do you use fuses on each balance lead coming from the BMS to each cell?
JK BMS Cell Count Problem on B2A24S20P
- Thread starter dakamalu
- Start date
dakamalu
New Member
No.
it might help to install some. if there is some sort of cell surge on the balance lead it would help protect the BMS if thats the issue? also might help with diagnostics if you are blowing fuses on that suspect cell 9?
dakamalu
New Member
Sounds good, I'll work on that when I get the stuff to build a new harness, or buy one. Soon!
Just a small update: I've not had time yet to investigate further. I need one of my 16s batteries to test some things on the BMS. I'm rehousing my batteries anyway, so perfect time for this. I should have time for this one of the following weeks when things are less hectic with work.
dakamalu
New Member
Thank you!
I hooked it up to one of my batteries today and can confirm two cells are not detected. Now I can go find out what's broken.
Found an issue:
There are two blown resistors (one of them shown in the picture) that correspond to the non-detected cells. These are 0.01R resistors on the input of the balance leads, before the mosfets. I think these are used here as a fuse, so it did it's job (although using resistors as fuses is a bit iffy). Of course, the question remains if this was a one-off event that caused it, or something persistent. I'll find a few replacements and test - but not sure when I will have time; it might take a few weeks.
There are two blown resistors (one of them shown in the picture) that correspond to the non-detected cells. These are 0.01R resistors on the input of the balance leads, before the mosfets. I think these are used here as a fuse, so it did it's job (although using resistors as fuses is a bit iffy). Of course, the question remains if this was a one-off event that caused it, or something persistent. I'll find a few replacements and test - but not sure when I will have time; it might take a few weeks.
dakamalu
New Member
Thank you so much. I mentioned that we manually transfer between the grid and solar a few times a week. I have made a few modifications to the transfer process and have reduced the balancing current. Looks good so far!
I also noticed when I was running the full 2A balance that there were occasions where the balance current exceeded it by as much as 0.4A.
I also noticed when I was running the full 2A balance that there were occasions where the balance current exceeded it by as much as 0.4A.
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That might be an issue. Assuming these are 1/16W resistors (62.5mW), running 2.5A through them would be their rated power limit (P = R . I^2 with R = 0.01Ohm). Let's see once I replace these...
Yes, its' failure mode is to short circuit the gate to the drain, so it's prudent to have some sort of 'fuse' here. Most car audio amps have the exact same protection.
Interested to hear your outcome with this, most likely a failed mosfet. I have unit on the bench to repair as well.
dakamalu
New Member
How are things going? My third BMS is still working with the reduced balancing current.
Sorry, I have not had time to test. The resistors are replaced, but I need to hook it up to one of my packs to test. I should get to that after next week when things should be less hectic here.
dakamalu
New Member
How are things going?
I'm testing it this weekend - I've been completely swamped...
So, changing the resistors fixed it. I've not run extensive tests because I had the PCB out of the enclosure (less cooling) but it powers the load and balances cells. All 16 cells are accounted for in the app.
I did notice in the app that balancing start voltage was set to 3.0V which is very low. Not that this should really be an issue, but maybe it was just balancing all the time and this caused those resistors to give in.
dakamalu
New Member
Thanks so much to upnorthandpersonal for his help. I could hardly express how thankful I am to him.
But as many have pointed out, there must be something causing the problems in my 16S configuration with this JK BMS. Cell number 9 was always involved. And believe it or not, a week or so before I got the repaired BMS back from Finland, the one I was using failed. Three of the balancing lead resistors went bad and once again, cell number 9 was involved. I have also noticed that cell 9 is the one that seems to always be taking current when balancing is on.
Can I replace that single cell?
But as many have pointed out, there must be something causing the problems in my 16S configuration with this JK BMS. Cell number 9 was always involved. And believe it or not, a week or so before I got the repaired BMS back from Finland, the one I was using failed. Three of the balancing lead resistors went bad and once again, cell number 9 was involved. I have also noticed that cell 9 is the one that seems to always be taking current when balancing is on.
Can I replace that single cell?
Yes - you can. Did you set the balancing start voltage to something higher than 3V (i.e., 3.45V or something)? It's not normal for those resistors to fail like that (they act as fuses, but still). Anything special about cell 9? What is its rest voltage? Do you have a multimeter and a power supply?
dakamalu
New Member
I set it to 3.45V. I had it there originally, but things were failing so I tried a lower balance. It didn't help, so we are back to 3.45V. We'll see. I may have to improve my soldering skills. I have many multimeters. Power supply went bad, but at the moment I am charging the battery using the BMS you returned and it looks good for now.
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