diy solar

diy solar

Well that was a slight miscalculation.

Stircrazy

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Jul 5, 2020
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so I am charging 5 cells in parallel for top balancing my cells (4 for the battery and one spare) and my power center is only putting out 4 amps at 3.65V and the cells were down to 30% when I started, so needless to say it is taking a long time as it is over 1000AH I am putting in in parallel (my first bone head move forgetting that parallel would take more amp of charging haha..

up until now I have been seeing regular gains every day in cell voltage but the last couple day it has been painfully slow.. like going from 3.330V one day to 3.332V the next. is that extremely slow voltage change normal around the 90 - 100% range?

any yes I have realized I should have put it into a 12V configuration then put it in the camper solar to bulk charge it to 95% then tore it down and did a top ballance, but its to late now.. its just pure stubbornness that's getting me through it now haha
 
yes I have realized I should have put it into a 12V configuration then put it in the camper solar to bulk charge it to 95% then tore it down and did a top ballance, but its to late now.. its just pure stubbornness that's getting me through it now haha
No, you’re doing it the right way. It will take a while, my 16 cell 230 ah packs generally take most of 2 weeks. Nothing seems to happen for a long time, then you reach a point where a lot happens very quickly!
 
1000Ah x .7 / 4A = 175h (7.29 days)

When did you start?
well I was doing it while I was awake on days off. so was here and there for the first 40 to 60 hours. the last 3 days it has been charging 24/7 and I'll leave it like that until I figure there is less than 10 hours of charging left.
 
You are still in the flat part of the curve. Around 3.36v is where it should move faster.
ok great, that's good to know. I went out and bought a fluke multimeter the other day as I thought my old radio shack one was messed up haha, I did fine the radio shack reads 0.006V higher than the Fluke. I have been just going with the fluke but I might have to get a buddy to bring his over to see what his says.
 
You'd be better served by getting a balancer that can handle it, then just connecting everything and putting it in use. They have really good active balancers now.

And yes what you are doing takes forever. That is why you should generally charge in series first until BMS cutoff with a faster charger before you put them in parallel, that way you only have to do the very end.

But better still is what I put first, then you can check it a month later to verify the top balance happened or just skip that step entirely.

Also a spare is not necessary. You'll want to discharge it back to 30% for longevity as well, although pulling it down even 10% is probably enough. Consider how you want to do that with a single cell.
 
You'd be better served by getting a balancer that can handle it, then just connecting everything and putting it in use. They have really good active balancers now.

And yes what you are doing takes forever. That is why you should generally charge in series first until BMS cutoff with a faster charger before you put them in parallel, that way you only have to do the very end.

But better still is what I put first, then you can check it a month later to verify the top balance happened or just skip that step entirely.

Also a spare is not necessary. You'll want to discharge it back to 30% for longevity as well, although pulling it down even 10% is probably enough. Consider how you want to do that with a single cell.
ya my first battery I built I was flying by the seat of my pants and didn't know much about the top balancing so I just put it together and let the BMS top balance it. I wanted to do it this way to see if I notice any differences. as for my spare, it is the one that was replaced because it had a slight dint and scratch on an edge, so I am charging it up to make sure it is fine, then I will either use it for a stand alone project, or discharge it a bit and like you said store it. Im just trying to figure out what I can do with only 3.4 ish volts right now.
 
ok so, I got it up to 3.58V and unplugged it while I was at work so I could finish the 3.65 on my days off while I could pay attention to it. Just went to check the voltage and after 5 days of rest the batteries are at 3.48V does that make sense I was expecting 3.4V at the highest. any they are all within 0.001V of each other. should I call that good and assemble the 12V battery?
 
On my 8s 280Ah pack, I connected the BMS, charged until one cell hit disconnect, then connected a 3.55V power supply to each low cell until they all hit 3.55, then the pack should be in balance.
 
I'd call it plenty good enough.

FYI, if the bus bars are still connected, they are what's holding all the cell voltages identical.
 
Just went to check the voltage and after 5 days of rest the batteries are at 3.48V
Resting voltage might be one of the less well defined aspects of the chemistry in the community. Frequently surprises are found that run counter to the established "facts".

But also use two multimeters.
 
Sorry for hijacking,
I see the consensus here is to top charge all cells until the current drops to "0" for preliminary balance.
I know that cells degrade faster at higher then 80% soc. In this method you're keeping the cells at close to full soc for days.
Is it really the best option?
Why not discharge all cells to 3.2v, 0a current as an example?
 
Sorry for hijacking,
I see the consensus here is to top charge all cells until the current drops to "0" for preliminary balance.
I know that cells degrade faster at higher then 80% soc. In this method you're keeping the cells at close to full soc for days.
Is it really the best option?
Why not discharge all cells to 3.2v, 0a current as an example?
If you mean to DISCHARGE them down to 0% to reach bottom balance, you would be searching for 2.5V not 3.2
3.2V us somewhere in the middle of the knee, and is a useless voltage to balance to.
 
well hit another snag, went to start throwing together the battery in 12V configuration yesterday and found my BMS used 24AWG wires, now I have to find some 24AWG ring termanals......
 
Meh, the 14 red rings work great if you fold the 22 on itself.
ya, I was going to see if I can find some locally before I double stuff up. I could also dig out another plug set and make a jumper with larger wire if I have to.
 
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