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Cell top up time

gregcron

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Jul 19, 2020
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I've just got my cells in (14 out of 16, anyways) and am doing an initial top-up before building my battery bank.

These are the cells I got: https://www.alibaba.com/product-det...a2756.order-detail-ta-bn-b.0.0.4f792fc2H6rvdU

There are 16 cells total - I have 14 so far. They are wired in parallel and being charged by this power supply: https://www.amazon.com/gp/product/B081SKNHTV/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The power supply is set to 3.6 volts.
It's been charging for about a day and a half now and is still sending 1.5 amps of current. I'm wondering if this is the best way to do this top up.. if my math is correct, the 16 cells together are 4480ah. So if they're even at 90% capacity, they still have 448ah of charge needed, and at 1.5 amps from the charger, this would take something like 300 hours?

Just wanting a quick sanity check to make sure I'm doing things correctly.

Thanks for any help!
 
Yep. Worth checking your actual voltages with a voltmeter. You may find that there's a notable difference between the power supply and the direct measurement of the cells.
 
Thanks for the reply - I just ran out and checked and looks like the cells are at 3.36 volts.
So realistically could this process take 5+ days? Not the end of the world if it does, but just to set my own expectations..
 
Dial the PS up to 3.9V and max current. Monitor it every hour. Once the cells hit 3.65, you're done. If you can't monitor it, dial it back to 3.65.
 
Thank you for the replies.
So for a total of about 4 hours yesterday, I turned the charger up to 3.9V. The cells were still in the 3.37v range.

I left it overnight (turned back down to 3.6v), and they hadn't significantly changed by today. The charger was still outputting a couple of amps.

So today, following Will Prowse's top-up video, I decided to take 4 of the cells, wire them in series, and charge them on a standard 12v car charger.
I let that charge until the charger said it was complete.

When I took the cells off, the voltage is now varying pretty significantly -- all the way from 3.68v to 4.1v across the 4 cells.

So... good news is they charged quicker. Bad news, no idea what to do now. If I put them in parallel back on the variable charger, will the 4.1v cells come back down to level out with the others, or do I now need to discharge them?

If I need to discharge them, what's the most common way to do so?

Thanks
 
I wouldn't repeat that with the 12V charger. If your 4 cells ranged from 3.68-4.1, that's an average of about 3.9 meaning the charger may have pushed the battery to >15V. No good.

They're going to settle anyway. Once they're within 0.2V of each other, I'd put them back in parallel with the rest and continue charging.

When you turned the PS up to 3.9, did the current increase?
 
I wouldn't repeat that with the 12V charger. If your 4 cells ranged from 3.68-4.1, that's an average of about 3.9 meaning the charger may have pushed the battery to >15V. No good.

They're going to settle anyway. Once they're within 0.2V of each other, I'd put them back in parallel with the rest and continue charging.

When you turned the PS up to 3.9, did the current increase?

Yes, the current ranges 1.5-2 amps when at 3.6v. When at 3.9v, it's higher, around 4+ amps iirc.

Noted re: not repeating with the 12v charger. Just wasn't sure what kind of timeline to expect only giving a few amps, as several hours up to 3.9v didn't seem to budge them-- maybe 0.01v after several hours at 3.9v. Cells have been at 3.3x volts for 2+ days on the PS.

When you say they will settle - are you saying the ones measuring 4.1v will settle to a lower voltage even if there is no draw on them? I.e, I may check tomorrow and they will have settled to a lower voltage?

Thanks for the help.
 
Yes, their voltage will drop over time. The 4.1 should drop pretty rapidly. I don't remember where they land, but it will eventually be around 3.4V.

If you have a 10A supply and will monitor it every 30 minutes, I'd go as high as it takes (or at least 4.15 as a safety measure) to get the current to peak available.
 
Thanks - I will check the cells tomorrow, put them all back in parallel, and turn the PS up a bit -- hopefully can observe some progress.
 
Yes, their voltage will drop over time. The 4.1 should drop pretty rapidly. I don't remember where they land, but it will eventually be around 3.4V.

If you have a 10A supply and will monitor it every 30 minutes, I'd go as high as it takes (or at least 4.15 as a safety measure) to get the current to peak available.

I've just checked this morning.
The two cells that had high voltage are still high - 3.89 and 3.99 volts.
I've wired the rest in parallel and plugged it to the power supply - just charging at 3.6 volts until I can be out there to check on it every half hour.

What should I be doing with the two cells that are still at the high voltage? Should I put them back in with the others in parallel on the power supply or do I need to address their high voltage first?

Thanks for all the help.
 
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You could wire them in series and use a 12V light bulb to pull them down.

Don't put them back in with the others until they're within 0.2V. The purpose of that is a >0.2V difference may represent a pretty substantial difference in state-of charge. This will result in a LOT of rapid flow of current from the high to the low. There is a risk of exceeding the 0.5 or 1.0C charge rating.
 
Why not put a cells in parallel and not on the charger so the higher voltage cells get sucked down by the lower cells.

Stop being in a rush to ruin your cells.

The time you spend now playing with over charged cells the proper top balance procedure probably would of been done by now. ;)
 
Why not put a cells in parallel and not on the charger so the higher voltage cells get sucked down by the lower cells.

Stop being in a rush to ruin your cells.

The time you spend now playing with over charged cells the proper top balance procedure probably would of been done by now. ;)
^ The post above yours suggested this is a bad idea as it risks damaging the cells...

Hey - I'm not particularly in a rush, just new to this figuring things out as I go. I followed this video and took his advice to use the 12v battery charger:
which is what appears to have over-charged the couple of cells.

It sounds like that wasn't the best idea, so I'm not doing that anymore.

I have 14/16 cells wired in parallel and back on the power supply now. I've had them going for another 30 hours now -- so probably 100 hours on that charger now and they haven't budged from 3.37v. Most of that time has been with the charger on 3.6v , but I have turned it up to 3.9-4.4.v while checking every half hour for probably a total of 8 hours. Cells aren't budging.
Edit: They've been on charger at 4.1v for about an hour this morning. Latest cell reading is 3.38v so it has moved slightly.

I believe a previous person told me not to put the 3.9v cells in parallel with the 3.37v cells as it could transfer too fast and exceed the cells' charge profile. Is that correct, or can I go ahead and put the two higher-voltage cells back in? They are at 3.8 and 3.9v as of this morning.

Right now the PS is set at 4.1v and pushing 4.5 amps. I guess my concern is that the bank is 280ah * 16 @ 3.2v = 4480ah. So if they are even just 10% discharged, it means they need to charge 448ah. So at 4.5 amp charge rate, 100 hours. Which isn't terrible, but that rate is when charging at 4.1volts meaning I need to monitor every half hour for 100 hours. So that means I can't charge overnight -- I have to kick it back down to 3.6v, 1.5amps, bringing charge rate up to 300 hours...
 
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No. Once again an end user was in a rush to top balance. Took out of parallel, put in series than on a 12v charger to "speed" up the process.
Then wonder why the cells puffed or over voltage.

Slow and steady or quick and worries.
 
Be forewarned when the voltage starts to rise it will happen quickly, playing with higher voltages best to keep an eye it especially since they've been on the charger for so long. ;)
 
No. Once again an end user was in a rush to top balance. Took out of parallel, put in series than on a 12v charger to "speed" up the process.
Then wonder why the cells puffed or over voltage.

Slow and steady or quick and worries.

Yeah for sure. I thought following Will Prowse's video was a safe bet. Now I know otherwise. :/

You recommended putting the 3.7v cells in parallel with the 3.37v cells. Is that the recommendation or is that dangerous to the cells?
 
That's what I would do and not put on the charger. Do it for a day or so the lower cells will draw off the higher cells.
 
Yeah for sure. I thought following Will Prowse's video was a safe bet. Now I know otherwise. :/

You recommended putting the 3.7v cells in parallel with the 3.37v cells. Is that the recommendation or is that dangerous to the cells?

It is a safe bet. It may take a very long time as he states.
 
Why not put a cells in parallel and not on the charger so the higher voltage cells get sucked down by the lower cells.

Never do that unless the cell voltages are almost equal. As someone else pointed out, the transfer of energy would be huge and could exceed the cells maximum charge rating.
 
Never do that unless the cell voltages are almost equal. As someone else pointed out, the transfer of energy would be huge and could exceed the cells maximum charge rating.
Alright.. I'll have to wire them in series and discharge them, then. Those two cells are still at 3.8/3.9v. I guess I'll wire them in series with 2 others for a 12v battery and plug the fridge into it for a bit.

The trickle continues on the charger.. still at 3.8v after being on it all day today. Maybe tomorrow's the lucky day.
 
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