Older Victron LifePo4 (90AH) Balancing

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bones83 asked Feb 26, '21

Older Victron LifePo4 (90AH) Balancing

Hi, I recently aquired 4 second hand 90Ah Victon Lifepo4 Batteries, that are around six years old (not smart model).

I received them at very low voltages (the lowest was at ~9V), but was surprised to see that they would all take a charge.

After they were individually charged, i then (again individually) did a capacity test on each of them with a 4.5A load, and found that they still had between 75 and 80 Ah of their original 90Ah.

I then fully charged them, and balanced them at 14.2V (again individually), until they each were only drawing 120-150mA. This took around 8 hours for each battery.

Now i have set them up to test them as a bank, they are connected in 2s2p configuration for 24V.

The bank has been charged now from a generator through a Multiplus 24/3000/16.

However, Once they reached float i decided to put the multimeter on each battery, and found that one battery on each series string is considerably higher than the other, at float one battery was at 14.5, while its friend in series was only at 13.6. The other series string was in a similar but slightly less drastic situation.

Does this suggest that the batteries are unsuitable for use together?

Or should i configure them differently in an attempt to balance them (both high units in series and both low units in series)?

Thanks for reading =)

edit: I just looked at them again - the generator is off and they are running the lights in my house at the moment which equals 40w, and now if i stick the meter on them they are back in balance, so it seems at the moment that they are only out of balance at the top of their charge cycle...... does this provide any clues?

Lithium Battery

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Answer 1 · 2021-02-26T21:08:30Z

seb71 answered · Feb 26, 2021 at 09:08 PM

Current non-smart Victron LiFePO4 batteries can only be wired in parallel. Not in series.

Maybe you could take out the cells and make your own pack by picking the closest matching cells.

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Matthias Lange - DE ♦ commented · Feb 26, 2021 at 09:46 PM

I guess he have some of the very first Victron lithium batteries.
They are like the currently available smart ones but without Bluetooth.

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seb71 Matthias Lange - DE ♦ commented · Feb 26, 2021 at 09:50 PM

You daisychain them to a BMS?

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Matthias Lange - DE ♦ seb71 commented · Feb 26, 2021 at 10:19 PM

Yes you dasychained them to a BMS like the ones currently available.
But you don't had any Bluetooth on them. They only got monitored by the BMS.

There also was a series available without the BMS wires.
A few weeks ago there was a question about that batteries in the community:

https://community.victronenergy.com/questions/77065/how-to-treat-this-victron-128v-battery.html

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Answer 2 · 2021-02-26T21:22:37Z

bones83 answered · Feb 26, 2021 at 09:22 PM

Hi seb, I have the user guide for the battery packs. Victron states in the guide that up to four 12.8v batteries can be series connected, and up to ten batteries or strings of batteries can be parallel connected. Is this information out of date? I know that originally these batteries were installed in a 2s2p configuration also.....

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seb71 commented · Feb 26, 2021 at 09:42 PM

I have the user guide for the battery packs. Victron states in the guide that up to four 12.8v batteries can be series connected, and up to ten batteries or strings of batteries can be parallel connected. Is this information out of date?

If you are sure that the guide you have applies to the batteries you have, then they are different than the current ones in this regard.

LiFePO4 charging curve has a rapid raise in voltage at the end of the charging. So it is easy to get out of balance there.

Similar for the other end - when discharged and SOC approaches 0%, there is a rapid drop in voltage.

Can you measure individual cell voltages (if the battery case has openings)?

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bones83 seb71 commented · Feb 26, 2021 at 09:51 PM

The battery case has no openings whatsoever unfortunately.

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Answer 3 · 2021-02-26T21:47:58Z

Matthias Lange - DE answered · Feb 26, 2021 at 09:47 PM

Do you have a BMS for that batteries?
Or are those batteries the "cheaper" ones without the BMS cables?

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bones83 commented · Feb 26, 2021 at 09:56 PM

Yes, they are connected to a victron V.EBus BMS. I have confirmed that the Chain is complete, as when i disconnect any cable in the chain then the multiplus instantly gets shut off. Whilst charging i had no error on the BMS so at least i know that no cell went above 4V =)

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seb71 bones83 commented · Feb 26, 2021 at 09:59 PM

You should have mentioned that in the OP.

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bones83 seb71 commented · Feb 26, 2021 at 10:03 PM

Ah, ok - my apologies! I was under the impression that a BMS was mandatory for LiFePo4 =)

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Matthias Lange - DE ♦ bones83 commented · Feb 26, 2021 at 10:05 PM

It should be :)

But Victron also had non-smart lithium batteries without that BMS cables.

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bones83 Matthias Lange - DE ♦ commented · Feb 26, 2021 at 10:08 PM

Ok, so we have the complete picture, i also have a CCGX connected to the Multiplus via V.E.Bus, and a mains detector between the BMS and Multiplus.

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Matthias Lange - DE ♦ bones83 commented · Feb 26, 2021 at 10:21 PM

With a BMS connected you should be safe.
The BMS should stop charging if the voltage of one cell in one of the batteries goes to high.

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bones83 Matthias Lange - DE ♦ commented · Feb 26, 2021 at 10:33 PM

Thanks! So do you suggest i continue to cycle them under normal use and they will eventually balance themselves?

Or should i try a different configuration of the packs in order to put the weaker packs in parallel with the stronger packs?

Otherwise I also have an old analogue desktop power supply that i could hook up with a set voltage limit to try and balance them at low amps, is this likely to help and if so how would you suggest I do this (e.g 1 pack at a time/all packs together/just the weak ones).

I would like to try and maximise the capacity of the bank if possible, whilst hopefully keeping the individual cell voltages from going too high (not just from a safety point of view) - as they are quite old batteries I would like to give them an easier life in the hope they will still last a few years more!

Thanks a lot for your help =)

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