Johannlog
The sun shines even on cold days
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Top Balancing "How to"
- Thread starter snoobler
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John Frum
Tell me your problems
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You should top balance.
Bluedog225
Texas
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I'm hoping the community can help me with mine...I'm in this same boat as here...yeah, like watching paint dry. ?
Got a Longwei CV/CC power supply, 4 @230A cells, arrived with all matching voltage at 3.290. I connected them parallel, made charging leads with 10awg and ring terminals as instructed, and started charging them at 3.4V. According to the 'manual' I could do this in steps. And frankly I was a little afraid of what might happen when I connected these two unknown entities (to me) together and started charging - unknown cells and unknown charger. That was three days ago. LOL After 3 days current slowed to a trickle, under 5A, and the cells aren't moving (up in voltage) - they're all still sitting at about 3.34V. Based on the current display on the power supply, and the length of time, I should have put more than 200 amps of energy into these cells.
Yesterday I could see they were going nowhere so I turned off the power and reset it to 3.5V and it took off again, now just over 9A. But after several hours it still had not moved the needle hardly any, they still all were sitting at 3.355 now. And current had slowed to about 7A.
This morning I thought I would see if I could at least get them all to 3.4V, so reset the power supply and started charging them again. Good current now, about 8A, but at noon they still had not budged, they're all sitting at 3.351. So I shut it down again to let them rest, thought I would try them at 3.6V tomorrow and see if I could get them to come up to full charge. After resting an hour they all match - they're all sitting at 3.343
Are my cells balanced? (enough?) Will they EVER get to 3.6 volts?
EDIT: I even tried setting the power supply voltage with my DMM, and while the adjustment is very sensitive, it's pretty accurate - at least to 50mA or so.
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That charge/discharge plateau is pretty large or long as in the time to charge.
Do not rush quality, have heard of great patience until an overcharge and damage.
It seemed like I was watching paint dry or a baseball game it took so long, but it will happen, steady as she charges.....
Do not rush quality, have heard of great patience until an overcharge and damage.
It seemed like I was watching paint dry or a baseball game it took so long, but it will happen, steady as she charges.....
I'm a little concerned about the cable you're using instead of bus bars. Given the low voltage and low amperage it should be OK.
The bus bars could be an issue. Numbering the cells from left to right, 1, 2, 3 and 4. The bus bar on the negative side that is on cells 2 and 3 isn't on the same plane as the terminal surfaces. It may not be flat on the terminal surface of cell 2 because the right end of it is raised up to fit on top of the bus bar that is on cells 3 and 4. Maybe you got the terminal fastener down tight enough to account for that and may be you didn't.
The bus bars could be an issue. Numbering the cells from left to right, 1, 2, 3 and 4. The bus bar on the negative side that is on cells 2 and 3 isn't on the same plane as the terminal surfaces. It may not be flat on the terminal surface of cell 2 because the right end of it is raised up to fit on top of the bus bar that is on cells 3 and 4. Maybe you got the terminal fastener down tight enough to account for that and may be you didn't.
I measured resistance across everything and the wire connectors are a little more (expected), but they all conduct.
Cell voltage wouldn't match so well if they were a problem, no? They wouldn't all charge the same level.
I'll pay much closer attention to mating surface on the actual pack build - tweak the bars, make sure everything lines up, super-clean the pads, etc.
What is frustrating is after three days of 5-8 amps they moved from 3.290 to 3.343.
Cell voltage wouldn't match so well if they were a problem, no? They wouldn't all charge the same level.
I'll pay much closer attention to mating surface on the actual pack build - tweak the bars, make sure everything lines up, super-clean the pads, etc.
What is frustrating is after three days of 5-8 amps they moved from 3.290 to 3.343.
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Just remember that when you put your cells in parallel Ah multiplies. So you are charging cells with a total capacity of 4 * 230Ah = 920Ah. If the cells were at 30-50% SOC when you received them you've got to add between 450-650Ah before they are full and balanced, at a best case of 10Ah per hour (10A) in the CC phase, and a real world average somewhat less than that. Voltage to SOC is not a linear relationship, most of that energy is contained within the flat part of the voltage curve, once you reach the 'upper knee' you will see the voltage increase quickly. Example:
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MisterSandals
Participation Medalist
I should have put more than 200 amp hours of energy into these cells.
8A x (3days x 24h/day) = 576Ah (at 3.4V) (= 1958Wh)
576Ah x (3.4V/12.8V) = 153Ah (at 12.8V) (= 1958Wh)
That's about (153 / 230) = .66 of your battery total capacity (230Ah x 12.8V = 2944Wh)
So...keep charging?
Math and electrics makes my eyes glaze over. Why I dropped out of the electronics class at the community college when I was 18.
I forgot about multiplying the 230Ah times 4. ?
Thanks guys. I'll hook them back up and set it for 3.6V. Keep watching it.
MisterSandals
Participation Medalist
If you're top balancing to 3.6V, then keep at it!
You didn't specify your technique for setting voltage to 3.4V but make sure you set that BEFORE connecting to the cells.
I like your conservative approach using 3.4V for your first go around with this equipment. Once you trust it for your next batteries (oh yeah, this is just the beginning) you can probably set to your target voltage and be a little more relaxed.
Good luck! I think you're on the right track and doing just fine.
What is frustrating is after three days of 5-8 amps they moved from 3.290 to 3.343.
You're headed in the right direction! LOL.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Yes. My guess is you are most of the way there. Normally I would encourage a pre-charge in series, but you are far enough along now that it is probably not worth breaking the pack down and re-wiring it.
Note: If you are not familiar with the series pre-charge, take a look at this:
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
diysolarforum.com
Yeah, I printed out the 'manual' and poured over it.
Voltage is set, supply turned off, THEN connected to the cells, hit power button. Even connected to the opposite ends of the pack for plus and minus for good current flow through all the cells. Checked continuity between the cells, and individual cell voltage. I'm happy that they're at least staying all the same voltage.
I really did forget about multiplying the four cells times the amps - it has to charge a LOT more than the 230A I assumed!
MisterSandals
Participation Medalist
No, certainly fewer than 230A, at 12.8V since it was partially charged when you received them.
Lets look at a single 230Ah cell (3.2V). On paper at nominal voltage, it contains 230Ah x 3.2V = 736Wh of power
4 of these contain (4 x 736Wh) = 2944Wh of power.
This 2944Wh can be expressed in amp hours in any voltage, lets use 3.2V and 12.8V.
2944Wh / 3.2V = 920Ah
This represents your 4 cells connected in parallel, at 3.2V.
or
2944Wh / 12.8V = 230Ah
This represents your 4 cells connected in series, at 12.8V.
Going a bit further, lets say you used an inverter to convert to AC (assuming 100% efficiency):
2944Wh / 120V = 24.5Ah
Converting to watts and watt hours is very convenient when converting between voltages, whether its DC or AC because watts are watts.
curiouscarbon
Science Penguin
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hello! ???? ? ⏱So...keep charging?
Math and electrics makes my eyes glaze over. Why I dropped out of the electronics class at the community college when I was 18.
I forgot about multiplying the 230Ah times 4. ?
Thanks guys. I'll hook them back up and set it for 3.6V. Keep watching it.
this plateau of patience is universal, by voltage alone it looks like nothing is happening! heck
lets talk amp hours, ignoring volts
one cell is 230 ampere hour
Connect Cell Parallel mean Add Amp Hours
so 1 ampere for 230 hour should charge it
or 230 ampere for 1 hour should charge it
there four cells parallel, so 230*4 ampere hour
230 times 4 is 920
so 1 amp for 920 hours should charge all four cell
bottom line. continue monitor voltage. calculate ampere hour (1ampere*1hour) expect for Full Charge
your pack is 920Ah in picture
so 1 amp for 920 hours
or 10 amp for 92 hours
or 100 amp for 9.2 hours
sort of deal.
good luck! sorry if i muddled the water further?
It seems to me that this process takes so long because us DIY guys can only afford low voltage/low amperage power supplies. If we could buy a low voltage, high amperage power supply then the process would be much faster.
Now the 'wire in series and charge' and THEN do the parallel makes WAY more sense. I could have gotten them close in a couple of hours with the 55A 12V charger.
This stuff all makes much more sense when you actually do it.
Now it's charging at 10.0A CC. When the voltage gets a little closer it switches to CV - it's set for 3.62V constant volts.
I'll keep an eye on it, should be mostly there. Probably tomorrow.
This stuff all makes much more sense when you actually do it.
Now it's charging at 10.0A CC. When the voltage gets a little closer it switches to CV - it's set for 3.62V constant volts.
I'll keep an eye on it, should be mostly there. Probably tomorrow.
Diesel Pro
New Member
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- Jul 21, 2021
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To charge my 8) 280ah cells I put them in 2 groups of 4 I series and used my 12v 40amp battery charger set to AGM. You really need to watch the cell voltages though so they don't get out of hand. Once you get close you can use the little charger.
Now I have the set assembled as 8s and I'm discharging at just over 100 watts so 3+ days steady then I will charge at 29v 10 amps with the BMS connected.
Now I have the set assembled as 8s and I'm discharging at just over 100 watts so 3+ days steady then I will charge at 29v 10 amps with the BMS connected.
So...keep charging?
Math and electrics makes my eyes glaze over. Why I dropped out of the electronics class at the community college when I was 18.
I forgot about multiplying the 230Ah times 4. ?
Thanks guys. I'll hook them back up and set it for 3.6V. Keep watching it.
Just set the power supply to 3.65v and let it run. Others have done the math, so I won't bother.
As the document in the resources section tells you, a good idea (too late now probably for you) is to hook them up as a pack with a BMS and charge in series. It's at least 4 times as fast.
https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/
