I’ve got (120) 21700 cells I need to somehow balance to a certain degree before ok to connect the bms. Im looking for a quick and simple way to put them all in parallel and then can connect to my power supply, and also wondering what voltage spread is acceptable to have between groups when connecting a bms
My plan so far is to connect as many in parallel as I can with magnets and steel strip that’s showing today.
You can make it easier by using copper strips and magnets instead of trying to connect each cell individually. Line up two long copper strips one for the positives and one for the negatives. Place your cells in a row with all positives touching one strip and all negatives touching the other. Then use neodymium magnets on top of each cell to press the strip down firmly and make contact.
This will quickly put all the cells in parallel and allow them to balance with each other. Just make sure the voltage spread between cells is small (ideally under 0.05–0.1V difference) before connecting, so the equalizing current isn’t too high. The thicker the copper strip, the better.
Also as alternative you can print this model for 3D printer that you can do from 10 at the time. The model is stackable and does not require welding. You need to insert the strip on the slots.
Yea doing two strips of steel n magnets was my plan. I guess that’s the easiest way.
If the p-groups have a .1v variation it’s ok I guess
Make sure you connect the positive in one side and the negative from the power supply in the other side to make sure sync well.
Probably 60 on each side
TL;DR Use aluminum foil to connect cells in parallel.
If they came in the typical cardboard box with dividers,
you can cut pieces of aluminum foil
to cover the ends of the cells while still in the box,
then cover the foil with soft thick carpet or soft open cell foam, to depress the foil into contact w/cells
(leave a bit of foil sticking out somewhere, for later)
close the lid, flip the box over, open box,
grab your multimeter, one probe on the bit of foil sticking out,
check individual cell balance, if close enough, 2nd piece of foil + foam or carpet
add something flat to compress the stack a bit.
Profit
p.s. make sure you have good fishpaper rings, etc.
That perfectly works and is very easy to do.
If I had 36 magnets I would have used them, but this was pretty easy too.
These lightly used 50E’s were all within 20mv of each other, and have not budged for a few weeks, so this was unnecessary.
Wouldn’t the easiest way to balance them, just be to connect each one to the same 1S charger, one at a time, until they are all charged?
if you’re were willing to just hook them up in parallel. can’t you just spot weld them into their pgroups make the pack, and then let the bms balance any diff in the pgroups per usual.
doesn’t feel as pure. but feels “fine”.. and saves a step?
This is how i’ve done it in the past. With a bit of organisation and grouping the cells well, you can end up with a pretty good result and the bms doesn’t have to do too much work
In my case of the 18 Samsung 50E’s, none are going in an esk8.
6 will be dedicated for 6s1p to power my TS101 soldering iron, I was considering just forgoing a bms entirely, or a BMS that balances, but did order one which supposedly does.
12 will be for a 3s4p, and I have a 40 amp BMS for it which supposedly does balance, but I don’t trust that it will, So I’d like to start with them as close as possible.
I was going to balance them all to 0.1mV and see which ones drifted, and then deicide which to choose to place into P groups and which to choose for the 3s4P and the 6s1P.
When I put the voltmeter on them before tightening the clamps I saw none had really changed at all since I first got them, and I didn’t really need to do any of this, but oh well.
