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Old 04-24-2019, 05:58 PM   #1
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Critique my LiFoPo4 Setup



I have forty 3.2V 30 amp hour LiFePo4 pouches that I got for real cheap from a colleague. My plan is to wire them up in parallel first (ten pouches in parallel) to increase the amps to 300, then wire four of these parallel packs in series to increase the voltage to 12. However, I also want to use a BMS and balancers with this setup, and charge it with an inverter/shorepower connection.



But I'm wondering where should I hook up the balancers? Like in the attached diagram? Or should I have the negative terminal of the balancer go to the last pouch in the parallel back, where the negative tab of the battery goes to the positive tab of the first battery in the next pack?


Any critiques welcome.
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Old 04-24-2019, 06:44 PM   #2
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Pouches as in soft packs, no prismatic hard shell case with bolt terminals?
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Old 04-24-2019, 06:53 PM   #3
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I have forty of these guys.
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Old 04-24-2019, 07:37 PM   #4
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I'd focus on the physical containment first, 1/4" end plates, four rods compressing longitudinally, then 3-sided protection nothing too stout required, or 5 sided if desired, then a cover to protect the wiring, accidental shorting.

Many like clear top so embedded voltage / amps SoC displays can be viewed but protected. Or design to fit in a Pelican-style case.

______
A 4S BMS will have a wiring diagram, 5 wires to the cells. 2 outermost circuits can also be for bulk, 3 go between cells, to the serial connections, see pic below.

I would not hardwire the BMS, but create a female "balancing port" for those 4 wires, 3.6V charging max, does not need to be more than 4A, JST XH style 20 AWG is good enough.

Thus you can swap out the BMS for a balance board, use a hobby charger to do periodic manual balances instead if you like, use a Cellog to confirm everythings OK or do discharge testing of SoH, etc.

Then a separate Anderson pair of sufficient ampacity say a 3C rate, even if you never go over .3C, using tinned fine stranded UL rated boat wire.

That's for normal cycling bulk use at 13.8V

Some like two of those, so charging bus / HVC can be kept separate from loads bus / LVC.

https://i.imgur.com/eEFKF6S.jpg
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Old 04-24-2019, 07:57 PM   #5
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Of course do some load testing to determine SoH %, see if they're worth messing with first.
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Old 04-24-2019, 09:29 PM   #6
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john61ct, thanks for the info... this is great stuff. I'm getting all the balancers, BMS, and inverter/charger from https://www.electriccarpartscompany.com and they have pretty detailed wiring diagrams there... this is the BMS (https://www.electriccarpartscompany....agement-System) and these are the balancers (https://www.electriccarpartscompany....ers-Equalizers)....



What about the balancers, and the series wiring? Do I have that down correctly? Referencing my shitty diagram, should I wire the negative terminal of cell a1 to the positive terminal of cell b1? Or should I keep it as the negative terminal of cell j1 connected to the positive terminal of cell b1? And do I have the wiring of the balancers correct, or should I have the negative of the balancer connected to the negative of row j?


I really appreciate the knowledge here.
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Old 04-25-2019, 01:05 AM   #7
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Think of each block of 10 in parallel as a single battery. They will self-balance just sitting there, faster than the BMS can do it.

It's when those four blocks are connected in series that you need active balancing, likely at that high rate.

Now the protective functionality, HVD / LVD, temperature, that's needed at the whole-bank level, doing it intrabank will IMO be too complex IOW prone to failure.

Monitoring voltage per cell, sure, balancing chargers, sure.

For redundancy, limp home mode, maybe better to build 5P blocks, then 4S those together, then 2P the two halves.

Discuss with Carl, ECPC's "resident specialist", but get everything clear before sending your money, it's a one-man show and he'll need to move on to the new customers pretty quickly.
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Old 04-25-2019, 07:15 PM   #8
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I've spoken with Carl, he's a great dude and he runs a great company. Based on his advice, I just ordered everything from him:


- 3kW Inverter/Charger
- 60 Amp 12V to 12V Converter (for charging off my alternator)
- 100 Amp BMS
- Four Balancers


Is it okay to drill a hole in the tabs of my battery pouches? I don't see any other way to either bolt terminals to the tabs or to rivet them.
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Old 04-25-2019, 07:59 PM   #9
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Probably better to ask in more specialist forums

example:
https://endless-sphere.com/forums/viewtopic.php?t=38761
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