"Dave" wrote in news:1122738906 snipped-for-privacy@spool6-east.superfeed.net:
> I am looking for resistance wire to heat up a piece of glass
> 250x300x4mm about 10° Celsius above room temperature. I've made some > > ....
> As pictured in the diagram - 240mm of wire every 10mm for 290mm =
> 240x29 + 10x29 = ~7,300mm. That's 7.3m of resistance wire. Assuming
> room temperature is 20°, the wire will temperature will need to be
> ~35°, to keep the glass at just under 30°.
>
> The wire will be attached to one side of the glass surface using
> self-adhesive clear plastic wrapper (similar to those used to wrap > books). >
> 1. Are these calculations/assumptions correct?
> 2. What kind of wire (thickness) should I be looking for?
> 3. What will my power consumption be (will 12V @ 1A be enough)?
>
> The general idea seems ok, but I wonder about heat losses and
> acceptable temperature variation. If the losses are significant, than
> the wire spacing of 10mm for 4mm thick glass sounds a bit high - glass
> is not a good conductor of heat. One approach might be to use a piece
> of printed circuit board (unetched), and place a continuous copper
> plane next to the glass, with heating elements attached to the other
> side (nichrome wire is good). The thin copper sheet will spread the
> heat to give a more uniform temperature. Based on experience with
> heaters for telescopes, 12W will not be enough unless the losses are
> absolutely minimal.
>
> Dave
>
Why try to bond wire to glass?
Paint or silkscreen resistive paint in a grid or other pattern like a auto's rear window defroster. You get better thermal transfer,it's far simpler. Bond connnecting wires with silver conductive epoxy.