The lithium (LiFPO4) battery project is complete. The 35lbs of batts in the pic are the equivalent of 300lbs of big deep cycle 12V wet cells. The cost of the batts and the BMS (Battery Management System) electronics, was a little less then the $500 it would cost to get the equivalent big 12V wet cells from Sam’s Club.
The BMS is the electronics visible behind the batts. It has wires going to each batt pair so it can equalize the batt pairs, a sensitive issue with Lithium batts.
Have to shop aggressively to get a good price on lithium batts. These came from a Chinese auction site and it required two attempts. The first set of batts got stopped at Customs.
This sort of thing is more complex than connecting a bunch of wet cells together. I learned a lot from this 3 month project and learning is always fun.
The first pic shows the 8x 3.5V batts set up in pairs to provide 160 usable AHr @12V. The second pic shows the positive connection point and the discharge switch. With the switch in the off position, the BMS won’t allow the batts to provide current–a nice safety and storage feature.
In order to fasten the batts together in a way that would make the entire thing mobile, I fastened them all to an old bookshelf then rigged up a rope carrying rig.
These batts will go into the trailer, doubling the amount of power storage in the trailer while significantly reducing the weight of the trailer’s batteries.