Hi people.

I'm fitting some lights to a project. The lights are single fillament 21w and want to run it at full 12v supply and also switch it to dim to around 4v with a 6ohm 25w load resistor. I can't remember if load resistors can be put in series with a fillament bulb to dim it? Before cutting the lights out I checked some values full power 12v 1.75a and 4v 0.6a. I will play around with the resistance to get the brightness but I rest can't remember if I can put a resistor in like that.

Sorry for the basic question!

 

If more than one lamp, why not use the method used on some auto's for DTRL's and place them in series?
Max.

 

Better to use a mosfet pwm circuit to dim the bulbs,like a 555 circuit.

 

Yes there's two bulbs doing the same thing. Didn't give that a thought. I have considered the pwm route this would save energy and reduce heat but if possible I'd like to keep it resistor based.

Thanks so much for the help.

 

Resistors make heat dropping the excess voltage, which is wasteful and needs cooling.

 

Resistors make heat dropping the excess voltage, which is wasteful and needs cooling.

But if two bulbs in series gives an acceptable dimming then it is simple and energy conscious.

 

I have done it by voltage divider with resistors, seems to be giving the right level of light. Hopefully it doesn't change too much with charging voltage

 

Just seen the abouve post, will try it tomorrow to compare. As you say it's a simpler and better for energy.

Thanks
Martin

 

My OLD's uses this method for DTRL and just use simple relay switch over for full and series V.
Max.