Differences between discharging/testing devices

DarkRaven

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Alright, I've been thinking about this for some days now. But before I dive into this completely I wanted to ask around. Can't imagine I'm the first one thinking about it.

Have you come across someone who tested various devices against each other (and maybe the same device several times) for consistency? Or done it yourself?Obviously it is no surprise that there are differences between different devices but I think it might be worse than at least I thought. Not worse as inthe end of the world, I'm not suggesting everyone re-test their cells, but as more and more people get into this the more important are reliable and comparable figures.

If we come to the conclusion that this hasn't been done before I will organize a little something. For science! :)

edit:
If we do this, maybe someone will borrow their device to me for the duration of the test? I'm prepared to buy some as well, but if we can manage it that way I would obviously prefer that. I will cover the shipping costs. I live in Germany so I guess this is EU only, makes no sense to ship something overseas.

Also we need a list of testworthy devices, I'd say the 4 to max. 8 most popular or so.

I have cheap purpose built testers made from chinesium as well as an SkyRC IMAX B6, a SkyRC MC3000 and a SkyRC D400 (which probably no one would buy just for discharging cells, but as it is here I can use it for comparison). So I need an Opus and ... (insert your suggestions!)
 

owitte

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I also thought about this and already did some (not really serious or scientific) tests with my 5 Opus chargers. Conclusion: There is a more or less random difference between devices, but since this israndom andspreads over thousands of tested cell, it doesn't really matter for me...

But it's definitely interesting for me and I'm curious, so what scientific experiment do you have in mind?
 

DarkRaven

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I'm thinking about comparing all popular devices against each other with the same set of cells. And also maybe some unpopular ones, we will see. If this has been done though then there is no point in doing it again. That's why I'm asking first if someone knows about something like this. I don't, haven't found anything, but that doesn't mean anything. Could have just missed it.

It is not going to be super scientific, there is no rocket science involved. But it is a more methodical approach to this and I think it could be of value. I'm prepared to buy some of these devices to do this comparison. But more on this once more people have read this and maybe also commented on it.
 

daromer

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Have had that idea too but at same time I dont care much about the difference and I personally stick with 1 type for all testing. With that said i would love to see such a test done.
 

DarkRaven

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SimonW said:
This is an excellent page : http://www.lygte-info.dk/info/indexBatteriesAndChargers UK.html
Not so much a comparison between each but a very thorough review/test of each.

A summary table is linked here : http://lygte-info.dk/info/roundCellChargerIndex UK.html

Same table but Analysers (capacity measure) only: http://lygte-info.dk/info/roundCellChargerIndex Analyzer UK.html

That looks like a very comprehensive list but doesn't cover the important part in detail, which is discharging. Nice page though!

daromer said:
Have had that idea too but at same time I dont care much about the difference and I personally stick with 1 type for all testing. With that said i would love to see such a test done.

That's correct and that's what I thought as well. However, this has limitations as well. I've realized only yesterday that my testing of my first 400 or so cells with the IMAX B6 was a bit of a waste of time because I wasn't thinking about what I was doing. And as soon as you start to talk with other people about it it all falls apart quickly. A 2000mAh isn't a 2000mAh cell, depending not only on how you test it (that is quite obvious) but what device is used. At least that's how far the theory goes and I reckon that this is not a negligible difference.
 

DarkRaven

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If we do this, maybe someone will borrow their device to me for the duration of the test? I'm prepared to buy some as well, but if we can manage it that way I would obviously prefer that. I will cover the shipping costs. I live in Germany so I guess this is EU only, makes no sense to ship something overseas.

Also we need a list of testworthy devices, I'd say the 4 to max. 8 most popular or so.

I have cheap purpose built testers made from chinesium as well as an SkyRC IMAX B6, a SkyRC MC3000 and a SkyRC D400 (which probably no one would buy just for discharging cells, but as it is here I can use it for comparison). So I need an Opus and ... (insert your suggestions!)
 

dougal

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Surely the most important quality for the buyer/tester/user is consistancy, to provide results that are at least comparable, regardless of 'absolute' accuracy, in order to permit classification of cells into bands of similar capacity.

One is looking for reproducibility (same cell same result on retest under same conditions) and minimal production variability (same cell same result on an 'identical' machine).

Obviously everything has a tolerance and any measurement its error band and thus confidence limits.So it would be unrealistic to expect precise reproducibility.

If one were setting up 'production' with plural parallel test stations, it would be reasonable to expect 'identical' test stations to produce more consistant and comparable results than a variety of different models with subtle variations in their automated routines.

But how consistent are the results from any one design of tester?
To that end, I'd be very interested to learn more about the "more or less random variation" seen on owltte's testing with 5Opus examples.
How much measurement variation (error!)is to be expected with thosedevices?
 

DarkRaven

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I think it was SimonW who said he is getting results with the Opus that are generally too high and vary even on the same device. If you now do tests across five different Opus the result will surely not get any better.
 

dougal

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DarkRaven said:
I think it was SimonW who said he is getting results with the Opus that are generally too high and vary even on the same device. If you now do tests across five different Opus the result will surely not get any better.

I was quoting owltte from post 2 in this thread.
 

DarkRaven

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I know. Just wanted to mention that even users of single Opus report issues, you can imagine what this might look like when you test across five units.
 

dougal

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DarkRaven said:
I know. Just wanted to mention that even users of single Opus report issues, you can imagine what this might look like when you test across five units.
Thanks, I'm hoping someone will quantify the variability!
 

Bert

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DarkRaven said:
I think it was SimonW who said he is getting results with the Opus that are generally too high and vary even on the same device. If you now do tests across five different Opus the result will surely not get any better.

about the higher values, apparently the opus discharges down to 2.8V and cannot be changed (
)
 

DarkRaven

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Simon reported values 5% to 15% higher than they should be. There is almost no noteworthy capacity between 3.0V and 2.8V for most cells so that doesn't explain it. And even if it was, it doesn't explain the variation between 5% and 15%.
 

SimonW

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Correct, on average the opus (*my* opus, yours may be different) is +11% on what an iCharger gives me. Regarding the cutoff of 2.8, that is a moot point as my iCharger can be set down to 2.5. For my testing it was set to 2.8. Regarding repeatability on the opus, I'll get back to this later when I get home. (On the road ATM)
 

daromer

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Yeah its around 10% above but its kind of consistent. Atleast its consistent enough for testing cells for powerwalls where you dont really stress the cells at all.
 
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