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How to select a proper potentiometer?

Eva713

New member
Hi, folks
I need a recommendation for a potentiometer.
I have an old 8mm projector that uses a 8v 50w bulb. The bulb works off a simple on/off switch. I would like to insert a potentiometer inline between the transformer and bulb to vary the intensity of light the bulb generates.

Even if I read theories like How to Choose a Potentiometer? (search recommendation, maybe there are some mistakes in it), my knowledge of potentiometer is not enough to figure out what part to use when there is no old part to use as a reference. I would sincerely appreciate any suggestions. Many thanks. :)
 

dl324

New member
You'll be hard pressed to find a pot that will dissipate more than a couple watts and the power rating is for the entire resistance. If you use it as a rheostat, you could easily burn it up.

Show the bulb drive circuit and specify your space and complexity constraints on solution space. How much do you want to vary the brightness and why?
 

Eva713

New member
I know any device used to lower the power to the lamp would need sufficiently high enough power rating. Here pot as such generally are rather low, perhaps 1/4w and not suitable. :(
 

dl324

New member
I know any device used to lower the power to the lamp would need sufficiently high enough power rating.
PWM is commonly used in this application. Since the device switching the lamp is either on or off, power dissipation isn't an issue. The switching device just needs to be able to handle the lamp current and voltage.
 
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