USB mains charger
Feb 22, 2007 at 6:34 AM Thread Starter Post #1 of 10

splaz

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Okay well I sort of volunteered to investigate this for a workmate. They don't have a computer at their house and want to be able to charge the nano.

So I said I'd look into it. Now there is the ever so simple option of a plugpack that is terminated with USB. Now 2 problems I have with that, 1 can't easily get inline sockets so making one up out of a PCB mount one would be somewhat dodgy although quite doable. More important problem to me is that I'm concerned with noise and spikes going to the nano and also what happens if something goes wrong. I know the plug packs usually have short circuit, thermal protection etc. but what if the plug pack itself bit the dust.

So then that got my thinking of making up a little filter/protection circuitry in a project box. Maybe an inductor, cap, MOV etc. One protection I've heard of is a 5.1V zener with a 5.6 or 6V plugpack then a fuse. Maybe substitute in a polyswitch instead of the fuse as this person isn't tech savvy at all.

Any thoughts ?

Ideally it will be using components that won't get too hot as it will have to be in a fairly sealed up box, to reduce the chances of things breaking. I was thinking about a regulator but then thought it may get toasty and isn't really needed
 
Feb 22, 2007 at 6:56 AM Post #2 of 10

cire

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If the Nano has firewire charge as well as USB on the dock connector, use that instead since I believe it is regulated, accepts a voltage between 9 and 35 and has protection built in. Feed a DC wallwart into those two pins and you're set.
 
Feb 22, 2007 at 7:16 AM Post #4 of 10

error401

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I built one for my sister's Nano 1G out of an old switching cellphone charger @ 7.5V. All I added was a TO92 7805 inside the case of the switcher. It doesn't seem to cause any problems. Smaller size and part count seems to be win-win versus a custom circuit. You might go with the TO220, but I don't think it's really necessary. I've also used a 5V switcher directly as a charger for my own Nano without issue.

Another point that might be worth mentioning is that USB devices are only allowed to draw 100mA without negotiating with the OS for more. Unless you want to include a microcontroller in your power supply, that's the best you can do. Obviously this hurts charging time and usefulness of such a device severely. Unless you're not going to have ready access to a computer it's not really worth it. There might be some kind of hack that apple uses in their own charger that you could duplicate as theirs seems to work at full current and I doubt it has a USB controller, but I haven't looked that far into it.

Finally, depending on your workmate's needs, he might find the minty boost useful as well. It's a simple single IC boost converter to power USB devices from 2AAs; ladyada sells the (tiny!) PCBs as well as kits. Total cost is less than $20. I use this far more than I use my USB wall charger, it's great for long flights etc. I really recommend it, took me about 15 minutes to assemble and is a lifesaver.
 
Feb 22, 2007 at 7:37 AM Post #5 of 10

splaz

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Well if it isn't a problem I may just hook it up directly...

You sure they can only draw 100mA though ?

The owner of an electronics shop said that sometimes extrernal hard drives/DVD drives can kill low current rated plugpacks powered over USB. Must've drawn well in excess of 100mA to do that.
 
Feb 22, 2007 at 7:58 AM Post #6 of 10

error401

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Quote:

Originally Posted by splaz /img/forum/go_quote.gif
Well if it isn't a problem I may just hook it up directly...

You sure they can only draw 100mA though ?

The owner of an electronics shop said that sometimes extrernal hard drives/DVD drives can kill low current rated plugpacks powered over USB. Must've drawn well in excess of 100mA to do that.



That's what the spec says. What devices do is another thing entirely...
 
Feb 22, 2007 at 9:54 AM Post #7 of 10

Calroth

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I know that this is missing the point by a long, long, long, long way, but...

Why not just buy an iPod charger off eBay?
cool.gif
 
Feb 22, 2007 at 12:47 PM Post #8 of 10

Yen

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Quote:

Originally Posted by Calroth /img/forum/go_quote.gif
I know that this is missing the point by a long, long, long, long way, but...

Why not just buy an iPod charger off eBay?
cool.gif



That's what I thought too! Wont even cost much...
biggrin.gif


Just search for "ipod home charger" and you will find one for under two bucks plus pp...
 

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