BIG Lifepo4 upgrade using old cells in my campervan.

nastypoker

New Member
Joined
Oct 12, 2021
Messages
5
Hello all, I have been researching upgrading to lithium.

Currently I have:

220Ah 12v deep cycle - 2P
AMC12-12-60 which is a 60A DC-DC charger running off my alternator
350w solar panel
30A Epever MPPT
1500W PSW inverter

I am looking to upgrade to lithium as I want more capacity to possibly run an air conditioner and be off-grid longer. The DC-DC can be programmed to work with lithium.
I have picked up 16x 200Ah single cell Lifepo4's that are well used. I want to arrange 4P4S and will be doing proper capacity tests soon but in the meantime, I have some questions.

1. If my cells have a wide variety of capacities, what should I do? Lets say 1 cell has only 150Ah capacity, then the low voltage cut off will trigger after 150Ah is used so not really a problem other than reduced capacity. If this is the case, I am not bothered but if it will damage something, then I should be worried!

2. Is there a device out there that can be a BMS, an active cell balancer and a cell monitor all in one, ideally with bluetooth or a remote display?

3. Any other tips or advice you can give someone new to lithium!
 

DThames

Photon Sorcerer
Joined
Nov 22, 2019
Messages
1,440
Test each cell for capacity and record the values. For each group of 4P, try to sort the cells so that each group of 4 has about the same sum. Then connect those groups in series. That is the first thing you should do.

Some BMS, are good to monitor and control but must are poor to balance.

Advice, think twice before you touch stuff like wires/terminals/tools together.
 

nastypoker

New Member
Joined
Oct 12, 2021
Messages
5
Test each cell for capacity and record the values. For each group of 4P, try to sort the cells so that each group of 4 has about the same sum. Then connect those groups in series. That is the first thing you should do.

Some BMS, are good to monitor and control but must are poor to balance.

Advice, think twice before you touch stuff like wires/terminals/tools together.
Thanks. Following some advice from reddit, I plan to do a full charge and discharge to check their capacity. Do a full charge and then leave them for a few weeks and then do another capacity test to see if they have any parasitic loss issues.

That is the exact BMS I was looking at. Seems good but I am wondering if there are large capacity differences, it will be a nightmare to actually get a full charge if the balancing charge is so low on such a large battery pack.
 

DThames

Photon Sorcerer
Joined
Nov 22, 2019
Messages
1,440
Thanks. Following some advice from reddit, I plan to do a full charge and discharge to check their capacity. Do a full charge and then leave them for a few weeks and then do another capacity test to see if they have any parasitic loss issues.

That is the exact BMS I was looking at. Seems good but I am wondering if there are large capacity differences, it will be a nightmare to actually get a full charge if the balancing charge is so low on such a large battery pack.
About all you can do is fully charge all cells (top balance) then after you build the pack, discharge only to a point where your weakest cell group starts to quickly drop off in voltage. Set BMS cut off about there. Then when they charge backup, they will be close to balanced. But even then there will often be a "runner" that takes of headed to a higher voltage rather quickly because it is fully charged before the other cell groups are. I have a used battery, so I have the same concerns/issue.

About that BMS, I saw someone else stocking and selling it in the US at a lower price. I will say that Overkill Solar has very good customer support from what I can tell and from what others say.
 
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