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ralphd avatar image
ralphd asked

MPPT momentary over voltage alarm

Hi,

My system consists of three LiFePo4 12.8V batteries in parallel, a MultiPlus II, three MPPT chargers, a Cerbo GX with touch screen and a Smart Shunt. The Smart Shunt is configured as the battery monitor. The Mutliplus II has the Bulk & Absorption voltage set to 14.35V and the float is set to 13.75V.

The three MPPTs are set for a Bulk & Absorption voltage of 14.4V and the float is set to 13.8V. The MPPT voltages are set 50 mv higher than the multiplus II to allow the solar charging to take priority.

The Smart Shunt High Voltage Alarm is set for 15.0V per the battery manufacturer (LiTime).

Now for my issue / question -

Each day I get at least one momentary high voltage alarm in the range of 15.1 to 15.2 volts. I say momentary because when I review the data it shows a momentary increase of voltage at the time of the alarm but never above the 15V alarm threshold. I believe that is because it occurs and resolves faster than the data sampling rate. It always seems to occur at the time the sun is rising and the MPPTs begin producing, or when traveling and orientation of the solar panels can cause solar production to stop and start. Luckily it seems fast enough so the BMS does not shut down the batteries.

My question is how can I prevent this without raising the alarm threshold? (which would resolve the alarm but not the overvoltage)

Is there a way to prevent this overshoot from the MPPT(s)?

Could there be an interaction between the three MPPTs that could cause this?

If not, is there a way to add a delay to the Smart Shunt high voltage alarm in either the Shunt or Cerbo?

I hope that the community has a solution for this.

Thank you,

Ralph


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klim8skeptic avatar image
klim8skeptic answered ·

@RalphD Have a look at This thread.


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ralphd avatar image ralphd commented ·
Thank you - seems to make sense. I just set the absorption voltage on the three MPPTs to the float voltage of 13.8V. If it does not spike in the morning then I will try to identify which one (or more) of the three has the imbalance and then try to rebalance them. Thanks again. I am also going to see if the other thread was successful at rebalancing using incremental absorption voltage increases.
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