diy solar

diy solar

ANT BMS shows clearly wrong state of charge

Tunnerus

New Member
Joined
Apr 7, 2020
Messages
22
Location
Finland
I have a couple of 24V LiFePo4 batteries in parallel each with its own BMS.

One battery is AliExpress sourced 135Ah with Overkill’s BMS, works flawlessly.

The other is a 100Ah Winston battery from GWL and controlled by an ANT BMS, using the iPhone app “ANT BMS” from mayibms.com. I have “SOC problems” with this second battery - it shows 14% at 26,5V while the Overkill BMS shows 98% at 26,61V. I just don’t understand how to reconcile these two readings when the batteries are in parallel.

I have emailed mayibms 1-2 weeks ago, no response yet.
 

Attachments

  • B61F099E-EE68-49F9-84F1-FFB1ADCFC217.png
    B61F099E-EE68-49F9-84F1-FFB1ADCFC217.png
    509.2 KB · Views: 32
  • 65614C7D-D526-4304-9BEE-25832DBD4450.png
    65614C7D-D526-4304-9BEE-25832DBD4450.png
    387 KB · Views: 32
  • ABF2C08A-719B-434E-84DE-538AF282EE2B.png
    ABF2C08A-719B-434E-84DE-538AF282EE2B.png
    940.4 KB · Views: 33
I wonder if there is a thread discussing this already in the forums. Seems like a situation many people might be wondering about. Have searched a little but not found anything exactly pointing to this yet.

Have seen comments that a shunt based %-meter would be the best option but nothing closer than that
 
I have matched ANT BMS 2021 450 amp. Not only do they not track SOC correctly even after setting them to 300ah once fully charge the total amp hour reading is off about 60%. I have better readings once I drain a back to have all cells at 2.8v and set the amp hour capacity to zero but, it doesn't stay very well. I have CATL 310AH 3.2V BATTERIES of 16 in each box with its own BMS but, test them separately. They show 140ah on the BMS for discharged down to 2.8v a cell but, running 300 watt an hour gives me exactly 50 hours. Yes, resetting the ah once fully charged to 300Ah fixed the guage for a little while but something is way off. I have the SOC method set at 3n, changing that?
 
I also have two 24v lifepo batteries in parallel , one with an ant bms, the other one has an overkill bms. I have observed the same problem between the two bms SOC being different, resets does help for a while then they drift apart from each other. What I did was buy a victron smart shunt , connected to the main cable coming off the paralleled batteries and only pay attention to its SOC. This gives me one true reading of what is going into the batteries and what is coming out of the batteries.
 
I also have two 24v lifepo batteries in parallel , one with an ant bms, the other one has an overkill bms. I have observed the same problem between the two bms SOC being different, resets does help for a while then they drift apart from each other. What I did was buy a victron smart shunt , connected to the main cable coming off the paralleled batteries and only pay attention to its SOC. This gives me one true reading of what is going into the batteries and what is coming out of the batteries.
Thanks, I am thinking (something like) this is what I want to do. Is the Victron smart shunt able to be read over Wifi by any chance? I would like to be able to remotely view SOC. My hybrid inverter sort of does that but only based on the voltage
 
The Victron shunt can be read thru Bluetooth, you can read it thru wifi but you need other Victron componence to do that. Check out Victron web site to fully understand how to read it over wifi.
 
Have anyone figure out how to fix the soc Reading?
My take is that the ant bms is, well, weak in the sense that the soc will not work properly no matter what.

Next season, maybe starting in April-ish, I will research and try some shunt. Hopefully there will be a nice cost efficient natively Wi-Fi enabled shunt but then ???
 
What about the setting of ANT, there is calculation? Could it make a difference?
 
ANT BMS uses various SOC estimation methods, it depends on what you set in settings as "SOC method"
The methods are:
- Voltage based -estimated by the given table -> You set % for given cell voltage
- Coulomb based - From zero -> When you full discharge, it puts capacity as 0% and then calculates by the Charged AH up to the maximum Ah for the given battery (Fox example if you charged 20Ah and battery is 50Ah, it shows 40%)
- Last method is as above, but it calculates from 100% charge and subtracts the consumed AH capacity

So the methods 2 and 3 are most accurate, but you must know the precise capacity of the battery and set the counter to 0%, when it is fully discharged.
 
I don’t know what happened over the winter but this season the problem has solved itself - both BMSs show the same. Maybe they reset themselves when the batteries were really empty at some point
 
So (re)setting the Ah in the “settings” is the way to reset the SOC? I will have a chance to try this next time in April.
Actually, I think I did try this at some point. Anyway, they have stayed well in sync for a few weeks now.
 
Discharged my 16S 280aH to 20% by itself, recharged to 100%. The lcd display works for a day or two, then says "connect bms". Otherwise, it is my most accurate, along with my AiLi shunt/meter on my 10 batteries.
 
Back
Top