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Subject: RE: Plugged in Car-charger - smoke out of my box - no charging

RE: Plugged in Car-charger - smoke out of my box - no charging

From: Chris Weaver <>
Date: Tue, 16 Mar 2004 20:50:46 -0600

Your reply is certainly not rude but it is a bit misleading as I agree was mine. You are correct that these are unregulated and if
the output current was an order of magnitude different and the load was far below the rated load then you are correct it might be a

A non regulated supply will certainly have a high output voltage with very little current draw, perhaps 10% of rated output and
lower. Specifically, the open circuit DC voltage output is 1.414 times the loaded voltage when using a full wave bridge rectifier.
However, this voltage will drop as soon as you start to draw any significant current. Also note that the Archos power input is
designed to handle this unregulated voltage and should be able to handle startup and low current draw voltages up to and exceeding
the open circuit voltage.

As a practical example, I have the V2 and the supplied 6VDC 700ma AC adaptor has an open voltage level of 9VDC which is identical to
the open circuit output of my 2100ma 6VDC adaptor. I contend that the Archos would operate fine with either supply as both will
operate in the same basic range of voltages given the Archos current draw. Although I admit that I have not measured either supply
under load nor am I familiar with the typical range of current draw the Archos demands my point is that the specifics are not of any
real concern as they are in the same basic range.
-----Original Message-----
From: [] On Behalf Of Fred Maxwell
Sent: Tuesday, March 16, 2004 4:52 PM
To: Rockbox development
Subject: Re: Plugged in Car-charger - smoke out of my box - no charging

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).

   Fred Maxwell


Received on 2004-03-17

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