-=PCTechTalk=- Re: Electronics, not quite PC related....

Hi Greywoulf,
    My initial reply was meant to cover a generic rule.  However, battery 
chargers are a different animal in that you're not looking to power an 
actual device, just supply a steady stream of current to the battery.  In 
this case, less current would indeed mean a longer charging time and should 
not negatively affect the battery.  One the other hand, I would not use a 
charger rated at 5V @ 2.5A to charge a 5V @ 2.0A battery.  Exceeding the 
battery's Amp rating will cause the battery temperature to raise higher than 
it was designed to withstand and could result in the battery exploding.

    All USB specifications include a small amount of power (5 volts) 
supplied across two of the four wires to enable items like a keyboard or 
mouse to run properly.  The maximum amperage rating varies according to the 
spec as follows.  A "unit load" is defined as 100mA in USB 2.0, but was 
raised to 150mA for the newer USB 3.0 spec. A maximum of 5 unit loads can be 
drawn from a port in USB 2.0 (0.5A) and that was raised to 6 unit loads for 
USB 3.0 (0.9A).  There are two types of devices: low-power and high-power. 
Low-power devices (mice, keyboards, etc.) draw no more than 1 unit load with 
a minimum operating voltage of 4.4V in USB 2.0, and 4V in USB 3.0. 
High-power devices draw the maximum amount of unit loads supported by the 
standard.  All devices default to low-power but the device's software may 
request high-power as long as the power is available on the providing bus. 
There is enough power on a single USB line to power a lighted keyboard or 
small fan.  There's more to this stuff (such as how different types of hubs 
handle power distribution), but the above should give you a good idea of 
what you're working with.

Happy Holidays,
Gman

"The only dumb questions are the ones we fail to ask"

----- Original Message ----- 
From: "DO1212SK" <do1212sk@xxxxxxxxxxx>
To: <pctechtalk@xxxxxxxxxxxxx>
Sent: Tuesday, December 30, 2008 12:26 PM
Subject: -=PCTechTalk=- Electronics, not quite PC related....


> Hi Gman
> Happy Holidays to you too, and thanks for all the great info and 
> assistance
> you've provided all of us over the years...  This forum, IMO, is one of 
> the
> most helpful (and often delightful) PC info sites to be found anywhere on
> the planet!! ">})
>
> Some further questions regarding this charging thing, and then I think 
> I'll
> just drop it and go out and spend the #*^$^*  $25 for another damn plug
> wart...!
> -If my recording device says it requires 5V and 2.0 amps current, and I
> already have a charger that puts out 5V and 1.5 amps current, would that
> still work and only charge the thing a little slower? Or would it be too
> weak to do the job at all? Or do I have it backasswards and my charger 
> would
> be too powerful for the device?
> (As you can see, I'm no electrical genius!) ">(
>
> Also, I'm curious here: I thot that USB connections were just for 
> exchanging
> data. How does it work then that my Tascam hand digital recorder (DR-1)
> would also get it's lithium battery charged by leaving it plugged in to my
> PC's USB connection? Is there 2.0 amps of current coming out of the USB
> connection then?  (-I don't get this at all??? ">})
>
> Thanks again,
> Greywoulf 

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