l.e.d and a cap

does anyone know what size capacitor i would need to keep a single l.e.d lit for 5~7 minutes?\

thanks in advance

bob

ac delco am radio and sparkomatic 40 watt sound exploder

What is the largest cap you have available?  How long does it keep the LED lit?

Up to 18mF (18,000uF) should do it.

i am an idiot wrote: What is the largest cap you have available?  How long does it keep the LED lit?

i dont have any right now just thinkin for a future build possibly? time as stated in the 1st post 5~7 minutes

thanks and thanks oldspark

ac delco am radio and sparkomatic 40 watt sound exploder

I would do it thru some FET or transistor timed circuit. Hence a much smaller cap is required; it is easy to adjust the delay; and you won't have dimming issues. And you can add more LEDs. The BIG cap method assumes a ~12V cap discharging into a 2V LED and its resistor. As the voltage drops from 12V to 2V, the LED will dim (though maybe not much). But around 2V (or 1.7V or 3.4V - whatever the LED voltage), it will stay very dim for quite a while - it won't be a clean shut off. But that might be ok in your case....

ok ill take that into consideration thanks, i never messed with fets to turn things on or off, i reserched it a wile back. i do want a slow fade, thats why i was thinking of a cap.ac delco am radio and sparkomatic 40 watt sound exploder

FYI - from my DELETED reply (with apologies) to the simple way to make a time delay relay thread.... It's merely from a quick search, and for relays, but substitute LEDs instead... From Electronics Today - Circuits Cookbook #5, page 84:

And from (or based on) Bill Bowden:

(PS...) And from an unknown source:

thanks so much oldspark, i appreciate it i doac delco am radio and sparkomatic 40 watt sound exploder