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babyrocket asked

LiFePO4 battery problem - need help!

I have an all-Victron 12v system (diagram attached) with a MultiPlus II 2x120 and 4 100Ah LiFePO4 batteries installed in our RV. It has worked extremely well for 18 months, and this past weekend we had a problem with faulty power at our campsite power pedestal. I have an EMS permanently installed, and it did its job by preventing the power from entering the trailer.

We were in a hurry when setting up camp, and when the "pilot" light came on in my 50A plug I failed to double-check that the trailer was in fact receiving shore power. It was hot inside so I turned on both ACs, not knowing that they were being powered only by the inverter and batteries.

After a while, I happened to see that the MultiPlus was blinking low battery and I checked the GX Touch 50 to notice that the batteries were at 1%. I immediately turned off the ACs, fired up the generator, lowered the AC input current limit to 20A and plugged it in. By that time the lithium batteries had reached 0%. Once plugged in all was well with trailer power, and that evening they fixed the power pedestal so we plugged into 50A for the remainder of our trip.

When we broke camp to leave, I double-checked that the batteries had charged to 100% and displayed 14.4v. Once we unplugged from shore power, however, the slide moved very slowly and then stopped so I looked at the system and saw that while the battery was reading 100% the voltage was only 11.7v. I plugged back into power to retract the slides, and the battery voltage jumped back to 14.4v. Unplugging power the final time showed the batteries still at 100% and back down to 11.7v.

I'm unable to charge the batteries since they show 14.4v when plugged into shore or generator power, but they are virtually empty when unplugged despite showing 100%. I understand there is a possibility that running the batteries down to 0% may have damaged them, though I'm holding out hope that this is not the case. Is there a way to test for this? And if it's not a battery problem what are the troubleshooting steps I can go through to find the problem?

Sorry for the long post, and thanks in advance for any help you all can provide!

Patrick

Grand Design 303RLS Power Diagram v1.png

Multiplus-IILithium Battery
grand-design-303rls-power-diagram-v1.png (450.7 KiB)
5 comments
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ingo21 avatar image ingo21 commented ·
your diagram does not show any BMS ( battery management system )

do your batteries have a internal BMS to balance and protect them ?

11.7V/4=2.92V per cell that should not kill them.

assuming the cell voltages are all about the same......

if the batteries have and internal bms and one cell goes to low the bms might not start recharging until being reset



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babyrocket avatar image babyrocket ingo21 commented ·

Thanks for the quick reply. They are GoPower batteries, and the specs say that they do have a BMS:

  • Built-in Battery Management System (BMS)
    • Over and under voltage protection
    • Over and under temperature protection
    • Charge and discharge over current protection
    • Short circuit protection
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mvas avatar image mvas babyrocket commented ·

What is the Under-Voltage setting for the BMS to disconnect the battery, from the load? From your message, it appears that the battery voltage never got low enough for ALL 4 BMS's to disconnect? If just one, two or three of the four BMS did disconnect, I doubt we will ever know.

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babyrocket avatar image babyrocket mvas commented ·

Thank you all for your help. I picked up a LiFePO4 charger with 0v charging capability and then tested each battery. Each was disconnected and voltage tested individually, and surprisingly each tested at 13.3v. So I reconnected them all and plugged into the generator. Unlike the last time, it now charged the battery bank for about an hour until it was full. Voltage at that point was 14.4v.

I disconnected the generator, and the voltage of the batteries dropped to 13.7v. I moved the slides in and out several times connected only to battery, and they moved as normal.

So it appears that all is now well. Is it possible that somehow the BMS of the battery (or batteries) that were the problem reset on its own? Any other tests I should perform to confirm that I'm in good shape?

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seb71 avatar image seb71 babyrocket commented ·
What's your Inverter shut-down voltage set at? Should be set to 12V or higher.


Do not discharge a LiFePO4 cell under 3V.

Assuming perfectly balanced and matched cells, that means never go under 12V battery voltage in your case.


If the cells are less well matched, increase that limit accordingly. By how much it's difficult to say unless you can measure the voltages of individual cells.

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3 Answers
Ivar Eisma avatar image
Ivar Eisma answered ·

So you have 4x 100ah 12v in series correct? If so it's possible one battery switched off triggered by the BMS. It would be very hard to permanently damage a battery with a BMS, it's there to protect the cells.

Disconnect all batteries and wires so you have just loose units. Measure voltage with multimeter on all 4. Leave them for an hour. Measure voltage again. If one is very low and didn't recover, you have to wake it up. The BMS shut it off and won't turn on unless the voltage is higher, but this is different for each brand.

Mine was at 3.7v and fully recovered, here what the manufacturer recommended:

"Please reactivate the battery as follows: Disconnect all connections and leave the battery aside for 30 minutes, please check if the battery recovers. (If this method does not work, please try the following two methods to reactivate the battery). Method 1: Use a charger with 0V charging function to fully charge the battery; Method 2: Connect an 18-36V solar panel and controller to charge the battery for 3-10 minutes in sunshine. If the two methods I have suggested do not work Please contact me as soon as possible and I will keep in touch with you until the battery problem is fully resolved. "

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mvas avatar image
mvas answered ·

A 2.7 volt drop ( = 14.4 volts - 11.7 volts ) may be, one or more, more weak cells. Try charging at a much lower amperage, for a much longer time, such that you stay below 14.4 volts

What is the "resting" voltage of each battery, with no load? Disconnected from each other.

Can you access the BMS via Bluetooth?

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Alexandra avatar image
Alexandra answered ·

@babyrocket

You need to verify that all your batteries are on and working. The only way would be to remove them from the system and test or charge them as individuals.

It sounds like your bms' are switching off.

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