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Opus inconsistent readings?
#1
In the middle of charging the next lot of cells, something struck me as odd as the only tester I got at the moment (C3100) states the cells are full, yet the voltages are all consistent at 4.17v on all 4 cells. Tried the next set, ~4.17. If it is switched to discharge, it is the same reading. Multimeter is 4.14, 4.15 right after coming off the charger. Allowing the Opus to charge/test, the voltage reported on the Opus jumps to 4.21, 4.23 at the start. Verified the multimeter is reading correctly, new battery. 

Could this variance possibly skew the capacity testing as well? Need another tester to verify...
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#2
This is normal behavior.   Remember that as soon as charging stops, the voltage can drop a couple of milli-volts.     The 4.17 vs 4.16 type of thing is normal (8,000 cells and counting).   The test results will vary from test to test - even on the same cell due to various differences in resistance, cell, ambient temp etc.    Its not ment to control voltage +/- 1mv or to give test results within 5mah. I have 3 OPUSs and one of them reports pretty consistently 50mah lower than the other 2.

The OPUS (for cheap price) can easily get you with 100mah between cells  - e.g.  2930, 2955, 2960 can be lumped as '2900-3000' box, and 2550, 2520, 2585 can be lumped into '2500-2600' box, etc.   Its normal to sort cells by 100mv difference and then distribute them evenly for use.
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#3
But here is the odd thing; it seems the Opus is ok with only an almost full charge, whereas the dummy charger (Trustfire multifunction) will stop once the cell hits 4.2v, and is consistent between multiple cells. It may not seem like a large difference, but the $10 dummy charger seems to be a lot more accurate than is $30 counterpart. I am of the thinking that an almost full glass, still isn't a full glass.
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#4
This is why most ppl charge with another charger, even the TP4056's will pretty much charge up to a consistent amount. Even if not all them do, get enough so you can weed out the misfits. Then use the Opus only for discharge testing for capacity. Afterwards, the Opus can be used for general recharge that doesn't need to be specific voltage.

And yes, if a cell only charges to 4.14 instead of 4.2, it will throw off the capacity of that cell compared to the datasheet. You need to discharge capacity test from 4.2 down to the datasheet specs. Otherwise, the number you get will not be accurate enough to determine if the cell is bad, or was just a weak reading.
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#5
Its normal. Just Read the Specs. Tp or any other have same variance. Just stick with the Opus. There is nothing to gain and No it Will not throw off the capacity in such a way that it affects the result. It may vary 20mAh but the tester itself anyway have a variance of 100+.... So dont bother.

Its just a total waste of time since it doesnt gain anything
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#6
And Bte its not Ah .... Its mAh.
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#7
(01-01-2020, 11:32 PM)daromer Wrote: And Bte its not Ah .... Its mAh.
Yep - sloppy typing, thank you.  I corrected my post Smile
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#8
Think I'll go ahead and get some TP4056's anyways to speed things up, over a 1000 cells so far and a single Opus it takes time only charging/testing at 500mA. Come tax time I'll pick up another Opus as well.

Thanks for the input. Still makes me curious, if the voltage is sagging during charge could it also be sagging on amperage as well? It would make the tested cells have lesser capacity, but knowing that the Opus reports ~10% higher capacity according to other peoples tests, maybe it makes for a more accurate result. Without another more accurate tester I won't know.
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#9
Test at 1a instead. And get another Opus. Less whacking cells in and out and you Will do atleast 8cells per Opus and Day and you dont have to constantly fiddle around.


I run 10 of Them and process 80 per Day. I value the time i spend moving cells between boxes Smile

Ignore the Number part. Sort them in 100mah bins and your good to go. Note the expression. "pollish a turd" Smile
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#10
I have 3 OPUSs sitting at my desktop in my office...  kind of an ongoing background task.    
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