how do i charge 3 AAA rechargeable batteries for my led flashlight using USB on my laptop or connect my flashlight to the usb to recharge?
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M$3 Answers
The site underneath states that max draw from a USB port should be 100mA.
Wiki says: "The capacity of an alkaline AAA is typically 900 to 1,155 mA·h" Since your batteries are in series (probably), that stays 900 to 1,155.
So that means that if you want to charge a 1,155 mAh AAA battery at 100mA you would need 11,5 hours to do this. That's a lot. If I where you i would use an adapter that you can just plug in to the net. If you still want to do this with a usb charger, you can either just buy it at:
http://www.everfast.com.hk/catalog/usb-stick-battery-charger-aa-nano-usb-battery-charger-aa-aa-p-78.html
(It has a flip switch for AAA and AA batteries)
This one is at makecircuits and charges 2 AA batteries. Those have the same voltage as AAA batteries, they are just bigger and have more mAh's. U could use this for two AAA batteries. I can't find one for 3 right now, sorry
http://makecircuits.com/blog/2008-12-25-usb-battery-charger-for-aa-nimh-and-nicd.html
Normally they go the other way around and use a few of batteries to charge USB gadgets :p
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M$It turns out managing batteries is not all that simple. There is a whole industry making special chips to do this for NICD, NIMH and of course LION cells. To make matters more confusing - different battery manufactures will most likely specify different charging techniques for their batteries.
WRT flashlights - most people spend their time hacking in a "boost" switching power supply to provide constant LED brightness until the batteries are dead. I've not seen many add USB charging. I think the best solution here is to buy such a flashlight. If you search on amazon with this string "USB Rechargeable LED Flashlight Keychain" you should pull up a <$3 flashlight - however the shipping @ >$7 is a killer.
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M$
My bike generator question
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M$
USB busses generally support a minimum of 500mA total for all devices plugged into it. Some computers may support larger amounts of current.
This is why larger USB hubs generally have a separate power plug to power many USB devices simultaneously.
the link of makecircuits shows that you can use 500mA but I doubt that you can use other usb devices which use usb bus power at the same time.