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From: "Phil Allison"
Subject: Re: Higher loads on triac light dimmer ???
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Thu, 19 Sep 2002 17:25:36 +1000
NNTP-Posting-Date: Thu, 19 Sep 2002 17:14:43 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"CS" wrote in message
> Hi, I'm moving a coffee machine from the USA 110V to Australia 220V which
> has a heating element rated at 1300W.
> Rather than using a bulky & expensive step down transformer, I would
> to use a standard thyristor light dimmer to control the heating element
> since it is just a resistive load, but every light dimmer I've seen is
> limited to about 600W.
> Is it possible to modify something to get this to work, like add a
> to the 600W light dimmer ??
** A device called "Travellers Friend", or other similar title, has
been on sale for decades for just this purpose from places like Wal Mart and
large comsumer type hardware outlets. It has a 16 amp triac dimmer cct
inside adjusted and fixed to fire at about 62 degrees before each zero
crossing. This conduction angle produces the same rms current in a resistive
heater or lamp designed for 110 volt supply when used at 230 volts AC.
The one I saw on sale here in Australia carried a 1300 watt load
The exact same idea is also used when 110 volt PAR lamps must be
operated from 230 volts AC for professional stage lighting dimmers.
If the coffee maker has any electronics inside it (uP etc) then I
would not try it since the peak voltage is 300 volts using this trick as
against 160 volts for a sine wave supply of 115 volts AC.
BTW A standard AC meter (average responding but calibrated for rms
value on sine waves) has a large error with the chopped sine pulses from a
triac dimmer and in this case the reading would be only 63 volts. A true
rms meter would however read 110 volts, as expected.
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