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Battery voltage is too low and I have no way to charge

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ruiz.manuel94

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So a couple days ago my 3.2V 230 Ah LiFePO4 cells arrived, but my BMS didn't. I decided to assemble the battery and with that my whole system, knowing that the battery would be running without a BMS, and I would have to be careful.

Now today when I checked the battery I noticed that the voltage is at 12.0 V, which is about 9% SOC according to charts on the internet.

My solar panels arrive in two days and I am still not going to have a BMS for another week.

I am a newbie and I am very worried to have damaged my new cells.

I have the following questions:
-Have I damaged my cells permanently?
-Should I charge my battery as soon as possible to avoid further damage? (charging options are limited, see next question)
-Is it safe to charge using any of these: 50 A car battery charger (came with my ambulance PM) or this other battery charger?
-Should I wait till I get my BMS and panels to recharge? (1 week without further discharging, obviously)


Please help me I am very worried.
 
Wait, wait.

Voltage may not be a good indication. 2.5 volts per cell is lowest cutoff, and you are above that. When capacity testing you go tp 2.5 volts. After my capacity test the cells went from 2.5 to 2.8 overnight, just by resting. Your cells average above that.

Don't rush yourself and wait for the BMS.
 
sunshine_eggo said:
What did the CELLS measure when you received them?
What do the CELLS measure now?
Click to expand...
They were all 3.23 V and now they range 2.98 - 3.00 V
chrisski said:
Wait, wait.

Voltage may not be a good indication. 2.5 volts per cell is lowest cutoff, and you are above that. When capacity testing you go tp 2.5 volts. After my capacity test the cells went from 2.5 to 2.8 overnight, just by resting. Your cells average above that.

Don't rush yourself and wait for the BMS.
Click to expand...

Ok so no damage can happen for letting them sit a week at 2.98V ???
 
ruiz.manuel94 said:
They were all 3.23 V and now they range 2.98 - 3.00 V


Ok so no damage can happen for letting them sit a week at 2.98V ???
Click to expand...
I missed top balancing. Are you going to do this? Charge cells individual to 3.6 or in parallel to 3.6 with a power supply.

IMO less chance of damage from waiting them putting them on a car charger. Some of those have profiles that can damage the battery.
 
ruiz.manuel94 said:
Have I damaged my cells permanently?
Click to expand...
No, LFP is okay at 3 volts per cell.
ruiz.manuel94 said:
-Should I charge my battery as soon as possible to avoid further damage? (charging options are limited, see next question)
-Is it safe to charge using any of these: 50 A car battery charger (came with my ambulance PM) or this other battery charger?
Click to expand...
You could use that to get the batteries to 50 percent [ about 3.15 volts per cell or 12.6 volts. to do that you would need to watch them carefully as they rise in voltage. The best thing would be to use a power supply and parallel balance them to 3.5-3.6 volts.
ruiz.manuel94 said:
-Should I wait till I get my BMS and panels to recharge? (1 week without further discharging, obviously)
Click to expand...
You can do that but parallel top balancing is my preference before installing a BMS.
 
Ampster said:
You can do that but parallel top balancing is my preference before installing a BMS.
Click to expand...
I was under the impression that bottom balancing was the way to go for LFP, is it not?

In any case, parallel top balancing would mean to charge the pack (with MPPT) up to about 3.6V per cell and then connect them in parallel for a few hours?

Ampster said:
No, LFP is okay at 3 volts per cell.
Click to expand...
So glad to hear that! In that case I will just wait for my BMS and panels

sunshine_eggo said:
Not worried about the ~3.00/cell, but I'm very worried about them dropping from 3.23V in a couple days.
Click to expand...
Well it was actually like two weeks of using the interior LED lights at night to work on the build and some inverter testing with my tiny fridge. So I'm actually quite pleased with the capacity so far.


Thanks everyone for your responses!!! this forum is the best.
 
0% LFP is 2.5V per cell… so you are fine so far.
I wouldn’t charge them with an improper charger without a BMS. Too easy to OVERCHARGE a cell and destroy the pack.
I ordered a 5 amp variable buck/boost controller, and set it to 3.65V, 5.5A, and let it rip the cells up to 3.65- 0Amps. It will take a few days on large cells, but it is safe.

Amazon got the controller to me in less than a day.
 
ruiz.manuel94 said:
I was under the impression that bottom balancing was the way to go for LFP, is it not?
Click to expand...
It depends on your use case. Bottom balancing was popular with some in DIY EV crowd who do not trust BMSs. Most BMSs balance at 3.4 volts and above so a bottom balance will be unwound by a top balancing BMS.
ruiz.manuel94 said:
In any case, parallel top balancing would mean to charge the pack (with MPPT) up to about 3.6V per cell and then connect them in parallel for a few hours?
Click to expand...
Not exactly. There are a number of threads on the subject. You will need an adjustable power supply that is capable of at least 3.65 volts You can use an MPPT to get them close but you actually need to apply voltage and some current while in parallel to get them to equal voltage. Watch them carefully as they approach 3.6 volts. Anywhere above about 3.5 volts is close enough to the steep part of the charge curve to finish them.
 
Just to be safe you should check the individual cell voltages.
 
Actually my panels are arriving today!! (480W, and I have a 40A MPPT)
Do you guys think It is okay If I charge using solar WITHOUT BMS?, just to check everything is working fine. I would monitor voltage just to charge up to like 50%
 
Probably. Assuming your cells meet spec, you should safely be able to input 50% of the Ah into them; however, you should not leave it unattended.

But really...

YOU are the BMS. Human BMS are notoriously unreliable. Recommend you stop taking risks and start top balancing them per the written guide in Resources.
 
ruiz.manuel94 said:
Actually my panels are arriving today!! (480W, and I have a 40A MPPT)
Do you guys think It is okay If I charge using solar WITHOUT BMS?, just to check everything is working fine. I would monitor voltage just to charge up to like 50%
Click to expand...
If doing this just watch the cell voltages which isn't going to be easy because you'll have it connected as a pack. Set the the charger to 13.6 (bulk/ absorb) and use the least amount of time on the absorb time. This will by you time till the bms gets to you. But without top balancing once all the cells and you up the voltage after the bms is hookup you might have shutdowns do to individual cell runners.
 
Last edited:
ruiz.manuel94 said:
In any case, parallel top balancing would mean to charge the pack (with MPPT) up to about 3.6V per cell and then connect them in parallel for a few hours?
Click to expand...

Not without a BMS! If you series charge to 3.6V per cell, you WILL overcharge at least one cell.

You may connect in parallel and charge to 3.6V in parallel with a CV/CC supply set to maximum 3.6V BEFORE connecting supply to cells.

ruiz.manuel94 said:
Do you guys think It is okay If I charge using solar WITHOUT BMS?
Click to expand...

No.

Do not charge in series without BMS.

(Also, do not discharge in series without a BMS.)
 
For small loads using cells without a bms isn't the end of the world KNOWING nothing is protecting the cells.
 
When I pre-charged mine for a top balance, I hooked it up to a BMS And charged to 3.45 per cell, so for 4S that would be 13.8. I then topped the batteries off to 3.65 which took about three hours after this pre-charge. THree hours is better than a week.

Don’t do this BMS. There are times you do builds without a BMS. Perhaps a well designed wheel chair build where the current can’t cut off while someone needs to speed up crossing a street to avoid getting hit by a car. ”I really, really want to because I would rather not wait,” is not a reason.
 
Sojourner1 said:
For small loads using cells without a bms isn't the end of the world KNOWING nothing is protecting the cells.
Click to expand...
I do agree with that, but how about charging to 3.6 per cell (14.4 volts) on new to him lithiums that are not grade A because they were delivered at 3.29 per cell but have since dropped to 3.0 per cell with no BMS? I would not do that with mine.

I’m only on my third lithium build, the first two were basically toysgetting me ready for the third I’m building, so I could very well be wrong.
 
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