Multiple cell charging

RetiredAutoTech

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Been taking apart dewalt 9ah batteries and pulling 80% chargeable cells. Inr21700-30ts. Charging and testing on two bt-c3400. If I connect 25 parallel together what would I set my charge at? 4.2 volt but what ampage? Cells are rated at 3000 mAh and 1.5 amps is normal charge rate. Trying to save some time by pre charging before testing.
 
Welcome to the board!

Been taking apart dewalt 9ah batteries and pulling 80% chargeable cells. Inr21700-30ts. Charging and testing on two bt-c3400. If I connect 25 parallel together what would I set my charge at? 4.2 volt but what ampage? Cells are rated at 3000 mAh and 1.5 amps is normal charge rate.
When you connect cells in parallel - they are the same as a single cell in terms of voltage. So yes, 1 cell or 25 cells in parallel - both are fully charged at 4.2v. The difference is it would take 25 times as much current to charge all 25 in the same time period as 1 cell. As you mention, this spec - https://www.dnkpower.com/samsung-inr21700-30t/ - says 1.5a charge / cell. So you could do up to 25 * 1.5a = 37.5a for 25 in parallel.
 
Waiting for my ir tester to show up. Says it will be here first week in February. Also need to adjust the bt-c3400, been using it at .5 amp and taking 12 hrs to cdc 8 cells. Thanks for the information!
 
Don't overlook the potential issues of paralleling a bunch of cells at different voltages in order to charge them up. I opened that can of worms several days ago.

Cheers, John
 
So there isn't a good short cut unless you build a 25 slot charger and then test them on an analizer separately. The other problem I am having is the last box full of batteries I got were all filled with 21700 and the bt-c3400 I have doesn't list that size. It fits and seems to work just fine. Will I have any issues using it?
 
So there isn't a good short cut unless you build a 25 slot charger and then test them on an analizer separately. The other problem I am having is the last box full of batteries I got were all filled with 21700 and the bt-c3400 I have doesn't list that size. It fits and seems to work just fine. Will I have any issues using it?
No problems using CTs other than cells fitting in the slots - e.g. lithium-ion volt range is all the same regardless of packaging. You could use smaller magnets to clamp extender wires from the slots and then more magnets to clamp wires to the cells or some hack like that to use all 4 slots. But of course it may be more work than gain as you can also buy more chargers if $ aren't an issue so much :)
 
I bulk charge 24 cells at a time, using TP5100 charge controllers -- one chip and one cell holder per cell (so 24x each). This has the effect of not paralleling the cells, but allowing you to use a common power supply to all the chips. I basically built a "charge board" on a scrap piece of plywood. It has 24 cell holders, each one wired to the power output of a TP5100 chip.

The TP5100 chip power inputs are all wired in parallel to a lab-style benchtop power supply (which lets me control voltage and current). You could use a much cheaper power supply, since the TP5100 accepts a range of input voltages. Just make sure the power supply can provide enough current without overheating, etc.

As I said, this keeps the 24 individual cells separated -- they have no direct parallel connection to one another, so there are not weird surges between unbalanced cells when they are inserted in the holders. The TP5100 chips pull from the common power supply and charge each cell independently, to about 4.2v.

It really is a pretty simple setup. It might sound complex or expensive, but it's neither. I think I paid about a buck apiece for the TP5100 chips, and maybe $10 total for the cell holders. I have spares of all, because periodically something will fail and need to be replaced. It has worked well for my individual 18650 cell testing. (I do my discharge testing 24 cells at a time with calibrated ZB2L3 units, also cheap, but that's a topic for another thread. The combined setup lets me process ~100 cells per day pretty easily.)

Cheers, John
 
I'm guessing the power supply needs to put out enough ampage for the 24 cells. 36 amps in the 21700 example I'm working with. Would anything else be needed other then the tp5100 chips. Like a step down converter?
 
I'm guessing the power supply needs to put out enough ampage for the 24 cells. 36 amps in the 21700 example I'm working with. Would anything else be needed other then the tp5100 chips. Like a step down converter?

Ideally your power supply should be able to provide full current for each device attached to it, with some headroom so you're not overworking and overheating the supply. So, input current is going to depend on the draw of the TP5100 modules, not on the battery cells you are charging. I don't have the specs in front of me, so please double-check me, but I believe that my TP5100 chips charge cells at 1A. That's the output of the TP5100. The input current will vary depending on the voltage supplied to the TP5100. I forget the acceptable voltage range, but in my head it is something like 6v - 15v. Again, please double-check. I power mine at ~12v.

The TP5100 handles the voltage step-down to 4.2v on the output for the cells you are charging. You don't need any additional hardware for that.

CAUTION: This just came to me. Do make a mental note that the TP5100 is a dual voltage charge controller -- it can output 4.2v or 8.4v. Put another way, it will do 1s (single cell) or 2s (two cells in series for 8.4v) charging. However, when operated in 2S mode, it does NOT balance between the two cells -- so there is no guarantee that both will wind up at the same voltage. I use all my TP5100 modules in 1s / 4.2v mode. The chips I bought all came set for 4.2v mode, and there's a jumper you have to solder if you want to run them in 2s / 8.4v mode.

Also, the TP5100 is supposed to have built-in protection for reversed polarity -- in case you get careless and accidentally pop a cell in your holder backwards. Even the best amongst us will make a mistake sometimes. I can tell you from experience that the polarity protection works sometimes and...not other times. I've fried one or two TP5100 chips this way. You won't have any trouble knowing when you've done so -- they smoke briefly on the way out!

Hope that helps --
Cheers, John
 
Sound good I have a NPS605W DC Power supply , 300w 0-60V 0-5A should work. If it starts getting hot I'll have to upgrade. Only have 5 21700 holder and have 20 18650 showing up Saturday. Thanks for all the help.
 
Also most TP5100 modules in 2s mode need some extra parts to make them function "correctly". Otherwise a good chance the device will pop.
So best to just use them in 1s mode only.
And as DG98 mentions it does not do any balancing at all. So to be safe all around, only do the 1s mode.
Would anything else be needed other then the tp5100 chips. Like a step down converter?
TP5100's can take up to 19VDC input. They are the step down converter. They just only output up to 1A. So if you connect a bunch in parallel you can just make sure your PSU can output the number of banks in amps; ie 10 parallel chargers, 10Amps PSU output
 
Trying to add a volt/amp display to the circuit. The volt meter should be easy but I believe the amp meter should go in series after the tp5100 chip, Should I put in before the battery holder red wire or after in the black wire?

The digital meter is one of those cheap 3 dollar one off Amazon and has 2 plugs. Plug one has two wires and plug two has 3 wires.

Sumklin 5PCS 0.28" Digital Volt Amp Voltmeter Ammeter Meter DC 100V 10A 3 Bits Red+Blue Display Voltage Current Tester​







  1. Sumklin 5PCS 0.28" Digital Volt Amp Voltmeter Ammeter Meter DC 100V 10A 3 Bits Red+Blue Display Voltage Current Tester


 
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I would put the meter between TP/Load and battery. This way you could detect charge current and load current.
Not sure if those devices are bidirectional, probably not considering they don't have coulomb counting as well.

But at least you'd know how much juice is going to/from the battery.

However, things get more complicated if you have it so that you can have the TP plugged in *while* also the load connected. At which point, I'd put the meter between TP/Battery and Load
 
I made a tester that could test 100 cells a day on all 7 steps, that was pretty time consuming, yes.

Now check only v and divide them into 3 groups.
0-2v
2v-2.8v
2.8v-4.2v

Below 2.1v----> they go swimming in a bucket of salt solution.
2 to 2.8v get a separate grid with more checking.(4x5 cells and check evry 6 hours)

2.8v and up---> when i have 20 cells i solder them all together and i put a small psu on it to 4.2v.
C ya tommorow....
Then i desolder one side.
C Ya next month.

What is stil above 3.9v i keep

20230206_144356.jpg


20230206_144509.jpg


Hope this was helpfull.
When i have a box full, around 300, i will start up again, and so on.
With best regards Igor

With best regards Igor
 
Watch out for those green ones with the black insulator rings. They are the infamous Sony GR series that had oddly high IR and don't play nice with other cells. I have been setting mine aside and might turn them into a project with just them or sell them to someone that wants to do that :)
 
Now check only v and divide them into 3 groups.
0-2v
2v-2.8v
2.8v-4.2v
Are you also checking IR before you do the charging?? This would drastically increase your good cells ratio in the end without wasting energy/time. Even with cells that are low voltage, like 2V, could still be just fine. Just because they dropped that low doesn't mean they are bad, or will go bad. IR gives a much better status of the cell.
 
Are you also checking IR before you do the charging??
Yes.
How ever i do it with a:"french swing", meaning:
I check the ir with my yr1035 everything above 65 is away.
But there are as i call them: machine cells, used in power tool and ebike, those have a higher ir
those machine cells i keep up to 70 ish.

But my overall testing is changed a bit sinds i started on this site, but it was an excellent learning curve, in the beginning.
Many thanks to some wonderful and respected members!
I suggest (basically mandatory) for beginners to do the same.
I think i will make a update topic on how I test them now.(atm busy with a batch anyway:cool:).


Watch out for those green ones with the black insulator rings. They are the infamous Sony GR series that had oddly high IR
Those are one of the cells i call machine cells, they can deliver a higher output.(c rate)
I find them a lot in Hilti packs.
As long as they dont self discharge i dont have any problems with them.
Incl some icr and inr if i remember correctly have high ir
Same goes for those red sanyo's

My cell counter is about hitting the 25.000.....
 
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