question

rhea avatar image
rhea asked

How is SOC calculated after adding a battery?

Hi there,


I’m a rank beginner at this and know very little. We are completely off the grid and initially had a 5Kw storage battery system installed in November 2018. - The two batteries that we had installed are BYD Rechargeable Li Type B-plus 2.5Kw.

In March 2023 we ordered and had installed another one of these batteries so the total battery capacity is now 7.5 kw.

It was installed by someone else and not the original installers.

Since then I am pretty sure that the SOC % does not correlate to the actual amount of energy used. For instance, we might use 1.4kw by running the dishwasher but the SOC will fall more than 19% (1400 being about 19% of 7500)


I think this might be because the total capacity of the system needs to be reset to 7.5 Kw but I don’t know how to do this.

Can anyone help please?

Thanks

Rhea


SOC
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3 Answers
kevgermany avatar image
kevgermany answered ·

Probably a smart shunt or battery monitor (BMV) installed.

What tells you the state of charge? Screen, phone app? If it is a screen, what is it called?

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rhea avatar image rhea commented ·

I have both a phone app and also the screen on the ‘colour control’ monitor. They both give the same information. I am certain however that the sum of the discharge hour per hour does not equal the amount the batteries’ charge falls by - if that makes sense.img-4820.jpeg

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rhea avatar image rhea rhea commented ·
Thank you very much for helping me with this problem. I very much appreciate it.
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nickdb avatar image
nickdb answered ·

BYD batteries would be connected together as per their installation doc, and then connected to the GX via their BMU. It would update capacity automatically if it is configured correctly, this would be visible via both their app to the BMU, or in the details section under the BYD entry in the GX, via remote console.

Each battery has a BMS which tracks the individual battery charge. The master will aggregate all the data.

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rhea avatar image rhea commented ·
Thank you for your answer.

If I assume that it was installed correctly and the system knows that it now has 7.5kw capacity (as opposed to 5kw), then as I said in the answer above, it’s pretty clear tome that the sum of the kw discharge does not equal the percentage that the batteries’ charge falls by. What could be the reason for that?


Thank you again

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nickdb avatar image nickdb ♦♦ rhea commented ·

Cell imbalance can cause issues, it is guessing really without screenshots of vrm charts, or seeing the details tab from the GX.

The batteries should report min/max cell.

I would contact the installers if you are struggling to do this yourself, it is outside of victron's control.

The BYD setup guide can also be found here:

https://www.victronenergy.com/live/battery_compatibility:byd_b-box


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Masquelier Pierre avatar image
Masquelier Pierre answered ·

Hello, It is very strange that your input power in the battery is greater than your solar output energy. Obviously, the energy must be equal or less. Another entry must certainly be present and not count in the SOC. Or the apparatus isn't well calibrated. Or the batteries are not realy in parrallel. do you have a shunt? in that case, you should verifying that the additional batterie is not connected before the shunt.

Pierre

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nickdb avatar image nickdb ♦♦ commented ·
Not really. The battery is reporting what it receives and the timing of metrics from different sources doesn't always align exactly all the time. So it isn't unusual to see small difference, especially at lower power outputs where the devices are less accurate.
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Masquelier Pierre avatar image Masquelier Pierre commented ·

15w @ 4 month, give 1.8kWh = 24% of SOC error for the 7.5kWh batterie. if there has been no good resyncrhonization of the SOC since.

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