Help with 352AH Li-Po battery case

[GXMnow]

The high cell group is creeping down. What are you using to balance it? Is it just the BMS balance current? DO you know how much balance current the BMS is rated for? You could try connecting a light bulb to that high cell group. But if you do that, make sure to monitor it so you can get an idea how fast it is pulling it down. That is 109 amp hours of battery. If it has a 30 ma balance current, it would take something like 36 hours to burn off 1% of the state of charge. If you use a light bulb that pulls 1 amps, that would pull off 1% in just over an hour. Big difference. BMS says you are at 66% SOC, so you could pull an amp for 20 hours without danger.

 

[Substrate]

@RyanAK - please tell me that's not the only multimeter you own!

Without sounding like a multimeter snob, for doing stuff like this, especially with Lipo (where unlike LFP, small errors in voltage setups can mean success or total disaster)

How do you know ANY of your voltage readings are close, in the ballpark, or totally off? You need a reference before you start tweaking voltages and settings all over the place. Especially using meters that may be totally off from each other.

Maybe that cheap multimeter is ok, but how do you KNOW?

All I'm saying is that your spending bucks on gear, but with DIY, spend just a little on tools. Like a Fluke multimeter. Doesn't have to be top-of-the-line, but not a gray-market import version either.

There are many GREAT low-cost multimeters out there. Pick one to make it your reference. My choice of Fluke is personal, mainly because I don't have to worry about "did I get a lemon?".

Like some others, I'm a bit freaked out by your setup. It would be a total shame if an overall system error of only 0.2v meant the difference between a succesful build, and a house fire.

 

[rippersoftware]

This is a great thread for info on Lipo. I am also using Battery Hookup Lipo packs at 3.75 volts 5ah per pack. I want to be more conservative and build smaller individual batteries with 12vdc and 5vdc hookups to run small lights and charge technology.

I am looking at 4s4p or 4s5p with a decent BMS, pwm charge controller and AC power supply. These would be used in the house for emergencies. These could also be charged off my shops' solar system since I went all solar with it this year.

For now, Lithium is an experiment to find a good and manageable method of producing a battery that can then be used in the house in a parallel setup to handle the "need to be on" items when main power goes out. I have read a lot of info and searched for the necessary parts. Peoples horror stories resonate about how you can get in trouble real fast.

For example, Battery Hookup recommends that you don't solder these packs. Instead, use connectors to go pack to pack of make a buss bar that will take the bullet connector as a customer did on there projects page. That will be my route. Also considering splitting the pack and removing the BMS. Jury is out on that at the moment.

My parallel experiment will be 18650 batteries and the very familiar s/p packs everyone creates. That should be fun to do. My son is buying Prismatic cells as he has spare change. Fun times.

Rippersoftware