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docloboto asked

500A Smart Shunt - SoC wrongly calculated

Hey community,

as I'm now in the 4th or 5th month of using the Smart Shunt in my van, I’m still puzzled, how the SoC is calculated.

I only have a 92Ah AGM battery and according to this I set the maximum discharge level (I don’t know the right term) to 50% which means roughly 46Ah of energy can be taken (yeah, depends on current and so on, I know). But how could it be, that the SoC then still shows around 95%, when I took already 7Ah (which would be around 15%). Is it, b/c the current was that low (just around 50-70 mA) but for a couple of days? It seams odd to me and I thought, the Peukert exponent kicks in with high currents.

Secondly, how long does it take the Smart Shunt to calculate the maximum remaining period? I plugged in my freezer and while the current and voltage was fairly stable, even after 7 Min. of dropping and dropping (startet at 23h remaining) it wasn’t finished. Now after over 15 Min. it became stable and counting downwards relatively accurate. Is it that complex to calculate the remaining time until SoC is 0%?

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SmartShunt
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2 Answers
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pwfarnell answered ·

The SOC is based on the total Ah capacity of the battery. For the numbers you gave 7Ah out of 92Ah is 7.6% used, but as it was at a low draw rate Peukert calc reduces this to 5% so SOC is 95%. A full battery is 100%, a totally discharged battery is 0%.

The discharge floor at 50% is only used in the calculation of the time to go. It is not used in the SOC because what would happen if you discharged the battery below this, the calc would show negative SOC.

All this is explained in the manual along with the time to go.

https://www.victronenergy.com/media/pg/SmartShunt/en/operation.html

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docloboto avatar image
docloboto answered ·

Sorry, those details are not written in the german manual. There is pointed out, that the discharge floor is relevant for the remaining period but NOT, that the SoC doesn’t reflect the discharge floor.

We can discuss, what is more practicable, in my opinion, when the SoC tells me, it is 50% but the battery hits low voltage and the load steps out would be kind of confusing. Nobody awaits to have negative SoC but it can keep at 0% when it hits discharge floor. My opinion. :)

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kai-fuchs avatar image kai-fuchs commented ·

Had the same miss understanding of my SOC, but I quickly realized that the Discharge floor would not affect the SOC calculation. But you are right I think it's confusing.

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