charging a lithium ion  16s battery pack - Page 1
Forum section: electronics / projects

author: m3vuv
author_rank: Super Contributor
timestamp: September 30, 2019, 09:24:49 pm
content: hi all,ive a 16s Lithium Iron Phosphate battery pack,fully charged its about 56v,my bms wires broke,long story short,im charging each bank of cells individualy,its to try and get it to a stage where the charger can take over,its going to take forever using my cc cv psu,is there a way of charging the individual strings of cells individualy but all at once,ie using diodes,i dont want to bulk charge it ie 67v across the whole battery?,its tying my brain in knotts!!.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 01, 2019, 08:53:21 am
content: 1) Separate,isolatedchargers. One for each cell. Yes, expensive.2) Charge each cell separately, sequentially, using a single (STILL ISOLATED) charger. Yes, slow.3) Dismantle the pack connections,verify similar cell voltages (within about 10-20mV) (important), then connect the cells in parallel, and charge as a one massive cell, using one charger.4) Charge the pack as a series string (the normal way). If you have no BMS you can trust and there's a possibility the cells are not in balance (charge balanced at top), you act as a BMS by peeking around with a multimeter. Don't worry, they won't suddenly go bang in seconds. In a 16s pack, you can easily scan through the whole string in about one minute, which is quick enough. You can slow down or stop charging if any cell voltage starts rising considerably faster than the others or getting near the limit (say >3.5V for LFP). After the first cell hits the upper limit, go for method #2 for the rest of the cells. This is the fastest way and assuming you have little imbalance, you are done in an hour or two.Diodes do not help you.

author: jbb
author_rank: Super Contributor
timestamp: October 01, 2019, 11:19:48 pm
content: As usual Siwastaja is right.Another option is a balancing battery charger, like people use for radio control helicopters etc. Many of these have a balance port and monitor individual cells.If you can get a 7 (or more) channel unit you can wire it up the first 7 cells, balance charge, then wire it up to the last 6 cells and balance charge again.

author: jbb
author_rank: Super Contributor
timestamp: October 01, 2019, 11:49:58 pm
content: Oops, can’t count: I mean an 8 cell charger, to do lower half pack then upper half pack

author: james_s
author_rank: Super Contributor
timestamp: October 01, 2019, 11:53:48 pm
content: There are lots of reasonably priced 8 cell chargers intended for RC hobby use. There are even dual chargers but personally I prefer to use two separate single chargers over one dual unit.

author: m3vuv
author_rank: Super Contributor
timestamp: October 02, 2019, 01:54:07 pm
content: im charging each string individualy at the moment,the trouble is my proper charger wont output unless it sees a certain voltage,once i get them to about 35v ill try and series charge them using the charger,could do with finding a way to defeat the charge low volt protection but not sure how,i assume theres some sort of comparitor that cuts output when the pack voltage is below a certain point for safety.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 02, 2019, 02:08:19 pm
content: Maybe I didn't understand your problem.Is your charger refusing to charge because the cells are overdischarged?Or, is your charger mismatched to your pack size, for example, meant to charge a higher voltage pack, and hence, the low-voltage detection threshold is too high, as well?