24V Lifepo4 discharged to 18V - How badly am I screwed?

[Riley]

I left my RV at a repair shop for a week and since my Growatt is not charging the next day morning without a hard restart, my ampere time battery has run out.

I noticed I can still measure an 18V voltage, so the BMS didn't cut off when it's low! are batteries screwed?

also, I don't understand why it's running it so low, my Growatt inverter and 48-12 DC-DC should cut off way before 18V.

 

[sunshine_eggo]

Likely not screwed.

The BMS DID protect. It probably has a setting somewhere around 2.3V.

Not great for them, but far worse has been done for far longer.

Just charge it back up. You might need to get an alternate charger on it if the Growatt won't activate at such a low battery voltage.

 

[John Frum]

Your growatt should be set to disconnect at ~24.0 volts so that the battery bms doesn't have to trip.
If you have any pure dc loads then you should consider a Victron smart battery protect https://www.victronenergy.com/battery_protect/smart-battery-protect

I say that because I suspect the ampere time batteries are not awesome quality including their bms.

 

[Horsefly]

I'm not sure what kind of BMS you are dealing with, but if it is FET based and is still disconnected, there will be a lower voltage showing even though current is not able to flow. I have a 4S2P setup in my garage with JBD 150A BMS's on each 4S pack. If I disable discharge on both of them, I can measure 4.2V across the positive to the combined C- out of the BMS's.

 

[Riley]

I went to the repair shop to discuss some repairs. I will go back and check the battery again in a few days when they finish the repair and try to charge it.


Since I still have until Jan 31 to return it, not sure if I should do that? It shipped from the seller instead of Amazon, so the returning process would be nasty.



I did set a low voltage cutoff for Growatt, and other than that, I have a 48-12 DC-DC charger connected to a 12V battery that has no load on it (all lights off). I am not sure how my battery can be run down to 18V.

Still a bit worried. I need to use it for a long time, and they are super expensive($3500+)

 

[Horsefly]

My point (in post #4 above) is that you don't really know the voltage of the battery / cells if it is still in low voltage disconnect. Once you hook up a charger to it, it may back off the disconnect and you'll see the voltage is in fact fine.

 

[Riley]

My point (in post #4 above) is that you don't really know the voltage of the battery / cells if it is still in low voltage disconnect. Once you hook up a charger to it, it may back off the disconnect and you'll see the voltage is in fact fine.

I will do it in a few days, hope that's the case

 

[SpongeboB Sinewave]

It's is probably OK especially if none of the cells reversed polarity.
The BMS may work a bit hard trying to balance the cells when you charge them so MAYBE want to charge at a somewhat low charge current to start with.

Would be interesting to see what others think about that opinion.
boB

 

[TheBestDIYGuy]

Probably okay - charge it up using a charger if needed but likely there will be no long term damage or issues.

 

[740GLE]

I did set a low voltage cutoff for Growatt, and other than that, I have a 48-12 DC-DC charger connected to a 12V battery that has no load on it (all lights off). I am not sure how my battery can be run down to 18V.

Wait, this is a nominal 48v battery that is showing 18v?

Is it two 24v amperetime batteries or four 12v batteries to reach 48v?

 

[Riley]

Wait, this is a nominal 48v battery that is showing 18v?

Is it two 24v amperetime batteries or four 12v batteries to reach 48v?

It's a 2P2S 48v system with 4x 24v batteries. I checked one of the batteries and found 18v.

 

[MisterSandals]

Still a bit worried. I need to use it for a long time, and they are super expensive($3500+)

I will do it in a few days,

If the batteries were this important to me, i would be there at 8am waiting for the shop to open, tomorrow. then would charge from alternator or other charger ASAP.

In a few days? They may be door stops by then.

 

[time2roll]

Nothing is harder on a battery than a visit to an RV dealer. Get a charge on asap. Then test your systems that failed. Then test capacity.

 

[meetyg]

I would charge up slowly at first, don't push 10s of amps on a 18v battery. Below 2.5v per cell you can damage them if you charge too quickly. I'm not sure if 2.3v is that bad, but just in case, do it slowly until they reach say 2.8v per cell (22-23v total). Then you can charge them up as usual.

 

[Riley]

I think I will try to go there tomorrow 3-4 PM, when the sun is low, and connect my extra 48V 20AMP MPPT to my solar array to charge it. That's the time when I have a lower PV output that can feed into a small MPPT charge controller. (The array is 2680w! 48|20 MPPT can handle about 1400w)
I do not have a 48V charger; they cost $170+.

From the rotten smell from the freezer, I can tell the battery was drained for many days. If the damage is already done, I did better just to return the battery and get them replaced anyway. Would a capacity test verify if there is any damage done?

 

[740GLE]

It's a 2P2S 48v system with 4x 24v batteries. I checked one of the batteries and found 18v.

What were the other batteries voltage readings?

Also how can you return the batteries when you caused the damage?

 

[Riley]

I want to give an update on this issue, the battery was charged and recovered with no noticeable damage, but I did not do a capacity test. Ampertime told me that "If the BMS didn't cut off the battery, it means the battery still has some capacity and didn't discharge fully. Our batteries are manufactured by 8 Automotive Grade LiFePO4 Cells with higher energy density, more stable performance & greater power. You could feel free to use the batteries if it didn't cut off by the BMS."

However, they also kindly offered me a full refund and a prepaid shipping label. I decided to order ZOOMS 12v 200AH batteries that are $200 cheaper. It saved me over $800 in total and gave me newer batteries, so I don't have to worry it's been over-discharged.