How to power a 12V 20W halogen?

[grantg55]

Hello, I want to use an arduino to power a 12V 20W halogen bulb using a relay or a TIP120 (not dimming, so don't need a MOFSET, just on/off).

If I have it right (using P = IV), the bulb is rated for 12V at 1.7A. Am I safe to use and old charger rated for 12V and .8A? Or will the bulb draw too much power and create a dangerous situation?

Thanks,
Grant

[zener]

If the charger is only rated for 0.8A and the lamp wants to draw 1.7A then the charger will be overloaded. Exactly what will happen then will depend on how the charger is designed, but proper operation is not one of the things that will happen. You would need a supply rated at a higher current.

[phild13]

An Arduino output can not power the bulb directly so you would need some type of switch that the arduino can control.. The Arduino output could be connected to FET or a plain old transistor that can handle the current rating with minimal hassle. You still need a supply to handle the bulbs current draw though.