JK BMS issue with charging

[Becaris]

I purchased two of the JK BMS and received them from China. Then, I hooked up one to my 16s, 48v LifePO4 battery pack, making sure to test the leads to the cells with a voltmeter before plugging them into the BMS. All checked out. I connected the leads to the BMS. Then I connected a 9v battery between the P- and B- of the BMS and it activated with some beeps and the red LED came on. I loaded the software in my phone and configured it for my 16s pack, at 230ah, choosing the LifePO4 option for defaults, figuring I will customize them later. On the Status screen in the app I can see the cells already balancing. So far, so good.

Now for my issue. I hooked up my battery charger. The charger positive is connected to the main positive on the battery pack and the charger negative to P- (black) on the BMS, then B- (blue) goes from the BMS to the main negative of the battery pack. Just like JK BMS wiring diagram shows. Then, I went to Control in the software and turned on charging. My charger shows zero amps flowing to the battery.

If I bypass the BMS the charger instantly shows amps going to the battery. But, with charging turned on in the app, and the BMS active, and the BMS obviously on since I can see it balancing the cells, no amps are going from the charger to the battery through the BMS.

After double checking things, I wondered if the BMS was bad. Fortunately, I purchased two. I tried the second one and it behaves the same way. This leads me to believe it is user error (mine) but, for the life of me, I cannot figure out what I have done wrong.

I am new to this BMS and could have made a rookie mistake, but I do not know what it is.

Any help or suggestions? Thanks! Feel free to ask questions about my setup and I will try to answer them.

 

[MisterSandals]

Any help or suggestions?

Can you post a couple screenshots of your BMS app, with settings and anything potentially useful?
There are quite a few eyes here and almost half as many clever people to help.

 

[Becaris]

Here are images from my JK BMS app setup and one of my charger, while on, showing zero amps output.

 

[MisterSandals]

and one of my charger,

That looks like its a power supply and not a charger. I am not sure if this is your problem.

Your cell level over volt protection at 3.5V is lower than necessary. LiFePO4 cells are good to 3.65V and the BMS is a safety disconnect so "normally" the BMS safety feature is set to the cell limits. The BMS is NOT supposed to control charging (not sure if you're trying this but we see it quite a bit).

So i really don't have an answer, sorry. Maybe someone else see's something useful.

 

[Becaris]

That looks like its a power supply and not a charger. I am not sure if this is your problem.

Your cell level over volt protection at 3.5V is lower than necessary. LiFePO4 cells are good to 3.65V and the BMS is a safety disconnect so "normally" the BMS safety feature is set to the cell limits. The BMS is NOT supposed to control charging (not sure if you're trying this but we see it quite a bit).

So i really don't have an answer, sorry. Maybe someone else see's something useful.

Regardless of what my OVP is set at, it is above the current cell voltages of around 3.3, so the OVP of the BMS should not be activated. The power supply is also a battery charger, and has charged up my cells previous to using this BMS. In fact, if I bypass the BMS it charges the batteries just fine. I am not controlling charging with the BMS, just trying to charge my cells while this BMS is connected... which is not working. I have tried another cheap ass BMS I have on hand, and it works fine charging these cells in this same configuration. Therefore, the issue is with the JK BMS setup or configuration.

Also, I tried the JK BMS defaults (which were set at 3.65v) and that made no difference.

 

[John Frum]

Why are the discharge fets disconnected?

 

[MisterSandals]

Therefore, the issue is with the JK BMS setup or configuration.

Agreed. Everything you said seems reasonable. Would be odd to get 2 DOA units...

I was not <trying to> imply that your BMS high voltage was cutting off, it was just a general observation in your settings.

 

[upnorthandpersonal]

Turn on discharge.

 

[Becaris]

Why are the discharge fets disconnected?

I currently have no loads connected. But, turning on Discharge has no effect, I tried that.

 

[upnorthandpersonal]

Could the over current charging limit of 25 amps cause an issue?

It would indicate that fault on the main screen in red text.

 

[Becaris]

Could the over current charging limit of 25 amps cause an issue?
I agree that the charge and discharge should be on for normal operation.

I don't know. The maximum charge I can send from the Riden is 18 amps. 25 max seemed fine (and is the JK BMS default).

 

[upnorthandpersonal]

Ok, let's do the IT thing: turn it off and on again.
Also, turn on/off both charge/discharge switches, disconnect/reconnect the power supply.

 

[Becaris]

Ok, let's do the IT thing: turn it off and on again.
Also, turn on/off both charge/discharge switches, disconnect/reconnect the power supply.

I tried that... but I just did it all again. No change.

 

[upnorthandpersonal]

Can you add a load to it and see if it discharges? Light bulb would be fine for testing.

 

[Becaris]

OK, I figured out. I have to turn on the Charge and Discharge, which, for some reason, turns off the Riden charger. Then, turn on the Riden Charger again with both still on. That got it working. After that, I can turn on or off the discharging on the BMS and it no longer turns off the Riden. Go figure. Thanks for the attempts at help!

 

[upnorthandpersonal]

OK, I figured out. I have to turn on the Charge and Discharge, which, for some reason, turns off the Riden charger. Then, turn on the Riden Charger again with both still on. That got it working. After that, I can turn on or off the discharging on the BMS and it no longer turns off the Riden. Go figure. Thanks for the attempts at help!

Right, that would have been my next suggestion - replace the Riden. Happy you figured it out! Have fun

 

[jesfl]

The discussion above is the closest to my current problem I've been able to find on the Forum. So, I am posting here. If there is a better place or procedure, please let me know.

Quick background: last year I had 3 150 Ah LiFePO4 batteries just stop working. Still have no idea why. But folks here guided this very limited-knowledge novice to the built-in BMS on the cells. That turned out to be the problem.

I finally had the guts to tear apart one of the failed batteries and I began to understand how it worked. So I ordered a recommended-here 4s 120A BMS -- supposedly the same as the Overkill -- on AliExpress. When it arrived, I hooked it up to the cells from one failed battery (not changing any BMS settings) and it worked perfectly. Amazing to me. So, later, with some hope, I ordered 2 more of the BMS units for the other two "failed" batteries. The additional BMS units arrived, but I cannot get either of the other BMS units to work with the failed batteries. And, I have no idea why. I've been trying things and reading for several weeks, assuming I am making some simple mistake, but I cannot figure it out.

Batteries the same. BMS the same. No BMS settings changed from the manufacturer settings (either for the previous successfully working BMS or the current non-working BMS units.)

I can charge the batteries fine if I bypass the BMS. Similarly, I can discharge fine using a 12-volt headlight bulb when I bypass the BMS. But no charging or discharging through the BMS. I've tried turning on/off switches and on/off charger/lightbulb with no success. It is very frustrating.

Screenshots of the BMS app and the settings follow. At the moment of this screenshot this afternoon, no charging mechanism was attached to the cells/BMS. But, the 12-volt headlight bulb was attached and working by bypassing the BMS. The Charging switch will come on and stay on, but the chargers (I tried 3 different chargers) will not charge through the BMS. The discharge switch will not stay on ever, whether the 12-volt lightbulb is or is not connected to the system through the BMS. It seems to me the switches are set to work automatically when there is a battery charge or discharge through the BMS? Is that correct?

What am I doing wrong or missing? Any suggestions are very welcome.

Thanks in advance to all.

jesfl

 

[upnorthandpersonal]

What's up with the temperature? It seems the BMS is in low temp protection mode (can't read the entire warning). Is the probe plugged in properly?

 

[jesfl]

(1) Bloody good question, per your Adams quote above.

I hadn't even bothered to plug in either of the two (2) temp sensors since I am just testing the BMS and it is not permanently mounted to the battery. The battery/BMS is inside my RV where high+low temps are a nearly constant 21 degrees Celsius. Newbie mistake.

With temp sensors plugged in and toggling the Function key, I now can both charge and discharge through the BMS. I am now charging and presumably balancing the 4 cells via the new BMS.

(2) Curious why the 2 new BMS units (from same company, same model) came with 2 plug-in temp sensors vs. only one permanently-attached sensor on the previous BMS unit (bought mid-2021)? No instructions or other info included, of course. Any thoughts?

(3) Double-checking just now, I do see that the older BMS came with slightly different factory settings than the 2 new units. Should the settings of all 3 BMS be exactly the same?

Thank you, thank you, so much for taking the time to respond and redirect this newbie fool!

jesfl

 

[upnorthandpersonal]

Curious why the 2 new BMS units (from same company, same model) came with 2 plug-in temp sensors vs. only one permanently-attached sensor on the previous BMS unit (bought mid-2021)? No instructions or other info included, of course. Any thoughts?

Welcome to Chinese products that go through all kinds of revisions without any documentation