I have taken my "conclusions" from later in this thread and decided to edited them right into the top of the thread for all to see more clearly:
From Post #60 in this thread:
- All WF-139 chargers, regardless of what "version" it is. Use a Constant Current only charging algorithm that can reach *charging* voltages of ~4.25-4.35+V during charging depending on the capacity of the cell being charged.
- Charging a small unprotected cell in with this type of charger could cause charging voltages of 4.4V or higher to be reached in theory.
- Most would agree that this charging method does not follow most li-ion manufactures recommendations for charging, and will probably reduce the life of the cell.
- Charging a small unprotected cell (like a RCR123) in this charger, could come with increased risk of fire/explosion.
- The Older WF-139 chargers, will measure ~10-12V open circuit, and will continue to trickle charge cells after the charge has been terminated. This could lead to fire/explosion if left unattended for long periods of time.
- If the charge is terminated by the cells protection, which is very common when protected RCR123 or similar size cells are charged in this charger, the cell will not be trickle charged because the cells protection will hold the circuit closed after it has tripped.
- Newer WF-139 chargers, will measure ~5V open circuit, and will not trickle charge after termination.
Video is of a pair of 3.7V protected AW brand RCR123s on a WF-139 charger.
When voltage got to around 4.30V I had to grab the camera.
http://www.youtube.com/watch?v=w05TzgYHayY <watch this video.
This amazed me.
Ever wonder what's going on behind the scene with your WF-139?
I decided to run some tests to explain some of the weird behavior of this charger.
MANY people have reported that when charging AW RCR123s in this charger, they "terminate" at around 4.16V. I have speculated that the charge was being terminated by the cell at a voltage much higher than this, and then settling down to 4.16V without a supply voltage, I was correct. This video not only proves that (notice the voltage jumps to the open circuit voltage of the WF-139 when the charge "terminates"), but also that during the charge, the WF-139 is indeed holding the cell in a state of over-charge.
Here's a picture of the cell moments after charge was terminated:
THE WF-139 DOES NOT APPEAR TO HAVE A CV STAGE AT ALL.
The WF-139 is holding a CC stage until the cell is somewhere in the 4.3X volt range, and then, terminating with the expected result of the cell settling to around 4.20V. This charge method is not considered terribly bad, but it's not terribly good either.
If you notice in the video, the voltage reading fluctuates, it "dips" down during the charge every few seconds. I believe the charger takes a "reading" of the cell voltage with the charge stopped every few seconds to see how much farther it needs to go to get to around 4.20V open circuit. My multi-meter is probably not showing how far down the cell voltage is compared with the charge voltage on these little "blips" because it's not responsive enough to catch it, so to speak. It's probably "RMSing" the value a bit so we're not seeing the whole picture.
On a smaller cell, the voltage is ramping up a lot faster than on larger cells, all the way to the point of tripping the PCB before it even makes it to 4.20V open circuit. This is why the smaller protected cells are not coming off the charger at 4.20+V like larger cells often do with this charger, the PCB is not only terminating the charge, it is also holding the circuit open until the input voltage is removed, this prevents the WF-139 from being able to do it's famous over-charge via trickle method.
More testing Observations:
On a pair of AW brand protected 17500s:
Charge voltage was at 4.31V when the charger terminated the charge and voltage dropped to 4.22V still on the charger. ~20 minutes later this had settled to 4.21V. I'm going to leave this on the charger with the volt-meter in place for another hour or more and try to capture the voltage rising as I expect it to from trickle charge.
More test results and pictures to follow.