Finally something with electricity that doesn’t come from a welder!

I picked up these Headway 38120 cells a while back with the intention of supplying some serious amps to something just wasn’t sure what that was going to be. The voltage chemistry of the lithium phosphate cells lends itself to replacing a 12v battery nicely in a 4s configuration. So after having the project sit dormant for way too long I saw a yellow pelican case on eBay that looked like it would house things nicely along with some Blue Sea OLED voltage and current gauges.

The BMS is an Amazon special so I can only assume it is the finest money can buy, it is rated for 100A but I haven’t come close to that yet. The bus bars are 1/8” solid copper with 4-40 holes tapped in for the individual cell measurements to the BMS. For the main system switch I used a 200A breaker, not counting on it to trip in a 200A event but we’ll deal with that short when we get there. From there the power goes through the current shunt and out to the load. After a few discharge cycles with a 5A load I discovered that the 8Ah rating of the cells was more like half that before the BMS decided the a few of the cells were too low to continue. Turns out it was right to do so at like 2.5v for two of the 4 cells. So the real bummer is that after charging the individual cells to make sure everyone was on the same page voltage wise they still died before the other cells.

Next challenge is getting the amps outside of the case while maintaining some sort of water resistance. I was thinking about an Amphenol connector that can support a decent amount of current that doesn’t cost $400. Final application might be something like a silly electric mini bike. 8Ah isn’t a ton of capacity but also I’m not trying to ride an electric minibike further than I can push it back home when I find out that the DIY copper bus bars didn’t hold up or the BMS dies or some other unknown :-)