Jiabaida BMS settings; spontaneous change of Designed Capacity

[Theo74]

I own a Jiabaida (JBD) 4S 200A BMS which is connected to a 300Ah LFP battery pack.
(Cells are brand new automotive grade, from Ganfeng.)
In the BMS app, I made the settings and set the "Designed Capacity" to 300000mAh.



After a short time of usage, I saw in the BMS app settings that the Designed Capacity value had changed, to somethting like 279850mAh.
Because I did not do anything in the BMS app or settings, this change of the Designed Capacity value must be done by the BMS software.
What caused this Designed Capacity to change, and why?
I've change the Designed Capacity manaully back to 300000mAh, but I would like to know how to get this value fixed then. Realy strange...

 

[justgary]

The image doesn't seem to agree with the numbers in your text. You show 8 cells and 30,500 mAh, not 4 cells and 300,000 mAh.

By the way, which app is that?

 

[Theo74]

That is why you see under the picture: (Example picture for the yellow capacity part, not the real situation)
At this moment I have no access to the batterypack/BMS, so I used a example picture for the explanation.

 

[Quattrohead]

I think this is the difference between actual capacity and reasonably usable capacity. I know my 280s actually show a 234 usable capacity so that would be down to 10% up to 90% or something like that.

 

[MisterSandals]

You can try the Overkill app too. Both work for me. They have a slightly different user interface.

Did you click “BMS Write” after making your changes?

 

[Theo74]

The "Designed Capacity" is a value you need to set manually, because the BMS can not know this.
That is why I don't expect the BMS to correct this value after some charge/discharge actions...
I can think of the actual- and the reasonable capacity, but this doesn't seem to be the case here...
And Jiabaida is not mentioning anything about this value change/correction in their manual either...

And yes, I did use "BMS Write" after I made the changes. I also did the first time after setting the rest.
Would a different app make any difference in this case? I think they basically work the same, isn't it?
LFP battery brand Liontron also works with JBD, so their app could also be used, but I dont see why.

 

[MisterSandals]

Would a different app make any difference in this case? I think they basically work the same, isn't it?

You reported an anomaly and hypothesized it was BMS software (did you mean firmware?) was changing the designed capacity value unexpectedly.
You can narrow the problem (feature?) down by using a different software to read/write the value.

I would hope everything worked great and as expected but when it doesn’t, common debugging involves narrowing down the things that could be at fault.

 

[Theo74]

You got a point there… I might do the second app/opinion test then, to see what this brings.
In the mean time I’ve tried to contact JDB about this issue, but unfortunately the don’t reply.

Could this changing of the set Designed Capacity value be a bug then, or does the BMS it self calculate the capacity during charging and discharging? In other words; are more JBD or Overkill BMS users familiar with this phenomenon?

 

[MisterSandals]

Could this changing of the set Designed Capacity value be a bug then, or does the BMS it self calculate the capacity during charging and discharging? In other words; are more JBD or Overkill BMS users familiar with this phenomenon?

Since designed capacity (as I understand it) cannot change, the value should never be calculated.
If actual capacity is measured or degrades, the user can/should change this value.

Maybe a translation issue?
Xiaonxiang and Overkill have “total battery capacity” and “total cycle capacity “ which is clear to me.

What app are you using and what version?
Your screenshot looks very similar to my Xiaongxiang app, but does not have “designed capacity”.

 

[HRTKD]

I recall reading a thread where it was found that the BMS (maybe the app) couldn't handle a capacity number any higher than X. Set it over X and it wouldn't take the value. Reduce the value and see where it actually accepts the value.

 

[sunshine_eggo]

According to my recollection of the overkillsolar manual:

Design capacity is the rated capacity of the battery.
Cycle capacity is the actual tested capacity of the battery. Cycle capacity is the denominator in the SoC calcuation.

 

[Theo74]

@MisterSandals Indeed, the Designed Capacity is the hard value of the cell pack, and therefore it should not be changable by the BMS.
Changing this value manually is possible when needed, but it could not be that this value changes by it self.
The screenshot I've used in the start post is taken from the net, and not from my BMS app. I had no possibility to make my own screenshot because the battery is in my RV, and stored somewhere else. And I use the paid JiaBaida iOS app (blue elefant) version 1.3.1, Build 7662

@HRTKD When I programmed the BMS for the first time, I set the Designed Value to 300000mAh, and this value did not change the first days/weeks of use. Only after a couple of charge/discharge actions, when I wanted to check the settings, I saw that the value was changed to a strange 289578mAh like value. (Don't know the exact value anymore, but something like that.)
I can not think of the fact that a 4S 200A BMS can not handle a capacity value of 300Ah, and there is nothing mentioned in the manual either...

@sunshine_eggo Indeed, the Designed Capacity is a fixed setting by the user. The cycle capacity probably will be calculated by the BMS during the charging and discharging over the time of usage. More or less like a smart shunt does with calculating the SoC.

 

[Tino]

I have noticed this problem, my JBD BMS just seems to change the Total Battery capacity in the Overkill Solar app. I don't know why it's suddenly decided that it's a 241ah battery now when it used to be 302ah.

 

[sunshine_eggo]

@sunshine_eggo Indeed, the Designed Capacity is a fixed setting by the user. The cycle capacity probably will be calculated by the BMS during the charging and discharging over the time of usage. More or less like a smart shunt does with calculating the SoC.

No. Cycle capacity is entered by the user.

See the overkill manual 3.2.2

 

[Theo74]

UPDATE:

I've changed the picture in the first topic message, into an original and recent screenshot of my app.
Here you can see that it's not concerning the "Designed Capacity", but the "Total battery Capacity".
And indeed, you need to set this value manually, this is not done, or calculated bij the BMS or app.

In the past time this value did not change anymore, it is still fixed on the true capacity of 300Ah.
So for now and can't say that this value changed again in the mean time... (Maybe a bug afterall?)
Maybe I'll install the Overkill Solar app, and Liontron app too, to compare the values in between.

Here's an extra copy of the screenshot:

 

[daved1911]

Has the issue been resved? I have a similar situation.

 

[moridinbg]

I have had the same with a JBD BMS since the beginning. I set it to 280Ah and it suddenly resets to 100Ah. I thought it was due to the iOS app I was using, switch to another - same thing happens. It super annoying, as I loose the current SOC every time it does that.

 

[featherlite]

My Overkill Solar JB BMS changed the AH Capacity value when I installed the latest software upgrade.