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From: root@bio73.unsw.oz (Karl Redell )
Newsgroups: sci.electronics
Subject: Re: American electronics on European power?
Message-ID: <1272@bio73.unsw.oz>
Date: 3 Aug 90 03:15:45 GMT
References: <1990Jul31.154929.27950@ux1.cso.uiuc.edu> <8798@uhccux.uhcc.Hawaii.Edu> <1990Aug1.215056.1316@bellcore-2.bellcore.com>
Organization: Uni of NSW, Sydney, Australia
Lines: 29

I would be surprised if a 240/120 power converter used just a 1/2 wave
rectifier.  It is much more likely to use a triac or sometthing similar.

I tried to convert a 120V hot air corn popper to run on 240V.  It was not
easy.  First I bunged a diode in series with the thing - thinking that
half of 240 was going to be 120.  The corn popper motor screamed and looked
like a light bulb. (That is the heater looked like a light bulb).  It took
awhile to figure out what was going on here because everyone I asked also
thought that half of 240 was 120.  Then, one day, my friend Mark Hellier
said "That's easy - you've still got 240 on the thing.  Power is proportional
to the voltage SQUARED so without the diode you are putting in 4 times as
much power as if it was running on 120 volts.  The diode then cuts it back
to twice as much power.  No wonder it's running hot!"

A light dimmer worked just fine for the heater element, but the waveform
was no good for the motor.  It looked like I might have to build a 30V
2 amp supply for the dinky motor, but I got around that by putting a
suitable arrangement of fluorescent light capacitors in series with the
motor and the 240V supply.

One final note - if your equipment is not rated for 50Hz, then you MUST
reduce the voltage to your equipment by the ratio of the frequencies -
in this case 120V X 50/60 = 100V. (does not apply to heaters and other
resistive loads, of course)  Failure to do this will cause induction
motors and other such devices to burn out in as little as 1 hour.

If it was me, I'd leave your stuff at home.

karl@bio73.unsw.oz.au