question on relay use

Printed From: the12volt.com
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=34952
Printed Date: May 10, 2025 at 11:06 PM

Topic: question on relay use

Posted By: DaveK
Subject: question on relay use
Date Posted: July 02, 2004 at 10:33 AM

I have a question on the diagram for the auto unlock w/o alarm diagram.

posted_image

Why is the coil connected to +12V on both sides?

Thanks for any help.

Replies:

Posted By: xetmes
Date Posted: July 02, 2004 at 1:47 PM

the coil is not connected to +12 on both sides all the time

the fused +12 is always +12

then the ignition is on the cap discharges (no voltage across it)

then the vehicle is shut off, the cap draw a good deal of current (displacement current) to charge the cap, this triggers the relay on, after the cap is fully charged the current stops flowing.

this causes a momentary pulse that turns the relay on for a short period of time... this then triggers the door lock actuators

Posted By: DaveK
Date Posted: July 06, 2004 at 2:10 PM

I need to wire this in series with the +12v from the battery to the ignition switch or is the ignition +12V in the diagram actually +12V from the ignition switch?

Sorry to be difficult. I'm just having a hard time visualizing this application.

Posted By: xetmes
Date Posted: July 06, 2004 at 9:00 PM

no not in series, branch off the +12V ign to the ignition input in that diagram

Posted By: DaveK
Date Posted: July 07, 2004 at 12:42 PM

But wouldn't the diode on the ignition wire prevent any current from flowing from the ignition switch?

Posted By: xetmes
Date Posted: July 07, 2004 at 4:00 PM

yes, while the ignition is on, that keeps the relay off until the vehicle is shut off...

Posted By: MattL
Date Posted: September 04, 2004 at 4:15 PM

Sorry so the diagram above is unlock the doors when i switch the ignition off??

Is there a diagram for locking the doors when ignition on?

I dont want to invest in an alarm, i have some good quality relays lying around anyway.

Thanks

Matt

Posted By: DaveK
Date Posted: September 05, 2004 at 3:54 PM

https://www.the12volt.com/doorlocks/page3.asp

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