12V 4S 100A JBD BMS acting strange

[dubaron]

In August of 2020 i installed a DIY 150aH LiFePo4 battery with a JBD 100A BMS into my VW camper. The battery is charged with a Renogy DCC50S using the alternator, I have not connected a solar panel to the system yet.

I recently installed the Overkill BMS app on my iPhone, I was using the XiaoxiangBMS app. I loaded up the 4S template config in the Overkill app and since then I've been having strange issues. I went back to the XiaoxiangBMS app and wrote a previously saved config to the BMS and it started to behave. I thought things were good, they aren't. The SW switch enable is disabled, the Load function is disabled as well, both of which caused funkiness after loading the Overkill template.

This past weekend during a 3 hour drive to a campout, I noticed that the discharge current was not showing and the charging current was under 10amps. Then the charging current stopped and the discharging current was displayed. It would flip back and forth, it never showed both charging current and discharging current simultaneously. The load was the stereo and the fridge, about 5 amps.

I have disconnected the BMS power for a few minutes and then applied the power, no change.

I downloaded the Overkill BMS app because the BMS was misreporting the SoC - it would drop to 15% charged but showed 13.3 volts. Changing the "Total Cycle Capacity" value from 120000 to 135000 and then back to 120000 would cause the BMS to report the percentage being far closer to reality, 70% or there about.

Is my BMS dying? Is there a way to "hard reset" it?

-Steve

 

[Bob B]

The app you use to view the BMS doesn't make any difference to what the BMS is doing ..... It's possible it could make a difference when writing settings but I haven't seen that.

We are going to need some screen shots of what the BMS is doing and also some screen shots that show your settings.

The other thing you need to be aware of is that the SOC reverts to a voltage guestimate based you your settings every time you write any setting change .... if the BMS is cycled and at least one cell reaches the cell full voltage setting the BMS will go to 100% SOC and start tracking based on current in and current out instead of voltage .... any setting change starts it over again.

 

[dubaron]

There are two screen caps which show the charge and discharge currents are not shown simultaneously. With the fridge on it's drawing nearly 4 amps. I started the engine and after 15 seconds it switched from showing the discharge current to the charge current. I'vre included screen caps of the settings as well.

 

[Bob B]

Theoretically, a battery won't charge and discharge simultaneously ...... If the current from your charge source exceeds the load, the battery will charge ... unless it is already fully charged.
If the load exceeds the charge current, or there is no charge source, the battery will discharge.

Frankly, I'm not sure if this is how the JBD BMS is supposed to displays things ..... The way I use my pack with a JBD BMS, I charge it then use it ..... repeat.

If the BMS was switching between charge and discharge while you were traveling, it is possible it had reached full charge and disabled charging ..... then the pack would discharge to the return threshold and start charging again.

Is the manner it displays charge and discharge the only issue you are having?

 

[dubaron]

Is the manner it displays charge and discharge the only issue you are having?

another issue is the SoC percentage will go from some high value to a very low value overnight with no load on the battery. the voltage never changes, just the SoC percentage. forcing a refresh gets the SoC value back up to the high value.

 

[Bob B]

another issue is the SoC percentage will go from some high value to a very low value overnight with no load on the battery. the voltage never changes, just the SoC percentage. forcing a refresh gets the SoC value back up to the high value.

I have no idea how the SOC would change radically with no current used and no voltage change.

How are you forcing a refresh?

 

[dubaron]

I have no idea how the SOC would change radically with no current used and no voltage change.

How are you forcing a refresh?

by changing the "Total Cycle Capacity" value from 120000 to 135000 and back again.

on my 3 hour drive when the charging/discharging flip flopping was happening, the battery never charged. the fridge was drawing 4 amps and the Renogy typical supplies 30-40 amps. in the past while driving with the fridge on the battery would charge from 60% to 100% in about 2 hours. it stayed at 60% and the voltage stayed low. i was never getting more than 10 amps as the charging current on the BMS.

 

[Bob B]

by changing the "Total Cycle Capacity" value from 120000 to 135000 and back again.

on my 3 hour drive when the charging/discharging flip flopping was happening, the battery never charged. the fridge was drawing 4 amps and the Renogy typical supplies 30-40 amps. in the past while driving with the fridge on the battery would charge from 60% to 100% in about 2 hours. it stayed at 60% and the voltage stayed low. i was never getting more than 10 amps as the charging current on the BMS.

That doesn't sound like a BMS problem to me .... It sounds more like a bad connection or other problem in your charging system.

If you had recently written a setting change, the BMS was tracking the SOC based on a guestimate from on voltage.
It's critical to understand how the SOC tracking works in the JBD BMS .... If you do a search, you will find a lot of threads on the subject.

Here's an example of a quick search. https://diysolarforum.com/search/2523379/?q=JBD+SOC&o=relevance
I'd read thru those threads til I completely understand the how the SOC tracking works and how it can be tracking amp in and amps out or a guestimate based on voltage.

 

[dubaron]

That doesn't sound like a BMS problem to me .... It sounds more like a bad connection or other problem in your charging system.

If you had recently written a setting change, the BMS was tracking the SOC based on a guestimate from on voltage.
It's critical to understand how the SOC tracking works in the JBD BMS .... If you do a search, you will find a lot of threads on the subject.

Here's an example of a quick search. https://diysolarforum.com/search/2523379/?q=JBD+SOC&o=relevance
I'd read thru those threads til I completely understand the how the SOC tracking works and how it can be tracking amp in and amps out or a guestimate based on voltage.

i appreciate your taking the time to help.

i have an understanding how the SoC tracking works, which is why when overnight it goes from a very high value (expected) to a very low value (unexpected) it's concerning. the battery was isolated from the system, no load possible, not connected to one, and all cell voltages as measured with a meter are 3.35V. this is what led me to think there was an issue with the BMS.

i'll do some more testing.