Testing

I brought my melted battery holders to work today to do some more testing. I wanted to see how much current i could run through the 24 gauge wires before they got too hot. The AWG rating in free air is 3.75 amps, but they're always really conservative. I decided to start my testing at 2 amps and increment from there 1 amp at a time. 2Amps: wire stayed at room temperature 3Amps: wire warm 4Amps: wire very warm 5 amps: wire melted through plastic. Fail. So there you have it, don't build battery packs the way I did. Why is this a fail? My voltage sense wires are only designed to detect the voltage on each cell. Unfortunately, when a cell dies (remember the one at zero volts), the power from the other 15 cells in series travels around the dead cell via other live cells. Here's a simplified picture with 4 sets of 4 cells in series (my pack is 20 sets of 16 in series): So When all the cells in a particular row are at the same voltage, very little current has to flow through the purple wires, which are 24 gauge. If one cell dies, the other three cells will dump a lot of current through the purple wire, until it heats up and melts the plastic, which is exactly what I saw in my failure. Back to the drawing board. I think I'm going to expand the packs all out linearly. I'll post pictures showing my reproduced failure when I get home.