Project #2 Part 3

I've been very slowly building a boost converter as part of the grand plan for the iphone charger. A boost converter takes power from one source and then outputs power. What makes it special is the voltage it provides is higher than the input voltage. It does this by storing energy from the source in an inductor and then disconnects the inductor from the source and dumps the power onto a capacitor. The output draws power from the capacitor.

While 4 batteries in series works as a perfectly good charger for the iphone (I actually used it on the lost coast trip). It doesn't fit into the desired case, is hard to charge from USB and can be higher than 5V, which is fine for the iphone but technically above specifications.

The Maxim MAX1703 does the whole job of boost converting with just a few external components. And should be able to handle more current than needed.

I spent some time thinking about how to position the big components which I'm kind of happy with. However, when I went to actually connect things I just started putting things in one by one without a grand plan (obviously I had a schematic of what connections to make, just not where to physically put the wires). I think the technical term for the soldering style I ended up using is: crap. I was going to say rat's nest, but that actually is a technical term. Thanks in part to the poor style at first I had missed a couple connections when I hooked up the battery and the chip got very hot. Not sure if I did damage or not. Once I got that corrected the output was 4.6 V (within spec of 4.5 to 5.5). But when I connected a 10 ohm resistor the voltage dropped to 3.8 V (so it was only able to source 380 mA instead of 500 mA).

When I connected my ipod mini it charged for a moment than stopped. The ipod mini only requires 200 mA. So this is really a story of failure :(. I have more of all the components so I may try the same thing again and see if better wiring and not cooking the chip will work better.

I also learned the limits of 90 second epoxy. Its strong, but some inadvertent lever action can overcome it. Also, when the two sides mix it gets a little hot - not a big deal unless you don't know that and get some on your fingers and wonder what on Earth is happening to you.

I'm also going back and forth on if this is really the right approach or if it makes more sense to just find a nice case for the 4 series battery option.