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Recharging batteries while in a project

So I'm thinking of a few projects using rechargeable batteries and I wanted to try something. I want to have a power cord attached to the project that can plug in to a standard AC socket to recharge the batteries. I have no experience with rechargeable batteries beyond putting them into the box and sticking it in the wall. I want to be able to hook up 6 AA rechargeables and have no idea what DC voltage I should be using. I have an old charger for a two way radio that runs at 9V and was designed to charge the 4 AAA batteries inside. Would this work? It would be nice because it's small and even has an LED to indicate the charging status. Is this possible and is there anything other than DC voltage I need to worry about? Also, is it safe to hook that up as long as there's a switch to disconnect the batteries from the project? Any help is appreciated!

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chief tyrol8 years ago
If I hooked it up to a USB port, would it charge? it's four batteries in series, so 4.8 volts. and I believe that it's 2000 miliamps.
110100101108 years ago
as long as its not too sensitive stuff you can just connect the charger as if its just the batteries or keep the switch off when you charge you can build easily charger without or with overcharge protection. the charger without protection consists of voltage source higher than batteries + resistor + diode and thats all as long is there is no break in the battery connections the voltage won't rise too much above that of the battery. but if a battery becomes loose you get your device conected directly to the charger. make sure the charger output canot damage the device (example - electronics may get damaged instantly. motors and relays and leds will overheat but usually survive such accidents. if the charger output resistor is large compared to the device (slow charger and heavy device) then it won't ever get higher voltage at all)
chief tyrol8 years ago
I have built a rechargeable battery powered flashlight, and was wondering if there would be any way to charge them while in the circuit. This is the circuit that I currently have, and was wondering what voltage would be ideal to charge it. I am using 4 AA Ni-MH batteries hooked up in series, and I believe that they are 2000ma.
flashlight.GIF
jdog110 years ago
If a guy were to get a rechargable drill at a yard sale that had no charger and used a w/wart that was slightly over the battery voltage could that take out the forward drive? Just curious. Smoke Tester
InventingMan10 years ago
LasVegas, you are right. I overlooked the fact that the charger is going directly into the circuit and will fry it. This may only work if you were to isolate the batteries from the circuit while charging.
InventingMan10 years ago
You could take apart a standard AA battery charger and wire it to the project and ac plug like in the picture.
charger.bmp
Absolutely not! A battery charger does not contain the necessary filtering to protect the battery powered device and could very well fry the electronics. A complete charging/supply circuit would be required for this to work.