S/V Johanna Rose: Test Setup for a DIY LiFePO4 Battery and BMS System

6AH LiFePO4 DIY Battery System for Testing and Developing

Here is an idea inspired from Andy at the Off-Grid Garage. Andy has a wonderful YouTube channel covering all things solar with emphasis on testing and the the understanding concepts. Check him out at https://off-grid-garage.com.

I recommend that anyone interested in building a reasonably sized DIY LiFePO4 battery (100AH or more) that they build a simple test/development battery using 4 small 6AH LiFePO4 cells and a decent BMS. Ideally, one would want to use the BMS intend for use in the big DIY battery build. This a great way to test and understand the BMS operations and limitations. These small cells cost only a few dollars. Simply connect the 4 cells in a 4S series configuration. Connect the 5 BMS balance wires and the BMS negative input to the battery's overall negative terminal. Plug the BMS balance connector into the BMS and the battery system is operational.

The image below shows 4 cells (type 32700 6AH LiFePO4) purchased from Ebay ($24) connect to make a 4S 12V battery system. In this case, the cells were simply clamped together between 2 scrap pieces of HDPE(or any good insulator) with 1” wide tinned copper braid(or any good conductor) for making the 4S battery cell connections. The flat wire braid worked well at making good battery cell connections and it was easy to insert a bolt in the braid for a wire terminal connection.

Here are a few links:

eBay LiFePO4 cells:

https://www.ebay.com/itm/283963906954

BMS:

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/

This particular BMS is highly recommended by the solar DIY community. The image of the BMS shown below has the options: 4S 120A Lifepo4 With UART and RS485. To use the RS485 com port with a computer requires the optional purchase of the the $7 RS485 communication module for USB connection. This simple setup is great for developing simple computer programs for interfacing with the BMS. The last image below shows the output of a simple python program running on a raspberry pi 2B+ connected to the BMS via a USB to RS485 bridge and plotting the 2 hours and 48 hours performance.

The RS485 interface is a nice option for those folks interested in developing custom monitoring features, but most individuals may not want or need these features. The Bluetooth interface and the available Xiaoxiang BMS iPhone or Android app works very well and is all that most will need. There is also a free MacOS version of the BMS Bluetooth app available in the Mac App store: "SmartBMS Utility".