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ralphd avatar image
ralphd asked

AGM voltage drop under load with high SOC - Multiplus 2

I have a Multiplus 2 with a smart shunt and five 100AH AGM batteries connected in parallel. I also have solar panels with two MPPTs that charge the batteries when not on shore power.

The problem - the batteries can be at a full state of charge with a voltage of 12.8V. If I run a heavy load like the microwave, the voltage will drop instantaneously to ~12.1 volts which will cause a low voltage alarm to trigger. When the heavy load is removed the voltage returns to 12.8 volts.

I measured the voltage at the batteries and confirmed that there is less than 0.1V drop between the batteries and Multiplus 2.

Is there some way to dynamically set the low voltage cut off based on the battery state of charge to prevent this from happening?

I don’t want to just lower the threshold since under a light load and low SOC the batteries would be over discharged.

I appreciate and help that you can provide.

Thank you,

Ralph



Multiplus-IIAGM Batterylow battery warningshutdownvoltage drop
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4 Answers
mvas avatar image
mvas answered ·

I think, the MultiPlus has a "Disconnect battery based on Low SOC" setting.

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kevgermany avatar image
kevgermany answered ·

It's annoying, but normal behaviour from the AGMs. It might be an indication that the batteries are getting tired.

Had the same problem.

The low voltage alarm in the Multiplus is set using an MK3 to USB adapter and VE.config software. I couldn't find another way.


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pwfarnell avatar image pwfarnell commented ·

If the Multiplus is connected to a GX device then you can change the settings via VRM if you have VE Configure 3 on a PC / laptop. You can download the Multiplus settings, edit them in VE Configure 3 and then upload the new settings. The Cerbo GX may need to have certain specific settings enabled such as 2-way communication. I have successfully used this method through a Cerbo GX. You do not need the Mk3 to USB cable this way.

https://www.victronenergy.com/live/vrm_portal:remote-veconfigure

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marc-heide avatar image
marc-heide answered ·

1686123344213.png

Maybe this helps?

When the voltage drops too much the battery's are probably damaged.

1c would be 100A for a 100ah battery.

0.5 would be 50A for 100ah battery.





These are third party charistics.


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ralphd avatar image
ralphd answered ·

Thanks for your input. My thoughts are this - the AGM batteries are only a year old and I have load tested each one individually with good results. I believe that the internal series resistance of the AGM batteries are causing the low terminal voltage when under a heavy load. When under a heavy load, knowing that the batteries are close to 100% state of charge, it would be nice to have a dynamic alarm and voltage threshold which would not trigger. For example, if the SOC >75% under a heavy load the Multiplus 2, or cerbo gx, would use a lower alarm and shut down threshold. Is anyone aware of a workaround using either the Cerbo gx or Multiplus 2?

Thank you,

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derrick thomas avatar image derrick thomas commented ·
You could cook something up to make it behave just about any way you want using node red
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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

Multiplus-II GX Online Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes

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