question

Deutch avatar image
Deutch asked

Batteries voltage drops quickly when Multiplus switch to inverter mode

Hello Everyone,

Since December 2020, I have installed a backup system to help me to overcome the electricity problems in my offices, and since the commissioning all the system was working properly.the system is composed of 12 gel batteries 12V-210Ah C20 brand Leoch, a Color control and a Multiplus II 48V-5000/70.The installation powers only a few laptops, a few lamps and a small printer, so that our power consumption never exceeds 1200W.

Everything was working well and we had more than 8 hours of autonomy without the SOC of the batteries even reaching 70%, however for the last 4 days, in case of a power cut, after 5 minutes the low battery alarm sounds and the multiplus turns off.

Checking each battery individually in a chain of batteries in series forming a group of 48V, I noticed that the difference in voltage between batteries was enormous, one has a voltage of 9.87V, while the others are at 11.35, the other at 12.35V, this difference in voltage surprises me enormously and I wonder what could be the cause of this because everything was working properly, the settings of the charger well configured in VE configures for a Gel battery, and the room well air-conditioned to optimize the life of the batteries.

What makes it even more complicated is that the Color control mentions an SOC of 98%, but the voltage drops rapidly and the MultiplusII shuts down, followed by a High DC ripple message.

Can you please help me?

Thank you in advance to @Guy Stewart (Victron Community Manager), @Alexandra @Thierry Cortassa (Victron Energy Staff) ,thank you also in advance to anyone who can help me find a solution to this problem, because it's already been three days that I am forced to turn to the generator and the fuel costs are starting to weigh on my business, the pictures of the system are here if that can help.

WhatsApp Image 2021-08-22 at 17.16.27.jpegWhatsApp Image 2021-08-22 at 17.16.27 (1).jpegwhatsapp-image-2021-08-19-at-150834.jpeg




Multiplus-IIMultiPlus Quattro Inverter ChargerCyrix Battery Combinerlow battery warning
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whatsapp-image-2021-08-22-at-171627.jpeg (51.8 KiB)
whatsapp-image-2021-08-22-at-171627-1.jpeg (31.3 KiB)
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2 Answers
Rob Duthie avatar image
Rob Duthie answered ·

Hi

Looks like bad battery cells, do a battery impedance load test this will tell you a lot about there true condition. Also what are your battery cable termination like? correct size cable bus bars etc. battery balancing etc. One bad cell will drag the whole lot down.

Regards

Rob D

NZ

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Deutch avatar image
Deutch answered ·

Hello @Rob Duthie ,

Thank you very much, what surprises me is that the batteries are well wired with a good section of cables, well tightened, could this problem be due to poor quality batteries ... the batteries are connected in series and each group consisting of 4 batteries is connected to a Lynx power of Victron energy so we should not have this kind of problem normaly.

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Rob Duthie avatar image Rob Duthie commented ·

Hi

Just looked at the battery photos, i don't think the batteries are balanced wired correctly.

All the series and parallel banks must have the same lenght cables or bus bars identical, other wise battery banks and cells will suffer over time. You need to read Wiring unlimted from Victron on this matter as attached, As i have seen this with installations done with wrong lengh cable etc and batteries failing quickly over a year.

What size are your cables from batteries to Lynx and to the inverter, looks to me like 35mm2? or 25mm2 in pairs to the inverter?

Victron Wiring-Unlimited-EN.pdf

Regards

Rob D

NZ


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victron-wiring-unlimited-en.pdf (8.6 MiB)
Deutch avatar image Deutch Rob Duthie commented ·

Hello Rob,

thank you for your answer, for the section of the cables in the manual of the inverter Victron energy recommends a section of 2x50mm for a length of up to 10m, I had put 2x50mm for 8m length, I had even made the measurements of voltage drop between the batteries and the inverter at full power and it was 0.017V.

Everything worked fine for 8 months, but I had never discharged its batteries above 70% because their autonomy was good, is the fact of not discharging the batteries could damage them? do they often have to be discharged and then recharged?

Thank you

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