Update
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Order
You can order the AASaver from my hobby shop. The kit comes with a pre-soldered circuit board, four AA battery clips, a pair of bright white LEDs and resistors (for use as flashlights), and two 2-pin headers (for use as breadboard power supply).
Overview
When your electronic devices report that the batteries are ‘dead’ and need to be replaced, do you ever feel frustrated that there is often still a lot of juice in them? Don’t throw away the batteries yet! You can use the remaining energy to do a lot of things, such as powering LED flashlights. This is possible by using a boost converter, which can bump the low battery voltage to a higher voltage, enough to light up LEDs or even power breadboard circuits.
Based on Microchip’s MCP1640, the AASaver is a small boost converter that can help you harvest the remaining energy in AA batteries. It has a few nice features:
- Takes up to two AA or AAA batteries. Start-up voltage as low as 0.65V.
- Outputs regulated 5V or 3.3V, selectable by an on-board switch.
- Up to 300mA output current (actual current output depends on the battery condition and the selected output voltage).
- Fits two on-board flashlight LEDs, so the circuit can be used directly as a flashlight.
- Three sets of pinouts to provide power for breadboard.
It works perfectly as a small flashlight. The boost converter generates enough sustained current to power bright LEDs. Even running on a single low-voltage battery (starting 0.65V), it can still power the LEDs for a long time. Now I never have to worry about keeping fresh new batteries for my flashlights — I have so many old AA batteries that are pronounced ‘dead’ by various electronic gadgets, remotes, clocks. I can use them all! This makes me feel a little greener 
I also enjoy it a lot as a compact breadboard power supply. It does not require any external power adapter, which is quite convenient. It also allows me to choose between 5V or 3.3V output, which is flexible. With a pair of fresh AA batteries, it can provide more than 300mA output current, enough for many breadboard circuit experiments.
Updates
Version 1.1 has the following changes from v1.0:
- Moved both flash LEDs to the same side so they point to the same direction.
- Added an on-board resistor (R1) for the flash LEDs.
- Added a separate flash LED switch.
- Moved the power switch to the bottom side.
These changes were made to improve its usability and convenience.
Usage Details
To find out usage details, including how to use it with only one battery or AAA instead of AA battery, check out this page.
Download
The schematic and board design are available for download here.
Feel free to leave a comment or suggestion below. Thank you.
I also had the same idea a while back to use low current
leds to get the last juice out of used batteries for a free
flashlight effect.
It worked but some of the batteries oozed out chemicals after
doing this and ruining my contacts , so i stopped doing it.
This depends on the quality of batteries. Even with no boost converter, if you leave them in the circuit for long enough, some will ooze and leak chemicals. So I don’t think boost converter is the direct cause of this.
Yes my point exactly ,dont bother doing this with cheap , nobrand batteries.
I guess mine were cheap as well.
[...] AASaver @ Rayshobby. I was on Show and Tell two weeks ago and I demonstrated my project called AASaver. Thanks a lot for providing this great opportunity for DIYers to talk about projects. Here are some details about my project, in case you find it interesting to post on Adafruit blog. [...]
Awesome project! The breadboard connection is a great idea as well. Building your own long-run flashlight is easy with this – thanks for sharing this!
I just built two of these kits (Nov ’11 version). This would be an excellent kit for those learning to solder.
I have more zombie-AAAs than AAs, so I decided to buy one of these kits:
http://www.amazon.com/Bluecell-Converter-Adapter-Battery-Storage/dp/B0069YEOPS/ref=pd_cp_e_0
They are a more upscale (1%? LOL) way to fit AAAs where only AAs are supposed to go.
Hi Dave, this is a great idea. Someone suggested that I add another set of PCB holes for AAA batteries so the same board can be used for both AA and AAA. Using a converter like you mentioned is obviously a solution too.
Hi Ray, I like the AAsaver idea. I am interested in sucking the power out of 1.5 V batteries and using it to charge an HTC phone and Ipod Touch. I was thinking of using rechargeable batteries, perhaps fully charged to serve as a way to charge my phone using when grid power is down. I don’t exactly know how much current my HTC phone sucks down while just sitting idle and charging may be really slow. Do you think this idea is practical? What if I use a plastic 3 or 4-battery holder soldered to the appropriate input pins of the AAsaver?
Thanks
Hi Richard, the maximum output current is 350mA. This is probably not enough for iPod Touch, which requires 500mA, but I think it should be ok for HTC phones, which I think require only 100-200mA. I don’t know for sure, but I have a couple of low-current USB chargers that always work with HTC phones but not iPhone. The output current will not increase even if you use more batteries. You can only increase the output current by connecting two AASavers in parallel, or by using a different chip. You should check out Adafruit’s MintyBoost. It uses a stronger switching regulator that can output 500mA, but the downside is that the start-up voltage is also quite high, which means it won’t work with low-voltage batteries.
Thanks for your thoughts. I was considering using more batteries to supply more usable power to the charged device, and maintain higher output currents rather than operating at the lower limit of the device, where current output is less. I agree that this may not put out enough power. Having a charger that can charge a phone quickly is a big bonus, especially if it operates on batteries that other devices reject as spent because of poor design, when we know there is more usable power in them. Great idea, and your kits appear to be the highest quality! Cheers to you!
Ray.
The AASaver seems a great idea. Is the output clean? Do you have any specification for the output noise level?
Martin