question

Fra avatar image
Fra asked

Is charging efficiency much higher at very low charge currents?

Is it possible that the charging efficiency is much higher with low charging currents than at high charging currents?
My smartshuunt has set a charging efficiency of 95%.
But when in abs phase, and the tail current is> 2% (index of about 99% soc), my smartshunt always indicates a 95/97% soc.
It means that it slightly underestimates the soc and that the actual charging efficiency is higher.
I always charge with a current of around 2 to 8 amps.
And my average dod is 15/20%.

Is it possible that the charging efficiency in these conditions is very high?

I add that the smartshuunt already loses about 10% of efficiency as it is designed.
In fact it counts the AH in discharging and recharging but not the WH.
This means that the AH in discharge are at 12.x v.
While the AH in charging are at 13.x-14.x volts.
This already means a 10% intrinsic inefficiency, in the way of counting the smartshuunt, regardless of the settings we make.
battery chargingSmartShunt
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klim8skeptic avatar image klim8skeptic ♦ commented ·
Specify the C rates you are talking about.
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Fra avatar image Fra klim8skeptic ♦ commented ·
C rates are for discharge.

Anyway, I discharge on average at 0.05C.

And recharge on average is at 0.05C/0.1C.

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1 Answer
snoobler avatar image
snoobler answered ·

Your smartshunt isn't configured properly. It should be set to ensure it is triggered when the fully charged criteria of the charger is met.


Charging efficiency in the absorption phase is notoriously inefficient, regardless of charge level.


Don't confuse power/energy efficiency (Watts/Wh) with current efficiency (amps/Ah). The smartshunt is concerned with current efficiency.

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Fra avatar image Fra commented ·
Ok. These means that my agm have a real charge efficiency of 95 %? Is very high. Especially considering that I recharge ever only from 80 to 100%.

The part of recharge with the worst efficiency.... Like you said.


Maybe the high efficiency is because the low charge currents??

In fact absorption generally cover de last 20% of recharge.


But in my case, with low charge currents, abs cover only the last 10% or the last 7% of recharge.

The first bulk phase cover from 80 to 90/93%.


Almost always, wehn the battery reach abs voltage is just 90/93%, due to the low charge current.

Maybe these increases the efficiency of recharging process.

If i recharge with 20A probably the abs voltage would be reached at 80%,and the charging efficiency would be less efficient.


Waht do you think?

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