Overkill BMS and xiaoxiang software funny readings

[kdiver58]

Overkill BMS and xiaoxiang software are giving funny readings sometimes. I charge my 24 volt 100ah battery using my growatt solar inverter. After it's all charged, and in about 4 hours (edit: with the inverter off and no usage) , I look at the app and it's showing 65% capacity. Seemed odd so I fired everything back up and plugged the inverter in to charge the battery. Within 30 minutes it's balancing and drawing only an amp or so. Everything looks good I shut off the inverter , switch the battery cutoff to the inverter off, check capacity all good, switch off the bms. I fire everything back up and it's showing 62-68% capacity. It's obvious that the battery was not at 65% the first time as it charged back to 100% so quickly. When I plug it in to charge I have it limited to 18amps. I've done a capacity test and everything is fine. Why am I getting the odd readings now and then? Just curious . Thanks. K

 

[Horsefly]

It's late, so maybe I'm just confused by what you have described. Your app showed the battery at 65% capacity. You charged for a while, and somehow it showed 62-68% capacity. They you say that some something is wrong because it was at 100%. When was it at 100%? You say you "switch the battery cutoff to the inverter off". What exactly are you doing, and why? And you say you "switch off the bms". Not sure why you would turn off the BMS, and I'm not sure how you mean when you say you turned it off.

Have you actually fully charged and mostly discharged your battery? The Overkill / JBD BMS uses the 80/60/40/20% voltage settings to approximate your SoC, but once you get it fully charged it seems to mostly use the Coulomb counter (amps out and in) to tell you how full your battery is. I don't understand what you are seeing, but if it isn't right it sounds like your BMS doesn't think your battery ever got full. That means your settings are wrong.

But, since I don't understand what you have described, I probably shouldn't speculate on what is wrong.

 

[kdiver58]

Both times it was 100% charged. The growatt stopped charging and finished absorption. The BMS finished balancing the cells and was showing no amp flow nor did my clamp on meter. The app shows 100% when all is finished it just changes it's mind after a few hours .. LOL
*** I switch off the BMS to stop any bleed down when I'm not using the pack. It was in the manual for the BMS and I saw no reason to not shut it off.
"An optional external switch can be wired to the BMS via the included 2-pin pigtail (JST-XH, red/black wires).
If the configuration option is enabled within the BMS, discharging will be disabled when the switch contact is
open"
I've used the battery down to 20% capacity and it all works fine. I'm just wondering why the app gives odd readings now and then.
I need to be more detailed in my descriptions.
BTW I added that the Inverter/battery was not used after charging when I went back and looked at it to my original post. I should have had that in there.

 

[Pierre]

Just leave it all connected. You are confusing the hell out of your BMS connecting / disconnecting it. Every time it is turned back on it has to re-calibrate itself. Only the inverter will have a standing current when not supplying a load.
The BMS cannot report SOC by voltage alone. It has to measure current over time as well.

 

[740GLE]

What are your charging settings for the Growwatt?

I believe the BMS uses voltage for SOC so once voltage bleeds off it maybe seeing the lower voltage as SOC.

This is why so many people use a dedicated shut to determine SOC.

 

[kdiver58]

What are your charging settings for the Growwatt?

I believe the BMS uses voltage for SOC so once voltage bleeds off it maybe seeing the lower voltage as SOC.

This is why so many people use a dedicated shut to determine SOC.

It looks like a dedicated shunt is in my future . The primary reason for my original post was to to find if there was a setting or a refresh button in the Xiaoxiang software to fix the glitch. The more I dig into it the feel I just need to ignore the SOC in the Xiaoxiang software. I have the growatt set for 18amps charging max ( I want to be able to plug it in anywhere) and a 90 minute absorption time. Thank you all.

​

 

[Horsefly]

It looks like a dedicated shunt is in my future . The primary reason for my original post was to to find if there was a setting or a refresh button in the Xiaoxiang software to fix the glitch. The more I dig into it the feel I just need to ignore the SOC in the Xiaoxiang software. I have the growatt set for 18amps charging max ( I want to be able to plug it in anywhere) and a 90 minute absorption time. Thank you all.

I have both a Victron Smart Shunt and the Overkill / JBD 8S 100A BMS on one of my batteries. I've generally seen they track pretty close to each other on SoC. I think blaming the BMS or its app is just searching for a scapegoat. I don't have a model of the BMS that can be "turned off" but as @pierre pointed out there is a good chance that turning it off makes it lose whatever it knew about your current SoC.

 

[740GLE]

Is he turning the Growatt inverter off or is he also disconnecting the BMS sense leads, powering off the BMS?

To me it reads he just turns the Growatt off and BMS remains on (as he should). If this is the case that shouldn’t do anything to the software SOC charge.

I have compared various JBD softwares on iOS and android and it does appear each software judges SOC differently when initially pairing up. Same BMS same battery, same SOC.

 

[Horsefly]

Is he turning the Growatt inverter off or is he also disconnecting the BMS sense leads, powering off the BMS?

To me it reads he just turns the Growatt off and BMS remains on (as he should). If this is the case that shouldn’t do anything to the software SOC charge.

I have compared various JBD softwares on iOS and android and it does appear each software judges SOC differently when initially pairing up. Same BMS same battery, same SOC.

I'm just taking his word for it.

switch off the bms

*** I switch off the BMS to stop any bleed down when I'm not using the pack. It was in the manual for the BMS and I saw no reason to not shut it off.
"An optional external switch can be wired to the BMS via the included 2-pin pigtail (JST-XH, red/black wires).
If the configuration option is enabled within the BMS, discharging will be disabled when the switch contact is
open"

So, to me, it sounds like he is actually shutting down the BMS, not just the inverter.

 

[HRTKD]

Make a screenshot of the BMS parameter settings and post that here. It will require more than one screenshot.

 

[740GLE]

I'm just taking his word for it.


So, to me, it sounds like he is actually shutting down the BMS, not just the inverter.

Ahhh I see that now, I’m more curious at how he has a switch wired to his BMS.

If he’s using the external contact switch which “switches off” the BMS, I thought that just turned off the ability of the BMS to charge and discharge (similar to toggling it in the app) but the BMS balance leads are still connected.

Some pictures of the BMS and how it’s “switched off” would be handy.

 

[Horsefly]

Ahhh I see that now, I’m more curious at how he has a switch wired to his BMS.

If he’s using the external contact switch which “switches off” the BMS, I thought that just turned off the ability of the BMS to charge and discharge (similar to toggling it in the app) but the BMS balance leads are still connected.

Some pictures of the BMS and how it’s “switched off” would be handy.

Yeah, I think you are right. Although I have several JBD (one Overkill), I've never used the switch connection. Now that I think about it, it only disables the charge and discharge, and doesn't really "turn off" the BMS. My bad.

 

[740GLE]

Either way I think the BMS SoC is a guess at best and I’d never take it for gospel.

Shunts are cool everyone should have one ?

 

[kdiver58]

Either way I think the BMS SoC is a guess at best and I’d never take it for gospel.

Shunts are cool everyone should have one ?

Thank you for the input .. Yep SOC on the software is just a best guess. I did a little more digging and found other people were getting odd readings too. I ran my camper off of it for 12 hours and it works fine. I'm just going to ignore it.

 

[Vi s]

Thank you for the input .. Yep SOC on the software is just a best guess. I did a little more digging and found other people were getting odd readings too. I ran my camper off of it for 12 hours and it works fine. I'm just going to ignore it.H

Solved the "funny" readings issue now.
Read in detail here.

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...

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