I used to live in a world where eBikes were powered with a Crystalyte Hub and a lead-acid battery, and you were tech savvy if you had a 1200 baud modem. Now I pay for my TekSavvy instead. I recently completed the build of a 14S2P battery pack for an eBike (52V), and then discovered the BMS had sh*t the bed! I may have blown it by connecting the sensors flat cable (appears to be a Molex PicBlade) to it before I soldered the B- lead (I'm not sure if I did or not). All the cells were new 21700 LG M50's.
Being a Rule Breaker, I charged it sans BMS. Then, I wanted to try it out, so I took it for a 45km ride, and then recharged it without the BMS. I think to myself, "Balancing' is not complicated"". If you have a 14S pack, then 14 neighbors need to have about the same amount of electromotive force. If they don't, then the 'have not's' will steal from the 'haves' and everyone ends up poorer, much like the world we live in withal. A battery pack with all the sense wires connected but no BMS is like a new subdivision that has all the houses built and wired, but not connected to the grid. I simply moved into my house before City Hall started to send me utility bills.
When it was done, I was able to check each cell group (consisting of 2 of the 21700 cells in parallel) because luckily I had attached the sense wires when I did the build, and the Molex PicBlade 1.25mm female pitch connector contact points are accessible to my multimeter. 3 of the cell groups were between 4.0v and 4.1v, while the rest were at 4.2v. So I thought it would be nice to be able to balance those three nascent cell groups and continue to monitor and enjoy the use of my battery pack while I wait for a new BMS to arrive from China. (I will probably check the cell groups after each charge).
I was able to dig up a 2 pin wire-to-wire JST RCY connector, and a single cell 18650 charger I had on hand, and with a bit of soldering, connect one end of the JST harness into my charger through the bottom. That enabled me to insert the tinned ends of the 26 AWG wire on the distal end of the JST into the Molex flat cable connector that has the sense wires from the battery pack, and start to charge each cell group one by one.
What follows is the timeline of the steps taken to give substance to realizing the successful balance charge of this battery pack without the benefit of a BMS:
00:00 The 52v 14S2P battery pack
00:15 The faulty BMS
00:40 Using Molex connector BMS flat cable to check individual cell voltages
01:00 Using a 2 pin wire-to-wire JST RCY connector and soldering it to a single cell 18650 charger
02:00 Soldering the JST
03:15 Time lapse of soldering JST to charger PCB
03:45 Testing charger MOD
04:00 Connecting charger wires to the battery's flat cable Molex connector
05:50 Start of elapsed time to charge first cell bank
06:25 Starting on next bank of cells
06:30 Emergency Exit due to She Who Must Be Obeyed.
07:15 End credits
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