Xiaoxiang BMS App Miscalculates SOC and Decreases SOC when Charging (Happens on Two BATTS!)

[jahman]

Hello!

On two BATTs, the Xiaoxiang BMS App at:

å°è±¡çµå¨ - Apps on Google Play

Little Elephant Electric 2.0 is an APP specially developed for lithium batteries

play.google.com

The App mis-calulates the BATT SOC: When I charge the BATT the SOC decreases! When I use the BATT, the SOC increases.



This happens on two different batteries!

I have uninstalled the App, re-started the smartphone and reloaded the App and the problem persists.

The App is the latest from the Google Play store and Android 10 is up to date with all patches.

One thing is I haven't used the batteries in the last few months. Perhaps this makes the BMS's miscalculate some parameter that then makes the Xiaoxiang App go on a wild ride? Just a thought...

Any help much appreciated.

Many thanks!

 

[PreppenWolf]

My guess is you have a runaway cell that is peaking voltage. Because I see you have battery protection and balancing off. Please don't burn down your house.

Battery voltage is not equivalent to cell voltage. 13.36 volts only tells you the TOTAL ADDITIVE VOLTAGE OF THE CELLS. This is in no way related to the CAPACITY state of your batteries.

What are the individual cell voltages?
What type of cells are these?
Have you ever top balanced them?
Have you ever run the battery below min voltage or above max voltage?
Are there any events recorded by the battery?

 

[jahman]

Many thanks PreppenWolf for your reply!

My batteries are both 4-Cell LiFePO4's and have BMSs.
All individual cells are balanced and show the same voltages in the BMS App.
The batteries have been hardly used and have been well taken care of.

 

[PreppenWolf]

Grade cells?

Check all your connections are tight.

Did you ever test the capacity?

You may also want to see if you can use the Overkill Solar app instead and see if it will connect.

 

[jahman]

The Xiaoxiang App used to work fine on both BATTs. Now I went to recharge my BATTs (I keep them at 50%-60% for long term storage) and as I recharged them I noticed on boththe SOC was going down instead of up!

I tried the Overkill Solar App but it's way too complicated for my needs. And as I said, the Xiaoxianf App used to work "fine" with all it's quirks (but is now unusable).

 

[OTRwSolar]

If the charge current calibration was done while discharge current was flowing, or vice versa, it could potentially result in the readings you're experiencing. You may want to consider recalibrating both the charge and discharge current. FYI, some apps have this function, some don't. I know the iOS Overkill BMS app is able to calibrate current.

 

[jahman]

Many thanks for your input, OTRwSolar!

I didn't recalibrate anything. When I purchased the batteries the Xiaoxiang App worked as advertisied, until now. Also, I don't have write privileges set for the BMS: They are locked by the manufacturer for both batteries.

How would I go about recalibrating the charge currents? Is this something I need to do often? I ask because I would think this calibration was "set and forget". Also this is happening with TWO batteries at the same time, i.e. two BMSs are involved. THis would seem to indicate the BMSs are OK and it's something to do with the App? Has anyone else run into this problem after not using their batteries for 2-3 months?

-jahman

 

[OTRwSolar]

Did you get the same incorrect SOC readings while using the Overkill App? The iOS version of the Overkill App provides complete write access to nearly all the BMS's presets and calibration functions. Hopefully you're not getting the same incorrect SOC readings on two different apps . . . while accessing two different BMS's . . . that would be beyond strange. If this occurring I'd suggest using a different phone to make sure it isn't the phone--lol!

From my experience, the JBD apps do no additional calculating in terms of SOC. It may convert temps from C to F, but not much more. Typically, all the data (voltage, SOC, etc.) is simply relayed verbatim from the BMS to the app display.

For what it's worth, you can also access the JBD BMS (and calibrate current) via the UART/bluetooth port using a JBD USB/UART module using the JBD and/or Overkill Windows app.

 

[jahman]

Howdy, OTRwSolar!

Couldn't get the Overkill App to run because I refused to give it access to my GPS location, something it really doesn't need to do. Also the App looks quite complicated with a lot of parameters I better not learn about because I knpw if I do I'll start messing with them and I probably shouldn't. Also the manufacturer doesn't provide me with write access to the BMSs or I'll void the warranty, so that also rules out accessing the BMSs via the UART port.

From my experience, the JBD apps do no additional calculating in terms of SOC. It may convert temps from C to F, but not much more. Typically, all the data (voltage, SOC, etc.) is simply relayed verbatim from the BMS to the app display.

Aha! There's something for me to go back to the manufacturer with! But it's still odd both BMSs went out Re: Calculating the SOC.

Cheers,

- jahman.

 

[PreppenWolf]

Overkill doesn't use GPS data. The requirement has something to do with phone OS not Overkill.

 

[jahman]

Ah, yes, indeed, it's requesting Bluetooth access (of course) and not GPS. My brain gears must have skipped a few teeth. Access granted, App loaded! Shows the Bluetooth signal strength for my two BMSs in dB and makes an instant fan out of me.

Then Android asks me to allow access to photos and media. Not sure why the Overkill Solar app needs to see my photos. Maybe Overkill Solar is a fan of me?

OK, so now both the Xiaoxiang and Overkill Solar apps show the same erroneous SOC calculations on two different batteries! How weird is this? So OTRwSolar was right about the BMSs doing all the calculations and with the BMS App on the phone just receiving th data and posting it on the screen.



I'll revert to the manufacturer about the buggy BMSs or whatever caused them to miscalculate and then post back how the issue was solved.

Thanks to all!

Cheers,

- jahman

PS: Pet peeve for both Apps: Would love a summary page that shows me the SOC, voltage and current for both my BATTs without having to switch "Devices" from one BATT to the other. Seems to me both apps could show up to six BATT summary infos. Then just tap the BATT you want to see detailed info (main Page). Would be nice.

 

[OTRwSolar]

Glad you're making some progress. Have you had a chance to verify whether any discharge or charge current (values displayed at the top of the app between the switch and icons) are reversed? In other words, is 10a of discharge current shown as 10a of charge current (or vice versa)?

 

[jahman]

Actually yes, charge and discharge currentss are reversed and I'm sure that's part of the problem. Any idea what could have caused that? For to BMSs at the same time?

 

[rodrick]

I see 3.33 volts per cell and you say it’s 95% how are you determining the state of charge do you have a shunt
is your battery only 10ah?
have you fully charged the battery to 3.6 to 3.65 per cell which should be 14.4 overall battery voltage
looking at the cell voltage thats about the voltage that cell are shipped at which has to be 30% or less to ship
due to the flat discharge curve of Lifepo batteries voltage is not a accurate measurement of charge

 

[meetyg]

Are these DIY batteries? If so, just a wild guess: Maybe you reversed the leads on the BMS? One goes to the battery (Usually marked "B") and the other goes to your load/charger/negative terminal (marked "C" or "P").

 

[OTRwSolar]

Actually yes, charge and discharge currentss are reversed and I'm sure that's part of the problem. Any idea what could have caused that? For to BMSs at the same time?

It may be time to do a current calibration. It should correct your SOC problem . . . plus a more serious problem that you may not be aware of. With the current calibration "reversed", the BMS is no longer providing proper current protection. For instance, when/if you experience a high current discharge fault, the BMS will likely turn-off/open the charge mosfets and leave the discharge mosfets on/closed. The exact reverse or opposite of what it's supposed to do. All your current protection is reversed. It's also possible the BMS is routing charge current through the discharge mosfets (and vice versa). The mosfets don't do well with reverse current, so lots of voltage drop and heat when there's high current.

 

[Browneye]

Perhaps I've misread here, but what are the settings in the bms that tell it what SOC to report based on cell voltage?
They are set as milliamps, up the scale. I found mine got set wrong, not sure how, and battery charge level got kind of whonky.

Do a read on your bms settings and a screen capture off the app and post here, perhaps that will reveal the issue.

Here's what Overkill says they should be:

 

[TomC4306]

Put a charger on them set to 14 volts and let it run recharge each and see if it doesn't autocorrect to 100% once they are fully charged

 

[OTRwSolar]

Are these DIY batteries? If so, just a wild guess: Maybe you reversed the leads on the BMS? One goes to the battery (Usually marked "B") and the other goes to your load/charger/negative terminal (marked "C" or "P").

Ditto on this! Great suggestion! Jahman, verify the B- and C-/P- connections before doing a current calibration.

 

[jahman]

rodrick - I see 3.33 volts per cell and you say it’s 95%

That's an estimate based on voltage vs. SOC tables on the web. These atables are only accurate 100% if they apply specifically to the cell make and model, but in any case what the BMSs are showing is way off.

meetyg - Are these DIY batteries?

No, they were assembled by a professional manufacturer.

OTRwSolar - It may be time to do a current calibration. It should correct your SOC problem

Yes! I am in the process of finding out how to do this.

OTRwSolar - a more serious problem that you may not be aware of. With the current calibration "reversed", the BMS is no longer providing proper current protection.

This is really important! I hadn't thought of this. Thank you so much for pointing this out!

Browneye - Perhaps I've misread here, but what are the settings in the bms that tell it what SOC to report based on cell voltage?

That's a good point, but the BATTs were both purchased assembled with the BMSs pre-configured and working. But I'll take a look just to make sure.

TomC4306 - Put a charger on them set to 14 volts and let it run recharge each and see if it doesn't autocorrect to 100% once they are fully charged

Thanks a bunch for your suggestion! I am headed in that direction and in the process of gathering info on how to do this.

OTRwSolar - verify the B- and C-/P- connections before doing a current calibration.

That's a good point, but the BATTs were both purchased assembled with the BMSs pre-configured and working, so the wiring ought to be good..

Thank you all so much for all the suggestions! I've got enough to go on to solve this conundrum and when I do I'll revert back with the solution.

- jahman