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bobybayo avatar image
bobybayo asked

Question about Smart Lithium batteries in parallel and their voltage

I started my battery bank with 2 Smart lithium battery 24 v in parallel (diagonal). In Victron connect they both showed the same voltage. A month later I added a third battery and noticed that the battery in the middle was now 0.10v below the batteries at the ends. Now I added a fourth battery in parallel using Bus bars and noticed that battery 1 and 3 have the same voltage and 2 and 4 voltage is 0.10 below 1 and 3. I thought that by using bus bars (diagonal) they would show the same voltage. Any clues?

Lithium Battery
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4 Answers
JohnC avatar image
JohnC answered ·

Hi @bobybayo

This is an old article from a mob who no longer exist in the same form. But it might help explain what you're experiencing (and one of the reasons why I hate paralleled batteries).. http://www.smartgauge.co.uk/batt_con.html

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bobybayo avatar image bobybayo commented ·
So the Bus bar connection is not the most efficient?
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snoobler avatar image snoobler bobybayo commented ·

properly wired to bus bars can give the best results.


Start at page 18:


https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

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snoobler avatar image
snoobler answered ·

I would assume calibration issues between the batteries OR slight voltage differences due to resistances and heavy loads.


Concerning the latter, ensure all connections are properly torqued and of high quality.

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bobybayo avatar image bobybayo commented ·
The connections are good. I did not charge the individual batteries before connecting in parallel. Could that be an issue?
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snoobler avatar image snoobler bobybayo commented ·
Could be. If you've noticed those batteries are closer together now, then that could explain it.
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bobybayo avatar image
bobybayo answered ·

1d8f6205-d2e5-49db-b871-96a8e9c8401a.pngSee photo where you can appreciate the pattern between batteries 1/3 and 2/4. The voltage difference is small. I just want to understand the why of the variances as shown.


1d8f6205-d2e5-49db-b871-96a8e9c8401a.png (494.0 KiB)
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snoobler avatar image snoobler commented ·
Measurement error. Check them with a voltmeter, and you'll likely get a different reading entirely.


Consider that this is only about 0.4% difference.


There may be a way to calibrate the voltage, but I don't know how.



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bobybayo avatar image bobybayo snoobler commented ·
Measurement across battery terminal shows that they are within 0.01 V from each other.
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snoobler avatar image snoobler bobybayo commented ·
Right, and that is to be expected, but is that 0.01V variation different from the four reported values?


My point is voltage measurements depend completely on calibration. There's no such thing as a 100% accurate meter.

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kevgermany answered ·

Might also be new batteries that are not fully charged due to internal cell imbalances that the BMS's haven't yet ironed out.

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