Portable USB charger will make you never miss a beat

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By jonahbc
Posted 2009/01/27 @ 9:25 pm
Category Craft, Electronics

ï¿¼Here’s a cool how-to on building a portable USB charger for your gadgets. We’ve covered similar builds like this on Make before, but this one has a good parts list and walks you through each step of the build with attention to detail. This kind of thing is handy when you need to charge your gear and are nowhere near a laptop or a MintyBoost. Just don’t use this charger indiscreetly when flying on an airplane.

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6 Responses to Portable USB charger will make you never miss a beat

The Oracle on January 28th, 2009 at 5:38 am said:

Yeah…from the article, that’s a 5 Volt linear regulator, not a transformer, and the rest of the article shows just as much ignorance of basic electronics.

It’s very poor design to connect a 9V battery to a linear regulator because the capacity of the battery is so tiny and you’re burning off 4/9ths of the battery as heat in the regulator.

The rated capacity of a 9V Duracell is 310mAh, but at a high load like charging an iPod it drops to 90mAh. And iPod classic G5 battery is 1230mAh, meaning this project will not even give you a 10% charge from a brand new Duracell. Even the G2 shuffle has 220mAh of battery capacity, the lowest of any iPod, and you still won’t get half a charge out of a full 9V battery.

I’m trying not to be overly critical on this blog anymore, but this project is absolute stupidity and this post my fool people into thinking it’s a good idea. Go buy a minty boost.

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The Oracle on January 28th, 2009 at 5:56 am said:

Yeah…from the article, that’s a 5 Volt linear regulator, not a transformer, and the rest of the article shows just as much ignorance of basic electronics.

It’s very poor design to connect a 9V battery to a linear regulator because the capacity of the battery is so tiny and you’re burning off 4/9ths of the battery as heat in the regulator.

The rated capacity of a 9V Duracell is 310mAh, but at a high load like charging an iPod it drops to 90mAh. And iPod classic G5 battery is 1230mAh, meaning this project will not even give you a 10% charge from a brand new Duracell. Even the G2 shuffle has 220mAh of battery capacity, the lowest of any iPod, and you still won’t get half a charge out of a full 9V battery.

I’m trying not to be overly critical on this blog anymore, but this project is absolute stupidity and this post might fool people into thinking it’s a good idea. Go buy a minty boost.

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Sebbi on January 28th, 2009 at 8:10 am said:

As the oracle pointed out, this is a very poor design, because of the used 9V battery. Using a booster with 2 AA cells is much more efficient.

But even so, it will not really charge an iPod. Those devices (as many cell phones) check for different voltages on the d+ and d- lines, requiring a special circuit to be “chargable”. Sad, but true …

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jammit on January 28th, 2009 at 9:05 am said:

As mentioned before on LadyADA’s website and mentioned here, the D+ and D- lines need to be brought to 2.5 volts through a 15K ohm resistor. What I use is two series connected 30K ohm resistors connected to +5 and GND to create the equivalent 2.5V/15K ohm for the data lines. I use two voltage dividers, one for each line. This “fakes” the USB device into thinking there’s a computer attached and causes the charging circuit to turn on. Some devices will charge the battery without the resistive divider, but will only do it at a lower trickle charge overnight “cheapie AC power wall wart” current level.

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Phillip Torrone on January 28th, 2009 at 9:11 pm said:

hey gang, i am just catching up reading all the posts and comments today — this one isn’t a good one for charging ipods — sorry about that, jonah will see this comment once i post it, but at this point, the post should stay… thanks for commenting and correctly identifying it.

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