With all the talk about exploding Li-ion cells, it is hard not to become paranoid about the situation. Even though I charge my cell phone and iPad without any concern, I can’t help worrying about my 18650’s and 14500’s when they are charging. I’m not paranoid about it but rather superstitious. I am afraid that because I know of the issue, that by not doing anything about it, will cause it to happen.
From what I have read about the issue, it would seem that the biggest risk factor is overcharging. If the charger misses the cutoff voltage and the cell is overcharged, things can happen.
To minimize the risk, one should be sure to have good cells that are in good condition, a good charger, and one should be present during the charging process so any problems can be dealt with immediately. There have been many times that I have started charging cells with the intention of monitoring the process, perhaps doing something else, but still being present in the same room. Often times I would forget, and leave. Many times I would find myself suddenly realizing that I had left the charger on and I was now miles away. Common sense would tell me that everything would probably be OK, but there is always that slight chance……… 
I hate that feeling.
One strategy that I use is the “cut my losses” strategy. That is do my charging in the car while I am driving. In that way, I am present during the charge. If anything goes wrong, at least I’m present. Second strategy is to charge in the car parked outside away from the house at night. Then if anything goes wrong, well, it’s only the car.
Even so, there are many times I need to charge cells in the house and knowing how it can go, I have rigged a setup that gives me some peace of mind.
What you see here is an in wall mechanical 1 hour timer installed in a metal junction box. The 2 chargers when plugged in will run for a maximum of 1 hour depending on how the timer is set. It might take a couple of sessions to fully charge depleted cells, but at least I don’t have to worry about something going wrong and having them over charged. For the times I need to charge more than 4 cells at a time, I can add a power strip.
Here is what it takes to build one. I will not show how to do the wiring because if someone does not know how to do this, they should not even try. The voltages involved are dangerous and this should only be done by qualified individuals. As they say on Myth Busters, “Do not try this at home!”
The parts:
Also needed is a metal junction box with rounded corners Rounded so as not to scratch the surfaces that the finished box is placed on.
I used a rectangular box with rounded corners in spite of the news of Apples recent court victory against Samsung 
Here is the story on that (It cost Samsung $290 million)
http://www.theinquirer.net/inquirer/news/2308671/samsung-dealt-usd290m-blow-in-apple-patent-infringement-case
Anyway, back to the real world, I had to make some modifications to the parts to install them in the junction box. These modifications are nothing new and are provided for by the parts makers when they manufacture them. It is not uncommon to mount this switch and receptacle in this box.
First I partially disassembled the timer to remove the mounting tabs.
The mounting tabs then come right off.
To mount the timer to the face plate, I had to file a sightly larger opening for the stem of the dial to fit.
I also had to file 2 more rounded corners for the timer to fit. (I hope Apple doesn’t find out) :bigsmile:
As with the switch, the mounting tabs on the receptacle have to be removed. It will not fit in the box as is.
Once again the manufacturer has made it easy to do, as there is a crimp already in place so that they will snap off with a twist.
The timer is held on with a nut and the receptacle is installed with the provided screws and nuts.
After installing the switch and receptacle, I wired in the cord and plug.
For the third time, I had to infringe on Apples patent! Notice I had to file 2 more rounded corners on the plastic dial plate! Rounded corners, what a great invention, Apple!
Remember, only a qualified individual should attempt the wiring.
Lastly, I installed rubber buttons on the bottom to help prevent scratching.
BTW, I find this timer to be useful when I use my chop saw or table saw. Anything that I use intermittently that I would be afraid to leave unattended. Also useful for the wife if she ever uses a steam iron, hair curler or electric heater.
How many times has anyone left their soldering iron plugged in? Lots of uses.
