Hi,
First of all, I don't have a dash dimmer, and none of this is from direct
experience, but it makes sense to me. As always I'm open to corrections.
>Here is what I have.
>Linear-Taper Potentiometer 50k-Ohm
>500vdc , .5w rated power.
50K is way too high, and 0.5W is far too low a rating. I assume that the
lamps that are dimmed are similar to those used for illumination in my
Spitfire IV (1971 UK), 4 2.2W lamps. I also assume that the current through
these lamps is constant (not true, but probably good enough for this purpose).
Current is about 750mA ( (2.2x4)/12 ).
I assume that the dimmer works by reducing the voltage across the lamps. You
would probably only want to drop this to half (maximum, maybe even less). So
at maximum dim, need to drop about 6V at 750 mA. Therefore need an 8 ohm
resistor, so the original 10 ohm is about right.
The power dissipated in this resistor would be 4.5W at max dim.
So a 10 ohm, 5 Watt pot would be fine, but would get quite hot. I don't know
if Radio Shack do these. At this power rating it will almost certainly be
wire-wound and a bit pricey. It may be similar to the ones used to control
loudspeaker volume (the ones that you mount in the speaker enclosure), but
you'd have to check.
The easy solution would be to get one from another Spit. I don't have the
dash dimmer, but find the illumination a bit dim anyway.
Hope this helps
Robert.
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