Subject: Re: Higher loads on triac light dimmer ???
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Date: Tue, 17 Sep 2002 21:01:46 -0700
NNTP-Posting-Date: Tue, 17 Sep 2002 20:56:56 EDT
Organization: Optimum Online
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!
"John Fields" wrote in message
> CS wrote:
> > Hi, I'm moving a coffee machine from the USA 110V to Australia 220V
> > 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 ??
> Unfortunately, it's not that simple.
> First, you've got the dissipation of the TRIAC to consider. When it's
> fully on, you've got what amounts to a diode drop from MT1 to MT2, so
> with that diode in series with a 600 watt load you'll have about
> 600W/120V = 5A flowing through it. Assuming the drop across the TRIAC
> is 1V means the TRIAC will be dissipating about 5W when the load is
> dissipating 600W. If you try to use it with a fully-on 1300W load the
> TRIAC will need to pass about 10A (and dissipate about 10W) which it's
> surely not rated for if it's being sold with a 600W load limit. On top
> of that, it's going to have to stand off 220V because you're going to
> have to fire it on the far side of 90° and 270°. So, what you could do
> would be to get a TRIAC capable of standing of 220V and handling 12A,
> then phase control it so it fired at the right time. Or, put a 110V
> 1300W iron in series with the coffeemaker and (have your wife) iron your
> clothes while the coffee's brewing. ;^)
> John Fields
> Professional circuit designer