Cell Phone Charger

[valterra]

My cell phone (a Pocket PC PPC6700) uses a mini-USB jack.  I already made a cord for it to plug into a dc power supply, so I am very familiar with the required voltage, pins, etc.

For some reason, I cannot find a cheap cigarette lighter adapter for it.  So I'm running it by using its AC adapter plugged into an Inverter.  

Anyway, I was looking at LM317's and thought - couldn't I just use an LM317, plus a couple of resistors and just build my own?  Seems simple enough.  SEEEEEEMS that way.

[Ungrounded Lightning Rod]

How about using a USB powered hub with the wall wart replaced by a Radio Shack switch-the-voltage cigarette lighter adapter to form a USB-as-power-source adapter?

[valterra]

USB is 5VDC.  If it was 12vdc it'd be a little easier.  :-)  Unless I'm misunderstanding what you mean.

[RogerAS]

Hi valterra,

I don't think you wanna do that LM 317 thing.

Sure you can, but like the line from Jurassic Park, should you? The small li-ion battery can overcharge real quick with a setup like that if your phone isn't internally regulated. Without a state of charge feedback AND a tapering off of the current the battery might just explode and or start a fire. I think that might make the morning commute a real pain! If you wanna do this get the specs for your phone.

If you build a system based on the amp hour rating and consider the experimenting time involved you will better swerved to just use one of those tiny cigarette lighter little plug in inverters and use the AC charger that came with the phone. IMHO.

You could replaced the li-ion battery with a nicad pack and use the LM317 but that could be an ugly hack. A 9V transistor radio type nicad, the LM317 circuit and an adaptor to fit the USB connector could be used, IF you made up a null li-ion connector (no li-ion at all). Nicad chargers are much much easier to come by. You could keep several of these nicads charged and ready to go, or parallel several to add air time. The last time I bought one of those 9V batteries it was over $10. These little plug in inverters are under $20 at most electronics big box supply stores.

Another alternative is to use one of those USB universal chargers.

Google turned up this one on the very first listing, for $3.99, for your phone.

http://www.bargaincell.com/audiovox6700_charger_4003.html?gclid=CKe31PjK8pICFQHBsgodrEYP5A

Enjoy.

 

[wiredwrong]

They make a universal usb charger for the cigarette lighter, I have seen them at WalMart but thy could be had much cheaper online.

 like this...

http://www.cellularaccessory.com/zippwrdc.html

[yuandrew]

A LM-7805 fixed regulator would already give you 5 volts out by default. You may add a 22uf Capacitor onto the output to filter power going into what ever you are powering.

http://www.engadget.com/media/2006/06/diagram-usbalarm.jpg

Many cell phone now use the USB connection for their power supply and normally would already have the charging circuit on board. All it needs is 5 volts input.

The problem with linear regulators is that they are not too efficient (I think about 60 to 70 % at most). Power has to be dissipated in dropping the voltage down and it will become heat. A small heat sink such as Radio Shack Catalog #: 276-1368 should be attached to your regulator.

[yuandrew]

A LM-7805 fixed regulator would already give you 5 volts out by default. You may add a 22uf Capacitor onto the output to filter power going into what ever you are powering.

http://www.engadget.com/media/2006/06/diagram-usbalarm.jpg

Many cell phone now use the USB connection for their power supply and normally would already have the charging circuit on board. All it needs is 5 volts input.

The problem with linear regulators is that they are not too efficient (I think about 60 to 70 % at most). Power has to be dissipated in dropping the voltage down and it will become heat. A small heat sink such as Radio Shack Catalog #: 276-1368 should be attached to your regulator.

[ghurd]

Say the battery is at 14V.  The 317 or 7805 output is 5V.  The phone is taking 400ma.

The regulator will be hot, using a bit over 3.6W itself.  (14-9=5V, 9Vx0.4A=3.6W)That makes them really hot.

And the 400ma into the phone is a bit over 400ma from the 12V battery.

There are cheap little switching regulators available now.  They don't get hot.  And 400ma into the phone means maybe 200ma from the 12V battery.

G-

[valterra]

okay.  Thanks.  I'll just look for a cheap one.  This is MINI-USB, but that is probably the most common connector on ipod-type devices now days.  

As far as the phone being regulated - the AC adapter isn't a fancy switcher AFAIK.  It is just a wall wart that puts out 5vdc, so the phone itself must regulate the current.

[SparWeb]

Maybe you want to make one of these:

More on this website.

http://makezine.com/12/diyhome_lego/