Minty Boost, AA Based USB Charger

Limor a.k.a. Ladyada has been a long standing staple in the Hack-A-Day community and we were more than happy to hear about her latest project. The Minty Boost is an improvement on the idea of building a battery powered USB charger. Most designs (including ours) use a 7805 linear regulator with a 9V battery. Even in the best case the regulator is only about 60% efficient which means you’re losing at least 1/3 of the power to heat. Limor’s design is a much more efficient boost converter design and uses far more common (and rechargeable) AA batteries. She’s got a thorough write up on how to build the converter in an Altoids gum tin. The end result is 82% efficient and can effectively double the play time of a video iPod.

The guide doesn’t end there. Limor actually wrote this as a demonstration on what goes into a making a kittable project. She covers the entire process from component selection, to mass PCB production, to what her final cost break down is. The guide is full of pictures thanks to some good planning as well. Of course the most interesting thing we learned from the guide is this: despite using the tins all the time, Limor finds the taste of Altoids gum disgusting.

[The guide is on her site, but we’re linking to the version on Instructables since we’ve managed to DDOS her site in the past… by announcing that her site was back online.]

39 thoughts on “Minty Boost, AA Based USB Charger

  1. Mmm maybe I am blind or something, but it looks like she didn’t use the shutdown pin for turning the boost convertor on/off. You’d have to disconnect a battery, else you’d lose some capacity to the quiescent draw over time. Other than that, good to see people documenting this stuff.

  2. I’ve gotta ask… Why didn’t she just use 4 batteries and a slightly bigger tin (like a mint tin instead of the gum tin)?

    4 rechargable batteries at 1.25 V each = 5 volts. No regulator, no efficency losses. Full power every time, and you have at least twice the battery life of what this thing gives you.

    Okay, +1 for extreme design, but -3 for breaking the KISS principle.

  3. well first off, 4 AA’s dont fit in a larger tin. Only 3 AA (the holder is a bit bigger)

    second, you should still regulate it to 5V so as the battery voltage on the rechargables drops, it may be too low to charge the battery (li-ions need 4.2V to charge)

    third, 4xAA is really heavy and large, i think people appreciate only having to carry around 2xAA in a small tin, especially if you have a smaller ipod.

  4. otto (#4) I think it also depends on how you apply “KISS”. KISS for the builder and KISS for the user are two different things. Typically a little extra effort on the builder side can offer a lot in terms of benefiting the user.

    I look at it this way: even if the builder/user are the same person, you only build it once but you use it many times…

    The benefit of having a much smaller and lighter package out weights the small inconvenience of building a tiny circuit.

  5. ee? any decently good 15-year-old electronics hobbiest could design and build a circuit like that. not to take away from it, it’s still the nicest, best-designed one of these I’ve seen.

  6. I believe 500ma is the spec for a usb hub (4 ports), so if you have multiple devices connected it can supply enough current to all of them.

    She states in her documentation that 100mA is the standard usb current draw for a single device.

    I would suspect the device takes whatever is available, to a limit. Try checking for yourself: plug in a chargable via usb device, go to device manager, open up USB hub device, and check the power tab.

  7. so, usb CAN provide 500mA but if a device wants that much current it needs to negotiate with the host for it. Since there’s no chip/computer to negotiate with here, devices fall back on the standard 100mA draw.

  8. Dan, first, decent 15 year old electronics hobbiest are harder to find now a days. No more thru hole parts. Atleast not at easy to get radioshack. Second, if a decent 15 year old can do it, why did it take so long for someone to make a non-7805 circuit? How come you didnt do it?

    And third, Ladyada has built her own gd mp3 player. From scratch.

  9. i have some Q’s about this usb charger. first off does it charge while you listen to songs? and secondly does it stop charging when the ipod battery is full? i know these kinda sound like dumb Q’s but i was just wondering thanks

  10. cde:
    There are plenty of non-7805 micropower solutions out there, like the one she ended up using. They’ve been availible for years. I have a feeling this is not the first homemade micropower usb supply either. And simply put, I didn’t have any reason to build one. :P

  11. PhillyJ (23):

    It charges when there is a current draw on it.
    It will work the same as when your iPod is plugged into a charger. It will charge the battery and play if there is enough power, and will play the ipod until the AA’s run down- then the ipod will use its own batteries.

  12. Cool design, certainly the best ipod usb battery ive seen. i was thinking about making one myself untill i realised a nearby pc store was selling a four battery usb charger for $10(thats canadian too!). in canada its cheaper to just buy that than pay for the parts from radio shack.

  13. Something interesting which I have noticed, Altoids are made in the UK, but the only place that I can find them on sale is on America! So I got my dad to buy me some went to America, so now I’ve got a couple of these I can make some!

  14. i have a e260, and what i did is cut up my old zen micro ac wall charger and it works fine..its doesnt say CONNECTED (like it does when you connect it to the computer) you can play music and charge your battery at the same time!!

  15. I just bought minty boost and when I finished assembling it I put the batteries into the battery pack and the boost converter chip heats up and gets really hot. Also when I went to see what the voltage was for the USB output it wasn’t get the 5v like it is suppose to. If you know what the problem is will you please let me know.

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