DIYbanter - View Single Post - 600-watt light dimmer overheats

In article ,
wrote:

A dimer turned wide open should not be hot. That should be it's coolest
operation. The heat associated with dimmers comes from converting energy
that would otherwise go to the lights to heat instead by use of
resistance.

I have never seen a dimmer like that in use in anyone's home. I once
saw one in a school theater that worked that way, and it was big.

There are some advanced dimmers that use pulse width modulation to
regulate instead, and they run much cooler.

The usual household dimmers work basically that way.

The thing is that a 600 watt load draws 5 amps, and the triac (switching
element that is part of the circuit that chops the AC waveform to achieve
dimming) has a voltage drop of a volt or somewhat more when it is
conducting.
This means that with a 600 watt load, the triac produces 5 watts or
somewhat more than 5 watts of heat. This is a little more heat than is
produced by a typical magnetic ballast for a 15 watt fluorescent lamp.

- Don Klipstein )