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First Time Discharging and Then Charging New BLS 190Ah LiFePO4 Cells.....Is This Right?

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Calothrix

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1. Received 8, new 190Ah BLS cells back in April that will eventually be used to construct 2, 12-volt, 190Ah batteries that will be connected in parallel (4S2P configuration).

2. Voltages upon arrival of the cells were all either 3.261 or 3.260.

3. Initially connected the 8 cells in series and tested them by running my DC fridge (can run on 12 or 24V). Ran the cells down to ~ 2.9V (voltages varied from 2.870 to 3.006). I disconnected the pack from the fridge and then connected the batteries in parallel and after a few hours they were all at 2.950V.

4. Decided to let them sit for a while and monitor voltages. I expected the voltages to increase, but not for 6 weeks (or more, just didn't want to wait any longer)! Initially, the voltages increased about 4mV per/day and this trailed off to less than 1 mV/day after 6 weeks. So, voltages increased from 2.950V to 2.996V as they sat over the 6-week period. Is this normal? good? bad?

5. Kept cells in parallel and decided to top balance with my adjustable power supply/charger (0 - 30 volt and 0 - 10 amp). As per Will's video, I set the voltage to 3.65. I tried to set the current at 6A but the power supply would accept a maximum of only 1.98A.....why is that? To get a current of 6A, I had to turn the power supply up to 5.05V; however, the wires from the power supply quickly warmed up at this setting, so I decided to turn the settings back to 3.65V and 1.98A.

6. After charging for 3 days, the cells went from 2.996V to 3.220V.....but the rate of cell voltage increase had slowed to almost nothing and the current on the power supply had dropped from 1.98 to 1.31A. So, I increased the power supply voltage to 4.95 and this resulted in a current setting increase from 1.31A to 4.85A. After 7 days at this voltage setting, the cells increased from 3.220 to 3.313V and the power supply current has decreased from 4.85A to 4.83A.....but again the rate of cell voltage increase has now slowed to a crawl! Is this because the cell's resistance is increasing? I'm guessing I am getting pretty close to the upward "knee" of the charge curve and I do not want to overcharge the batteries, so how do you recommend I proceed? Should I turn the voltage setting up again and then at some point turn it back down to 3.65? I am not in a rush, but do I have hours, days or weeks before these cells are fully charged?

Thanks!!!



 
2. IMHO, X.XXX is noise. Rounding to X.XX is more meaningful. Yours are closer than a gnat's ass.

3. The loaded variation of 2.87 to 3.01 is concerning.

4. Normal.

5. Limitation on power supply? Cheap units can't necessarily supply the full range of both numbers. They can also be power limited at different voltages. It could also be malfunctioning. If wires got warm a 6A, you need better wires. High resistance in the wires might also mean that the PSU is seeing 3.65V at the set 5A, so it's going into constant current mode. Actually, I bet this is your issue. Are you using the stock leads, or did you make your own? What wire gauge and how long are the leads? Are you connected at opposite ends of the battery?

6. you have 1520Ah of rated capacity you're charging (8 cells in PARALLEL). It will take you a month to charge them at 2A and 12d to charge them at 5A. 3 days at 1.5A is 3*24*1.5 = 108Ah. Another 7d at 4.83 = 811Ah. In total you have put in about 920 Ah.

IMHO, you have time to order a cheap LiPo RC charger that can actually charge at 5-6A or more and will have no issue with 3.65V termination, or get a different power supply.
 
1) Eight 190 AH assembled as 2Px4s would be a 380 AH pack. You need to make sure each two cells put in parallel are best matched.

2) 3.261 or 3.260v per cell is mid to slightly below mid state of charge. Did you bring all cells to full charge (3.65v) before building array? Full charge is only way to ensure all cells are at same state of charge.

3) By running them down without fully charging first just is going to make your job of balancing state of charge a bit harder.

4) LiFePO4 have high efficiency charge and discharge. They will settle a little after heavy load or charging but it doesn't take long for them to settle to their rested state. A few hours max. Specs on LiFePO4 batteries are 3% per month self discharge although good battery will be 1-2% per month.

5) Because you discharged them first, it will take a very long time to top balance them. I cannot speak for your power supply but sounds like it is current limited but not current limit settable causing the the drop to 1.98 amps to prevent overheating of power supply.

6) It will take two to three weeks at that charging rate to top balance cells to 3.65 vdc.

Suggest to buy one of the $50 switching power supplies capable of 30v/10 amp output with voltage and current settable limits. Do not raise above 3.65v as if you do not watch them carefully you can go to higher power supply voltage setting and damage cells. It is like watching grass grow.

On the good side, doesn't look like you have done anything to damage cells.
 
snoobler said:
Are you using the stock leads, or did you make your own? What wire gauge and how long are the leads? Are you connected at opposite ends of the battery?

Thanks snoobler and RC! I am using the stock leads and they are connected at opposite ends. They are about 40" long but gauge is not written on them. They appear to be slightly smaller than the 12 awg leads on my fridge, so I am guessing they are 14 awg.

Here is the link to the power supply I am using: https://tacklifetools.com/products/...0v-10a-with-course-and-fine-adjustments-mdc02

Should the current on my power supply start dropping quickly when I enter the knee portion of the charge curve? Thanks again!
Click to expand...
 
It may sound drastic but you should be able to short power supply leads and adjust the current limit. With open leads set voltage.

When load exceed current setting the voltage on power supply will drop until it hits your set current limit. You should see the same current limit you set with shorted leads.
 
snoobler said:
IMHO, you have time to order a cheap LiPo RC charger that can actually charge at 5-6A or more and will have no issue with 3.65V termination, or get a different power supply.
Click to expand...

I have been at odds with myself as to whether or not to parallel top balance. It seems to me batteries that are well matched should not need this so I have been leaning against it. Also have the worry about ending up with puffed cells using an adjustable power supply. But I do have lots of time to do whatever and had thought about getting one of those cheap r/c chargers, or a single cell charger that will terminate the voltage at 3.65 volts. This would be the safest way to go. Do you or anyone else have any recommendations for something in the $50.00 range?
 
Matched batteries and batteries at different state of charge are two different things. Issue with LiFePO4 batteries which is also a good thing is their discharge holds a pretty contant voltage so you in mid state of charge range you cannot rely on voltage level to determine state of charge. Only way to be sure is to take all cells to full charge at 3.65 vdc with charge current dropping to low levels (less then 0.05 C in amps).

Resistor dump BMS only are intended to compensate for difference in cell leakage current. Do not rely on a resistor dump BMS to balance batteries at different state of charge.
 
Last edited:
Calothrix said:
Here is the link to the power supply I am using: https://tacklifetools.com/products/...0v-10a-with-course-and-fine-adjustments-mdc02

Should the current on my power supply start dropping quickly when I enter the knee portion of the charge curve? Thanks again!
Click to expand...

I have something similar. Was about $30 cheaper, but looks like the same unit in white. I wouldn't trust it to do what you're trying to do.

Consider that you're charging at very low voltage. Low voltage means "low pressure" when trying to push current. Thin wires and alligator clips (I effing hate those things) perform very poorly at low voltage If those are really 12awg, it shouldn't be so bad, but if they're actually 18awg (which would work safely for 10A) with alligator clips, you could easily see a 0.3-0.4V drop due to the resistance of the connection over 40". Use the shortest, thickest wires you can get, and use ring terminals, or just smash a bare wire under the terminal bolt.

The current on the supply will not drop quickly because you're not pushing much current relative to the size of the battery. If you were pushing hundreds of amps charging at the maximum safe current for the cells, it would fall fairly fast. You will probably only notice a slow falloff as the days pass.

Gazoo said:
I have been at odds with myself as to whether or not to parallel top balance. It seems to me batteries that are well matched should not need this so I have been leaning against it. Also have the worry about ending up with puffed cells using an adjustable power supply. But I do have lots of time to do whatever and had thought about getting one of those cheap r/c chargers, or a single cell charger that will terminate the voltage at 3.65 volts. This would be the safest way to go. Do you or anyone else have any recommendations for something in the $50.00 range?
Click to expand...

10A
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20A
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Charsoon Antimatter 300W 20A Balance Charger Discharger For LiPo NiCd PB Battery

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Both need 12V power. Both can act as dischargers INTO a 12V source (battery).

300W is clone of iCharger 206b. I have dozens of similar clones, and I highly recommend them for what they can do. The are LFP smart and can charge/discharge cycle cells and have a 200mA balancing port for up to 6S.

30A monster for 10S:
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Charsoon Antimatter 1000W 30A Balance Charger Discharger For LiPo/LiFe/NiCd/PB Battery

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Clone of icharger 3010b

All of these can spit out charge/discharge log data to DataExplorer or LogView.

I also have several of the 30A units. Love love love them.
 
Thanks for the suggestions and they look like awesome chargers. But like you said they all require a DC source so that would mean more expense.

On the other hand they support measuring the internal resistance of 1 lithium cell. Does this apply to a lifepo4 cell? If so that would negate the need to purchase an IR meter.

There is not a big price difference between the 10 and 20 amp one. Looks like there are discount codes too.
 
The 20A unit is truly nicer. A lot of people have old defunct 12V computer supplies laying around that can supply plenty of power on the 12V rail. 85A 12.4V PSU adapted from servers run around $80.

IMHO, once you own one of these, you become something of a battery wizard being able to charge all the the most obscure chemistries and tweak them as you like.

Provided your connection is very high quality, and you're using the balance board to record individual cell IR, they are reliable. The main leads suffer from voltage drop affects, but the balance port leads are measuring voltage without current, so they tend to be accurate. Note that they are only accurate to single mΩ. If you're looking for decimals, you're out of luck. They're also not necessarily absolutely correct, but they are consistent and very useful for comparison purposes. These are targeted at low resistance/high drain packs for the RC community.
 
Thanks again...got it. I think I am going to settle on one of the R/C chargers from Amazon. Something like this but not necessarily that one:


I know I could get a single cell charger from China that would have a higher charge rate. But a R/C charger like the one I linked would be a much better option due to the versality and it comes with an ac plug with the option to be powered by DC. If I was in the R/C hobby then I would go with one of the ones you linked to. In fact I would already have something like those knowing me:)

Generally speaking there is no doubt in my mind this is safest way to top balance. I would be very nervous using a bench top power supply.
 
Seems like you have been around a few blocks with R/C chargers. I appreciate your knowledge. Thanks for that link. So my batteries will be 8 200 amp cells. Hooked in parallel that's 1600 amps. That charger is capable of 6 amps so roughly 8 days to top balance if the batteries arrive around 50% SOC. uggg lol. But it's ok. Like I said I have plenty of time and will still be keeping an eye on the battery voltage with my DMM.
 
Gazoo said:
Seems like you have been around a few blocks with R/C chargers. I appreciate your knowledge. Thanks for that link. So my batteries will be 8 200 amp cells. Hooked in parallel that's 1600 amps. That charger is capable of 6 amps so roughly 8 days to top balance if the batteries arrive around 50% SOC. uggg lol. But it's ok. Like I said I have plenty of time and will still be keeping an eye on the battery voltage with my DMM.
Click to expand...

Yep. I have somewhere around 60-70 of them. I have a problem.

Sure you don't want to find a computer power supply laying around and get 20A? :)
 
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