question

rolandchart avatar image
rolandchart asked

AGM super Cycles Cerbo Percentage not reflecting the voltage

I’ve a bank of 4 170amp super cycle AGM batteries. They are great batteries and I’ve been careful not to discharge them too deeply over the couple of years I’ve had them


One thing that’s never seemed to work properly is the percentage on the cerbo in terms of it matching the voltage. It’s way out as the screenshot shows.


I’ve searched the forums and can’t seem to find a solution that works. Any suggestions welcome

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cerbo gxSmartShuntSOCAGM Battery
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Alexandra avatar image
Alexandra answered ·

@rolandchart

When are talking years and AGM you will need to be compensating for capacity loss.

You are right 12v is not 74% especially with a 69W load. What are the AH drawn?

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rolandchart avatar image rolandchart commented ·

272Ah discharged. I’m sure it’s never reflected properly.

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pwfarnell avatar image pwfarnell rolandchart commented ·
Is most of your discharge at low rates because if it is the Peukert calculation will be showing that the SOC is falling slower than the consumption of Ah due to the higher capacity at lower discharge rates. I calculated that for my Victron AGM telecom batteries that the Peukert coefficient is about 1.13 so you get less of a capacity boost in the SOC calculation with low discharge rates.
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rolandchart avatar image rolandchart pwfarnell commented ·
I’d say yes. We have a 12v fridge that is always in. Then lights at night, charging etc with sporadic use of the inverter for high loads.
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pwfarnell avatar image pwfarnell rolandchart commented ·
Try reducing your Peukert coefficient to 1.13 rather than the default 1.25. Your use is similar to mine and I found an improvement.
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Alexandra avatar image Alexandra ♦ pwfarnell commented ·

272ah from 680ah is closer to 60% on a new bank.

But you will definitely have less than 680AH now. 12v is almost 100% dod with almost no load that is close to it's resting votage.

So as a rough estimation that is close to your current usable bank capacity.

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rolandchart avatar image rolandchart pwfarnell commented ·
I will give this a go. I have fully charged at base and plan to see the AH drawn down to 12v, from that I will tweak the Peukert. Will report back soon.
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