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Ideas for Single AA and AAA batteries?


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I have some AA and AAA batteries lying around and looking for some ways to use them. Like when you buy a 4 pack of batteries, and the product only needs 3. What to do with the left over one?? I try not to mix batteries so I'm looking for some ideas on how to use them.

Some ideas like a single AAA flashlight, maybe a clock? Any other ideas?

I bought a 0.9V-5V DC-DC boost converter but it sucked, could not deliver even 50-100mA without large drop in output voltage

Also is it really a big deal if I mix two brands of Alkaline batteries, with similar levels of charge??

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You could build a single cell LED boost driver like the third schematic here, using only 2 transistors. Or you can use ZXSC310 IC to build a boost LED driver working for as low as 0.8V input voltage like this schematic here: http://www.homemade-circuits.com/2012/05/1-watt-led-driver-circuit-using-single.html

Alternative you can build a 1.2V to 5V boost DC-DC converter able to provide 1A max output current, like the second schematic here.

For drained AA and AAA batteries you can build a Joule Thief that is able to draw the last available juice from the almost dead batteries. Like the first schematic here.


LED Driver (1).png




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You want a power of 5V x 500mA= 2.5W. An AAA cell voltage is 1.5V when new and drops to about 1.0V so its average voltage is 1.25V. To produce 2.5W its current must be 2.5W/1.25V= 2.0A. The voltage stepup circuit will get hot with 2A so will use maybe 500mA extra current making the heat. Then the battery current will be 2.5A which is too much for a little AAA alkaline battery.

The datasheet of an Energizer AAA alkaline cell shows that its internal resistance is a maximum of 300 milli-ohms so its voltage loss will be 2.5A x 0.3 ohms= 0.75 V so its voltage will be 1.5V - 0.75V= 0.75V when brand new and its voltage will drop as it is used. But since the voltage to the stepup circuit is only 0.75V then its current must be 5A which is impossible from a little AAA cell. 


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Thanks, that puts things in perspective - I checked out the datasheet of Energiser AAA and even if I only want 100mA at 5V (0.5W) and I draw 400mA-500mA at an average of 1.25V to get there, my mAh capacity of the AAA would only be around 450mA in total as per datasheet capacity discharge curve. That's a huge drop, as it could be as high as 1100mAh at 25mA, and 900mAh at 100mA.

I think it could be fun to build a joule thief and use it as a little night light though

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