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> Modified Usb Charging Cable, Exactly 5v delivered.
deluxe
post Feb 20 2006, 10:40 AM
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I decided to build myself a USB charging cable, but didn't want to fry my sl-c1000. I had an unused USB cable, so cut one end off of it and tested it to see which leads were providing power, their polarity, and the voltage. My PC USB port provides 5.2v as determined by my voltmeter, so I decided to step it down to 5v exactly by means of a small solid-state rectifier/regulator ($2 cost) that's designed to step around 6v down to 5v (there are others that'll convert, say, 7v or more down to 5v. I didn't want those).
So, 10mins with a soldering gun, a strip of brass to dissipate any heat produced, and a tip and connector from Radio Shack, and I am in business. It provides exactly 5v as measured using my Voltmeter.
Little to no heat seems to be dissipated in use, the Z charges faster than with the Sharp 1w AC charger, and it's all pretty compact. I have used it about 6 times now, with no issues.
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bam
post Feb 20 2006, 11:43 AM
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actually its just a regulator a standard 7805, which is actually very precise in regulation, cool idea! Although you might wanna throw a 10uf cap on the output just for the sake of catching noise that might be generated by your usb port, but probably not needed...also provides less charging current than the supplied charger, the regulator can handle around (up to) 1 amp.
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Mjolinor
post Feb 20 2006, 12:35 PM
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If you have a 1 watt Sharp charger then I suggest you buy a proper one. It should be 5 or 10 watts depending on the model.

As far as I know the voltage is not htat critical, I regularly use 6 volt to charge mine.
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bam
post Feb 20 2006, 02:55 PM
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QUOTE(Mjolinor @ Feb 20 2006, 12:35 PM)
If you have a 1 watt Sharp charger then I suggest you buy a proper one. It should be 5 or 10 watts depending on the model.

As far as I know the voltage is not htat critical, I regularly use 6 volt to charge mine.
*



I would be careful overvoltage will shorten the life expectancy of your charging circuit.
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Mjolinor
post Feb 21 2006, 01:17 AM
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QUOTE(bam @ Feb 20 2006, 11:55 PM)
QUOTE(Mjolinor @ Feb 20 2006, 12:35 PM)
If you have a 1 watt Sharp charger then I suggest you buy a proper one. It should be 5 or 10 watts depending on the model.

As far as I know the voltage is not htat critical, I regularly use 6 volt to charge mine.
*



I would be careful overvoltage will shorten the life expectancy of your charging circuit.
*



Well if Sharp have not designed for 20% overvolts then it aint no good to me and they shouldn't be making retail goods. smile.gif
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seinfield
post Mar 6 2006, 12:00 PM
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Your circuit doesnt need the 7805 reg, you can connect 2 diodes to the power line in order to reduce 1.4v. But...

The usb port is 5v (sometimes 5.2v); you never tested the voltaje dropdown after conecting the Z directly to the usb port, that i think it will give you 5v exactly powering your Z.

And you can connect your Z directly to a PC supply (ony the 5v output).

6 volts will be dangerous to your Z charging circuit.

Now the usb port cant give you more than 500 ma, so i recomend you to buy a external usb hub with its own supply and use it, cause in the case of a short circuit the only thing that will blow out will be your hub and not your pc usb port.

Regards
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mbaush
post Mar 21 2006, 05:05 AM
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Very interesting deluxe. I also tought of plugging a 9V battery for emergency use.. could a regulator work for this? I saw an existing adaptor for an IPAQ pocket pc which used a 9V battery..

That could really be useful...
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deluxe
post Mar 22 2006, 02:53 PM
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I have made another cable that uses a 9v battery, and a regulator(different one, since it needs to step voltage down from 9 to 5volts this time).........so yes, it's very possible.
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mbaush
post Mar 23 2006, 04:21 AM
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Very very interesting.. How about the mA's ? I'm not sure how to get this information from a 9V battery. My power tester seems to go up to 200mA only..
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Da_Blitz
post Mar 23 2006, 04:37 AM
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Actually that circuit isnt even working as a 7805 dosent do any regulaton below 6v, for that you would need a low drop out regulator (and 5.2v would be too low for that) or a zener diode
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speculatrix
post Mar 27 2006, 10:23 PM
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providing overvoltage protection with (poly)fuse is probably much more desirable than tightly regulating the 5.2V to 5V.
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bam
post Mar 28 2006, 12:15 AM
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QUOTE(Da_Blitz @ Mar 23 2006, 04:37 AM)
Actually that circuit isnt even working as a 7805 dosent do any regulaton below 6v, for that you would need a low drop out regulator (and 5.2v would be too low for that) or a zener diode
*



oh yea, the 7805 supply is around 9-14vdc, if I remember correctly. and a zener in this case would be a good solution.
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daniel3000
post Mar 28 2006, 12:43 AM
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QUOTE(Mjolinor @ Feb 20 2006, 10:35 PM)
If you have a 1 watt Sharp charger then I suggest you buy a proper one. It should be 5 or 10 watts depending on the model.

As far as I know the voltage is not htat critical, I regularly use 6 volt to charge mine.
*


Well, caution!
I have heard of cases when even only 5.5V destroyed the charging circuit.
I have used up to about 5.4 V without any problem...

daniel
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speculatrix
post Mar 28 2006, 11:43 PM
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QUOTE(daniel3000 @ Mar 28 2006, 09:43 AM)
QUOTE(Mjolinor @ Feb 20 2006, 10:35 PM)
If you have a 1 watt Sharp charger then I suggest you buy a proper one. It should be 5 or 10 watts depending on the model.

As far as I know the voltage is not htat critical, I regularly use 6 volt to charge mine.
*


Well, caution!
I have heard of cases when even only 5.5V destroyed the charging circuit.
I have used up to about 5.4 V without any problem...

daniel
*



Note that most of these DC power supplies have a no-load float voltage above the specified output - so whilst it might be specified at 5V, with just a voltmeter it may read 5.5 or even 6. You'll need to measure the voltage under load, at least with 100mA load or so.

This might explain why some people specify they've been safe at 6V, others with a true 5.4V supply have destroyed Z charging circuits.
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