Hot dimmer switch

[Htwjr]

On my '67 M20C the overhead instrument light dimmer switch gets hot. Is this normal? If not what can be done to correct it? Thanks

[Hector]

Have a 67C as well that I purchased a year ago. Mine is VERY hot as well. I keep it turned all the way down Sent from my iPad using Tapatalk HD

[OR75]

if the dimmer works like dimmers you can find in a house , and i believe they do, it reduces the current by absorbing some of the current. so actually when you dim the light to very low, the dimmer has to absorb more current ( and gets warmer as the dimmer uses a resistance to abosrb the current)

try to turn up all the way up, and your dimmer shall stay cool. ( the heat is released by the ligh bulbs)

[mikesalman]

So in other words brighter or dimmer you are still drawing the same amps? I have always been under the impression dimmer = less draw.

[N601RX]

It uses a ungrounded Resotat which is a variable resistor.  At full brightness, little if any voltage is dropped across it and it shouldn't to excessively hot.  As you dim the lights the resistance of it increases and more voltage is dropped across it.  The dimmer the lights, the hotter it will be. 

[OR75]

So in other words brighter or dimmer you are still drawing the same amps? I have always been under the impression dimmer = less draw.

in summary, same draw no matter how dim . the dimmer absorbs part of the energy when the lights are dim.

[N601RX]

The current will be less as the lights dim.  According to the wiring diagram it is a variable resistor with one end open in series with the lights. The resistance can change from almost 0 to approx 25.   The difference is with the lights dimmed the power (watts) is being dissipated across the pot instead of the producing light in the bulbs.

[OR75]

in other words, you are not saving your battery by dimming.

Same goes for dimmers at home, you are not saving electricity by dimming lights.

[DrBill]

In my E model, the 25 ohm reostat is in series with the dash bulbs (unknown draw) and the two "map"lights which are 0.6A at 13.5V.

let's just consider the two map lights. With the reostat at "0" (full bright) the battery will deliver 1.2A at 13.5 volts which is equivalent to a load of 11.25 ohms.

Now is we turn the reostat to 1/2 bright (12.5 ohms) th total resistance is 23.75 ohms and the current will drop to 0.57A. Thus, the reostat dimmer does in fact reduce the load on the battery . Some models may use an electronic dimmer (like your home dimmer) which turns the bulb on and off at various rates to control brightness. These also reduce the bulb load to the battery.

 

The reason the reostat gets hot is that over time, more bulbs are added to the dash circuit which decreases the net resistance of the bulbs. The reostat is designed for a given maximum load. at full dim. 7.3 watts in this case (25 ohms, 13.5 v).  At half bright (12.5 ohms) that power would be exceeded (over heat) with a load of 0.8A or roughly the equivalent of 4 map light bulbs. I think my panel has about 10 bulbs plus the 2 map lights and although the dash bulbs are smaller and use less than the map lights, it is easy to see that tha reostat would be overloaded at 1/2 bright or less.

 

I'll be glad to share the technical detail with anyone if interested.

 

BILL

[kellym]

in other words, you are not saving your battery by dimming.

Same goes for dimmers at home, you are not saving electricity by dimming lights.

There is an off position which will minimize the current draw.