How to revive a neglected system.

[Yankeroo]

Afteroon everyone.
I have a one of those MPP Solar LV2424 all in on hybrid inverters and a 24v 8s LiFePO4 DIY battery bank.
I know this all works and had no issues until life got in the way.
I have a 1 year old, and right about the time my kid was born, the batteries drained and I didnt have time to properly shut down the system.
Now a year later, I finally am circling back to this.
I just did a voltage test and my batteties have just shy of 7 volts worth of charge. My inverter, of course wont turn on with out the batter.
How do I get the batteries to a level where I can get the inverter back on and charging the batteries?
Any help or guidence here would be appreciated. Hoping I didnt just kill this battery bank!

 

[Supervstech]

Does the system have a BMS on the battery? 7 volts shouldn’t be possible with a 24V battery protected by a BMS…

Odds are good the cells are destroyed.

You need to disassemble the pack, put every cell in parallel, and SLOWLY like 1A output… charge them back up to 3.4V for a MONTH… with a dedicated power supply…

Anything else will completely destroy the cells…

 

[Yankeroo]

Does the system have a BMS on the battery? 7 volts shouldn’t be possible with a 24V battery protected by a BMS…

Odds are good the cells are destroyed.

You need to disassemble the pack, put every cell in parallel, and SLOWLY like 1A output… charge them back up to 3.4V for a MONTH… with a dedicated power supply…

Anything else will completely destroy the cells…

Bummber that what I feared. I do not have a BMS. hence the problem. How would I trickle charge at such a slow rate?

 

[Rednecktek]

What are the odds the BMS has just shut off and a quick hit with a 24v charger will bring it back online?

 

[v_green57]

What are the odds the BMS has just shut off and a quick hit with a 24v charger will bring it back online?

Forget what I say below. I just noticed that you have individual cells.

I need to slow down and read entire threads...

++++++++++++++++++++++++++++++++++++++++++++++++

Maybe. It is possible that a BMS'd all-in-one battery will still show some completely unpredictable but low voltage. Had that happen with a Weize.

Did the "jump start" thing and got the BMS to reconnect and it's back to normal.

What range of electronic stuff do you have available? If it were me, I would connect a 25 ohm power (10W min.) resistor across it and check for current flow while at the same time watching the voltage. If you get some current, things aren't completely dead. Jumping directly to another 24V battery sounds a little scary since we don't really know what's wrong. Could be exciting. The resistor will limit current.

Next step would be to take the same resistor and apply 24V to the battery, again whilst watching current and voltage. The 25 ohms will again limit the current to 1A or less. If the whole stack takes some current, and the voltage starts to rise, let it go that way for awhile checking periodically with your hands (or an IR camera if you have one) for excessively warm spots on the battery. You could use a lab power supply to do this as well - keep the current low at the start.

If you are able to kick the voltage up some, try drawing current again and compare the voltage and current to the first time. See if it has improved.

Lather, rinse, repeat.

 

[SparkyJJO]

Lesson learned- you need a BMS.

 

[Rednecktek]

Wait, you built a battery with no BMS??

Do you have an adjustable power supply? Did you top balance your cells? If so, or if you can beg/borrow one, you can hook all your cells in parallel, connect the charger, and do a slow top balance. 3v, then 3.2v, 3.4v, 3.6v, then reassemble with a BMS and fully charge it.

You may have lost capacity but you can probably save the cells.

 

[400bird]

You need to disassemble the pack, put every cell in parallel, and SLOWLY like 1A output… charge them back up to 3.4V for a MONTH… with a dedicated power supply…

If it were me, I'd individually (and very slowly, as suggested) charge up the cells. This way, if you have a survivor, the heaters and dead cells won't drag them down.

Preferably, I'd actually recommend recycling the cells, buying replacements and using a BMS.

 

[Supervstech]

Yeah, individually would be safer, but the best way to trickle charge would be with them all in parallel. That way the charge would be divided across the cells.
I would measure each cell before paralleling them and only tie cells with equal charge together.
At less than a volt each IF none are dead... they will be tough to charge, but at such a low soc, it will be VERY easy to damage them irreparably.
Get a quality DC voltmeter, measure EVERY cell and record the precise voltage, parallel ONLY cells with the exact same charge then connect a power supply previously set to 3.00 volts until zero amps are absorbing... then once all cells have the same 3.00 volts tie them all together and bring the bank up to 3.40V and let it charge until zero amps are absorbing...

Figure itll take a week or more to get this done.