Measured cell diameters? Please add your data.

[John]

Hi,

I pulled out my digital calipers and started measuring a bunch of cells, with the wrapper on. Most of my cells seem to be out of round. The average minimum diameter seems to be around 18.15mm, And the average max is 18.25mm. The absolute max dia. I saw was 18.29mm

I am working through a batch of new old stack and all of my cells seem to come from at most 2 manufacturers.

I would be interested in data from others to try to figure out the range of cell diameters in the wild.

This data may be important to folks that are designing automated cell handling equipment. Either the data will show the diameters to be boringly consistent, which makes things easy, or the data will show that there are a significant number of outliers, which will make things interesting.

So I guess the reporting format is:

18.15-18.25 (18.29)

 

[Scepterr]

You can check the data sheets for whatever cells and it'll tell you diameter range to expect

 

[John]

You can check the data sheets for whatever cells and it'll tell you diameter range to expect

Scepterr,

Yes. But "as-designed" and "as-manufactured" are frequently different in the real world. I am curious about the "as-manufactured" dimensions.

We may find out that all of the cells are manufactured to a tight tolerance, and the data is boring. But we don't KNOW that until we actually bother to take the measurements.

If I had access to a bunch of cells from different manufacturers over a range of time, I would just measure them up and post the results. But I think all of my cells are from one, maybe two, manufacturers from a relatively short time period. So, statistically, I have a sample size of 1, maybe 2. Not enough data to form a conclusion.

-John-

 

[Scepterr]

Cells that are outside of the spec range for diameter should never have left the factory. If it's one of the top 5 manufactures I'm not worried about it. If it's something generic then who knows.

 

[John]

Cells that are outside of the spec range for diameter should never have left the factory. If it's one of the top 5 manufactures I'm not worried about it. If it's something generic then who knows.

Scepterr,

As an engineer that has worked in the manufacturing sector for decades, all I can say is that I wish that were true. Spec sheets frequently just parrot the relevant standards and have no direct bearing on the manufacturing process. And even if they left the factory in spec, by the time we get them they may no longer be in spec. I suspect that the ovalization I am seeing in my cells may come from handling and assembling the cells into batteries.

I will also add that just assuming everything is according to the spec sheet is a sure way to get your a** handed to you as an engineer. Never assume, test and measure...

Anyway, just for fun, could you measure some of your cells and post the results?

Thanks,

-John-

 

[Korishan]

I can also see that measuring we could potentially find out which cells maybe low mAh. Or cells that are not wanting to hold a charge, or are getting warm during charge or discharge.

It's possible that ones that are larger than spec could be getting near end of life, or getting hot/warm.

 

[owitte]

I don't really think cell diameter is in any way related to capacity or cell health. But until now, I didn't think of exactly meassuring it, was ok for me if it fits the holder... of course there may be a manufacturing tolerance, but since the manufacturing process is highly automated, it should be in the 1/100 mm for the cells that hit the market.

I don't have a digital caliper, but I'll get one, meassure my cells (those that are not in production) and get back here.

Hace sun!
Oliver

 

[Wattsup]

I think cell weight would be more pertinent to capacity.
Carry on as you were

 

[owitte]

I think cell weight would be more pertinent to capacity.
Carry on as you were

yep, especially for those from China filled whith wheat... I got one of those with a pocket light saying it has 5000mAh. After it was empty for the first time, I tested it and found less than 500mAh! then I weight it, had only 40gramms instead of around 60 like a "real" cell...