Gunnar said:
It says "konstantan" on the package. I think I've heard that that is a
material that changes its resistance very little with temperature.
It is true that over some operating temperature range, that alloy
changes resistance little.
According to:
http://www.goodfellow.com/csp/active/STATIC/E/Constantan.HTML
the maximum operating temperature is 500 C.
The calculation with my little finger and 6 watts, what do you base that on?
The normal size of resistors conservatively rated for similar power
dissipation. They are normally coated with ceramic or silicone
material which has a higher temperature rating than epoxy.
The plan is to wire the strands around a piece of wood. The epoxy, is that
to fix the wires so they don't get in contact with each other, or does it
have any other possivitve effects when it comes to heat disapation?
The coating not only provides electrical insulation, it helps the heat
to spread from the thin wire to the nearby surface, to allow it to get
out into the air with a lower temperature rise. By the way, epoxy is
limited to something like 100 C and wood will shrink at less than
that. I suggest you use something mineral, ceramic or glass. If you
can scrounge up some much higher resistance 10 watt resistor, that
would make an ideal body for your custom resistor.
I have some of that termal paste you use under your heatsink in the
computer, might that be of any use?
Not if you intend to use epoxy, also. Those materials are usually
based on silicone grease, which prevents epoxy from bonding. But the
thermally conductive solids they contain make a good additive to
epoxy. Some examples would be zinc oxide, alumina and powdered
aluminum. But this enhancement is of little importance because the
main thermal resistance is not that between the wire and the surface
it is wound on, but between that surface and the surrounding air.
Very good thermal contact with the resistive wire is only important
when brief, large pulses of power must be handled.
Sorry for the bad english.
I hadn't noticed. If anything I say is not clear, please ask for me
to say it another way to help your understanding.