From: John Fields
Organization: Austin Instruments,Inc.
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Subject: Re: Higher loads on triac light dimmer ???
NNTP-Posting-Date: Tue, 17 Sep 2002 16:00:44 CDT
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Date: Tue, 17 Sep 2002 21:00:44 GMT
> 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 prefer
> 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 heatsink
> 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. ;^)
Professional circuit designer