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JK BMS: This doesn't seem normal

MountainmanBill

MountainmanBill

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Feb 20, 2021
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134
JK BMS 2A 200AMP managing 16s 48-volt battery bank.
The Victron BM SOC says 93% and the JK says 100%. They are never in agreement.
The two Morningstar Tristar 45-amp 150-volt Charge Controllers are set at: 56-volts Absorb and 54.8-volts Float.
All is well until the battery nears full SOC. Then the BMS turns off and on the charging every few seconds, for about ten minutes. Then it turns off the charging until it feels like turning it on again. That on-again off-again can't be good for anything.
Even when it's off, the BM is showing wild fluctuations in the battery voltage.
This doesn't seem like this would be a normal operation.

What also puzzles me is that a fully charged battery is 58.4 volts (3.65x16). The BMS shows a voltage of 55.68 volts and says the battery is fully charged. How is that correct? How about some guidance here? Thank you very kindly...


IMG_0652.PNG


IMG_0649.PNG

IMG_0654.PNG

IMG_0635.PNG
 
Why is no cell voltage for cell 10?
Have the cells been top balanced? 130mV with pack voltage > 56V suggests they are out of balance - if this is a meaningful figure.
JK "Start Balance Volt" should be 3.4V so that balancing only occurs when pack is fully charged.

Work out what's happened to cell 10
Then maybe would hold cell pack at or near 56V and allow top balance to bring delta V to less than 0.010V and reassess.
 
Most of your BMS setting seem pretty low to me but I have no experience with this BMS.
I feel like full charge should be 3.55-3.6 and OVP should be 3.65. Start balance at 3.0 seems low to me as well.
 
The balance lead for cell 10 is either misplaced or have a bad cable or crimp/plug.
Fix that first.
Btw. your settings in the BMS via the app is all over the place and incorrect.
Fix your wires first and we'll talk.
 
Last edited:
No idea why people are commenting about cell 10 - are you not seeing it on the screenshot ?
Its there , it has a voltage of 3.532 and its being balanced FROM to cell 08 with 3.404v
What bothers me are 2 things :
1. BMS settings are very wrong - they need to be redone from scratch - take a look at off grid garage on youtube to understand JK BMS settings
2. Voltage spiking on the shunt - is there actual load connected or anything else that might cause it to drop so fast ? Also Why is the charger pushing it above 58V
 
alexalex said:
No idea why people are commenting about cell 10 - are you not seeing it on the screenshot ?
Click to expand...
Its in blue as the highest cell and on my screen virtually invisible, its only because the error message of a missing cell is not showing that clued me to it being there.

This is Andy's setting video, but its old and several firmware versions down from the last V15 and is even more out of sync with V19.

 
kommando said:
Its in blue as the highest cell and on my screen virtually invisible, its only because the error message of a missing cell is not showing that clued me to it being there.

This is Andy's setting video, but its old and several firmware versions down from the last V15 and is even more out of sync with V19.

Click to expand...

Did you open the actual screenshot or are you just looking at the thumbnail of it thats posted on the forum as a preview of the actual screenshot ?
Are you looking at this image https://diysolarforum.com/attachments/img_0652-png.323324/ ?
 
Switch the bms off and back on,also do a calibration to a shunt or a decent voltmeter or towards the victron.Start from there and get your settings right ,for ex. the balancing start voltage is too low,which can mess up balancing ....Do one step at the time,to get the SOC better,try different capacity settings....best of luck👍
 
kommando said:
Its in blue as the highest cell and on my screen virtually invisible, its only because the error message of a missing cell is not showing that clued me to it being there.

This is Andy's setting video, but its old and several firmware versions down from the last V15 and is even more out of sync with V19.

Click to expand...
He has videos for V19 i just didnt want to waste time to go over all his videos to figure out what exact videos talked about V19
 
I did a top balance before I placed the pack into service. After connecting everything, the pack was at 57.13 volts with a difference in individual cell voltages within .008 volts. This was an overnight resting voltage. The only time there is an issue with cell balancing is when the bank nears full charge. As suggested, I set the "Start Balance Voltage" at 3.4-volts.
"Cell OVP" is set at 3.60 volts, and "SOC- 100% Volt" is set at 3.56 volts, and it won't let me change either one. It gives me a "Sending Failure" notice.
I'll get the bank to full charge today and remove all loads and charges in an effort to balance the cells and take it from there.
 
alexalex said:
No idea why people are commenting about cell 10 - are you not seeing it on the screenshot ?
Its there , it has a voltage of 3.532 and its being balanced FROM to cell 08 with 3.404v
What bothers me are 2 things :
1. BMS settings are very wrong - they need to be redone from scratch - take a look at off grid garage on youtube to understand JK BMS settings
2. Voltage spiking on the shunt - is there actual load connected or anything else that might cause it to drop so fast ? Also Why is the charger pushing it above 58V
Click to expand...
There was no load to speak of on the system. Maybe a ceiling fan and a small fridge. And when I now look at the same time period on the Victron BM, all those spikes are gone. This is quite perplexing. As far as the charger pushing the voltage so high is also a mystery. The SCC even set a fault (High Battery Voltage) and shut off charging. ???
 
MountainmanBill said:
There was no load to speak of on the system. Maybe a ceiling fan and a small fridge. And when I now look at the same time period on the Victron BM, all those spikes are gone. This is quite perplexing. As far as the charger pushing the voltage so high is also a mystery. The SCC even set a fault (High Battery Voltage) and shut off charging. ???
Click to expand...
First fix the JK settings , then check all bolts if they are properly torqued
Keep a multimeter on the batteries while charging to see the actual real voltage
Figure out which measures where and keep notes
Voltage should be the same on batteries as on inverter - else something is not properly torqued
 
I've made a discovery, but I don't know what the information is telling me. If I place my multimeter probes on the Shunt and positive bus bar, that's where the wild voltage fluctuation occurs. If I flip off the breakers to the solar panels, the fluctuation stops. Then I isolated each SCC from the system. As long as both SCC's (either one) are not connected in the system it works fine. But as soon as I connect them both to the bus bars, I get the fluctuation again, unless the solar panels are turned off. Only one SCC can be connected to the system or it doesn't work properly.

So right now I have everything connected (except for SCC #1) and the system is maintaining a voltage of 55.81, and the voltage difference between cells is .097. That's high, I know, but I'm hoping this will straighten out in a day or two now that the system appears to be working correctly.

But the question is, why can't I have both SCCs in the system? They are connected in parallel to the positive and negative bus bars, which in turn feed the battery and inverter. Is this not an acceptable connection practice?

Also, SCC #1 isn't off even though the negative cable to the bus bar is disconnected, as well as the breakers in the Combiner Box are off. Where is it getting its power from? It's not charging or discharging but it's still lit up. ???
 
Last edited:
Set Continued Charge Current to 140. That is 0.5c. At 100, your two charge controllers may be peaking above that.

Charging at 56v is 3.50v per cell. I would put SOC-100% at 3.49v. I would start balance at 3.4v. 3.0v is too soon.

On your charge controller, I would set absorb and float at 55.0v and let your cells balance. Then increase in 0.25v increments until they can charge at 56.0v.
 
Last edited:
DIYrich said:
Set Continued Charge Current to 140. That is 0.5c. At 100, your two charge controllers may be peaking above that.

Charging at 56v is 3.50v per cell. I would put SOC-100% at 3.49v. I would start balance at 3.4v. 3.0v is too soon.

On your charge controller, I would set absorb and float at 55.0v and let your cells balance. Then increase in 0.25v increments until they can charge at 56.0v.
Click to expand...
I've gotten a lot of good advice on this thread to help steer me to a solution dealing with the issue on my new system. I've already made some setting changes to the BMS including a starting balance voltage of 3.4 volts. I like the idea of creating a new setting on my Charge Controllers so tomorrow I will lug my computer outside and make those changes as well. There should be enough sunshine tomorrow to get that voltage up there to see if these new setting cure the problem.
 
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