Date   : Mon, 30 May 2005 12:59:54 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Electron power supplies

On Mon, 2005-05-30 at 00:44 +0000, Richard Hobbis wrote:
> According to online sources (which are very sketchy when it comes to power
> supply ratings) it's supposed to be either 18 or 19v AC and 14W - this equates
> to about 800mA.

Funny you should say that; I thought they were 18V but I've just pulled
the user manual off the shelf and it says 19V. 

The AC's only presented on a couple of pins of the expansion connector,
but otherwise is rectified and regulated to various DC voltages inside
the unit - the Electron itself makes no use of the AC. (So I was told by
lots of people when I asked this a year or so ago anyway :)

Looking at the schematic, the Electron itself only uses +5V and -5V
rails. You'd probably find that if you really wanted to you could
disconnect the Electron's internal supply (it's a seperate board inside)
and feed +5V and -5V straight into the Electron from a scrap PC power
supply. (I only say probably because I'm not sure what sort of current a
PC supply can deliver on the -5V line and what the Electron would need -
the +5V would be more than adequate)

Having said that, I expect a lower-voltage AC PSU would work (down to
about 15 or 16VAC) hooked up to the normal power-in on the Electron, in
case you find one.

As for the current, I expect you can get away with 600mA. I'd expect
extra capacity was designed in to drive expansion units (they wouldn't
bother putting power rails out to the expansion connector otherwise)

If I could get to one of my Electrons I'd measure current for you, but
they're a bit buried at present.

Oh, I'm pretty sure older HP Deskjet power supplies were 18VAC by the
way (probably at an amp or two); a visit to the local tip would probably
find one :)

cheers

Jules