i wonder if this is ok, 12v power sources

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=113114
Printed Date: May 17, 2025 at 12:55 AM

Topic: i wonder if this is ok, 12v power sources

Posted By: ///oss
Subject: i wonder if this is ok, 12v power sources
Date Posted: April 13, 2009 at 5:01 PM

Quick question... I have 2 separate power sources and i need one to cut off when the other is active so I figured id get an SPDT 12VDC relay.

Im having a doubt on the wiring though...

lets say I use 30 for the 12+ volt output common, and the primary or initial 12V to be used will be on 87a. then the secondary 12V into 86 and 87, so when that kicks on the coil switches to 87 and feeds off that source.

Ground will be on 85.

Will that have some sort of issue?

Im curious if the secondary source can act as the control wire simultaneous when it kicks in?

and also I will add a diode across the coil as well just to make sure no spikes go on.

any other suggestions are greatly welcomed... trying to DIY this

Replies:

Posted By: howie ll
Date Posted: April 13, 2009 at 5:19 PM

You have it right and yes diode with it's band to +coil (86)

Posted By: ///oss
Date Posted: April 13, 2009 at 5:36 PM

so its safe to say that this is correct?

posted_image

will a 6V drop in the 87a matter once the coil is on and feeding power from 87 onto 30?

Posted By: KPierson
Date Posted: April 13, 2009 at 7:04 PM

So you basically are trying to output 12vdc to the LEDs when the ignition is on? Why don't you just use an ignition source?

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Kevin Pierson

Posted By: dualsport
Date Posted: April 13, 2009 at 11:45 PM

Yeah, that seems like a solution looking for a problem- just connect the LEDs to the 12V switched source directly.
Relays are generally only needed when trying to control a larger current with a smaller signal or isolating circuits; doesn't sound like either one applies.

Posted By: howie ll
Date Posted: April 14, 2009 at 2:51 AM

Yes Kevin and dualsport are correct, I would add a voltage stabiliser to the LEDs.