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Portable PDA/USB device Battery Charger - help please!

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Newbie level 1
Feb 24, 2006
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I'm quite the newbie trying to figure out how to make a portable battery charger. Forgive my imprecise terms:

Objective: to power (and/or charge) a USB device using another battery (e.g. 9V, or 4xAA=6V).

I've searched around on the internet (and found a couple of pages in https://www.hackaday.com plus https://www.audiotstation.com/forum/showthread.php?s=&threadid=25715&highlight=usb+battery) that actually answer some of my questions. They used an LM7805 voltage regulator IC, a standard 9V battery, and a 9V connector. Three simple items, and if wired up correctly, will output 5V of power (which is, as they claim, the voltage that USB ports use). The excess 4V are let out as heat. I don't find a heatsink any problem, so i'll skip that.

I am dumbfound as to how much amperage these chargers churn out. I'm trying to charge a PDA device and the manufacturer stated that the DC output of their chargers are at 5V and 1A.

So here are a few questions:

1) How do I know the amperage that this charger will churn out given a 9V battery input? (Or is the drain on the battery due to the needs of the PDA?)

2) If the first question is relevant, can I, instead, use a rechargeable battery pack consisting of 7 or 8 pieces 2/3 (two-thirds) AA rated at 1500mAh or 2000mAh (voltage would then be 8.4V for 7 pieces and 9.6V for 8 pieces)?

3) If the second question is relevant, does the high ampere-hour rating of the battery pack have any bearing or strain on the PDA/USB device?

Forgive the newbie-ness. I have a totally non-working knowledge on electronics, and this would be my first project.

If anybody is wondering why i'm trying to make this, it's just for fun, and a growing interest in electronics. Plus a way for me to have an emergency charger for a PDA if and when the need arises. :D

Thank you in advance for those who can help!
BTW, if the first question is irrelevant, please do tell me. So I could stop wasting your time :D thanks again!

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