Panel Light Rheostat

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6277
Posts: 233
Joined: Tue May 01, 2018 7:00 am
Name: Ray Hunter
Location: Ann Arbor, MI
Aircraft Type: C-140
Occupation-Interests: Retired AF, retired B-17 pilot for Michigan Flight Museum
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Panel Light Rheostat

Post by 6277 »

Some years ago, I replaced the panel light rheostat with an Ohmite 25 w 8 ohms PN 0144. The six bulbs are 1893 GE. I don't fly much at night so I never really checked the rheostat although I knew that it got warm. My panel lights are connected to the position light circuit. Now that I have the ADSB tail beacon and position lights on constantly, I find that the rheostat is heating up. It's almost too hot to touch. I have temporarily disconnected the wire from the rheostat to the panel lights. Any ideas why the rheostat is heating up?
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6643
Posts: 2544
Joined: Tue May 01, 2018 7:00 am
Name: John C
Location: KLCI, NH
Aircraft Type: 1946 C140/C90
Occupation-Interests: A&P, semi-retired
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Re: Panel Light Rheostat

Post by 6643 »

The simple answer is because it's a resistor. If you turn the panel lights all the way it'll make less heat (0 watts,) but the 6 bulbs will get hot (28 watts). If you turn them all the way down the total heat (bulbs plus resistor) will be at a minimum but the resistor will be dissipating 8 watts. If you have extra bulbs above what is original, attached then it will get hotter than designed.

I see no reason you couldn't have a switch for the panel lighting installed and have it logged as a minor modification.
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