hooking up led
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=134119
Printed Date: June 03, 2024 at 1:58 AM
Topic: hooking up led
Posted By: musclesoh92467
Subject: hooking up led
Date Posted: April 29, 2013 at 8:51 AM
im hooking up a led as a alarm warning light.id like it to blink when car is off but turn off when car is running//would i use a SPDT or other relay..appreciate any info....
Replies:
Posted By: oldspark
Date Posted: April 29, 2013 at 9:43 AM
LED+ to constant +12V
LED- to IGN +12V
Posted By: musclesoh92467
Date Posted: April 29, 2013 at 2:02 PM
my LED only has a positive and a negative..doesent it need ground if i hook up one side to + constant and - to ignition +?
Posted By: oldspark
Date Posted: April 29, 2013 at 10:57 PM
The way it woks is the LED GNDs thru the Ignition in the OFF (or ACC loads on ACC & IGN) position.
When IGN (or ACC) goes to 12V, there is zero or <1 volts across the LED hence it extinguishes.
No need for a relay, but a relay should be an SPDT aka 5-pin relay with 85 & LED- to GND, 86 to IGN, 30 to fused +12V or IGN (or ACC) & 87a to LED+. Hence the relay switches off to light the LED (otherwise you'd be using a relay that drains typically 40-200mA for a max 20mA load and draining the battery far worse).
Interchanging 87a & 30 does not matter.
I often connect the output loads from 30 and the power source +12V to 87a or 87a. That means there is no naked +12V 87a or 87 in either state - ie deenergised (its most common status) or energised. That saves fitting insulation (an unused spade) on 87 or 87a.
Posted By: musclesoh92467
Date Posted: April 30, 2013 at 9:10 AM
so i dont need a relay for led but should i still use a fuse on both sides of led and i was gonna tap into radio harness under dash for the power wires should that be good and led wont drain battery?
Posted By: oldspark
Date Posted: April 30, 2013 at 9:51 AM
No, you don't need a relay.
And you only ever need a fuse on one side of a load. For LEDs it's in the +12V supply. but it's only to protect the wiring because no fuse will protect a LED.
Of course the LED will drain (discharge the battery) - it is an electrical load.
But a 20mA LED should take several days to drain a battery enough to effect cranking, and a flashing LED should take less.
Most alarms etc take over 40mA. A typical 30A relay takes over 200mA.
Posted By: musclesoh92467
Date Posted: May 02, 2013 at 2:23 PM
i hooked up LED as you said and works great..thanks for info i apreciate it...i connected positive side of LED into my positive radio wire and the negative side of LED into my radio switched positive.this is a good location and i wont have any battery drain except for the blinking led correct?
Posted By: oldspark
Date Posted: May 02, 2013 at 7:57 PM
It should only add the drain that the LED uses.
Only on some circuits could extra drain occur - eg, if for a modern HU, LED+ to Const and LED- to IGN and if there is no IGN load to keep the LED- grounded with IGN off.
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