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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 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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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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