Battery Bank Part 2 (Build)

Top Balance

To prep the cells to be combined into a battery I will need to top balance them. This involves connecting all the cells in parallel and fulling charging them so they start all evenly charged. My bench top power supply is an inexpensive one rated at 10A max. To speed up the process I built the 12v packs with BMS and did a initial charge until one of the cells reached 3.65v and it cut off. I then rewired the cells in parallel and set the bench top power supply to 3.65v and waited for the amperage to drop to less then 1 amp. After the top balance I reassembled the pack into a 12v battery with BMS. I then used a capacity tester to run the pack down to 11v (2.75v/cell). I was able to pull 312.9Ah out of the first battery, which I am more then happy with. I could have probably got another few amp/hr out of the pack if I ran it all the way down to 10v (2.5v/cell). The goal will be to run the pack between 12v (3v/cell) to 14v (3.5v/cell) in normal use which will provide 304+Ah.

Enclosure (Battery Box)

I am using 3/4 plywood to create my box/enclosure for the cells and BMS.

BMS is mounted via screws from the outside of the box. A few washers are used keep a gap between the rear heat sink and the wood.

BMS Mounted to box with 2x 6awg DIY “Y” cables.

Cutting mats used between cells. The blue insulation tape on the cells is very thin.

BMS “Y” cables attached and rope handles added. These are extremely heavy.

Cells rewired in parallel for top balance. I wanted to be able to top balance with the cells in the enclosure.

Bench top power supply set to 3.65v for top balance.

Positive terminal. 2awg used for bus bar and stud connection.

Battery Managment System (BMS)

The BMS I am using is from Jiabaida (JBD) and has a Bluetooth module which works with an app called xiaoxiang. Below are some screen shots during the initial change, top balance, and capacity test of battery 1.

Cells after BMS cut off. Cell 1 reached 3.65v. The pack is unbalanced because I ran a capacity test on two of the four cells (1 and 3) this fall.

After top balancing I started a discharge capacity test to 11v

Cell voltages after capacity tester stopped at 11v

At the end of the capacity test 312.9Ah had been pulled from the cells in battery 1.

Battery 2 pulled 313.7Ah running down to only 11v vs 10v. Both performed within 1Ah of each other and over the 304Ah rating.

It is not good to leave the cells at a very high or very low state of charge for a long period of time so I charged the pack back up to about 50% capacity. I will now install the batteries, build the enclosure and finish the DC wiring.

Both finished batteries take up a total of 17″ x 15″ x 12.5″. This is less space per amp hour then off the shelf batteries. It’s about 33% denser then a 100Ah or GC3.0 from Battle Born and 13% denser then a popular prismatic cell based battery the SOK206.