Many of you know me as a fairly good deck-maker, but what you don’t know about me is that I’m a truly terrible battery builder
Take, for instance, my most recent attempt. I built the battery, started charging it, checked back when it was about 50% charged and found that p-groups 1-10 were charging, but 11-15 hadn’t budged. Somehow I managed to get electrons to flow from high to low potential while skipping 5 p-groups. Isn’t that literally fucking impossible? Can anyone tender an explanation or did I break physics?
I would have had to accidentally aligned all of the cells with a different capacity into p-groups 11-15 in order to get this result if differing capacity is the issue.
I am, but I don’t think that’s possible. If I understand correctly the BMS just checks to see if any of the groups reaches 4.2v and then turns off the charger. It can’t actually delegate the charge. If a current is passing through the entire deck, then all of the p-groups should charge until one hits the upper limit.
I want pics, how are the parallel connections made? Is it possible the balance leads are connected to the cells that have disconnected from the p group? Definitely something is getting charged on the p-11 to p-15 sets it just isn’t connected to the balance leads i think
In my experience, if balance leads aren’t properly connected, the battery won’t charge.
The battery is currently covered in foam and tape. I’m going to have to break into things to take some pics.
There isn’t any charge current that passes through the balance leads so as long as the bms sees a normal voltage it will allow charge and discharge.
If you connect a balance lead to one battery and use a second battery for the bms output you can charge the battery. It just won’t cut off if any one group strays outside nominal. Also the bms doesn’t care about balance as long as all the groups are within the cutoffs. One group can be 3.1v and another group 4.1 and it will still happily charge or discharge the battery.
It looks like the cell capacity for groups 1-10 is lower than groups 11-15 so they are charging faster. If it is all connected and welded well then maybe you have old and new cells mixed. If not that then fake cells? If not that then just amazingly mismatched cells.
How many opts you really got, i mean its (not) too many options
I’m going to break into 11-15 later and do a full visual inspection. I bought these cells from Lithiumionwholesale.com and they all tested to very similar voltage before I started welding them.
It’s not very likely that I put 20 bad cells into groups 11-15 by coincidence. There has to be something else going on.
Could one bad cell in p-group 11 cause a problem in groups 11-15?
It seems to me that groups 1-10 could be a problem and not 11-15. All guessing right now though. You really came up with an odd one . Get that bad boy open so you can get more info
If you get enough pictures showing how or if those groups are charging, we can work backwards and figure out what the capacity is for each pgroup and figure out what’s going on. Time it or snap screenshots that have the time stamp showing. Try to grab them at regular intervals
Do both your charge and discharge connectors measure the same 55.7 V as the BMS is showing for the total voltage?
I’d just be worried you somehow created two separate circuits for part of the pack, and you’re charging one while measuring the other. In that case, you could end up overcharging the circuit you’re not measuring.
Also, what voltage were the cells initially at? I’m assuming they were around 3.5, so 1-10 charged ~0.3 V, and 11-15 didn’t move. That really seems impossible. If you didn’t say the multimeter confirmed, I’d bet almost anything it was the BMS pins being in the wrong spot or something.
. Get that bad boy open so you can get more info