Relay-based switching between 12v sources
Printed From: the12volt.comForum 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=142599
Printed Date: May 02, 2025 at 7:34 PM
Topic: Relay-based switching between 12v sources
Posted By: funkyd
Subject: Relay-based switching between 12v sources
Date Posted: February 12, 2017 at 10:53 PM
Hi everyone and thanks in advance for your time and advice.
I've researched this topic ad nauseum, and have fried more components than I care to remember in trying to achieve what I believe should be relatively simple. I'm completely frustrated and decided to swallow my pride and ask for some help.
The pic below illustrates my goal - to appropriately power a single set of LED strips (C) using either the constant 12v source (A) or the ignition-only 12v source (B), based on one of the following conditions:
1) Ignition off + door open = lights powered by 12v constant
2) Ignition off + door closed = lights powered by 12v constant
3) Ignition on + door open = lights powered by 12v ignition
4) Ignition on + door closed = lights powered by 12v ignition
Can someone please connect the dots for me? I can easily power the LEDs under any of these conditions, but the switching between configs has me stumped. I've used a variety of relays in a number of configs - either it didn't work at all or it melted beyond recognition by the time I cut the power to it. In my research I've seen mention of the use of MOSFET components and diode-only configs in addition to relay-based switching... Instant parts availability is a bit of a problem, relays are easy enough to procure very quickly and using them seemed easiest but if someone can recommend an alternate but relatively simple solution I would be forever grateful.
Thanks again,
D
I've researched this topic ad nauseum, and have fried more components than I care to remember in trying to achieve what I believe should be relatively simple. I'm completely frustrated and decided to swallow my pride and ask for some help.
The pic below illustrates my goal - to appropriately power a single set of LED strips (C) using either the constant 12v source (A) or the ignition-only 12v source (B), based on one of the following conditions:
1) Ignition off + door open = lights powered by 12v constant
2) Ignition off + door closed = lights powered by 12v constant
3) Ignition on + door open = lights powered by 12v ignition
4) Ignition on + door closed = lights powered by 12v ignition
Can someone please connect the dots for me? I can easily power the LEDs under any of these conditions, but the switching between configs has me stumped. I've used a variety of relays in a number of configs - either it didn't work at all or it melted beyond recognition by the time I cut the power to it. In my research I've seen mention of the use of MOSFET components and diode-only configs in addition to relay-based switching... Instant parts availability is a bit of a problem, relays are easy enough to procure very quickly and using them seemed easiest but if someone can recommend an alternate but relatively simple solution I would be forever grateful.
Thanks again,
D
Replies:
Posted By: the12volt
Date Posted: February 13, 2017 at 7:01 AM
A single relay will solve the issue with powering through the ignition switch when the ignition switch is on (see below), but why not power straight from the battery regardless of ignition switch position?
#85 and #87 to ignition 12V+
#86 to ground
#87a to constant 12V+
#30 = 12V+ output
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the12volt • Support the12volt.com
#85 and #87 to ignition 12V+
#86 to ground
#87a to constant 12V+
#30 = 12V+ output
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the12volt • Support the12volt.comPosted By: funkyd
Date Posted: February 13, 2017 at 6:28 PM