Charging and top balancing with 10A bench power supply

JustAGuy101

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Well, I think I've read all the related threads about this topic and am encountering a condition I don't understand.

I have 4 new 206 AH LiFePo4 Cells which arrived at between 3.265 and 3.269 volts each. I believe this is pretty standard and
represents a (roughly) 50% state of charge.

I have an overkill BMS with bluetooth module. I have watched Will's initial top balancing video and downloaded and read, several times,
the PDF file that explains how to charge and top balance.

First, I attempted to charge each cell individually , with the power supply as recommended by Will in his video but never could get any one cell to get above about 3.30V

I then assembled the cells into a conventional 4s, 12v battery with the BMS and attempted to use my 10A PS to charge/balance the cells that way (at 14.5V). According to the app that comes with the BMS, the battery reached 100% capacity with each cell only reaching a very consistent 3.349V on all 4 Cells. I verified this with two different multimeters.

I am currently attempting to top balance all 4 cells by connecting them in parallel and charging at 3.6V. I followed the instructions in Will's video as well as the instructions in the PDF file for balancing in parallel. I set the voltage on the PS to 3.6 and Amperage to max with the parallel pack completely disconnected from the PS. So far so good. Voltage on PS reads 3.6 and the CV light is on. However, when I connect the PS to the pack, the voltage display on the PS goes to 3.5V, Amps goes to 10.1A and the PS switches to CC. Is this OK? Will the PS switch back to CV at some point as charging continues? What is happening here?

Thanks in advance.
 
D

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This is expected behavior. The cells are holding down the voltage below its set point, so the current on the supply is maxed out (current limited charging, aka constant-current). Once they fill up in 10-20 hours or so it will switch to constant voltage mode, eventually reaching your voltage set point of 3.6V.
 

JustAGuy101

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This is expected behavior. The cells are holding down the voltage below its set point, so the current on the supply is maxed out (current limited charging, aka constant-current). Once they fill up in 10-20 hours or so it will switch to constant voltage mode, eventually reaching your voltage set point of 3.6V.
Thanks Paul. So, when the voltage begins going up on the PS display, the amps will begin to decrease and the PS will switch to CV mode?
Sam
 
D

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So, when the voltage begins going up on the PS display, the amps will begin to decrease and the PS will switch to CV mode?
Yes, or rather the current won’t decrease until it switches to constant voltage mode.
 

JustAGuy101

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Yes, or rather the current won’t decrease until it switches to constant voltage mode.
Thanks again. I kind of thought those events would occur but didn't want to sit here watching my new cells cook, not realizing I was doing something wrong. I watched videos where the PS would go directly to CV when connected to a paralleled pack of cells and the display would be around 4 amps or so. If my understanding is correct, that's because those cells were in a much higher state of charge (say...90%) while mine are at a much lower SOC. Therefore, the PS is using all it's might (amperage wise) until the cells get to a higher SOC.

Samm
 

JustAGuy101

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Adding this for the benefit of anyone who might read this thread in the future looking for info on top balancing.

Just an update, It took the better part of 3 days to top balance my 206AH pack with a 10 amp bench power supply
(I've ordered a 30 amp Victron). A couple of key observations here.

Whether charging a single cell or a complete pack, set the voltage on the power supply before connecting to the cell/pack and don't disturb it, even if it reads low when you first connect the cell/pack. The power supply will change from constant current to constant voltage pretty quickly and then, slowly, the voltage will come up to the intended level and the amps will decrease over time.

Be patient. The cell and pack voltages are very slow to respond to either charge or discharge due to the very flat voltage curve of the lithium technology. It seems like nothing is happening until you approach either end of the state of charge curve, then things happen quite quickly.

I also did a capacity test on my 206AH pack using Will's suggested Chinese load tester (can you say that or should I just say "load tester"?) It took 15.5 hours for the BMS to detect <2.5 volts on one of the cells and shut down the party but the pack ultimately gave up 218 AH (according to the tester). Much happy. I'm sure that capacity will come down over the next couple of cycles but I'm still happy.
 

aclosson

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Feb 15, 2021
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I have a bank of (4) new VariCore 3.2V 280Ah lifepo4 batteries wired in parallel with a 10A bench supply. Charging is based on Will's instructions and it has been between 3.5 and 4.5 amps for 60 hours so far and the battery voltage is been pretty stable at 3.2 volts. For those of you that have already done this, how long should I expect it to take to hit 3.65V?

Thanks,

Art
 

smoothJoey

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You usually have to make custom charging leads to get any significant current flow.
assuming you are getting full current.
Also assuming that your cells come ~50% charged which is typical.
280 amp hours * 4 cells * .5 state of charge / 10 amps = ~56 hours.
The voltage won't begin to rise until the very end.
 

aclosson

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SmoothJoey: When you say custom charging leads, do mean larger diameter cables compared to what came with the power supply?

Thanks,

Art
 

smoothJoey

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SmoothJoey: When you say custom charging leads, do mean larger diameter cables compared to what came with the power supply?

Thanks,

Art
Test with the leads that came with the psu and then try my suggestion.
For best results use10 awg pure copper with quality crimped ring terminals on both ends.

 

GXMnow

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When you get close to full charge, any voltage drop in the leads will cause the power supply to go into CV mode early, and start reducing current before the pack reaches full voltage. This can make the last 0.05 volts take far longer as your power supply drops to 2 amps instead of it's possible 10 amps. Reducing the resistance between the power supply and the cells helps a lot. So making up a set of short heavy wires from the supply to the cells can save a lot of time in the end. Some people try to fake it out by setting the supply voltage higher, DON'T DO THAT!! As the cells get close to 3.6 volts, they will start to climb much faster, even as the current falls. So please, set the supply voltage with no load, to 3.65, no higher, and leave it. You have to be patient and let it do the job. The lower resistance wires can shave off several hours, and still be safe. Turning up the voltage is not safe.
 

aclosson

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Gary and Joey: Thank you for the suggestion on increasing the charging cable size. I just made up a new cable using 10g wire and the current jumped to 9.1 amps! I'll bet that if I had done this from the start I would be done already! Before anyone asks, I did set the voltage prior to attaching the battery to 3.65V.


charging.jpg
 

Javalord1

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Gary and Joey: Thank you for the suggestion on increasing the charging cable size. I just made up a new cable using 10g wire and the current jumped to 9.1 amps! I'll bet that if I had done this from the start I would be done already! Before anyone asks, I did set the voltage prior to attaching the battery to 3.65V.


View attachment 44375
I did exactly the same . Thanks for the pic!
 

Got2Golf

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Jan 2, 2020
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Thanks for this thread. I have a ac/dc power supply that has a variable output voltage between 11 and 15V at 30A. If I set the supply to 14.4V and attach it to my LifePO4 100AH battery I should see a set number of amps (say 25) at the beginning at some voltage. As the battery fills the amps will drop naturally Heading toward 0A. If I stop the charging when the amps is about 2 or when the BMS cuts out this should be an ok approach to charging a previously balanced battery pack. Is that true? The battery will not be 100% but will be around 90%. Am I correct.
 

GXMnow

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14.4 is 3.6 for each cell if they are perfectly balanced. If you don't have a BMS, that is cutting it pretty close. One high cell could easily run away going that high on a 4S pack without a BMS balancing the cells. I would set the CV voltage down to something like 13.6 which still gets you over 90% charge. But even at that, a runaway cell could still go too high without a BMS. With 3 cells at 3.3 volts, and one could be hitting 3.7 volts.
 

Got2Golf

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Thanks GXMnow, I have a 100 A Simple BMS from ElectricCarParts. I like the idea of charging at 13.6 when using shore power. If I am on the road I will be using the truck alternator through a Sterling 30A DC 2 DC charger which has a customizable LiFePO charging profile with Bulk and Absorption and float. before when I was on Shore power, I was running the AC 2 DC power into the the DC2DC charger then to the battery. That has worked but is impractical when I transport the battery pack into the cabin or work site so charging direct from the AC 2 DC would be better. I am looking to find ammeter controlled relay circuit so I can shut off the power supply when amps drop below some threshold. For now I will use a timer and just watch it.

Thanks for your input.
 
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