12v or ground after key off?
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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=137996
Printed Date: April 29, 2024 at 3:49 AM
Topic: 12v or ground after key off?
Posted By: 2muchspl
Subject: 12v or ground after key off?
Date Posted: December 18, 2014 at 4:21 AM
Hey guys I have another custom project, I need a relay to provide 12v or ground when I turn key off (or remove 12v) to activate this timer https://www.youtube.com/watch?feature=player_embedded&v=-lb_hIS82EE to keep a device powered up after I cut vehicle off.
here is a sketch for visual purposes
https://www./itm/271680959330?ru=http%3A%2F%2Fwww.%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D271680959330%26_rdc%3D1
Replies:
Posted By: tonanzith
Date Posted: December 18, 2014 at 2:26 PM
Depending on the vehicle a true ignition wire may rest at ground when they key is off.
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Gary Sather
Posted By: tonanzith
Date Posted: December 18, 2014 at 2:27 PM
Or use a relay to achieve this when the ignition wire isn't powered.
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Gary Sather
Posted By: 2muchspl
Date Posted: December 18, 2014 at 2:36 PM
I really dont want to tap into the ignition wire even if it does ground with key off. Im tryin to do it with a switch 12v source. So is there a way to wire a relay when the switch 12v source turns off it supplies a ground?
Posted By: tonanzith
Date Posted: December 18, 2014 at 2:53 PM
I guess I'm confused as to what you're looking for then. Ignition wires are a switched 12 V source also accessory wires. Honestly if it were me I would use an ignition wire. I would use the ignition wire as a trigger for a standard Bosch relay that rests at ground when the ignition is off. Pin 85 to ground. Pin 87a to ground. Pin 86 to ignition. And pin 30 will supply ground to your timer when the ignition is off. Or you can provide 12 volt to the timer by switching pin 87a to 12v constant instead. Pin 87 is not used.
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Gary Sather
Posted By: 2muchspl
Date Posted: December 18, 2014 at 3:17 PM
Im sorry I might of confused you, ok what if I didnt have a ignition wire but a simple switched 12v as the trigger that when off can trigger a relay to output a ground. Did that make sense? Basically the opposite of the reverse polarity diagram on here. So 12 volts keeps the relay open, when the 12v is removed I get ground.
It doesnt have to be ground, it can be positive too for the timer. Just used ground as example. Appreciate your help btw!
Posted By: i am an idiot
Date Posted: December 18, 2014 at 5:03 PM
Posted By: howie ll
Date Posted: December 18, 2014 at 6:41 PM
Craig, that links back to this thread.
Original OP, use an ignition or ACC depending on vehicle (say 99% assuming NOT a P38 Range Rover) they ALL sit on ground.
Use a timer as you showed; please forget running a normal relay as this will drain your battery in about 14 hours.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: i am an idiot
Date Posted: December 18, 2014 at 9:59 PM
Not knowing how much current his timer draws I would not do that. An LED to make a fake alarm, all day. I know it linked back to the post that gave the instructions to do exactly what he wants to do.
Posted By: davep.
Date Posted: December 18, 2014 at 11:26 PM
howie ll wrote:
forget running a normal relay as this will drain your battery in about 14 hours.
Don't you mean 14 days?
A relay draw is 140Ma. .140a X 14 hours is 1.97 Amp Hours. For ~2AmpHrs to cause a problem would need a very tiny battery. My laptop has a 4.4Ahr battery, twice as big.
Now .140 X 24 = 3.36 Amp Hrs per day. 3.36 X 14 days = 47 AmpHrs. This might be a problem for many vehicles. Certainly after 3 weeks.
But 14 hours? No way.
Cheers.
Posted By: howie ll
Date Posted: December 19, 2014 at 1:10 AM
Yes sorry, thinking about load.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: i am an idiot
Date Posted: December 19, 2014 at 6:15 AM
The relay will pull no current when the vehicle is not running. We are using the normally closed contacts.
Posted By: 2muchspl
Date Posted: December 19, 2014 at 7:36 AM
tonanzith wrote:
I guess I'm confused as to what you're looking for then. Ignition wires are a switched 12 V source also accessory wires. Honestly if it were me I would use an ignition wire. I would use the ignition wire as a trigger for a standard Bosch relay that rests at ground when the ignition is off. Pin 85 to ground. Pin 87a to ground. Pin 86 to ignition. And pin 30 will supply ground to your timer when the ignition is off. Or you can provide 12 volt to the timer by switching pin 87a to 12v constant instead. Pin 87 is not used.
Ok Ima give this a go today when I get off work and report back on success & key off draw. Thanx a million guys!
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