Hi All,

Can anyone perhaps shed some light on how an inverter (Axpert King in this case) determines what the battery capacity is in percentage?

In my settings I have a "User Defined" battery and often find that during loadshedding the inverter starts falsely complaining about "low battery". According to the inverter the battery capacity is showing as 35%, while the actual SOC of the battery is 85% and the battery voltage is around 49 volts.

Any idea how this works?

Chris

 

Edited June 26, 20224 yr by ccronje

One of the reasons why you get the inverter complaining might be the moment you add more load. It measures at that instant.

Were the 35% and 85% readings taken at the same time?

Perhaps indicate what battery you are using as 85% SOC at 49V seems a bit high. Also mention what method is used that provides this figure.

There might be a possibility that the 35 is too low and the 85 too high?

47 minutes ago, Scorp007 said:

One of the reasons why you get the inverter complaining might be the moment you add more load. It measures at that instant.

Were the 35% and 85% readings taken at the same time?

Perhaps indicate what battery you are using as 85% SOC at 49V seems a bit high. Also mention what method is used that provides this figure.

There might be a possibility that the 35 is too low and the 85 too high?

Thank you for responding. I have an Averge battery, which shows the SOC on it's display panel. Will post some more information next time we have loadshedding.

 

9 hours ago, ccronje said:

Thank you for responding. I have an Averge battery, which shows the SOC on it's display panel. Will post some more information next time we have loadshedding.

 

Thanks. The 1st time I see what the Averge lithium looks like. It seems this is a 15 cell battery that's why it shows 85% at 49V

Edited June 27, 20224 yr by Scorp007

15 minutes ago, Scorp007 said:

Thanks. The 1st time I see what the Averge lithium looks like. It seems this is a 15 cell battery that's why it shows 85% at 49V

Thanks, it's a great battery. I reported someone selling stolen Averge batteries to them and they offered to sell one to me directly.

17 hours ago, ccronje said:

Can anyone perhaps shed some light on how an inverter (Axpert King in this case) determines what the battery capacity is in percentage?

In my settings I have a "User Defined" battery

In that case, you'll be getting the voltage based guesstimate that only works even half decently for lead-acid.

It's something like (battery voltage - cutoff setting voltage) x 10% + 2%.

Example: cutoff voltage setting (assumed to be 2% SOC) = 46.0 V, battery reads 50.0 V (typical for a 15S LFP battery at most states of charge, light load, no charging).

(50.0 - 46.0) x 10% + 2% = 40% + 2% = 42%.

If you use the default 42.0 V for the cutoff voltage, it will be 8 x 10 + 2 = 82%.

With the flat voltage versus SoC curve of LFP chemistry, this guesstimate is almost completely worthless. It can tell the difference between full, empty, and somewhere-in-between, that's about it.

38 minutes ago, Coulomb said:

In that case, you'll be getting the voltage based guesstimate that only works even half decently for lead-acid.

It's something like (battery voltage - cutoff setting voltage) x 10% + 2%.

Example: cutoff voltage setting (assumed to be 2% SOC) = 46.0 V, battery reads 50.0 V (typical for a 15S LFP battery at most states of charge, light load, no charging).

(50.0 - 46.0) x 10% + 2% = 40% + 2% = 42%.

If you use the default 42.0 V for the cutoff voltage, it will be 8 x 10 + 2 = 82%.

With the flat voltage versus SoC curve of LFP chemistry, this guesstimate is almost completely worthless. It can tell the difference between full, empty, and somewhere-in-between, that's about it.

Thank you very much, that is interesting.

Edited June 27, 20224 yr by ccronje

Hi all.

I have a bit of a somewhat similar problem. My battery 4.8kWh LiFePo4 is reading SOC 100%, FCC 56Ah and Rm 56Ah. The problem is that its at the middle of 3 similar batteries connected in parallel and the top and bottom ones are reading SOC 100% FCC 100Ah and Rm 100Ah when full. In the morning when I check the middle battery will be at SOC 2.6% FCC 56Ah Rm 8Ah but the other two will be at SOC 35% FCC 100Ah and Rm 36Ah.  

Does this mean the middle battery is dead or can I reset the battery to read the correct readings when fully charged. 

When I these batteries I was told they have 5 year warranty and I bought them in March 2020 but started using them in July 2020.

Thanking you advice

On 2022/06/27 at 9:09 AM, Scorp007 said:

Thanks. The 1st time I see what the Averge lithium looks like. It seems this is a 15 cell battery that's why it shows 85% at 49V

Why does the battery placard say 100ah yet the FCC is reading 105.1ah in the first picture??

Edited May 9, 20251 yr by Cyclic

1 hour ago, Cyclic said:

Why does the battery placard say 100ah yet the FCC is reading 105.1ah in the first picture??

My guess is the spec 100Ah is the expected value. Tolerances can have it below or above the 100Ah.