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Subject: Re: Plugged in Car-charger - smoke out of my box - no charging
From: Fred Maxwell (rockbox_at_anti-spam.org)
Date: 2004-03-16


Chris Weaver wrote:
> The ability of the charger to supply more current than
> required would not have caused the problem.
>
> It is no different than plugging in a stereo to a wall outlet that
> is rated for 15A or 20A. That is the max current.

Not to be rude, but you are incorrect. A wall outlet is voltage
regulated. It doesn't matter whether you plug in an alarm clock that
draws .1 amps or a space heater that draws 12.5 amps. The voltage will
remain almost identical.

Take a "9V" wall wart and measure the voltage with nothing attached.
The 9V, 600ma wall wart that came with my Archos measures 14.5v with no
load attached. Now, suppose I had a device that needed 9 volts at 10ma.
  If I plug the 9 volt, 600ma Archos wall wart into that, it's probably
going to be feeding it something on the north side of 14 volts.

You have to remember that the voltage and amperage are very much related
in an unregulated supply. When a wall wart is rated 9V at 800ma, that
means that it will put out 9 volts with an 800ma load. But there's no
guarantee about what voltage you will get with a 50ma load (bet on
something a lot higher than 9 volts, though).

Regards,
   Fred Maxwell

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