JK BMS jumped from 70% to 100% SOC

jdy2kgt · Mar 25, 2023

We just finished our first battery and the BMS was at 70% which sounds right as we hadn't charged them yet. When I started charging within seconds the BMS showed 100%. Anyone know why this jump occurred? It's obviously not at 100% as you can see from the pictures the cells are still at 3.3/3.4.

RvNaut · Mar 25, 2023

Yes... A cell topped 3.6 volts and the BMS shut down the charge to protect that cell. When it does this, it ASSUMES that the entire battery is full. It is a goober in the software.

RCinFLA · Mar 25, 2023

It is because the Columb counter reset to full.

Not sure exactly the JK criteria for resetting Columb counter to full battery. Some BMS firmware is pretty dumb on this. Most likely it is related to user cell overvoltage setting, perhaps a percentage of its value.

Should be reset when all cells are above 3.40 vdc during charging but might need to be a bit greater if charge current is fairly high. BMS has no knowledge of what the charger absorb voltage is set to.

Errors in Columb count will accumulate due to current measurement accuracy which is why the 'full' battery reference must happen periodically to re-reference a fully charged battery and clear accumulated errors in Columb counter.

timselectric · Mar 25, 2023

Is the capacity setting correct?
105ah

timselectric · Mar 25, 2023

It will need to go through a full cycle to learn.

jdy2kgt · Mar 25, 2023

timselectric said:
Is the capacity setting correct?
105ah

They are eve 105ah cells. I put 16 in series.

jdy2kgt · Mar 25, 2023

RvNaut said:
Yes... A cell topped 3.6 volts and the BMS shut down the charge to protect that cell. When it does this, it ASSUMES that the entire battery is full. It is a goober in the software.

Awesome! Any idea why when the charger first turned on it kept tripping the BMS overvolatge protection? A cell kept showing 3.9 even though they were only at 3.29. It only lasted a few minutes and stopped.

42OhmsPA · Mar 25, 2023

jdy2kgt said:
We just finished our first battery and the BMS was at 70% which sounds right as we hadn't charged them yet. When I started charging within seconds the BMS showed 100%. Anyone know why this jump occurred? It's obviously not at 100% as you can see from the pictures the cells are still at 3.3/3.4. View attachment 141223 View attachment 141224

If your voltages for cell 10 is correct I'd start discharging that pack quickly...
Did you top balance?

42OhmsPA · Mar 25, 2023

jdy2kgt said:
Awesome! Any idea why when the charger first turned on it kept tripping the BMS overvolatge protection? A cell kept showing 3.9 even though they were only at 3.29. It only lasted a few minutes and stopped. View attachment 141232

Did you verify every cell with a multimeter? Where did cell 2 go?
Pics of setup?

jdy2kgt · Mar 25, 2023

42OhmsPA said:
Did you verify every cell with a multimeter? Where did cell 2 go?
Pics of setup?

I'm bringing the pack up first and then will do a top balance. I measured each one when they first came in (3.29). Again cell 10 only did this for a minute and then showed correct, I was curious why. It seems to be running fine now. Here's a current screenshot.

timselectric · Mar 25, 2023

Double check all balance lead connections.
Wire to terminal and terminal to cell/bus bar.

RvNaut · Mar 25, 2023

My guess on the discrepancy...

Example - In assembling my battery (16x3.2cells) for the second time, I encountered really whacky readings on cells 5 and 6, inconsistent and nowhere near what the actual readings were. I proceeded to triple check all my connections and found the stud into the neg post of cell 11 was not tight, Once I remedied this situation, cells 5 and 6 returned to normal voltages.

Triple check all of your connection and cable assignments.

MisterSandals · Mar 25, 2023

jdy2kgt said:
It seems to be running fine now. Here's a current screenshot.

Can you post a pic of your BMS settings?

jdy2kgt · Mar 25, 2023

MisterSandals said:
Can you post a pic of your BMS settings?

MisterSandals · Mar 25, 2023

3.60V for cell over volt is pretty low/conservative. That means this will almost certainly trigger before (3.6V x 16=) 57.6V
Its safe to charger to 3.65V but i like it a little conservative at 3.63Vpc since i have a plenty large battery and i do not need to push it.
So you if you change this, you can bring OVPR up as well to 3.60V or whatever you are comfortable with.

Also, i think the consensus for balance start voltage is around 3.4V rather than 3.0V.

Is there a reason you have discharge current limit set to 200A? Thats pretty high, especially for a 105Ah battery.
The charge limit is set to 25A which seems pretty low (intentionally cutoff at this level?)

25A x 56V = 1400W charging limit (.25C)
200A x 56V = 11,200W discharge limit (2C)

Otherwise looks pretty reasonable.

DougfromdaUP · Mar 25, 2023

Why would cell 10's wire resistance be so much higher than all the rest?

jdy2kgt · Mar 25, 2023

MisterSandals said:
3.60V for cell over volt is pretty low/conservative. That means this will almost certainly trigger before (3.6V x 16=) 57.6V
Its safe to charger to 3.65V but i like it a little conservative at 3.63Vpc since i have a plenty large battery and i do not need to push it.
So you if you change this, you can bring OVPR up as well to 3.60V or whatever you are comfortable with.

Also, i think the consensus for balance start voltage is around 3.4V rather than 3.0V.

Is there a reason you have discharge current limit set to 200A? Thats pretty high, especially for a 105Ah battery.
The charge limit is set to 25A which seems pretty low (intentionally cutoff at this level?)

25A x 56V = 1400W charging limit (.25C)
200A x 56V = 11,200W discharge limit (2C)

Otherwise looks pretty reasonable.

Thank you. All those setting are initially what happened when I turned the bms on and set it to lifepo4. I've changed to the setting you recommended. But as of right now the charger stopped charging and I'm not sure why

jdy2kgt · Mar 25, 2023

DougfromdaUP said:
Why would cell 10's wire resistance be so much higher than all the rest?

Great question. I'm going to redo its connection and see if that changes anything.

MisterSandals · Mar 25, 2023

jdy2kgt said:
I've changed to the setting you recommended. But as of right now the charger stopped charging and I'm not sure why

Looks like the BMS is allowing charging so we'd have to have a look at your SCC.

jdy2kgt said:
I'm going to redo its connection and see if that changes anything.

Scrub the contact areas and clean any grease or gunk with isopropyl alcohol or other solvent. Check the crimp too, make sure its not crimped on the wire outer sleeve and firmly on the wire itself. This area is HIGHLY suspect.

jdy2kgt · Mar 25, 2023

Fixed #10 and now it's reading same as others but the charger still is not getting any of them to 3.6

JK BMS jumped from 70% to 100% SOC

New Member

New Member

Solar Wizard

If I can do it, you can do it.

If I can do it, you can do it.

New Member

New Member

What's in a title?

What's in a title?

New Member

If I can do it, you can do it.

New Member

Participation Medalist

New Member

Participation Medalist

Solar Enthusiast

New Member

New Member

Participation Medalist

New Member

Similar threads