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Old 02-25-2022, 11:38 AM   #1
Brob1969
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Default New to LiFePO4 DIY build...could use some guidance

Hey everyone, I've been researching Lithium power for my EZGO txt for a while now, but hadn't yet taken the plunge.
Recently I was given (3) Renogy LiFePO4 12v 100Ah batteries that wouldn't take a charge. I opened them up and discovered moisture inside and some corrosion on the BMS boards. The pouch cells looked in good shape though, so I measured the voltages and determined the cells to be good. The Renogy batteries state they cannot be connected in series, I'm assuming this is a function of the BMS setup.
My thought is to get a 12s 36v BMS and make one 36v battery out of the 48 pouches. I am thinking of using a BMS to monitor and balance the charging, and using a high amperage contactor to send the energy to the controller.

Right now, this is my first Lithium build and my knowledge is only tertiary. I really haven't been able to find any definitive information on how to set this up; so far the only responses I have received elsewhere are along the lines of "Why are you only doing 36v?" To which my answer is: economics...I have the cells for 36v, I have a charger capable of a Lithium profile, and I have a 36v cart with an alltrax 500a controller.

Currently the batteries are setup in 4 groups of 4 cells, with a 4s 12v BMS. I am assuming I'd need a 12s 36v BMS and a continuous duty 36v contactor.
I am looking for all kinds of information on how to set this up and recommended components.

This is my first Lithium build attempt, so I would appreciate not getting flamed right off the bat!
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Old 02-25-2022, 12:17 PM   #2
Volt_Ampere
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Default Re: New to LiFePO4 DIY build...could use some guidance

What is the current rating of those batteries? What you are trying to do is possible if you get a BMS designed for that type of cell in the correct 12S configuration. Make sure that those cells were not ever over discharged. Charge them and top balance them. Don't rely on the BMS for the first balance. Make very good connections! Not sure from your pix how you connect to the cells.
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Old 02-25-2022, 02:58 PM   #3
Brob1969
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Default Re: New to LiFePO4 DIY build...could use some guidance

Here is the spec chart I found for the cells.
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Old 02-25-2022, 03:59 PM   #4
Brob1969
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Default Re: New to LiFePO4 DIY build...could use some guidance

Here is how the pouches are connected. There are 16 3.2v pouches in each setup. They are already wired to this printed circuit board including a balancing wire on each parallel group.
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Old 02-25-2022, 04:21 PM   #5
Brob1969
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Default Re: New to LiFePO4 DIY build...could use some guidance

Here is how the pouches are connected. There are 16 3.2v pouches in each setup. They are already wired to this printed circuit board including a balancing wire on each parallel group.
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Old 02-28-2022, 11:24 AM   #6
bronsonj
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Default Re: New to LiFePO4 DIY build...could use some guidance

According to your spec sheet that cell is good for 75 amps continuous, 100 amps max for 10 seconds.

4 in parallel gives you 300 amps continuous, 400 max.

I would not try those at 400 amps and if you do opt to go with these cells then you need to make sure the cables used to connect your pack are capable of handling the amperage. That picture seems to show maybe a 12 or 10 gauge wire? Way too small for a golf cart, even if you use both wires for the connection so you'll need to spend some time looking at that and determining how you plan to connect these.

Also, pouch cells need compression. So you'll need a rigid case that you can compress the cells inside. I don't know how much compression you'll need but if you can reuse the factory cases for physically holding the cells and just rewire them that'd be good.
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