Battery voltage drops to 18,7V and up again on LiFePO4 24V system

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royer asked Sep 19, '19

Battery voltage drops to 18,7V and up again on LiFePO4 24V system

Hello.

I have 2 LiFePO4 12,8 V / 200 Ah Smart (series cabling) on Multiplus (via BMS and Ac detector).

When in the evening, I launch a dishwasher, suddenly the voltage which is arround 25,0 or 26,0 V, drop to 18,7V (2,33 per cells) and immediatly go up to 20,0 V, 21,0V... to reach 25,0 V again.

On multi-plus we can read : CA Input (2600W), CA Output (2600W), and state : "Main power assistance" or "Direct Capacity".

I just want to know if it's normal in this case (relay ot the battery, by the main current), and without consequences for the battery lifetime, or if we have to change parameters, knowing that multi-plus parameters and mppt parameters are fixed with the template for LiFePO4, proposed by the software interface.

Best Regards.

Lithium Battery battery system voltage

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Answer 1 · 2020-01-07T22:58:03Z

Justin Cook answered · Jan 07, 2020 at 10:58 PM

@ROYER I'm hoping that you've already worked out this issue since you originally posted the question, but in case not:

It is quite common to see voltage initially drop across a battery bank upon first starting up a large load, particularly motors, pumps, and etc which can have an initial inrush current of 4 to 5 times their rated draw for ~50ms or so, then after that first dip as the motors/pumps initially start turning, the load they pose significantly decreases.

As such, your initial description of what you're seeing does not strike me as aberrant and so long as your system continues performing as expected, I would not be overly concerned. If, however, the problem seems to worsen or that brief dip in voltage becomes longer or other symptoms develop, I strongly encourage you to consult a qualified DC systems installer to see if there might be a persistent issue somewhere in your system connections or elsewhere.

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Answer 2 · 2020-01-12T00:00:58Z

royer answered · Jan 12, 2020 at 12:00 AM

Thanks Justin for your answer.

Yes, meanwhile, I'have resolved the problem, and it was very simple. On the App's "Multiplus 24/5000/120 100", I just change the AC 1 entry limite : 3.0 A to 50.0 A.

Since that moment, Battery never drop deeper as 23.43V.

Thanks for your comment and best regards.

Laurent.

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