Build a 4 X AA USB Altoids Battery

Not long ago, I upgraded the hard drive in my laptop from an 80GB 4200RPM to a 120GB 5200RPM. Not wanting to let my old 2.5" drive go to waste, I bought a rather nice USB enclosure for it.

Ah, but there was a catch. USB ports can only supply a maximum of 500 milliamps. The hard drive will need 550mA, meaning that the use of an AC adapter (or special USB cable) would be necessary under high load conditions.

I HATE those clunky AC wall adapters. I don't see why we should have to deal with them. Why can't we just have a centralized 12 volt power system in our buildings? We have it in all of our cars! That would be much more efficient.

The way this HD enclosure "solves" the power problem is to include a special USB Y-cable that can draw power from two ports. So one port handles power+data while the other just supplies power. This means that sometimes I'd have to give up two ports for one HD (or use an after-market AC adapter.) Not cool.

But I'm not here to complain. I'm here to awesome this problem out of existence. And we do that with some bits from Radio Shack, and, of course, a tin of Altoids.

I got the idea from ladyada's article where she built a 2 x AA battery encased in a smaller Altoids gum tin. While it works and is super portable, it utilizes a power-management system that requires exotic parts (but you can just buy the whole unit minus Altoids from her.) Plus the output current is limited to about 200mA. Nowhere near enough power for what I need.

The beauty of using an Altoids tin for the project box is it comes with candy. While at the market, why not avail yourself to the fine selection of other snacks including (but not limited to) Pringles, Skittles, pizzas and beverages of your choosing. You're going to need them.

You'll first need to eat the Altoids. The candies make poor electronic components. You cannot store the candy in an alternate container. They will attract goblins.

I like the cinnamon flavor, but also quite partial to wintergreen. All other flavors are invalid and you are a horrible person for choosing them.

Now you have to get the parts that'll turn the tin into a battery. You will need the following:

4 x Single "AA" battery holders.
1 x Motherboard PCI-mount USB port. (the shorter the profile the better.)
1 x Tube of plastic-friendly cyanoacrylate super glue.

And you will need the following tools:

Wire-cutters.
Soldering Iron.
Screwdriver.
Small precision files.
Drill.

Simple, huh? You should be able to handle all that.

Now, I recommend getting an extra AA battery holder. You'll be monkeying around with them in the next step and you might accidentally destroy one... some more.

Four AA batteries can fit comfortably in the space provided by the good people at the Callard & Bowser company. However, the battery holders will not. We'll have to teach them a little lesson in space management!

Take the wire-cutters and carefully cut the ends and middle part off. Take a piece of fine sandpaper and rough up the surfaces that we're going to adhere to the metal.

Start off by sanding the inside of the tin. We want a nice rough surface for the super glue to hold onto.

You'll want to arrange the holders so that the batteries will be in a series circuit (5-Volts.) Make sure there are no shorts. The metal back of each contact is recessed in the plastic so shorts are unlikely, but it won't hurt to make absolutely sure there isn't any metal on metal.

Gluing the battery contacts to the tin is almost an art, so all I can tell you is try your best to keep the alignment of the 3 parts in true. Use a junk battery and glue on one piece at a time. The glue sets PERMANENTLY in about 10 seconds.

The USB port is too long for our needs. Take the wire-cutter and hack away all the excess. Be sure to leave behind enough plastic so it can still be securely mounted.

After about a half-hour of trimming, you should be left with a small nub of a USB port. Go ahead and cut the two center wires. We only need the red and black. Put a little dab of super glue on the back to make sure the port and pins don't move around. Carefully bend the back pins to one side so it'll fit in the tin.

While you have the PCI bracket handy, use it as a stencil and mark on the tin where you're going to drill the holes. Make sure you don't mark it too high or too low.

Use a nail to LIGHTLY tap little indentations in the center of your marks so the drill bit doesn't wander. The metal that makes up these tins is a very soft steel. So go slow.

Make multiple drill holes where the port is going to go. Take away as much material as you can. Think "connect the dots."

Take the small files and start making a rectangle. This is tedious. You might want to hire a schizophrenic clown to entertain you.

Having a USB flash drive on hand will be good for sizing.

Kinda looks like some weird anime expression don't it?

You need to connect all the battery holders together so that the batteries are in series. You will probably be using your teeth to strip the wires.

The little metal wire terminals swivel with a bit of firm (but gentle) force. Align each of them to their respective neighbor (baring the reserved master + and - wires.)

Solder everything together. You now have the basic battery.

Now, you could call it done. Simply affix the USB port and you're set. But (and I may be labeled a heretic for this) while the current setup has a certain novelty factor, the Altoids tin is pretty gaudy. So, if you like, let's add some paint to our work of art...

Standard procedure here. Primer and paint. Be sure to mask off the parts where the lid has to slide over the bottom part. You want the thing to close after all. Wet sand both the primer and paint if you really want a glossy finish.

A definite improvement, but... it's kind of boring. Mayhaps a little personalisation is in order?

Hell. Yes.

I made the Irken Invader logo in Adobe Illustrator and printed it out (two logos on the page.) I covered the top with masking tape and glued (with spray-on adhesive) the logo template onto the tape. Then, using a round-tip X-acto knife, I carefully cut away the white bits.

If you do something like this, practice on, like, a pop can or a piece of scrap metal first. That's why I printed out two logos. I used a bright "Ford Red" for the color.

After removing the stencil, I sprayed on a clear coat to protect the design.

I did a lot of research about batteries. Which you should appreciate because it's quite boring. Sifting through PDF after PDF looking for the right energy capacity and discharge profile.

The perfect battery for this is the NiMH Energizer E2 rechargeables. They come in a convenient pack that includes 4-AA batteries and and a charger for about $20. They have 2500mAh of current capacity and they hold their voltage levels up until the screaming end. Doing away with the need for any sort of voltage management hardware. These batteries are able to power my hard drive for up to 3 hours on their own! Three times as long when the HD is plugged into a low-power USB port.

If you decide to use alkalines, or especially Lithiums, install a diode on the positive battery wire to block current from feeding back into the batteries. It'll prevent them from overheating, leaking and "venting with fire." However, if you intend to use this only to charge your iPod or PDA, then It isn't necessary.

Please note that if you do use alkalines, or especially Lithium batteries, your voltage may be dangerously high for some electronics. So the NiMH rechargables are really the best (and most economical) option.

So there you have it. The whole setup weighs about 6 ounces. A tad heavy, but if you're seriously considering building this, then you are a geek. A geek who probably needs the exercise anyway.

UPDATE: 8-31-08

1) For those of you who want to charge your iPod with this, please read this supplementary Instructable. I figure you could wire those resistors into a short USB extension cable or something so they don't drain the battery.

2) If you're going to be using Lithium batteries, be sure to install a 1A Diode on the positive terminal so that there's no chance of electricity feeding back into the batteries. That would be bad.

3) You can use a 4xAA battery holder just fine, it may save you some trouble soldering together 4 individual battery holders.