Mass 18650 capacity test

[rg12]

I know those power wall builders who salvage cells test their IR and capacity and organize them in groups.
I noticed that they have a bunch of those 18650 chargers that show capacity on a simple LCD.
I was wandering how they measure capacity, because they need to discharge the cell and then charge it to full in order to get the real capacity.
Are those chargers smart enough to do and automatic cycle of discharging and then recharging to full?

 

[ichiban]

AFAIK, they test each 18650's capacity by charging it to full first and then discharging it to cut-off. That is the "discharge capacity" a cell can handle. Reverse to what you mentioned. I never compared results from discharging at various C, but think they should not be much off. I use Opus BT-C3100 charger to do that which is pretty reliable but not quite sure about the LCV. Come up with different values for various cells - spec wrote LCV=2.8V. Since whenever the cells or the charger (or both) get hot, it will pause for a longgggg while until temp drops back to almost normal - kind of irritating. That's the weakest point of this charger. Sometime it takes the whole day to test just 4 x 18650s, especially when dealing with old cells that tend to get hot (too warm) while discharging at 1000mA or so. I use a small 3" fan to blow the whole thing when discharging/charging. That helps.

If plan to do that in mass, you will need more of this charger - depends on where your budget and patience graphs intersect. However,it still takes a long time. Been there, done that. For learning purpose, it is OK though.

 

[rg12]

Does the Opus BT-C3100 measure internal resistance?
I'm reading about it and it seems that voltage reading updates every 30s (in the 2.2 version), isn't that super slow for you? what is the norm for these chargers?
Do you know where is the cutoff in this charger or can it be programmed?

 

[Hillhater]

Many/most of the better RC chargers (Turnigy included) will do auto cycling , capacity (mWh/Ah) and IR measurement.
Just check the specs in detail before you buy.

 

[ichiban]

Does the Opus BT-C3100 measure internal resistance?
I'm reading about it and it seems that voltage reading updates every 30s (in the 2.2 version), isn't that super slow for you? what is the norm for these chargers?
Do you know where is the cutoff in this charger or can it be programmed?

Yes it measures IR as Hillhater mentioned.

It is not the reading update of 30s, but it is the slow nature of charging+discharging cycle even you set the rate to the max 1000mA. Plus safety stops in between if it gets hot. It will take the whole day for a pack of 4 cells. Do the math then you will see what I am talking about.

See for yrslf...