Don't you just hate it when your brand new batteries arrive, and you carefully install them in your charger, only to have them go flying accross the room and bouncing off the floor when you go to remove them, and try to pry them out of the charger?
I see that as well. It’s normal on the newer TR-001 chargers.
I’ve examined these closely. The circuit that controls the two-colour LED is not digital. It has a crossover point where the red LED slowly fades with the charge current. Once the charge current drops below about 30-40 mA, you can no longer see the red and it goes green.
So, Red = charging, Orange = Almost done, Green = Done.
Side-Note: This charger does not terminate charging when it goes green. That’s fine as long as the voltage measured between the contacts without a cell in there is 4.25V or less. Both of my chargers were 4.24V on one of the slots. I’ve since modded them so they are 4.21V or 4.31V based on the switch.
This is not fine for LiIon. I you always remove the batteries with a few hours there will probably not be a problem, but keeping the voltage connected will wear down the battery.
The specifications for a LiIon battery usual lists a "termination current", this is the minimum current you are supposed to charge with, when the current goes below this limit you are supposed to turn it completely off.
Never had that problem, as I don’t use cheapish bay chargers, such as mentioned TrustFire TR00something.
I also don’t use oversized protected cells, so even if I had a cheapish bay charger, it most likely wouldn’t send my cells flying across the room.
Note: If you read this comment, make sure you read the last paragraph too.
Have you asked manufacturers about that directly? I have. Well, two manufacturers anyway. I used to think the same way, because of the manufacturer specs.
In a former life I helped design a solar Li-Poly charger that does not terminate, it just did CC/CV with CC at 5A and CV at 4.2V per cell (four cell packs).
My concern was that we did not add intelligence to cut off the charger when the charge current dropped below 150mA (3% of max charge current, the manufacturers termination spec).
The cell manufacturer stated that there is no issue with leaving the charger circuit connected as long as the output voltage does not exceed the max charge voltage of the cells (4.25V in this case). I’d give the manufacturer names but it was all under NDA. This was for Li-Poly, but the charge specs for Li-Ion is the same.
Apparently they would rather leave the spec open to interpretation. The natural response of most designers is to err on the side of caution (what I wanted to do) so they introduce a termination. The rest (like the design I worked on) go the cheap route. Later in the design, we switched to LiFePO4; these are much more tolerant to charge/discharge abuse that Li-Ion or Li-Poly.
Manufacturers generally state a termination current so you know when the cell is fully charged. The additional charge delivered by the charger after the termination current is negligible.
With this information, I still propose people do not trust their (especially cheap) charger to reliably never go above the max charge voltage.
The cell breakdown experienced by keeping a cell at 4.20V in a charger should be about the same as keeping a cell at 4.20V out of a charger. As part of my job, I have left packs connected to chargers for days, weeks even. No loss of capacity was detected.
Having typed all of that, I do not intend to alter anyone’s safe practices with this comment. It is for reference only. The two manufacturers I dealt with certainly do not represent all manufacturers. They also could be wrong. I urge everyone to charge safely by monitoring the process and removing the cells from the charger when they are done, within reasonable time. I do this, not because I think the cells will fail, rather because I don’t trust the chargers in general. If you do not trust a non-terminating charger to stay lower than 4.25V, why would you trust a terminating charger to terminate? I choose to trust neither of them. Do not leave cells in a charger just so you know they’ll be ready when you need them. Also, don’t panic if you happen to leave cells in the charger for a few hours after being charged; they are not damaged because of it.
No, but I would expect the guys designing LiIon charge chips has. All the chips I have seen they implement logic to turn off the charge at a specific current. They do also sometimes include automatic restart if the cell voltage drops below some threshold.
Just making something with constant output voltage and current limit would have been much simpler.