New Classic Finds and etc. (Long)

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon Jan 26 17:11:41 2004

>
> Doc... this is a BAD idea... I've fried numerous devices by using the
> wrong power rating... even if it was only 1mA off. The voltage almost
> never matters... as long as the power is correct. Hope this gets to u

Sorry, but no way.

The load (computer device, etc) will draw whatever current it needs. And
provided the power supply (AC adapter in this case) can safely supply
that current, everything will be fine _provided various other conditions
are correct).

A 1A mains adapter is one that can safely provide 1A. It will also quite
happily run something needing 100mA (1/10A).

The other conditions are :

The voltage. This _can_ matter. Most devices expect an unregulated input,
so the voltage probably isn't that critical, but I wouldn't want to use a
24V adapter on a device that expected 9V. In a few cases the AC adapter
also includes voltage regulating circuitry (in which case the output may
be something 'computer-like', such as 5V), and in this case you _must_
use a regulated adapter of the right voltage.

Whether the device expects AC or DC. Some AC adapters are just
transformers and give out AC. Others contain rectifiers and smoothing
circuits and give out DC. Gatting this wrong will fry things (and note,
it's not always OK to feed DC into a device expecting AC!)

If the adapater outputs DC, then the polarity is critical too. You need
to make sure the right terminal on the connector is +ve.

Some HP calculators and related devices use special transformers with
deliberately poor 'regulation' -- that is to say the output voltage is
designed to drop as more current is drawn -- they have an effective
internal resistance of >10 ohms. Using a normal transformer with those
may well do damage.

-tony
Received on Mon Jan 26 2004 - 17:11:41 GMT