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post #1 of 32 Old 12-31-2019 Thread Starter
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Battery Series Voltage Difference

Looking for theories/reasons why batteries 3&4 have such different voltages in this drawing. The difference stays consistent at different voltages and stayed about 0.3v different during a 3-hr equalization charge.

Thinking that somehow it was the jumper cable between the 2, I took it off and cleaned and tested its ohms. With the jumper off the voltage of 3&4 became the same, but they went back to having the difference after reinstalling.
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post #2 of 32 Old 12-31-2019 Thread Starter
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Re: Battery Series Voltage Difference

Well i measured those yesterday near close to fully charged and under solar charging. This morning at 82% state of charge and a charge of 1.2A voltages were closer

1 - 6.21
2- 6.27
3 - 6.25
4- 6.22

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post #3 of 32 Old 12-31-2019
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Re: Battery Series Voltage Difference

What’s the acceptable error on the monitoring meter?
Any parasitic loads? Or charger ie echo charger to one battery?


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post #4 of 32 Old 12-31-2019 Thread Starter
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Re: Battery Series Voltage Difference

other than the things on the paper that say "BM" everything was measured directly at the battery, sure there could be (and probably is) some error but it would apply to all the measured voltage readings

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post #5 of 32 Old 12-31-2019
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Re: Battery Series Voltage Difference

Is it possible that not all batteries are equal.? ie. some lead has a bit of cadmium (recycled wheel weights?)
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Re: Battery Series Voltage Difference

Quote:
Originally Posted by Capt Len View Post
Is it possible that not all batteries are equal.? ie. some lead has a bit of cadmium (recycled wheel weights?)
who knows, they are all the same age and batch

but, why would it change between an 8 amp charge, 1 amp charge, at rest?

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post #7 of 32 Old 12-31-2019 Thread Starter
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Re: Battery Series Voltage Difference

think when I'm feeling physical I'll move the batteries around and change the pairings and locations and see if it follows the battery or the location

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post #8 of 32 Old 12-31-2019
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Re: Battery Series Voltage Difference

This is why equalisation charging should be done on each string separately, really each unit if you're getting into this level of detail.

I assume not a brand new set?

Fact is no two cells in even the biggest set will ever be exactly the same.

The uneven flow through paralleled strings will cause uneven wear over time, thus a shorter lifespan overall compared to just one string of single cells.

paralleling multiple cells at the lowest level before serial'ing is next best

paralleling separate strings worst case.

Balancing the cells with their corresponding members across the strings would help, but violates KISS principles.

Some owners do rotate units to try to "even out" the wear,

people I tend to trust more say best to just keep them as is, but haven't seen an explanation as to why.
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post #9 of 32 Old 12-31-2019 Thread Starter
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Re: Battery Series Voltage Difference

I dont feel that explains anything.

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post #10 of 32 Old 12-31-2019
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Re: Battery Series Voltage Difference

They may all look good after charging. But operate much differently under load. I have four batteries in a series to make a 48 volt string. All batteries charged up the same. But, one would lose capacity rapidly after a few minutes under load. A quick test with my battery tester confirmed how bad the battery was.
You said your batteries are old so they are probably aging differently. Hopefully they were the same age when they were installed new. A simple test with a Centech Battery tester would show how each battery compares to the others internally as shown in the link below.
https://biankablog.blogspot.com/2019...tery-bank.html

Mike
Currently: Heading to warm waters over the winter on a variety of boats.

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Last edited by mbianka; 12-31-2019 at 05:24 PM.
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