Can you charge very discharged LiFePo4 cells temporarily at higher voltages?

[TommyHolly]

Hello everyone,
I’m wondering if you can charge very discharged LiFePo4 cells at higher voltages to temporarily charge them faster.

I’m guessing the answer is no, but I’m mainly wondering why. It probably has something to do with gassing?

I just got finished capacity testing 48 CALB brand 3.2v 100Ah cells. While one cell was being tested for 4.5 hours at a 20A discharge rate, I always had the previous one tested charging with a variable voltage 10A charger at 3.65v.

I connected all 48 cells in parallel, and placed both variable volt 10A chargers on opposite ends. (See picture) However this is taking forever to charge. I’m guessing it’s going to be a week or longer!?

I noticed these chargers drop the current down the closer the cell is to reaching the target voltage of 3.65A. Eventually when it reaches 3.65v the Amps go to 0.000A.

Right now both chargers are about 6.8A each. (See pictures) I used a DC clip on Amp meter to test the amps going through and it’s indeed what the reading on the charger shows.

Each cell tested was brought down to 2.6v during the capacity test. A single charger takes about 11-12 hours to fully charge a cell back up to exactly 3.65v after that. *Remember, I was charging the previous cell for 4.5 hours, which means that the cell needs another 7-8 hours of charging with one single 10A charger.

So I’m guesstimating that each cell needs about 50Ah of charging to get back to 100% SOC.
50A x 48 cells = 2,400A

Divide my two 10A chargers (20A total charging)
2,400A needed divided by 20A = 120 hours
120 hours is at least 5 days of charging.

*Maybe it’s more because the 10A chargers only deliver the full 10A directly after the capacity test and the cell was completely drained. Right now they say 6.8A each. So really that’s only 13A of current charging.
2,400A divided by 13A = 185 hours of charging.
185 hours is almost 8 days of charging!!
Maybe my math is wrong and I’d be glad to know how to really figure it out.

But my main question is, could I temporarily raise the charging voltage to 5v or something to help speed this up without damaging anything? The maximum charging specs for the 3.2v 100Ah CALB cells
Is 3.65v (See pic of specs)

This is more of a theoretical question since I really don’t know what would happen and don’t plan on attempting it.

 

[noenegdod]

Assuming the power sources are 30v 10a. Make 24v batteries out of the cells and charge at 29.2v and 10amps and cut your charge time way down. When you get close to full put them back into parallel and finish the top balance.

 

[MisterSandals]

I connected all 48 cells in parallel, and placed both variable volt 10A chargers on opposite ends.

You are mostly charging just the end 2 cells, one with each charger.
You need to have each charger have a lead on each end. + on cell 48, - on cell 1 for example.

 

[LB3]

Your spec sheet says not to exceed 0.3C or 30A per cell when charging so you can up the voltage until you achieve that charge current. You’re need to back off as your cells approach 3.65 volts.

 

[noenegdod]

Your spec sheet says not to exceed 0.3C or 30A per cell when charging so you can up the voltage until you achieve that charge current. You’re need to back off as your cells approach 3.65 volts.

I sense another "I just overcharged my cells, what do I do now." thread.......

 

[MisterSandals]

I sense another "I just overcharged my cells, what do I do now." thread.......

6 pages of "results" already...

Search results for query: overcharged

diysolarforum.com

 

[LB3]

I sense another "I just overcharged my cells, what do I do now." thread.......

Those threads always amaze me. Not pointing at the OP, but some people wait patiently for 3 months for cells to arrive then try to charge them up in 3 hours.

 

[noenegdod]

Those threads always amaze me. Not pointing at the OP, but some people wait patiently for 3 months for cells to arrive then try to charge them up in 3 hours.

6 pages of "results" already...

Search results for query: overcharged

diysolarforum.com

But my main question is, could I temporarily raise the charging voltage to 5v or something to help speed this up without damaging anything? The maximum charging specs for the 3.2v 100Ah CALB cells
Is 3.65v (See pic of specs)

To the OP. Please dont do this^^. As you see from the link MisterSandals has there are tons of cases where people have done exactly what you have suggested and the cost of failure is not worth it.

 

[TommyHolly]

Assuming the power sources are 30v 10a. Make 24v batteries out of the cells and charge at 29.2v and 10amps and cut your charge time way down. When you get close to full put them back into parallel and finish the top balance.

The power sources are variable 0-20v 10A chargers. The cells are all in parallel right now charging at 3.65v and each charger is displaying about 6.8A each.

Can I turn that voltage up to get more amperage?? I’m guessing not.

 

[TommyHolly]

You are mostly charging just the end 2 cells, one with each charger.
You need to have each charger have a lead on each end. + on cell 48, - on cell 1 for example.

That’s what I meant.
Charger #1 has the Negative wire on the left side and the the positive all the way at the other end on the right side.

Charger #2 is reversed. It has the Positive clip on the left side and the negative clip all the way on the opposite side on the right. So that the power has to flow through all the cells.

It’s just going so slow…

 

[TommyHolly]

Your spec sheet says not to exceed 0.3C or 30A per cell when charging so you can up the voltage until you achieve that charge current. You’re need to back off as your cells approach 3.65 volts.

Really!!?
Ok. Because I remember watching one of Will Prose’s videos and it sounded like he said something like that.

Currently both chargers are at around 6.8A each since they are set to exactly 3.65v. As I get closer to that 3.65v, the Amps also significantly drop.

If I turn up the voltage to around 7-8 volts, the charger maxes out at 10A each. I didn’t know if that 7-8 volts would harm the LiFePo4 cells though?

 

[robby]

The power sources are variable 0-20v 10A chargers. The cells are all in parallel right now charging at 3.65v and each charger is displaying about 6.8A each.

Can I turn that voltage up to get more amperage?? I’m guessing not.

No! Don't charge them above the maximum charge voltage on the spec sheet.
You really should be charging them one at a time and then creating the 48V pack or whatever size packs you plan on building with them when they are all charged and balanced. Then use a BMS and a proper charger going forward.

 

[TommyHolly]

I sense another "I just overcharged my cells, what do I do now." thread.......

That’s why I asked first. I’m aware of the dangers of over charging cells. And since I have 48 cells, setting the chargers to 3.65v as the amps in the chargers slowly drop down will take weeks.

What positive advice do you have to contribute regarding how to charge these cells faster?

 

[TommyHolly]

To the OP. Please dont do this^^. As you see from the link MisterSandals has there are tons of cases where people have done exactly what you have suggested and the cost of failure is not worth it.

That’s what I figured. I read through many of the posts. And I finished my OP with I likely won’t do this, I just want to hear about if you could and what the dangers were.

 

[TommyHolly]

No! Don't charge them above the maximum charge voltage on the spec sheet.
You really should be charging them one at a time and then creating the 48V pack or whatever size packs you plan on building with them when they are all charged and balanced. Then use a BMS and a proper charger.

One at a time???
This would take 6-7 hours per cell. And the cells have an internal resistance which drops about 3% after a few days so they would never be fully charged or matched to each other. Plus I have to sleep occasionally and be away sometimes so that’s a lot of wasted time making it even longer.

Will Prose and others have shown you connect all the cells together in parallel forming a giant 3.2v battery and charge that.

 

[robby]

One at a time???
This would take 6-7 hours per cell. And the cells have an internal resistance which drops about 3% after a few days so they would never be fully charged or matched to each other. Plus I have to sleep occasionally and be away sometimes so that’s a lot of wasted time making it even longer.

Will Prose and others have shown you connect all the cells together in parallel forming a giant 3.2v battery and charge that.

Not matched 100% but close. Yes you could charge them all together but with that tiny power supply it will take forever and I am worried that at this point you may have defective cells that might cause even more issues. That is why I would do them separately so that you can find any bad ones now. To start with you really need to undo them and at least check all the voltages and label them with tape so that you know what each ones SOC is. What is the voltage of the whole string right now without the charger on them?

Edit: I just reread your post and realized that you did not try the high voltage charging. So assuming all is well your just going to have to wait it out for several days or get a bigger charger or a better solution is to disassemble and check the SOC then match the closest batteries together into the packs and put them on a BMS with a proper charger.

 

[robby]

Assuming the power sources are 30v 10a. Make 24v batteries out of the cells and charge at 29.2v and 10amps and cut your charge time way down. When you get close to full put them back into parallel and finish the top balance.

THIS!

 

[curiouscarbon]

I believe in OP! We are all just trying to navigate this weird new technology?

 

[TommyHolly]

Not matched 100% but close. Yes you could charge them all together but with that tiny power supply it will take forever and I am worried that at this point you may have defective cells that might cause even more issues. That is why I would do them separately so that you can find any bad ones now. To start with you really need to undo them and at least check all the voltages and label them with tape so that you know what each ones SOC is. What is the voltage of the whole string right now without the charger on them?

Edit: I just reread your post and realized that you did not try the high voltage charging. So assuming all is well your just going to have to wait it out for several days or get a bigger charger or a better solution is to disassemble and check the SOC then match the closest batteries together into the packs and put them on a BMS with a proper charger.

For the last month I've been testing all 48 cells and performed both a standing resistance test and a individual Capacity Test for each cell. (See results on my other posts). Thats the reason why they aren't fully charged. (Also see the Matching SOC post I made.)

I do not have a 30v charger. My variable volt chargers are the standard 0-20v 10A versions. So no 24v batteries for me.

The Voltage of the entire parallel string of all 48 cells is about 3.3v without a charger so its roughly 50% charged.

 

[TommyHolly]

I believe in OP! We are all just trying to navigate this weird new technology?

Thanks. I guess I'll not take any chances and just charge the batteries at the standard 3.65v max.