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Old 04-18-2023, 08:22 AM   #1
ojo
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Default First Lifepo4 DIY Project

So, after waiting 3 months for a dirty cheap 100ah lifepo4 battery that never arrived (from China), i've found some nice lithium cells local, 120ah CATL lifepo4 and will start a DIY project. Shouldn't be too hard... Additional, i've ordered a JBD smart bms 200/400a mosfet/vacuum relais for high current and a cc/cv charger. Hoping nothing too bad for the experts I'll be back, if any questions occures.

Btw: continous discharge rate of the 120ah's = 120/240a 60 seconds > 40%+ SOC, should be fine in connection with the Navitas controller.
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Old 04-18-2023, 08:32 AM   #2
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Default Re: First Lifepo4 DIY Project

I'm no expert but sounds like the making of a good battery.. Make sure the bus bars you get are good for the current you will be passing through them. also compression of the cells if you can do it helps for longevity according to most cell manufacturers. If you dont plan to compress the cells make sure you get bus bars that will allow for expansion and contraction without stressing the annodes/posts.
I took the measurement of the cells and found a used steel enclosure I could stuff them into with pieces of flexible dollar store cutting board as insulation between the cells and a thin piece of plywood to take up the slack so they were snug and couldnt bloat.

you likely can use one of these with your bms as well as long as you got the version that supports both uart and rs485.. https://www.aliexpress.us/item/32568...andl_shipto=US
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Old 04-18-2023, 12:21 PM   #3
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Default Re: First Lifepo4 DIY Project

Thank you augie, yes, i'm planing to build a plywood (Multiplex) frame to compress the cells and either cover that frame with plywood or place it in a suitable metal box. I saw some examles for solar storage builds.
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Old 04-21-2023, 12:01 PM   #4
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Default Re: First Lifepo4 DIY Project

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Originally Posted by augiedoggy View Post

you likely can use one of these with your bms as well as long as you got the version that supports both uart and rs485.. https://www.aliexpress.us/item/32568...andl_shipto=US
I've ordered one of those from AliExpress (12 day shipping) and will make some better bus bars by myself.
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Old 06-24-2023, 06:41 AM   #5
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Default Re: First Lifepo4 DIY Project

Update:
After playing some time with the lfp pack, now it's finally installed in the cart. Cells were stored in a toolbox, which fits very well in the battery tray, one inch left on each side. Reduced the controller for the test phase to 200amps / 25mph. Most important, no sparks / heat up and no tripping during my first rounds
Nice to see the amps flow in and out while driving (in realtime)! Amps i saw so far between ~ 40 - 112 when accelerating. Nothing critical...
Had ordered a second bms with additional RS485 com port, hoping to run the battery touch screen in parallel ( with UART, either Bluetooth or the monitor is possible ). Biggest problem so far is, to ballance the cells properly. When charging, one or two cells raises up very quickly and running into " cell overvoltage ". As Pat recommended, i've reduced the charging voltage to 56.8 (3.55v p.c.), resp. to 55.2 (3.45v p.c.) now. One cell is still pretty low (no. 5).
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Old 06-24-2023, 07:36 AM   #6
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Default Re: First Lifepo4 DIY Project

Quote:
Originally Posted by ojo View Post
Update:
After playing some time with the lfp pack, now it's finally installed in the cart. Cells were stored in a toolbox, which fits very well in the battery tray, one inch left on each side. Reduced the controller for the test phase to 200amps / 25mph. Most important, no sparks / heat up and no tripping during my first rounds
Nice to see the amps flow in and out while driving! Amps i saw so far between ~ 40 - 112 when accelerating. Nothing critical...
Had ordered a second bms with additional RS485 com port, hoping to run the battery touch screen in parallel ( with UART, either Bluetooth or the monitor is possible ). Biggest problem so far is, to ballance the cells properly. When charging, one or two cells raises up very quickly and running into " cell overvoltage ". As Pat recommended, i've reduced the charging voltage to 56.8 (3.55v p.c.), resp. to 55.2 (3.45v p.c.) now. One cell is still pretty low (no. 5).
So the solution to keeping the cells balanced for me was using an active balancer and having it turn on and off automatically with a voltage switch. Off grid garage did a video on the a few month ago.

So far I have not needed to connect my cart to a charger at all while at our seasonal campground. As I predicted it charges off the solar panel and charges back to 99-100% in short order. Even though we cover it when not there.
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Old 04-18-2023, 05:41 PM   #7
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Default Re: First Lifepo4 DIY Project

Good choice of components there. Document the build as you go.
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Old 04-19-2023, 10:56 AM   #8
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Default Re: First Lifepo4 DIY Project

BMS + 300a fuse arrived today. Nice, solid looking part! The standard bus bars unfortunately not.
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Old 06-24-2023, 07:38 AM   #9
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Default Re: First Lifepo4 DIY Project

Looks good btw. Glad you got it built
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Old 06-24-2023, 09:13 AM   #10
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Default Re: First Lifepo4 DIY Project

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Originally Posted by augiedoggy View Post
Looks good btw. Glad you got it built
Thank you sir! I've just found an 4A active balancer (NEEY) at AliE..., 5 days delivery from Poland. But that means, another 20 wires to attach...
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