vonny232 avatar image
vonny232 asked

SmartSolar MPPT Load Output vs Absorbtion/Float voltages


I have a SmartSolar MPPT 100/20 with 400w of panels and a 24v flooded lead battery bank.

I have the Bulk -> Absorption threshold set to 28.8v and Absorption -> Float threshold set to 27.6v as per general recommendation.

Separately to this, I have the Load Output "ON" threshold set to 28v and the "OFF" Threshold set to 24.7v.

However, the load output triggers prematurely when Bulk voltage > 28v, even though the battery has not completed its charge cycle at that stage.

Conversely, I have seen recently a few occurrences of the opposite. Namely, the battery is already fully charged, so the charge controller enters float state. Whilst in float state, the battery level does not rise to 28v and therefore the load output is not triggered.

This essentially means I am losing energy as the MPPT controller is only harvesting a minimal amount of energy to trickle charge the battery, but the load output is incapable of triggering due to the trickle voltage.

Surely other people have experienced this problem? Does anyone have any advice here please?

MPPT Controllersbattery charging
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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

Why do you have the load output set so high?

The intention of the voltage settings of the load output is to prevent over discharge of the battery, rather than to turn on once the battery is fully charged.

This would normally mean that the load output turns of below ~24V and back on with a small margin.

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vonny232 avatar image vonny232 commented ·

Hi Mike,

I basically took "Conventional algorithm 2" (23.6v/28v) and modified it with a higher "Off" threshold as 23.6v would correspond to a DOD < 50% (and I want a 30% DOD as the battery is used as a glorified capacitor to allow me to power a water heater in bursts).

Also, if the "ON" threshold is too low, then surely it runs the risk that the battery would never charge to 100% capacity (and as per Victrons manual, the battery could be destroyed in a matter of months)??

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