Byron A Jeff wrote:

> > I have used this with excellent result in a 100w
> > incubator, using 7% volts drop on the resistors, and
> > I used 2 large 20w ceramic resistors because I have
> > heaps of that stuff in my junkbox. :o)
> > The incubator has done thousands of on/off cycles over
> > months, still the original 100w bulb.
>
> Roman, let's start here. How did you wire the incubator? Where did you wire
> the resistors relative to the light socket?
>
> There are two major problems in wiring the resistor, high voltage and heat.
> Of course this is the same two problems as wiring a light fixture, but with the
> light fixture the source of heat is out in free space.
>
> Ideally the resistor should be an a grounded, thermally coupled metal box
> that's mounted in free space. It may be possible to get away with a deep
> metal box at the light socket. Mount the resistor at the back of the box on
> the side away from the stud. The box would then act as a heat sink for the
> resistor. Note that IANAElectrician!
>
> Frankly the thought of a radiated heat source mounted in wall is quite a scary
> one.


I think you are geting the wrong end of the stick,
the 3w from the resistor is very little compared with
maybe 30w to 40w heat radiated from a 60w light bulb!!

Remember the resistor might get to 60'C, the bulb
gets to 85'C or more. Heating inside light fittings
is all relative. :o)

In the incubator I just mounted the resistors near
the bulb, it all heats the air for convection inside
the incubator cabinet anyway.

I agree not to mount a heat source inside the wall!!
Maybe in a metal light fitting, its a design decision
you have to make based on the application. It is ideal
for outdoor light fittings which are usually in a large
alloy metal waterproof box. There is no extra heat,
in total, as the mains voltage is fixed.
-Roman

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