l.e.d and a cap
Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=124241
Printed Date: June 17, 2024 at 12:43 AM
Topic: l.e.d and a cap
Posted By: 66sportfury
Subject: l.e.d and a cap
Date Posted: November 02, 2010 at 4:33 AM
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
Replies:
Posted By: i am an idiot
Date Posted: November 02, 2010 at 5:22 PM
What is the largest cap you have available? How long does it keep the LED lit?
Posted By: oldspark
Date Posted: November 02, 2010 at 7:31 PM
Up to 18mF (18,000uF) should do it.
Posted By: 66sportfury
Date Posted: November 02, 2010 at 10:25 PM
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
Posted By: oldspark
Date Posted: November 02, 2010 at 10:35 PM
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....
Posted By: 66sportfury
Date Posted: November 04, 2010 at 3:27 PM
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
Posted By: oldspark
Date Posted: November 04, 2010 at 6:39 PM
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:
Posted By: 66sportfury
Date Posted: November 05, 2010 at 12:07 PM
thanks so much oldspark, i appreciate it i do
------------- ac delco am radio and sparkomatic 40 watt sound exploder
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