breathment

I like cars that have the lights that DIM slowly when you shut the door. instead of just turn off imidiatley.. and i was wondering. and the easiest what i could think of to do this, would be a capacitor.. but i don't know crap about what size i need. (how many farad) so i went to Radio Shack and got the largest one they had. 4700 microfarad (.0047 farad i think) and it didn't do crap for even one light, besides get real hot, and take forever to charge. As expensive as capacitors are (.5 and 1 farad caps) i don't know if this is how they make the lights that dim, but if i were to use a cap, what size would i need.. and if i should maybe make a small circuit, what stuff what i need??

thanks..

EDIT: the biggest i could fine at jameco.com is a 10,000 microfarad.... for 3.95. cheaper then what i got for a 4700 microfarad at Radio Shack

Danno

Fist of all if the capacitor got hot then it was either the wrong voltage or you did not observe polarity. Large value capacitors such as that are referred to as polarized electrolytics. They will be marked with a plus which will go to the 12v and a - which goes to ground. Reversing polarity on an electrolytic will cause it to get hot and possibly explode. To calculate time for charge and discharge use this formula. Tc=RC, where TC equals time in seconds, R is resistance in ohms and C is capacitance in farads. This formula is the time required to charge the cap to 63% of the source voltage, and the time to discharge it 63%. To go to 99% of source voltage is approx. five times the number you get by using the formula. For example a 4mF capacitor with a 1 meg ohm resistance will take 4 sec to discharge 63%. (0.000004x1,000,000=4sec). You will need to measure the resistance in ohms of the lamps and then use the formula. If you run the numbers you will see that it is probably not practical as the bulb resistances are sufficiently low to make use of a very large cap. A circuit is more practical. I will try to cook up something simple when I get a little time.

Omega

iTrader: (1)

This guy has all sorts of cool toys.

http://www.webelectricmagazine.com/99/1/dome.htm

breathment

holy crap .. i have a new favorite website now.. ok second favorite website

85_ZED28

probably really old, but ttt