question

wysiwyg avatar image
wysiwyg asked

Suspecting SOC is not accuarte

Hi Everyone,

Needing some assistance please.

Running SmartShunt 500A, GX Cerbo and MPPT150/60

Last week has been cloudy and the batteries have receded to a much lower voltage, and yet SOC was still showing values above 97%, see images attached.

Now that the weather has cleared up, the voltages are creeping up again to normal.

It got as low as 48.45V, surely the SOC should have been representative of that voltage?

Am I missing something here or is this thing lying to me?

screen-shot-2022-01-27-at-100431.jpg

smartshuntSOC
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1 Answer
JohnC avatar image
JohnC answered ·

Hi @wysiwyg

I remember you, the guy with 1650Ah (1.3 tonne) of batts. So what you're seeing isn't unusual with such light loads. The SShunt doesn't consider V to calculate SOC. If you wanted it to do that then you could have bought some Chinee junk. And looking closely at the curves, your V is still good when crossing zero current.

Maybe my loads aren't too far off yours broadly, so you can compare with my 225Ah batts (that's 7.3 times smaller than yours)..

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(I had a bad day yesterday, ~70% my record low SOC)

So if you divide my drawndown SOC by 7, then your figures look reasonable. But it doesn't mean they're perfect. With such low loads the Peukert Exponent may underestimate SOC drawdown if you're using the default value. If you want to pursue this, get your batt C20 and C100 ratings and run them through Victron's Peukert Calculator. Post back here with your settings too, and we'll see if we can help.


1643252211924.png (40.0 KiB)
1643252314418.png (57.9 KiB)
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Yes thats me, however this is another installation with only 875AH @ 48V.

Thanks for the info, I would rather it overestimate than under, will play around with the Calculator.
Might also manually set SOC next time the batteries are at around 48V, set the SOC to 60% SOC and work on it from the other end of the scale.

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