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gls avatar image

Multiplus II Charging Problem

1) My 2 x Multiplus II are behaving strangely. When there is solar yield (2 x MPPT 250/85) the charging is fine. However, when the yield comes off the Multiplus takes over and the battery voltage/current start fluctuating. It seems like there is load that pulls the voltage down below the dynamic current limiter.

2) SOC is not dropping below 90%

I have 48v, 1000ah AGMs

Storage mode off

Grid connected but do not want to feed in excess

Shut down on SOC 45% and low SOC restart 50%

Dynamic cutoff defaults (this is where I think the problem is)

Any help on fluctuating batts and SOC greatly appreciated

Multiplus-IIbattery chargingSOC
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2 Answers
Murray van Graan avatar image
Murray van Graan answered ·

Hi @GLS, I know the SOC shows 100% but I doubt this is the case. What is the absorption voltage of these batteries? The charge voltage in the graph seems low, which means the battery won’t really be fully charged, and as such you won’t have much capacity from them. Ignore the SOC (as this is a desperate issue which you can fix by setting up the battery monitor) and look at the charging voltage, try and get the batteries fully charged and report back

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gls avatar image
gls answered ·

Hi @Murraynated Thank you for your reply. The absorption voltage is set to 54.12V, these are 2v 1,000Ah batteries. I have dropped the 2 lower dynamic current settings and tweaked the BMV settings and that seems to have solved the problem. This is a system that had defective inverter/chargers and has been running only off solar chargers, probably for at least 4 years (we just bought the house), I have ditched the Outback gear and installed Victron. Now that I am able to pull down below 90% and I am not getting the current fluctuations I want to run for a few days to see what the solar is capable of and will then go to charge only or possibly run an equalisation to ensure I am looking at a real 100% SOC. Thanks again.

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Hi @GLS

I'd first test the batteries: do a full charge on grid power, to recommended voltage by battery manufacturer (make sure temperature compensation is working, temp sensor installed). let it charge and equalize (if the latter is recommend by manufacturer).

Then do a full discharge, and watch the BMV for the discharged Ah's until empty and you know the state of your battery. Adjust BMV settings to 'real' capacity.