dangerously. It may be that each series bank is made of 4 LG and 3 Samsung cells in parallel for example. This is fine, so long as the capacities are close and the battery drained to the capacity of the weakest bank not the strongest.

Around 5 years ago it was economically viable to spend all this time salvaging cells (and don’t forget buying test equipment too). Now there’s not much in it as the price of new cells has come down a great deal.
Unless you get the cells to be salvaged for near free and they’re near new, buying something pre-built can make more sense.

All the info here https://endless-sphere.com/forums/ is worth a read if you’re in to e-bike’s etc!


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## Edwardoka (23 Mar 2019)

cheys03 said:


> I disagree with @Edwardoka and speak from experience.
> There are indeed all sorts of risks with second hand cells. The key is not to blindly wire cells together but to test them and ensure that the ones salvaged are no riskier than new cells. You do this with repeated charge/discharge cycles and leakage tests. Mapping the capacity of each cell accurately is crucial and allows matched banks to be built.
> 
> Is this example, 49 cells are used and the controller/motor is 24v. The battery will have cells in a 7series 7parallel arrangement. There’s nothing to suggest the mix of cells from different manufacturers is done dangerously. It may be that each series bank is made of 4 LG and 3 Samsung cells in parallel for example. This is fine, so long as the capacities are close and the battery drained to the capacity of the weakest bank not the strongest.
> ...


I gladly defer to your superior knowledge of how to go about actually setting it up. But a random diy ebike on ebay comes with no guarantees that any kind of sanity checking has taken place on the salvaged cells.


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## gbb (23 Mar 2019)

On a smaller scale, I made a 4x18650 15v cell pack for my lights ooh, maybe 9 or 10 years ago. I still had it until earlier this year when I think it gave up....but it gave reliable service. Recovered from a duff laptop battery (in which most of the cells were a totally ok, only a few had failed). The one thing I did get was a good quality charger and made sure I matched the cell voltages as closely as I could before assembling it.
Making a 36v ebike battery is something I'd not bother trying tbh.


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## cheys03 (23 Mar 2019)

Edwardoka said:


> I gladly defer to your superior knowledge of how to go about actually setting it up. But a random diy ebike on ebay comes with no guarantees that any kind of sanity checking has taken place on the salvaged cells.


Agreed - and you’re right to caution around something that can cause significant harm if not constructed and maintained correctly.


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## gbb (25 Mar 2019)

There are plenty of YouTube videos regarding construction of batteries but the one thing that comes to my mind...the work you have to put I to it all and the last thing I'd probably want was doing all that work only to find a shortened battery life because a cell or block of them deteriorated too quickly, that's possibly quite a risk with using used cells.


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## Sheffield_Tiger (25 Mar 2019)

cheys03 said:


> I disagree with @Edwardoka and speak from experience.
> There are indeed all sorts of risks with second hand cells. The key is not to blindly wire cells together but to test them and ensure that the ones salvaged are no riskier than new cells. You do this with repeated charge/discharge cycles and leakage tests. Mapping the capacity of each cell accurately is crucial and allows matched banks to be built.
> 
> Is this example, 49 cells are used and the controller/motor is 24v. The battery will have cells in a 7series 7parallel arrangement. There’s nothing to suggest the mix of cells from different manufacturers is done dangerously. It may be that each series bank is made of 4 LG and 3 Samsung cells in parallel for example. This is fine, so long as the capacities are close and the battery drained to the capacity of the weakest bank not the strongest.
> ...



Although - and this is just my sales pitch - I'd allude to a good level of working knowledge without going too deep into it if listing such a battery pack on eBay, same as I reference my Cytech and workshop experience when listing a serviced or restored bike. Could be that this seller also has a line in salvaged computer equipment and has found a good way to combine skills and reuse salvaged parts....just don't know if it is someone who knows their stuff or who has stumbled on an internet article and decided to have a pop

It's interesting though

Maybe the batteries could be placed in a large seat pack which, if not done properluy, could double as a winter arse-warmer when the cells heat up!


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## Sheffield_Tiger (25 Mar 2019)

Anyway if it is done properly someone got a good buy at £28, even just to break it for motor and general parts


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