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kiersten-cornwell asked

Slow solar charge and then very rapid

Any ideas or suggestions please? We don't seem to have a local Victron engineer, and I'm struggling to get support from our local distributor...we have a multiplus, solar charge controller, but no dongle.

We installed new 125Ah leisure batteries last week (not tested prior to installation by local electrician), and they don't appear to be coming up to full charge very well. They are coming up to full charge at the usual rate when charging with the generator, but not when charging from the solar panels. They are not dropping charge excessively overnight. This morning, the charge level continued dropping long after sunrise, until at least late morning, even with very little draw on the batteries.

Voltage from the PV to the batteries measured at approx 30V (Battery voltage was 12.9V). Unable to check voltage at battery terminals atm.

We were at -63.4Ah at 2:43pm this afternoon. All 12/240V appliances etc turned off for 30 minutes, and then we are at -59.99Ah at 3:15pm. Less than 60 minutes later, the batteries were fully charged!

Any ideas what could be occurring please?

MPPT Controllers
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
What device do you have to measure the used Ah?
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kiersten-cornwell avatar image kiersten-cornwell Matthias Lange - DE ♦ commented ·
We have a victron battery monitor.
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Ok then you have to check and adjust the "charge detection settings".

https://www.youtube.com/watch?v=4ReljfO3k6M
https://www.youtube.com/watch?v=mEN15Z_S4kE

I guess you have to adjust the "Charged voltage", "Tail current" and maybe "Charged detection time".
The SOC will jump to 100% if the voltage is above the "Charged voltage" and the charging current is below the "Tail current" for the "Charged detection time".
It can be tricky sometimes to find the correct settings for your system.

With a small PV array your battery voltage slowly rises above the "Charged voltage" and because of the small array the charging current is below the "Tail current" and the SOC jumps to 100% to soon.

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kiersten-cornwell avatar image kiersten-cornwell commented ·

Thanks Matthias, am I right in thinking then, that if the solar charge controller is switched off, it will revert to factory settings or similar? I have ordered the bluetooth dongle, so fingers crossed that should do the trick!

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ kiersten-cornwell commented ·
Switching off the MPPT changes nothing because it has nothing to do with it.

The "problem" are the settings of the BMV and that settings you can change directly at the BMV. Read the manual.

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kiersten-cornwell answered ·
OK... I have checked the BMV settings... can someone please clarify how we calculate battery capacity for the BMV? We have installed 8 x 125Ah sealed lead acid batteries (we previously had 8 x 110Ah non-sealed lead acid batteries). When programming battery capacity, do I put in 125Ah, or 1000Ah? (currently programmed at 125Ah).

I have made some small adjustments to the charged voltage, tail current and charged detection time, but the issue I am having is that on cloudy days, it seems the batteries are barely charging at all. I can see that a small current is coming in via the PV (4 x 280W mono)/Victron Solar Charge Controller (MPPT 150/70)... currently 182W/31V/5.7A (grey day). Does that seem right?


On bright days the batteries seem to come up to full charge quickly... by about 11am.

Overnight they seem to hold their charge reasonably well, although we were down to about 47% charge this morning.

However, our monthly usage is estimated to be only about 600kWh per month.... and we are having to charge the batteries every day, which doesn't seem to add up.

I don't have bluetooth for the BMV, but I do for the solar charge controller.
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JohnC avatar image JohnC ♦ commented ·
@Kiersten Cornwell

If you have 8x 12V batts wired in parallel, then you have 1000Ah. You won't see 47% SOC once you change that..

Grey days can be really disappointing for solar output, like below 10% of nameplate rating is common.

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