Large Charger for 21700 cells, 50-100 cells simultaneously

veer

1 mW
Joined
Sep 19, 2019
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18
Hello
I am looking for a charger that can charge 50-100 cells at a time individually. I have not been able to find any good options or reliable company's. Is there a solution that I can follow through for my requirement?

If there is an option of discharging like in the Cell aging machines big companies have, that would be awesome to have! lol :D
 
Cell count alone does not help.

Unless you mean at 1S voltage?

Are they LFP at 3.2Vnominal,

or the 3.6-3.7V li-ion type?

If at a higher voltage, do you need a balancing charger, or will you use other circuitry to handle that?

what is the series count?

e.g. 16S LFP is 48Vnom, 7S li-ion is 24V

Do you need adjustability for different use cases, gentle normal cycling vs stressful benchmark testing?

Then, what C-rate, stressful fast charge

or is gentle/slow OK? Do you also need that to be adjustable?

What input voltage, AC grid power or lower voltage DC?

Willing to roll the dice on cheap chinese only a few hundred bucks?

Or looking for a quality western unit more likely to be reliable for hundreds of charge cycles?

Does it need to be new or is eBay OK?

 
john61ct said:
Cell count alone does not help.

Unless you mean at 1S voltage?

Are they LFP at 3.2Vnominal,

or the 3.6-3.7V li-ion type?

If at a higher voltage, do you need a balancing charger, or will you use other circuitry to handle that?

what is the series count?

e.g. 16S LFP is 48Vnom, 7S li-ion is 24V

Do you need adjustability for different use cases, gentle normal cycling vs stressful benchmark testing?

Then, what C-rate, stressful fast charge

or is gentle/slow OK? Do you also need that to be adjustable?

What input voltage, AC grid power or lower voltage DC?

Willing to roll the dice on cheap chinese only a few hundred bucks?

Or looking for a quality western unit more likely to be reliable for hundreds of charge cycles?

Does it need to be new or is eBay OK?

hey thanks for the reply, my mistake for not providing enough info. I'll do that below.

I need charger for 1S. I will be charging and discharging the cells independently to see the capacity of each. I am planning to do a couple builds for me and my friends, and dont want bad cells to be added to the battery. I already have an IR tester, but no capacity measuring device.

I cannot use the normal capacity testers available in the market as of now as the max I have seen are 5 cells at a time. I will be testing 4000+ cells and even if I buy like 10 of these capacity testers, it'll just not be worth the time. Is there a faster way to test the batteries capacity before I spot weld them together?

also, what are the downsides of just using the cells without testing them for their capacity? From my understanding, the capacity of the whole pack in decided by the cell with the lowest storage. And if the difference is too high then the parallel cells might start charging the empty cell and cause a potential short! I want to avoid that at ANY cost.


- NMC 21700 cells,
- Gentle cycling is fine, but i need the faster solution, if stressful is faster, i'll prefer that.
- 1C charge and discharge is fine, as I need to measure the capacity only.
- AC grid power 220V preferred. Fine with DC too. Industrial grade 380V AC can also be arranged.
- New or old device both are fine.
- Chinese or western, both are fine as long as they are reputed and have a decent service life.

Hope I answered everything. What are my options?
 
OK, lots of bits to untangle here, as your understanding grows you will learn how to properly phrase the right questions

which of course is 90% of the way to the right answers.

And you may change your design along the way.

IR testing is very nebulous, not just accurate gear required but very strict adherence to protocols standardising test conditions, not just SoC% but current levels as C-rate and most especially temperatures.

Best to focus on capacity, then use ESIR as a secondary benchmark.

> charging and discharging the cells independently to see the capacity of each

Dummy load is the key term there, precisely timed CC discharge between 100% Full and your defined LVC. Ideally programmable cycling charge/discharge with data logging, export to PC for pretty graphs

more accurate than coulomb counting, wattmeters.

Low voltage range is key for single cells.

Amps rate also, small cells are OK with low currents, testers are available for cheap, even below $100 per cell

example:
https://www.ebay.com/itm/DL24P-4-WIRE-Battery-Capacity-Tester-Electronic-Load-Power-Tester-Discharge-Mete-/133833259226

big cells (hundreds of Ah) require higher currents, those get expensive, into the thousand$ quickly, not much available in between.


> Is there a faster way to test the batteries capacity before I spot weld them together?

Not at reasonable pricing afaik.

The only accurate units I've seen are one cell at a time.

Please link to examples that claim to handle multiple cells concurrently.

Are you just verifying new cells or binning used/scrapped ones?

For the latter such testing cannot be skipped. For the former spot-checking might be enough if the cell vendor is trustworthy.

Why use such tiny cells? so much easier to just have one string of cells at the pack capacity you need.

What total Ah are you looking for?

What is the use case for the packs? Size and shape available?
 
john61ct said:
Dummy load is the key term there, precisely timed CC discharge between 100% Full and your defined LVC. Ideally programmable cycling charge/discharge with data logging, export to PC for pretty graphs

Is there an example of this done by someone on the forum? I don't think I have skills enough for doing all that, but might be able to follow along.

Low voltage range is key for single cells.
I was under the impression that for NCM chemistry, lower voltages don't have much energy. Can you explain this a bit?

big cells (hundreds of Ah) require higher currents, those get expensive, into the thousand$ quickly, not much available in between.

Yeah, I got in touch with some sellers on Alibaba, they have a cabinet shaped cell tester facility for $3000. Tests 512 cells at one time! Lol
I'd like a smaller machine of the same time, like 50 cells or 100 at the same time. I'll attach an image of how that machine looks like

Are you just verifying new cells or binning used/scrapped ones?

The cells will be new. But I have seen people get variable capacity in cells from them. In a single 21700 batch from them of 3.7v 5A cell got capacity of 5.4a and 4.8a. That variable range will have a bad effect on the final battery right? But if that's just going to effect the final capacity, maybe I can leave that for now.

Why use such tiny cells? so much easier to just have one string of cells at the pack capacity you need.

What total Ah are you looking for?

What is the use case for the packs? Size and shape available?

Modularity, in a single word. There are plans to make a battery pack for a college project, with about 1600 cells, four 2-wheeler battery pack, 300 each, and solar storage for 2 medium sized homes. And keeping the remaining ones for future projects I have in plans. But since most of these will be car/bike battery packs, I'll use the same cells for solar aswell. Better negotiating power that way.

Shape is going to be rectangular mostly. With a couple of the 2 wheeler packs being slightly triangular. Those will be 20s12p packs. Solar I'm targeting 1000 cells in each of the two, so @ ~15wh that's be 15kwh. So that's 4s long packs. I haven't settled on the final configuration for those yet though.

Biggest problem is actually getting the cells from a reliable source!! Such a pain in the ass. If you have any information on that, I'd love that as well.
 
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