I built this simple charger / discharger for 3.7 volt Nickel Cadmium cordless telephone batteries. It could easily be scaled up to charge larger Nickel Cadmium battery packs. Those of you who work with these battery packs know that they must be completely emptied of charge before they can be recharged. This device makes that procedure easy.
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Signing UpStep 1: Materials Needed
You will need a number of simple materials and tools for this project. They include:
A wall transformer,or power supply; mine is 3.7 volts. The output of your charger will vary depending on the voltage rating of the battery you want to charge.
A small, incandescent lamp; this will use up the remaining power in the battery in discharge mode to prepare it for charging. I used a Christmas bulb, which works fine for 3.7 volts. You'd need a bigger one for a higher voltage.
SPST switch; for those who don't know, that stands for Single Pole Single Throw; it's the kind with three terminals on the bottom. I used a push button one, but any kind except momentary would work.
Wire; any kind that will carry the required voltage and current - which, in this case, isn't very much. You'll need about a foot, at most.
Clips or plug; You'll need something to connect the battery to the charger; my batteries terminated in bare wires, so I used clips (binder clips, as it happens, because I didn't have alligator clips). If your battery terminates in a plug, you could use a corresponding socket.
Something to hold everything, such as a small box. An altoids tin would work if you insulated it.
You'll also need something to cut the necessary holes in the box, and perhaps a soldering gun, although you could manage quite well without one.
A wall transformer,or power supply; mine is 3.7 volts. The output of your charger will vary depending on the voltage rating of the battery you want to charge.
A small, incandescent lamp; this will use up the remaining power in the battery in discharge mode to prepare it for charging. I used a Christmas bulb, which works fine for 3.7 volts. You'd need a bigger one for a higher voltage.
SPST switch; for those who don't know, that stands for Single Pole Single Throw; it's the kind with three terminals on the bottom. I used a push button one, but any kind except momentary would work.
Wire; any kind that will carry the required voltage and current - which, in this case, isn't very much. You'll need about a foot, at most.
Clips or plug; You'll need something to connect the battery to the charger; my batteries terminated in bare wires, so I used clips (binder clips, as it happens, because I didn't have alligator clips). If your battery terminates in a plug, you could use a corresponding socket.
Something to hold everything, such as a small box. An altoids tin would work if you insulated it.
You'll also need something to cut the necessary holes in the box, and perhaps a soldering gun, although you could manage quite well without one.
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sageserver
says:
Sep 25, 2009. 6:45 PMReply
what i do is just switch the dead telephone battery with the one inside the telephone and set the telephone in its own charger. I have two sets of phones that take 3 AA and 3AAA, so im set.
7
Deutschmann (author)
in reply to Sep 26, 2009. 9:03 AMReply
I don't use the batteries to power cordless telephones anymore; I don't even have the phones they came from. One of them, I just found sitting loose in the trash. What you describe would work, but this solution is significantly less bulky. I only mentioned cordless telephones because that's where they came from.
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