DIY LiFePO4 12V Batteries for Solar Power Electricity Storage in Camper

In 2017 I purchased two DIY LiFePO4 100Ah battery packs that were enclosed in ammo boxes. They have a cell balancer, but no BMS. I assumed that it would be ok to use them without a BMS because I had much more capacity than I needed, I have a 12V-12V Sterling brand charger to charge from the alternator and a Midnight Solar Kid solar charge controller setup for LiFePO4. What I did not take into account was the damage that could be caused by charging the batteries below freezing. We live in Atlanta, GA, and although below-freezing days are not common, the temperature does sometimes drop below freezing for a few days. Also, we travel to areas that have below-freezing weather. The batteries are inside the van, and typically the sun warms the inside of the van above freezing. However, if the van is sitting unused with the solar panels charging, the batteries could be below freezing in the morning when the sun comes up and starts charging, but takes longer to warm the van above freezing.


Ideally the Midnight Solar Kid should have a low temperature setpoint that stops charging. It has a battery temp sensor, but the only setting is for shutting off at high temperature. Midnight Solar sends out firmware upgrades that you upgrade through USB port. This low temp charging cutoff would be a simple firmware change incorporated into a future release.


Since neither charger has a low temp cutoff, that means I will need to install a BMS that incorporates a low temp cutoff.



Components

  1. LiFePO4 prismatic cells

  2. Interconnect buss bars

  3. BMS

  4. Enclosure

  5. 12V to 12V Charge Controller (to charge from alternator)

  6. Solar Charge Controller

Batteries - LiFePO4 Prismatic Cells


A lot of good information here: https://www.mobile-solarpower.com/raw-lifepo4-deals-page.html


EVE/Lishen 280Ah Cells - https://www.aliexpress.com/item/1005001563505796.html


BMS (Battery Management System)


https://www.mobile-solarpower.com/raw-lifepo4-deals-page-676969.html


Overkill Solar 12v 4S 120A BMS W/ Low Temp Charging Protection

This Overkill [Re]brand BMS is supposed to be of higher quality than the Daly BMS. They are limited to 120A, so it will be good for 2 100ah battery system where there is a BMS on each pack, so you can draw a total of 240A max (to power a 2000W inverter). It won't be suitable for a 280Ah battery, unless you don't intend to draw more than 120A.

The Overkill Solar BMS appears to be a rebranding of the JBD BMS, which is available much cheaper at about $73 with Bluetooth

https://aliexpress.com/i/4000445091437.html


From what I have researched, JBD is the manufacture of these BMS which are sold by Overkill Solar and others. Lithium Battery PCB is the retail website for JBD.

https://www.lithiumbatterypcb.com/product/4s-or-3s-12v-li-ion-or-lifepo4-battery-smart-bms-with-bluetooth-function-uart-and-rs485-communication-with-60a-to-120a-constant-current/


DALY BMS is another popular manufacture that have nice looking BMS. There seem to be more failure reports of DALY BMS, but that could also be because they are more popular and more people use them, and therefore more failures will be reported.

Daly 12V 4S 200A Smart W/ Bluetooth






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