MC3000 starting to show higher IR for 18650 batteries

klrman

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Feb 25, 2009
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All of a sudden my MC3000 reads higher IR on all 18650 batteries. Cleaning the tabs and battery terminals doesn't make a difference. Any negative effects to charging when this chargers displays higher IR readings? For example, I will have four samsung 30Qs with one reading 48 IR and others reading up to 300 IR in the same set.
 

sbj

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Feb 19, 2017
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That should have no influence on the charge.
Swap places with the IR measurement and press the slider against the battery during the measurement.
The batteries should not be empty and have normal room temperature.
 

Gauss163

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That should have no influence on the charge [...]

Actually it will have an influence on the charge if the higher IR reading is accurate. Namely, the batteries will be less fully charged (at the same charge settings). You can compensate by lowering the charge termination current (and/or slightly increasing the termination voltage).

Note also that IR increases significantly when a cell is near empty or cold (see below), so you should avoid measuring it in those conditions (unless that's what you seek).
6PkU4.jpg


Graph excerpted from p. 1-4 of Challenges and Solutions in Battery Fuel Gauging, by Yevgen Barsukov.
 
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klrman

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Thanks for the chart. They came at 3.4V and I charged them to 4.1V at 1A with termination at 0.1A. They did not all come in at exactly the same voltage after charging.

Not sure why the MC3000 does this only with any of my 18650 batteries. 26650 batteries are all good.
 

klrman

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Any thoughts as to why all of a sudden it's hard to get low IR readings with 18650 batteries but not 26650 batteries with the MC3000? I'm thinking of bending the negative tabs a little on the charger but not 100% convinced if I should do it or not yet.

I've cleaned tabs on the charger and terminals on the batteries, which used to make a difference but doesn't anymore.

Edit: I seemed to have found a way around it. By adding the cells one by one and testing each time for IR, it either gives a good low reading the first time or after one or two slight rotations thereafter. Then I move on to the next cell and do the same. Not sure why but all of a sudden my charger has a hard time getting good readings when I try to adjust the reading if I fill all the four slots first and then test for IR. Anyway, my workaround seems to have worked.
 
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