Monthly Archives: October 2018

Why a BMS for LiFePO4 cells is a bad idea.

Back when I was entering the EV game, before any Nissan Leaf came out, before Tesla had and vehicles sold the the public I thought I knew everything about batteries. After all, I was a great “internet engineer” read many articles, forums and youtubed the shit out of lithium batteries.

I installed many China sourced lithium LiFePO4 batteries in various applications with BMS with no issues. Over the next few years I noticed a disturbing trend, many cells would be discharged to zero, destroyed and bloated, and the culprit, every time, was the BMS causing the failure. I noticed a disturbing trend that the BMS allowed the cells to become overcharged or undercharged which led to diminished capacity and cell swelling/bloating. Unfortunately, many of the BMS’s out there, available to the public, fail over time, leading to more harm than good. They fail because of galvanic corrosion on the PCB, and usually overdischarge the battery.

Here is an example of over or under discharged, bloated batteries. These cells are no longer good, they have diminished capacity, dangerous and are ruined and were destroyed by a malfunctioning BMS.

In 2014, I met Michael at EV West, and asked him if he had similar issues with LiFePO4 batteries and he said yes. I asked him how he got around the issue and he told me not to run a BMS, I was shocked!

However, after installing many more systems in prototype vehicles, test stands and even my own solar systems I have seen ZERO CELL FAILURES. He was right. LiFePO4 batteries are not self balancing, but you can easily balance them yourself, by disconnecting them and wiring them in parallel, once a year every ~300 cycles or so.