question

pyrorider avatar image
pyrorider asked

SmartShunt: Ah and kWh calculated or measured?

Hi, I have a smartshunt as battery monitor for my chinese crap-battery, now I wondered that if I set the battery capacity to 80Ah, I receive different stats than when I set it to 70Ah which makes me wonder if the smartshunt doesnt even measure the Ah consumed/charged but instead just calculates them from whatever. (The smartshunt basically can not tell me the capacity of the battery as the graph for consumed ah readjusts to whatever I enter as setting in the first place.). Same for the kwh, there is no option to see the kwh the battery can really store (charge/discharge) and the calculated values seem a bit off too.

So which values are measure and which are calculated/estimated/drawn from a lottery?

SmartShunt
2 |3000

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1 Answer
Alexandra avatar image
Alexandra answered ·

@PyroRider

It is sort of a bit of both.

It measures amps through the shunt then calculates the rest between peukerts and the capacity you put in and battery voltage (So you are altering the variables on the calculation with the parameters you input).

Since battery consumption is never constant and amp draw can also affect capacity of the battery - c rating. It affects some battery chemistries (coupled with age) worse than others. Is a bit of an art to get right.

Some battery banks voltage collapse under load making the whole thing even more interesting. {Although i supppsed not really since watts is v x a which under battery bank voltage collapse will be more of the A... But watts stay the same.}

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Alexandra avatar image Alexandra ♦ commented ·

Cut and dried kWh is battery capacity x systen voltage.

This capacity is affected by the c rating draw- higher amps = less capacity. Opposite being true.

You can disable peukerts - put a constant draw on the battery and work from there for capacity. That is about the only way to know. Between the two voltages you choose to work between. (And even that 0.2v can be alter of capacity depending on the battery).

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kevgermany avatar image kevgermany ♦♦ Alexandra ♦ commented ·

@PyroRider also check charge efficiency, should be higher than the default if the batteries are lithium chemistry.

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