[SOLVED: (NEWBIE ERROR)] JK BMS (JK-B2A24S20P) 43.0V PD between B+ BMS cable & Battery +ve (16S configuration)

[dezfutak]

I don't get how you're seeing this, the plug shouldn't be plugged in to your BMS at all until it's wired to the battery complete.

B+ and 16th Cell wires are wired together, you shouldn't have them separated at all they should go to the same connection point and same fuse.

Basically the whole saga is due to being too cautious! I hadn't got the plugs seated in the sockets, but for some reason thought it would be prudent to do so prior to adding the B+ cable, saw the spark & then went down a rabbit hole.

Probably the over-cautious approach is due to the concern of not wanting to vaporize a lot of very nice kit.

Many thanks for your help!

 

[sijones2010]

MANY thanks Si - that's solved the issue; I've managed to start up up the BMS and it's now balancing cells nicely!

Don't balance them at a low voltage, set the start balance voltage to something over 3.4.

Have you top balanced the cells?

Please be careful if you're using my software with the inverter to charge them out of balance and even in balance you need to set things up, the inverter will charge them until 100% SOC, it doesn't care about one cell being high voltage, so make sure your BMS is set up correctly to stop and protect the cells.

 

[dezfutak]

Don't balance them at a low voltage, set the start balance voltage to something over 3.4.

Have you top balanced the cells?

Please be careful if you're using my software with the inverter to charge them out of balance and even in balance you need to set things up, the inverter will charge them until 100% SOC, it doesn't care about one cell being high voltage, so make sure your BMS is set up correctly to stop and protect the cells.

Yeah, I realised I should stop balancing at such a low SOC (it was just nice to see it working for a few minutes ).

I'll re-wire in the shunt, DC to DC converter et al tomorrow & then set-to with getting things set up properly.

 

[Steve_S]

Yeah, I realised I should stop balancing at such a low SOC (it was just nice to see it working for a few minutes ).

I'll re-wire in the shunt, DC to DC converter et al tomorrow & then set-to with getting things set up properly.

Sorry but I Have to Interject... Balancing starting at 3.4V is "Late in the show" to keep up and control any runners, if there are any runner cells they will start shooting upwards past 3.370 on average therefore starting @ 3.330 gets on top of it and does NOT Reduce the speed of charging and keeps the differentials closer meaning less balancing work. The "Target Voltage" you want post-charge is 3.400V.

Please read THIS POST in this thread I wrote which explains it and provides more context and info about the charging cycles & process.

Strange issue with 48V LiFePO4 system

One thing that may help people in providing guidance is first stating each make and model of the equipment you have in your system. It sounds like you have an AIO growatt type unit with an unknown BMS. That AIO should allow you to charge the battery from shore power at 20-30A and fully top up...

diysolarforum.com

 

[uksa007]

Balancing starting at 3.4V is "Late in the show" to keep up and control any runners,

Have to disagree on that one, I have a few cells that are runners right up till 3.45v, where they seem to be overtaken by the rest and then become the lowest voltage cells. I set my balancer to start at 3.45v and that seems to works the best for me.
Note LF280k cells charging at 90A
Yes I have top balanced them many times, it's just how they are.

 

[RV10flyer]

Have to disagree on that one, I have a few cells that are runners right up till 3.45v, where they seem to be overtaken by the rest and then become the lowest voltage cells. I set my balancer to start at 3.45v and that seems to works the best for me.
Note LF280k cells charging at 90A
Yes I have top balanced them many times, it's just how they are.

If you have runners below 3.40 something is seriously wrong with your cells. I also start balancing at 3.45.

 

[uksa007]

If you have runners below 3.40 something is seriously wrong with your cells. I also start balancing at 3.45.

Yep the cells are a bit dodgy I would say, it doesn't seem to effect them, still get full capacity out of them, it is only at high current charging eg 90A where they seem to run.
Probably why they didn't make it as A grade and were sold on Alibaba (one of the big recommended sellers).

Cell voltages seems to be a bit all over the place before 3.45v, that seems to be magic number where they all even out, and you see the real runners.

 

[sijones2010]

I've found in my battery packs that they go out of balance if trying to balance at a lower voltage, 3.4 (roughly) and above is best place for mine anyway.

 

[SeaGal]

Does it not depend hugely on charge current? I see cell voltage can be between 3.350 and 3.400 if charging at 10A vs. 30A for same SOC

 

[sijones2010]

Does it not depend hugely on charge current? I see cell voltage can be between 3.350 and 3.400 if charging at 10A vs. 30A for same SOC

if cells are in balance, (my understanding) then at higher SOC the current should tail off anyway. I limit current at higher SOC in the software to help balancers do their thing nearer the end of charge and help with run-away cells not happen too fast.

 

[Honuz]

You should have 52V at the Battery +- terminals, if not you have connection issues with bus bars.
Follow the instructions that came with JK BMS:
The BMS B-(blue) needs to go directly to the Battery -
The BMS P-(black) can go to circuit breaker and shunt.

Meter from the Battery terminals +- out one connection at a time till where the voltage drops, this will be your issue.
Sounds like issues with your B1 circuit breaker, are you using a suitable sized DC breaker?
You should only need 1 dual pole DC breaker
Normally they are dual pole and they break the +-.

View attachment 117854

I personnaly put shunt before the BMS, on the blue line and the B0 is connected on the Main negative of the pack.
Coming from :
- Pack negative i got in that order : B0 (bms), SHUNT, B-(bms), P-(bms) ....... 48V busbar
- Pack Positive i got in that order : B16 and B+ (bms), fuse, breaker (single pole)...... 48V busbar

 

[sijones2010]

I personnaly put shunt before the BMS, on the blue line and the B0 is connected on the Main negative of the pack.
Coming from :
- Pack negative i got in that order : B0 (bms), SHUNT, B-(bms), P-(bms) ....... 48V busbar
- Pack Positive i got in that order : B16 and B+ (bms), fuse, breaker (single pole)...... 48V busbar

You can only do this with one battery pack though, if you have multiple then the shunt has to be after the BMS's.

 

[terrango]

One thing i have found with this style BMS is if you just buy the BMS and not the power on button accessory, you may have to add extra voltage to wake the unit up. For some reason it needs to see a higher voltage before the bms will turn on. An easy fix is to jumper a 9v or 6v battery to the pack. The bms should wake up immediately.