Sam Goldwasser wrote in message ...
"James Sweet" writes:

"Sam Goldwasser" wrote in message
...
"James Sweet" writes:

"Sam Goldwasser" wrote in message
...
"Michael A. Covington" writes:

It is either a circuit very similar to a light dimmer, or possibly
just
a
rectifier.

A rectifier would cut the power in half compared to 230 VAC for a
constant
resistive load. This is not what you want.

I thought the high powered ones were nothing but diodes? They're only
good
for resistive loads, mostly they're made for irons and hair dryers.

A diode would produce half wave rectified 230 V. This would cut
the power in half compared to using raw 230 VAC but would still
be twice the power expected by a 115 VAC resistive load.

For example: 115 VAC 1.5 kW space heater.

On 230 VAC: 6 kW.
On half wave rectified 230 VAC: 3 kW.

Either would result in failure very quickly.

Or, did you have something else in mind?

I was thinking they had a chain of diodes and made use of the voltage drop,
guess I could be wrong though.

Let's see... Say 1.5 kW rating dropping from 230 VAC to 115 VAC. If half
wave rectified, that means it has to drop the peak voltage by about 100 V
(someone else can figure out exactly how much!) That means the adapter
dissipates or otherwise gets rid of several hundred watts. There
must be a mini-wormhole in there to dump the heat to another part of the
Universe.

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Sam is right.Power must be eliminated!!

I was thinking about a simple 220V SCR dimmer adjusted to fire around 45
degrees on each positive half cycle of the 220V line input.I guess that could
give about the 1500W required by an hair dryer,a toaster,etc. which operate
normally at 120V.

I found one of those 1500W converters (very small) but I cannot crack it open
to peek inside........They cost about $20 in Montreal.

The 50W model costs only $5 .It is a simple autotransformer.(220V to 120V)

Many thanks for the replies.

Jacques