Need help from one of our electrical guru's

[DennyDay]

Just added sport head lights to my '99, and found that the inboard low beam was not used. Since comapny requires Day time running lights, I came up with a way to power the inboard low beams only. Got it hooked up and everything works as I wanted it to, now I would like to decrease the intensity of only the inboard lights by about 40%. The load is 55 watts per bulb,and I need to know if a resistor in line on the negative feed will work and what value resistor I will need, or is there a better way? I can use one or two resistors, whichever is more practical.



Thanks for your help, Denny

 

[Ramboy]

Assuming your load will be 55w, with 22w across a resistor and 33w at the bulb, with about a 13v supply, there will be about 4. 2A flowing in the circuit. Solving for the size of the resistor using 4. 2A and 13v, you would need a 3 ohm-22w resistor. Probably not that easy to find. I would go with a rheostat.

Phil

 

[DennyDay]

Day time running lights

Ramboy -- I like the idea of a rheostat and never gave it a thought. Can you tell me what to look for, value etc. ?

Denny

 

[Great White]

The intensity of filament lamps is not linear with the current. By reducing the current /voltage by 10% you will typically reduce the output by 50%.

55w/14. 2v = 3. 87a

3. 87a/10 = . 387a

. 387 x 14. 2 = 5. 5 watts disapated power thru resistor.

14. 2v/ 3. 87a = 3. 66 effective resistance of lamp when lit.

3. 66/10 = . 366 ohms @ 10 watts should do it for 50% reduction of lamp output. Possibly a good choice of resistor would be the ballast resistor for a gasoline ignition system. Mallory makes a nice one.

Be prepared for reduced lamp life if halogen lamps are used due to the re=generative nature of the lamp. Halogen lamps need to operate near their effective temps.

Let me know how it works out!

Rich

 

[DennyDay]

Thanks Rich - - -Just what I needed to know. Will post when I get it done.

Denny