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From: John Fields
Organization: Austin Instruments,Inc.
X-Mailer: Mozilla 4.01 [en] (Win95; U)
Subject: Re: Higher loads on triac light dimmer ???
NNTP-Posting-Date: Wed, 18 Sep 2002 09:21:30 CDT
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Date: Wed, 18 Sep 2002 14:21:30 GMT
> "Mike Poulton" wrote in message
> > On 17 Sep 2002, "scada" said:
> > > Why not put a rectifier diode in series with the load! The coffee pot
> > > should be all resistive, unless it has an electronic timer or such in
> > > it!
> > Well... Half voltage does not equal half power. If you do that, you
> > will still be running the element at double the rated power.
> Half of 220V is 110V! Is that not what the pot is designed for?
> If the pot is resistive there should not be a problem!
As some other posters have mentioned, a series diode is not a good idea.
Look at it this way:
If the coffee maker is rated for 1300W at 110V and it's resistive, then
it will have a resistance of EČ/P = 12000/1300W ~ 9.3 ohms. Connected
across 220V mains it will dissipate EČ/R = 48400/9.3ohms ~ 5200W !!!
With a diode in series between the mains and the heating element what
will happen is that one half of each mains cycle will be blocked, with
the result that the element will be dissipating one half of what it
would be if the diode was not there. That's 2600 watts, which the
element would not be happy with for long.
Professional circuit designer
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