Jk BMS shut down and unable to restart

[fx99]

EDIT:
Problem still unsolved, but here is a TL;DR summary of the three thread pages we got so far:

my setup:
Lifepo4 8S EVE 280ah cells
JK BMS B2A8S20P-HC
Fchao 3000w 24v inverter

situation:
BMS installed, all readings in App are very good, no problems.
I tested the inverter for the first time for a few seconds with no problems, but I only tested for a few seconds.
2nd try a bit later the BMS shut down after a few seconds at 2000w.

BMS shut down because it measured one cell to be below the shut off voltage.

3 different Multimeters say that the cell is perfectly fine. <=1 mV deviation between cells. Measured directly on cells and also through the wiring harness, also tested with switched wires
conclusion: BMS is broken
But with new BMS and new wiring harness installed, problem still shows at the same cell.

Next step: load test

(I will keep this updated if I don't forget)



Hey guys, today I tested out my battery pack and im already having troubles with my bms ?
here's what happened:

my setup:
Lifepo4 8S EVE 280ah cells
JK BMS B2A8S20P-HC
Fchao 3000w 24v inverter


situation:
I tested the inverter for the first time with a 2000w load (heat gun). 1st try no problems, but I only tested for a few seconds.
2nd try a bit later the BMS shut down after a few seconds at 2000w. maybe something went wrong because I might have applied the load right away before the inverter was fully "powered up"?

Now there is no power on the P- side of the BMS.
The light on the BMS and on its start button is off. the light is on when the button is pressed, but there is no beeping sound and most importantly I can't connect my phone to see what's going on.


my testing so far:

I disconnected the BMS Balancing Leads and B- for a few seconds because I thought this might reset the bms.

I disconnected the BMS Balancing Leads again and measured the Voltage for every cell on the BMS . the balancing leads are wired correctly and no cell is drifting off too much.
3.32V/cell
26.6V total

I connected a charger (for the first time) and the BMS shortly turned on. I was able to connect via Bluetooth for a few seconds and looked at the system log. I think I read something about undervoltage protection before it shortly after shut down again and I wasn't able to turn it on/connect via Bluetooth again after.

I am not sure if I really saw an undervoltage fault, because it shut down while i was scanning over the log. Since my cells are at 3.3V it doesn't make any sense anyways, unless I mistyped the undervoltage protection parameter when setting up the BMS.

My last try would be to charge the battery again until it's completely full. My shunt and voltmeter say that my charger charges at 28.82V.
But when I measure the Voltage between the charger plus and the B- (not P- !) side of the BMS, my Voltmeter displays around 9V ?! Can someone explain that to me? Maybe my voltmeter is messing with me...

I haven't tried further charging yet, because im worried about something going wrong while charging with my old ass car/truck battery charger without the protection of the BMS.

thanks for reading all of this.
maybe someone can help me out? otherwise I might have to order a new BMS, because I have no idea what to do. I have very limited experience with solar installations and battery builds tbh. just learning by watching YouTube videos and reading forum post, like many people do I guess.


best regards
Felix

 

[LydMekk]

If you have the model with the on/off switch - attach it and use it.
If not, connect a desk powersupply with 5-6v MORE than the battery pack and the BMS should start up.
Not much amps needed, only the volts are important.

 

[timselectric]

Charge the battery for a while.

 

[fx99]

If you have the model with the on/off switch - attach it and use it.
If not, connect a desk powersupply with 5-6v MORE than the battery pack and the BMS should start up.
Not much amps needed, only the volts are important.

hey thanks for answering. I have the model with the switch. but it's not doing anything anymore. only lights up while being pressed, the light goes off when I let go off the button. no beeping sound, no power and no Bluetooth connection.

 

[fx99]

Charge the battery for a while.

I guess I will do that. as mentioned my charger charges at ~28.8V. is that enough? I've read that the charging voltage for lifepo is 3.65V/cell or 29.2 for 8s. close enough I guess?
I am worried about overcharging the battery though. the model of the charger is "absaar bbl 1224 20 ne". got it from my dad and I have no idea if it has any safety functions. guess I will have to stay around during charging and keep an eye on the battery voltage.

 

[timselectric]

Just keep an eye on it. Until you can get a proper charger for LFP.

 

[fx99]

Just keep an eye on it. Until you can get a proper charger for LFP.

alright thank you

 

[DIYrich]

9v after bms is the battery voltage with the bms turned off. There may be a bad connection somewhere between cells. Start with cell 1. Read the voltage. Move the plus probe to the next battery (keep negative at same place). Do you get an additional 3+ volts at each cell?

Disconnect bms wire harness from bms when you do it. If readings are OK, repeat with wire harness attached to bms.

When you charge (to get bms working) you will have to bypass the bms. The bms has to be on to let charge voltage through.

There is one parameter that will shutdown the bms itself (not turn on?). The Power Off voltage will keep the bms itself from draining the battery. Some possibilities: bad cell wire/connection. Bad battery wiring. Discharged cell. Value set too high. If the charger is on when you start the bms, enough current should flow to bring up the cell voltage unless one of the above problems, or you set the bms to not allow charging.

 

[fx99]

Quick update:

When I connected the charger my bms turned on again instantly. I went straight to the app to make some screenshots. When I was done with that I disconnected the charger again to first take look at the pics. Disconnecting the charger turned off the BMS.

It turned out the BMS shut down because it measured one cell to be below my power off voltage of 2.55V. I will attach a screenshot to show you the parameters I set.
But the measurement is not correct. I confirmed with 2 different voltmeters that the cell is, like all the other cells, at 3.35V.
(The BMS app says all cells are at 3.285V, except for #6 which was apparently below 2.55 V. After toroughly cleaning the contacts for balancing cable #6 again and reconnecting the BMS, the BMS turned on normally without the charger connected. On the flipside though it still measures incorrectly, and now displays around 2.85V for cell #6, so basically it still measures the cell to be empty and just barely above the power off voltage.

But as I said, I already measured the cell to be at 3.35V. I also, once again, measured the voltages on the plug side of the cable multiple times, to confirm that there is nothing wrong with the contacts or the wires. I will attach three pictures to show my measurements.
- I measured 20.1V between B- and cell #6
- I measured 3.35V or 3.36V between #5 & #6 and the same for #6 &#7 and "off camera" between all other cells as well to be safe

On the main page of the BMS app I got a warning saying "Warning: Equli. Res. too high" with 0.000 Ohm at cell #6.
Another warning says "Sample-wire resistance too large".

Am I correct in the assumption that my cells and the balancing cables and contacts are not the problem, but the problem is somewhere inside the BMS?
If so, I guess I have to get a new one, right? ?

Thanks for reading. If you have some ideas please share them with me ?

 

[timselectric]

It's possible that #6 pin in the plug isn't making good contact with the BMS. If you have any extra wires that weren't used. I would trying swapping one. If not, I would remove pin #6 and see if anything is obvious about it.

 

[tinyt]

It is also possible that the crimping of the terminal for pin 6 to the wire was not done properly by the manufacturer.

 

[fx99]

It's possible that #6 pin in the plug isn't making good contact with the BMS. If you have any extra wires that weren't used. I would trying swapping one. If not, I would remove pin #6 and see if anything is obvious about it.

Sadly I don't have any extra wires. I took a look at the plug and couldn't see anything odd about #6.
Do you mean I should remove the pin on the BMS side of the plug. the part that's mounted on the BMS and requires disassembly?


btw I think I should point out that the BMS was working fine without a load on the day before I connected the inverter. all resistance and voltage readings were very good. and the first time I shortly tested the battery with the inverter i didn't have any problems either ? I wonder how the connection could have gone all bad in such a short time

 

[fx99]

It is also possible that the crimping of the terminal for pin 6 to the wire was not done properly by the manufacturer.

do you mean the pin on the BMS side? is it possible for me to test that or take a closer look at the part?

 

[Skypower]

Did you you pre charge with a resistor right before you connected the inverter?

 

[tinyt]

On the white connector that plugs to the BMS. You can use an ohmmeter if there is continuity between the wire end that connects to the cell and the crimped pin 6 terminal that is in the white connector, Hopefully, there is no continuity, otherwise the defect will be on the BMS side.

 

[fx99]

Did you you pre charge with a resistor right before you connected the inverter?

to be honest I just had to look up what that even means. somehow I have never heard of that before. is it necessary at 24v? ?

 

[timselectric]

Sadly I don't have any extra wires. I took a look at the plug and couldn't see anything odd about #6.
Do you mean I should remove the pin on the BMS side of the plug. the part that's mounted on the BMS and requires disassembly?


btw I think I should point out that the BMS was working fine without a load on the day before I connected the inverter. all resistance and voltage readings were very good. and the first time I shortly tested the battery with the inverter i didn't have any problems either ? I wonder how the connection could have gone all bad in such a short time

I'm referring to the pin location on the plug. (The wire side)
You can also make a visual inspection of the BMS side. (Just from the outside)
If nothing is obvious. I would try switching #6 wire with another one. To see if the issue remains on #6. Or moves with the wire to the other location.
Beyond that, it might be time for a warranty claim.

 

[fx99]

On the white connector that plugs to the BMS. You can use an ohmmeter if there is continuity between the wire end that connects to the cell and the crimped pin 6 terminal that is in the white connector, Hopefully, there is no continuity, otherwise the defect will be on the BMS side.

wouldn't the continuity already have been confirmed by my previous test with the voltmeter?

serious question, I am honestly not sure

 

[fx99]

I'm referring to the pin location on the plug. (The wire side)
You can also make a visual inspection of the BMS side. (Just from the outside)
If nothing is obvious. I would try switching #6 wire with another one. To see if the issue remains on #6. Or moves with the wire to the other location.
Beyond that, it might be time for a warranty claim.

okay thank you for the clarification ? but couldn't the wire switching be harmful to the BMS? I am quite sure I have heard that it's very important to double check if all the balancing wires are at the correct cell before connecting it to the BMS for the first time, to not harm the BMS. is that not correct?

 

[timselectric]

okay thank you for the clarification ? but couldn't the wire switching be harmful to the BMS? I am quite sure I have heard that it's very important to double check if all the balancing wires are at the correct cell before connecting it to the BMS for the first time, to not harm the BMS. is that not correct?

Switch the wires completely. (Both ends)