XiaoXiang BMS Spontaneously resets Remaining Capacity display

[Vi s]

With cylindrical cells, I'm using:
Full: 3.45V
80%: 3.332V
60%: 3.293V
40%: 3.29V
20%: 3.24V

Prismatic cells might be like this. Some adjusting probably required.
80% 3.337
60% 3.302
40% 3.295
20% 3.251

Maybe those who have done actual discharge testing could post their results.

Could you kindly share your results from 100 to 0% at rest!? I would like to insert those via the PC Software.

Even though I have eve 50ah prismatic cells i observed similar results as your cylindrical cells. I did no test with the eb tester but i observed the values of my external coulomb counter.

Would be very much appreciated!

 

[Vi s]

Yes, that's exactly it. It does take time but I don't know how else it could be accomplished with a high level of accuracy. Copying someones settings might be close enough if the LFP cells are similar age, type & quality. With the exact test load known then it's easy to estimate when each discharge point will be reached and set a phone reminder to stop the discharge. Here's what 10% decrements looks like with my cylindrical LFP cells. You can see the voltage difference between discharge cutoff voltage and then the subsequent voltage recovery. I didn't realize that it takes around 24 hours rest to get the most stable voltage at first.

How much mV difference was there between the stop voltage and the settled voltage after 24 hours rest? Was the voltage difference between stop and settled always the same after each 10% mark? Did you monitor the voltage rise at reat every few hours to see the voltage rise behavior in relation to time?
Thanks!

 

[Vi s]

Other than replacing the BMS, has anyone found a fix for this? Is there a firmware update, or a different phone (or desktop) app which will allow tweaking of how the SOC calc works?

I'm doing a multi-day, low draw capacity test on my ~271Ah pack and I got down to 30% last night. Voltage was fluttering between 12.91 and 12.92V. I turned the 2A load off as I was going to sleep and I wanted to get regular (~hourly) capacity stats from the BMS and shunt at the top and bottom of the capacity range since voltage varies more. I checked on the BMS a few times to see what voltage the pack would stabilize at (ultimately 13.02V). Interesting thing was when the voltage had increased by 0.1V the BMS reset from 30% to 100% capacity.

Note that up until that point the BMS was showing pack capacity correctly, but once there was NO LOAD (and no charging) this happened. My 80/60/40/20% voltage settings are pretty darn close as is my cell full and cell minimal voltage, so I do not think the BMS should have been confused by the change in resting voltage. Definitely feels like it could be a firmware bug. When I pulled my battery off my trailer my Simarine Pico was showing 89% capacity but the BMS was showing 100%. I keep my charging profile set to try not to float my LFP pack above 90%, and before I did my test I topped off my battery (at 14.6V/8.5A it took maybe 6 hours) so it does seem like the BMS must reset each night once the sun goes down and the load drops to ~30mA.

Ultimately I'll live with the incorrect SOC as my Simarine Pico is highly accurate... I'd only use the BMS columb counter and SOC if I pull the battery off the trailer.

I also do face such issues, sudden change in SOC and left capacity in various situations (also after changing certain parameters in the android app).
The situation seems to have improved after i corrected (through the Chinese PC app) the 90 70 50 30 10 0% factory values which were totally off.
Wish those settings as well the "set remaining capacity" function would also be accessable through the phone app.

Currently i am still observing my pack to find the most fitting SOC values for the bms. Will probably take a few weeks till i can finalize them.

 

[WingNut]

How much mV difference was there between the stop voltage and the settled voltage after 24 hours rest? Was the voltage difference between stop and settled always the same after each 10% mark? Did you monitor the voltage rise at reat every few hours to see the voltage rise behavior in relation to time?
Thanks!

I did the test once and it was two years ago so I don't remember that much about it. I did record this:

13.331V 90% SOC
13.327V 80% SOC
13.325V 70% SOC (after 24 hrs rest)
13.174V 60% SOC (after 24 hrs rest)
13.164V 50% SOC (after 24 hrs rest)
13.160V 40% SOC (after 23 hrs rest)
13.102V 30% SOC (after 21 hrs rest)
12.960V 20% SOC (after 21 hrs rest)
12.818V 10% SOC (after 20 hrs rest)

I don't have the specifics of the stop voltage vs the settled voltage. Here's what it looked like:

The rate of discharge would affect that I'm sure.

Your multimeter will display different voltages than mine. That's pretty much guaranteed as they come with different specifications for accuracy and also will need to be calibrated at some point as they lose accuracy. There's also how they handle missing digits as some round, some drop digits.

Basically you have to do the test using your equipment. You can buy a Voltage Standard or Voltage Reference to check the accuracy of your equipment.

 

[Vi s]

I did the test once and it was two years ago so I don't remember that much about it. I did record this:

13.331V 90% SOC
13.327V 80% SOC
13.325V 70% SOC (after 24 hrs rest)
13.174V 60% SOC (after 24 hrs rest)
13.164V 50% SOC (after 24 hrs rest)
13.160V 40% SOC (after 23 hrs rest)
13.102V 30% SOC (after 21 hrs rest)
12.960V 20% SOC (after 21 hrs rest)
12.818V 10% SOC (after 20 hrs rest)

I don't have the specifics of the stop voltage vs the settled voltage. Here's what it looked like:
View attachment 95917
The rate of discharge would affect that I'm sure.

Your multimeter will display different voltages than mine. That's pretty much guaranteed as they come with different specifications for accuracy and also will need to be calibrated at some point as they lose accuracy. There's also how they handle missing digits as some round, some drop digits.

Basically you have to do the test using your equipment. You can buy a Voltage Standard or Voltage Reference to check the accuracy of your equipment.

Many thanks for all of this information and Tipps!

Ok that means i will have to do my own testing. Luckily i have all the tools needed for that including a zketech tester. Just waiting for the sun to top balance my pack again, then i will start to do almost the same as you did. Almost because I won't wait 24h but just a few minutes maybe because I observed after 8 hours of rest the voltage only rises or decreases (depending if you charged or discharged before) about 6mV. So i will add just that and save myself the long wait. As well my observations match with your graph pretty well, the voltage rose about 7mV during 21hours.

 

[Vi s]

These are the values i got after actually testing my 54Ah Eve battery.

All average cell voltage values after 30min rest
100% 3.500V
90% 3.333V
80% 3.329V (after additional 7h over night rest voltage increased by another 5mV)
70% 3.305V
60% 3.293V
50% 3.291V
40% 3.289V
30% 3.267V
20% 3.236V (after additional 7h over night rest voltage went up another 6mV)
10% 3.202

 

[Vi s]

Thanks Jim. So even if you only use a few Ah and then just replace the used Ah it will recalculate ?
I haven't seen my Xiaoxiang BMS do that yet, but I haven't cycled it much either.

Trying not to run them through too may unnecessary cycles.
Still not exactly sure why the remaining capacity reset itself. Also very difficult to connect to BT at times. was thinking it could be a BMS defect.

The other solution is to get the USB communications dongle so it can be connected to a PC and set manually through the PC software since the app doesn't have that capability AFAIK.

It's possible that installing the app on another device will automatically reset everything to factory default.
Trying to remember if I added the xiaoxing BMS app to another device before or after the reset took place.

Solved this common issue now. Many thanks for WingNut for pointing out the solution here https://diysolarforum.com/threads/x...-remaining-capacity-display.22472/post-295322

Also may see here how i did it then

JBD BMS - How to correct inaccurate SOC value ✅

*Edited, inserted instructions how to solve the SOC issue. All this here is based on WingNut's post here https://diysolarforum.com/threads/xiaoxiang-bms-spontaneously-resets-remaining-capacity-display.22472/post-295322 Greetings to all JBD BMS owners! Did you also notice that the SOC % value...

diysolarforum.com

 

[LazMako]

Hey Guys,

Just got a new pack and had the same resetting issue, where the available/remaining percentage jumped up and down for seemingly no reason. I've read through this forum and it seems I have managed to fix it based on WingNut's post (linked in the previous reply). I also have a theory of what's going on in most cases.

I have used both v3.1 of the Xiaoxiang BMS Android app and v3.2 (current PlayStore version) - each for a different reason.

So I think what happens is when you load the older looking app and reset to the "LiFePo4 Normal" or "LifePo4 Lite" defaults it resets the charge level voltages for 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%. When you then go to the "Parameter View" or the "Params Settings" screen to change them, you will only be able to adjust 20%, 40%, 60% and 80%. I guess the full/100% voltage is implied based on other settings.

If you then load the "new" fancier looking Android app (PlayStore version, v3.2 as of writing this) and go the the "Parameter" > "Capacity Voltage", you will have access to all percentages in 10% increments. In my case, these values were a mix of my custom values set in the older app and some defaults in between that I haven't changed or seen before. The resulting list wasn't at all linear, so for example, 50% was higher than 60%, 30% was higher than 40%. For the sake of the test, I have just set the values of 10%, 30%, 50%, 70% and 90% to be exactly halfway in between their neighbours - so for example 30% to be exactly halfway between 20% and 40%. Obviously this could be measured properly to get more accuracy out of the BMS, but this was good enough for my test. Once the values of 10%-100% were continuously increasing, the issue never happened again.

Obviously, if you don't use the PlayStore version of the app, you will never see this. Older versions only show a few charge percentages but the remaining percentages are still set in the back end regardless, they are just not visible on the old UI.

I hope this helps.

Cheers,
Laz