Mid Voltage Error

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adamw asked Sep 2, '22

Mid Voltage Error

Hello. I have a MiltiPlus II with 4x Lion Energy UT 1300 LifePo batteries wired in parallel. I also have the 500A SmartShunt inline on the negative side. I have the battery monitor wire connected to the positive terminal on the 2nd battery in the bank. See images below. I am getting constant mid voltage alerts from the SmartShunt module in Victron App.

What could be causing this? Perhaps settings or a bad battery or my connection is on the wrong terminal?

I have noticed that as the batteries are used the two batteries closest to the negative side connection tend to drain fastest while the two batteries closest to the positive connection drain slower. Almost as if the first two batteries are keeping the second two charged. Is that normal?

Thanks in advance.

Multiplus-II SmartShunt VictronConnect

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Answer 1 · 2022-09-02T17:06:26Z

dagamma answered · Sep 02, 2022 at 05:06 PM

The mid voltage measuring isn't meant for parallel batteries. It's only used when for example you use two 12v batteries where you have 24v in series and about 12v in the middle.

The 100% deviation is because you are measuring the same mid voltage as the total voltage, while it should be exactly half in a series battery bank.

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adamw commented · Sep 02, 2022 at 05:35 PM

Thanks for the quick explanation.

One follow up. In parallel config, I had in my head that the batteries would drain equally from all 4 batteries in the bank. so if the system says 75% charge all batteries would be about 75%. In my case, when it says 75%, the back two batteries might be at 50%, but the forward two batteries will be 100%. Is that normal?

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dagamma adamw commented · Sep 03, 2022 at 08:56 AM

They should all charge and drain equally in a parallel configuration. When working with more than two batteries I would recommend connecting them via a busbar with exactly equal length cables to each battery.

How do you know the charge percentages of each battery seperate?

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adamw dagamma commented · Sep 10, 2022 at 04:10 AM

Lion energy batteries have an energy meter on each battery. As the system drains, I can check the % charge on each. I noticed that two are draining almost completely when the other two are near 100%

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Answer 2 · 2022-09-10T04:32:30Z

Alexandra answered · Sep 10, 2022 at 04:32 AM

@AdamW

They do not drain and charge equally when they are connected like you have them because of ohms law.

They will eventually equal out in charge and voltage etc the way they are connected but the end batteries alway work the hardest.

If you want equal load and charge on all 4 you should connect them with equal lengths of cable to a bus bar.

See wiring unlimited by victron.

Mid point monitoring is usually used for 24v systems.

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adamw commented · Sep 10, 2022 at 04:44 AM

Thank you for the explanation. I'll check it out.

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