Help me make sense of WF-139 charging data

[EssLight]

I have a WF-139 charger and a pair of AW's protected 18500 cells that I bought from Lighthound. I have put the cells through four charge cycles so far, and I monitor the charging voltage periodically using a multimeter. I was concerned about the maximum charge voltage that the WF-139 would apply, and decided if I saw 4.26 volts, I would stop the charge. Each time, the charging voltage has reached 4.24 or 4.25 volts, and then the charging light turns green. But, when the light turns green, I measure 4.60 volts across the charger terminals. When I remove the cells and measure them out of the charger, they measure 4.00 volts. If I let the cells sit a while, or use them for a couple seconds in a light, they then measure 4.16 to 4.18 volts.

My guess as to what is happening, it is not the charger terminating the charge, it is the protection circuit in the cells being tripped. And because the protection circuit has tripped, that I why I only measure 4.00 volts from the cells right out of the charger. Is this the correct explanation?

Is AW's protection circuit designed to interrupt charging at 4.25 volts?

If the maximum applied charging voltage was 4.25 volts, does it make sense that the voltage of a rested cell is only ~4.17 volts? (I have let the charged cells sit for two days, and they do maintain that voltage.)

I have read that if you want to make the cell last longer, you should stop charging at 4.10 volts. Is that 4.10 volts measured while charging, or 4.10 volts when the battery is removed from the charger? If I remove the cell at 4.10 volts on the charger, out of the charger it only measures 4.06 volts.

Thank you for any help you can offer.

EssLight

 

[VidPro]

yes protection is ususally set at 4.25, some was set as high as 4.35 (long ago) but it was only for protection, it assumed that there would be proper charge and it was the last chance. the spec is something like 4.2 +- .05 but todays curcuits are pretty acurate. again totally dependant on the cell, even from the same dealer or manufacture , it could vary due to thier design at the time. but generally 4.25.

now here is the hard to understand part. depending on the RATE you charge something, the cutoff for the charger OR protection, could occur earlier THAN the cell itself has fully reached some voltage.
because
when you apply power to the battery that does not mean the battery is actually AT that voltage, it is at that voltage WHEN the power is applied.
when the power is removed, it will show the actual battery voltage, after a rest, it will drop a teeney bit further again.


so if you read the voltage with a charge applied, it will be both the battery and the charger, not just the battery itself.

IF (a big if) it is a voltage max charger, with an indicator light, the light will turn on at some set voltage. but the charger can continue to "top" off the cell to the voltage max of the charger. the indicator LED is just set to some voltage point, and varies a bit.

reverse this, and the same thing is true, if your drawing a LOT of power off the cell, specially leetel cells, the voltage drops down quite a bit, remove the load, and then you can read the "rested" voltage of the cell.

to complicate things further, li-ion charge alogrythm is actually supposed to slow down at the end of charge, if the charge rate is LOW enough, there is no real need to slow down.
but there are faster rate chargers that do not Bother to slow down near the end of charge. they will still work, but they arent following exactally what is supposed to be done.
IF the thing slows down near the end, it is MORE likely to reach a higher voltage, as opposed to cutting off quicker because the charge is still on when the voltage is read.

Some chargers like an OLD pila, would DEPEND on the protection curcuit, they will go OVER the normal voltage for a li-ion charger, and the "cut-off" will occur via the cell. that would be a terrible charger to use on an unprotected cell.

if your charger has an unloaded max of 4.6v then it is likely that it was intended ONLY for protected cells, or it sits different depending on the load.

i probably didnt make sence of your charger, but might have given you the tools to do that for yourself.

 

[VidPro]

weird analogies:
if you push a Boulder up a small hill , it will move a certain distance up that hill, when you stop pushing, it will roll down the hill a bit. eventually it will rest at some point, untill force is applied to move it in either direction.
when your pushing the boulder it will be moving , but not nessiarily because the boulder itself is moving by itself. it takes the outside force (the charger or load) to change its state.
if you want to know where the boulder will stop, you have to stop moving it.

lots of ultrafire cells are protected, but that charger is supposed to stop at 4.20 +- .05 like everything else.
makes me wonder if its a charger Designed to be used only with the protected cells?
or if your batteries in your meter are good , the only reason i mentioned this, is i got a free meter with some order, and when the battery in the meter was low, the readings it did were all over the place.