Date   : Tue, 01 Sep 2009 00:34:21 +0100
From   : afra@... (Phill Harvey-Smith)
Subject: Leccy @ Acorn World '09

Disclaimer:I'm not an electrician :)

Rick Murray wrote:
> Michael Firth wrote:
> A question I have - without actually measuring, how can one tell the 
> power rating? For example, I believe my RiscPC power supply is something 
> like 83W (it's the smaller of the two). My bigger PC is something like 
> 350W (gee, spot the difference!). Now these will apply to OUTPUT power, 
> yes? 

That is of course the maximum rated power that the supply can provide, 
it's like saying this PSU can provide between 0W and 350W.

>   The amount of ooomph given on the DC side. How does one translate 
> that into input? If the PC thinks it is taking 350W then I'd crap myself 
> as turning my room on would be akin to running an immersion heater! 
> Thankfully I know that's not true - just looked at the meter box and 
> it's a lot more docile than when a heavy load is on.

Well 350W would only be just over 1A of current, so not really a big load.

> Couple this with the fact that some stuff just plain lies. My satellite 
> receiver takes 30W. It says so. In actual fact, it runs about 3W in 
> standby and 20-22ish when running (prob. different LNB polarisation 
> power accounts for the difference?). Well, it's around 1/3 less than 
> quoted. Might not sound like a lot, but imagine if everybody at the 
> exhibition had one of them, the difference between quoted and actual 
> could be enough to allow a couple of coffee-makers to be included!

Again I would imagine that the quoted figure would be the maximum that 
the equipment can ever draw plus a few wats just to be on the safe side :)

> So there's the question. Is there any elecy-techy with some spare time 
> and 6502 kit who can provide some actual ratings of what stuff (Beebs, 
> co-pros, RiscPCs, cub monitors...) actually consume?

Well that will depend on what's fitted inside the machine, e.g. if you 
have an internal CoPro, beeb powered drives etc then you will use more 
power than a basic unexpanded machine.

I think the ratings on the back of the machine are prolly what we should 
be using to calculate as these are the max that it would ever draw, to 
use anything else could lead to the situation where we do draw too much.

> Would it be better to take LCD displays instead of "authentic" Cubs? The 
> power consumption is less, yes?

I did wonder about that myself, of course the AtomClone is running on a 
17" LCD TV. It also runs off a 5V 2A PSU, though I don't think the clone 
draws anything like 2A :)

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.