Hello,
Following on the post here:
I thought, i’d create this topic because maybe other tips and tricks for salvaging could end up here!
@TheTerribleTriplet - I started to take apart one of the 25.6V batteries I had lying around. This is what I found. Any hope/suggestions towards repurposing into a 51.2V array if I take 2 apart?
Please pardon the black plastic dust. From the hacksaw 
what brand/model batteries are those? looks like “drop-in replacement” types?
if so, many of those batteries allow series and/or parallel connecting them (no hacking required).
2 x 24V(25.6) series connected batteries = 48V (51.2)
These are Powerman LFP 2450 - 50Ah 25.6V batteries for UPS. I think they work as drop-in replacement even if not expressly sold as so.
Yes, my thinking is to put them in series, seems like the least work. I still don’t understand why they should not be put in series. Like what would break? Is it say a BMS limitation where if one battery breaks, then the other one doesn’t know how to deal with it?
Ideally then, I can just put 2 in series, hook up a Multiplus and I am done.
If the BMS does not specifically support this, then battery balance will be a problem.
If the batteries are not perfectly balanced, then the moment the first one is fully charged, the BMS will disconnect, breaking the series chain, and the other battery will stop charging.
So, on the next charge cycle, the imbalance is a little worse, and charging stops a little earlier. Imbalance only ever gets worse.
So, either the internal BMS needs to support series charging, or you need an external balancer.
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That’s what I missed - the disconnect.
External balancer needs to support a “cell” of 25.6V right? As opposed to the typical 3.2V per cell that they would normally support?
Remove the cells having removed the BMS’es.
Then connect the cells in series for a 48v bank with an appropriate new BMS for the 48v bank?
Unless I’m miss something?
Correct. Something like this:
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Nothing missed so far. I was confused around once cells are removed, the cells themselves the busbars look welded to the cell. I am thinking I probably don’t need to separate the cells anyway - but thinking ahead for faulty cells later and so on.
There are ways to detach the cells if you have to, if they are spot welded, it is worth the effort.
Me, take it one step at a time:
Step 1: I see in the pics there are nuts, so each 24v bank can be connected there in series for 48v?
Step 2: … just do step 1 first.
Worry about having to replace a cell when you have to worry about it.
BMS’es:
Unless the BMS’es are designed to run in series, the little bit I’ve read in the past, I won’t do that.
The fewer wires, the fewer connections, the fewer electronic parts, the better.
I know some will disagree, but that is my simple rule for myself, rule crafted from good salient advices for others over time, here on this forum. 
(And the fact that I’ve burnt out enough shiite to last me a lifetime.)
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Typically it works just fine. Each BMS balances its own set of 4 cells, and it all evens out. The issue, as @justinschoeman said, is that a fault condition can cause a disconnect in one of two places, and then because the two BMSes are not aware of each other, there is no real recovery to be done.
Victron’s SmartLithium’s with a VE.Bus BMS works a bit like this. The batteries are 12.8V modules each, with their own balancer inside (no disconnection hardware though), and they simply go in series. They have comms cables that connect together, and to an external “Bms”, creating a single point of control.
Details please! Reason, the cells inside the BMW i3 pack are welded in a similar manner. Not that I plan on ever doing anything, but I have often wondered what one would do if you ever need to replace cells. I mean, if you went DIY and didn’t just order a module from evshop.eu. The only solution seems to be new busbars… and your own welding tools.
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My go guys for ideas of this nature:
@Gman
@Gh3kko
It always makes me worried when people use words like “should”, “typical”.
Some BMS’es manuals clearly states: Not for use in serial connections, parallel only.
It “will work” is what we should be after.
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Aaah yes, that’s because the fault condition is not covered.
Let me be clear: If you know what you are doing and you’re willing to handle the situation on your own, or you are out in the sticks and the shops are all closed, this will work just fine, and you might be able to get away with it forever. I will not recommend it as a generic solution though, and that is why the manufacturers also won’t
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Part way there. Took it apart.
These are REPT 50Ah cells (e.g. QR 08ICB1400089BAD231416126). Anybody know of these? Any thoughts?
Measured each cell. Sitting at 3.32V. Don’t have anything more precise to get me the mV.
Don’t stress about that. To measure cells, need to charge/discharge each measuring what went in, drawn out. As EVE does when they give the ah per cell, all the stats actually, per cell.
Or the bank, less accurate. Still fine.
The bank, I see there are connections on each one to connect them in series using a DIY bendable busbars?
Sorted.
Bendable bus bars or the cables that were connecting the two sides within the case. Any harm in using cable?
Should I tightly tape the cells to maintain compression? Is that a thing still?
Perfect yes!
Compression, two comments on that.
- Molecular scientist explained, when a cell expands, nothing stops the molecules from moving apart.
- You compress them, not too hard, to make 1000% sure that the cells will never move.
Why?
The busbars will then put strain on the battery poles, and that is not good.
Or in a vehicle, that the cells can never chafe.
Lifepo4 cells, if the sides gets chafed exposing the metal underneath, it can cause a short.
Separate thought.
I once got cells out of a EV. They where all in brackets keeping them stationary, with ample ventilation between each cell.
It is a good idea to keep the cells apart for better ventilation.
Also have seen people using flexible busbars between the cells.
To mitigate any strain on the poles.
The poles being the weak spot.
Ok point understood then. It’s about avoiding motion that would cause wear of the outside case. otherwise ventilation is good.
Here is another example of batteries being salvaged. (apologies for the link)
What interests me is that these cells have a another life (after being worked hard in their first life)
So unlike lead acid which don’t have a second life LFP batteries do and can be sold by what life is left in them.
We are sure to see more of this as these batteries are replaced going forward…