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ruben40870 avatar image
ruben40870 asked

Batteries voltage falling rapidly?

Hi,

I have the following configuration:

  1. Victron Energy Multiplus 12/800/35-16
  2. Two Omnipower OPR120-12, 12V 120Ah Deep Cycle AGM/Gel Hybrid VRLA Batteries (connected in parallel)

I use the system for my desktop and TV set during power outages, they are quite common where I live. I have specced the system to last at least 2 hours as that's usually how long our power outages last. The average power draw for my desktop and Tv set fluctuates from 260W to about 310W. I use the Victron MK3-USB interface on my laptop to monitor the system.

The problem that I have been having is the voltage dips very quickly under this power draw, it typically starts at around 13.5V-13.7V (Float Voltage) and within 20min falls to 11.5V. I have my shut-off setting set for 11.5V but I know the minimum voltage for these batteries is 10.5V. At 11.5V the State of Charge according to the Victron App is still 97%.

The only thing I can think is wrong is one of my settings have to be wrong? I have added screenshots below of all my settings. Any advice will be greatly appreciated.

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Thanks again!

MultiPlus Quattro Inverter ChargerAGM Batteryvictron community
1636011255545.png (116.0 KiB)
1636011286051.png (116.2 KiB)
1636011308409.png (158.7 KiB)
1636011328541.png (142.6 KiB)
1636011350736.png (129.8 KiB)
1636011404418.png (131.3 KiB)
1636011430437.png (136.3 KiB)
2 comments
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nickdb avatar image nickdb ♦♦ commented ·
Just to add. Max charge current is 25A according to the specs with 10A recommended, yours is set too high at 35A. Your voltages seem fine.
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ruben40870 avatar image ruben40870 nickdb ♦♦ commented ·
I set the charging current to 35A since I have two batteries in parallel, so the current splits to 17.5A each. I know it's higher than the recommended but at that rate, it can take too long to recharge the batteries before the next blackout.
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2 Answers
kevgermany avatar image
kevgermany answered ·

How many cycles do the batteries have on them? And how deep do you normally doscharge?

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ruben40870 avatar image ruben40870 commented ·
The batteries are around 18 months old but I doubt more than 150 cycles. I only use them occasionally, and I kept the max discharge not below 50%. I only hit 50% a few times, about 20 times.
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nickdb avatar image nickdb ♦♦ ruben40870 commented ·

Without a shunt don’t assume the soc is accurate.

Also, imho, 50% is low to draw lead acid down to with any regulatory.

From the numbers quoted it doesn’t surprise me that they lasted 18 months.

I have seen less.

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ruben40870 avatar image ruben40870 nickdb ♦♦ commented ·
For most of their lives, I kept the voltage cut off at 11.5V. Looking at the datasheet of the batteries I'm not so sure anymore if that even is 50%.
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nickdb avatar image
nickdb answered ·

The most common reason will be that the batteries are on their way out.

If you want the longest life out of them, you normally don't want to draw them down below 70%.

I have a number of inverters with a similar setup where the batteries lasted 1 year. And that was around 150 cycles.


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ruben40870 avatar image ruben40870 commented ·

It would really suck if they were on their way out, they are practically still new. Surely not more than 150 cycles. And they were quite expensive.

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