MultiPlus 48/5000 stuck on Mains, Bulk/Absorption, and DC voltage fluctuations

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jligones asked Jul 23, '21

MultiPlus 48/5000 stuck on Mains, Bulk/Absorption, and DC voltage fluctuations

I recently replace my AGM batteries on my Victron Multiplus 5000/48 with 2p16s LiFePo4s. The system worked as intended the first day charging from solar panels and inverting. Since then, it would just stay on Mains (not inverting) and shift from bulk to float with the DC voltage fluctuating between 52v to 59v. I checked voltage at the battery terminals and it was a constant 52.6v. On the Color Control and BlueSolar Charger MPPT 150/70 it would show the wild swings in DC voltage. I tried switching the Multiplus off then on. After switching on it would go into inverter mode for about 10 seconds (DC voltage stable) and then would switch to mains and bulk and DC voltage would fluctuate again. I've checked the cables and battery connections and they're all okay. I've tested with loads disconnected. I also tried changing the Absorption and Float voltage settings to no avail. Any help or suggestions to a solution would be greatly appreciated.

This is my device list:

MultiPlus 48/5000/70-100

BlueSolar Charger MPPT 150/70 (VE.Can)

Color Control GX

BMV-700

32 x 280Ah LiFePo4

Daly Smart BMS 16S 48V 250A

MultiPlus Quattro Inverter Charger

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Kevin Windrem commented · Jul 23, 2021 at 06:32 PM

The Multi won't go into inverting if the grid is present and the loads are below the set input current limit. But if the loads exceed the input current limit, the inverter will go into Assist mode.

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Modifications Space

Node Red Space

Answer 1 · 2021-07-23T12:02:20Z

wkirby answered · Jul 23, 2021 at 12:02 PM

I know you said that you'd checked the connections, but there is definitely a bad connection somewhere. It is not possible to have stable battery Voltage (one end of the cable) and wild fluctuations at the other end of the cable without a high impedance along the way. A small Voltage drop is always going to be present, but that is too much of a swing.

Connections which are bad enough to case a problem like this can appear just fine. You might need to go through each connection in greater detail to find the culprit.

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Answer 2 · 2021-07-23T12:31:36Z

Alexandra answered · Jul 23, 2021 at 12:31 PM

@jligones

This is common on a built bank (and some bad professional ones) if the cells are not balanced and matched. What are your individual cell voltages? And have you fully charged your bank and held it there before making discharge cycles.

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Answer 3 · 2021-07-23T17:37:06Z

jligones answered · Jul 23, 2021 at 05:37 PM

Thank you very much for replying. I did check the connections again prior to my initial post and reseated busbars and tightened some nuts. Upon powering the system, the DC voltages were fluctuating again but have stabilized. I guess that was the issue.

The bank was balanced and fully charged prior to installation. Below is a screenshot of the BMS app showing the individual cell voltages.

I have not connected the load yet and the system is on Float at the moment. I will connect the load first thing tomorrow as it's 1:35 AM over here. Hoping the issue has been resolved and the Multiplus will go on Inverter mode. Thanks again!

screenshot-20210724-004640-smart-bms.jpg (401.0 KiB)

1627061684249.png (101.8 KiB)

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