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-   -   Gauge Light Dimmer (http://www.diychatroom.com/f46/gauge-light-dimmer-56171/)

navman28 10-28-2009 09:31 PM

Gauge Light Dimmer
 
I installed a 25 ohm 3 watt rheostat to adjust my gauge lighting. When on, the rheostat gets extremely hot. I dont know much about electricity, just enough to be dangerous. I am thinking that I can install a 47 ohm .5 watt resistor before the rheostat. What do I need to do to keep the rheostat from overheating?

Yoyizit 10-28-2009 10:22 PM

Quote:

Originally Posted by navman28 (Post 346695)
I installed a 25 ohm 3 watt rheostat to adjust my gauge lighting. When on, the rheostat gets extremely hot.

For 25 ohms to dissipate >3w you'd need sqrt (3x25) = >9v across it.

How much current do your gauge lights draw when full on? If they are incandescent lamps the calc. for a dimmer resistor gets really tricky. Does the 25 ohms make them dim enough?

navman28 10-28-2009 10:47 PM

I know the gauges are LED but dont know what they draw. Yes they do dim, just the rheostat gets really hot.

Yoyizit 10-29-2009 09:08 AM

LEDs should be easy to control, but you need to measure the current draw at full brightness.
I^2 = 3w/25 ohms so I is at least 0.8 A. That seems high for LEDs.


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