hotwaterwizard: dome delay relay

I have here a diagram that you drew up for a dome delay circuit. I'm curious if you know how long this will stay energized after the ignition power is released. Also, I'm trying to figure out exactly how the circuit works, and I'm not sure the purpose of the second diode making the loop on the relay. Care to enlighten?2000 BMW 540i 6 speed

that depends on the draw from the dome light. if you use it and the delay is or isnt long enough you can always put in a different cap.

for the diode i think that is to keep the 12volt from backing up through the relay. audiovox relays come with that diode already on them

not trying to step on peoples toes but you better put a resistor on the base of the transistor, granted the coil will provide some but a mere 200 ohms or so. The time on is a result of the transistor base current draw but is determined by a resistor (not shown?). Personally I would run an NPN in common emitter or use a PNP to switch the high side since the current in the relay will drag the emitter voltage up, but thats just me...

Well the draw of the lights shouldn't change the time, because the lights are on the other side of the relay. As far as the resistor, that is all greek to me. My knowledge in electronics is very basic, and while I always try to understand what's going on adding things isn't my specialty.2000 BMW 540i 6 speed

Well I only need a 30 second timer. I built the one xetmes drew up, and it clicks on the relay when power to the ign is applied but the voltage to the relay never drops low enough to click the relay off.2000 BMW 540i 6 speed

try mine with a 47uF capJohn DeRosa (Hotwaterwizard)

Stockton California

When in doubt, try it out !

try mine with a 47uF cap or a 10uFJohn DeRosa (Hotwaterwizard)

Stockton California

When in doubt, try it out !