electrical system shutdown

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=96400
Printed Date: June 17, 2024 at 9:56 PM

Topic: electrical system shutdown

Posted By: daveo1
Subject: electrical system shutdown
Date Posted: August 14, 2007 at 6:08 PM

Hi to all! New here been reading A LOT, nice info here. Im wondering if anyone has any info on a circuit or relay type system that will kill power to the car after the battery or system drops around 11 volts.

I have seen this on Nissan, and maybe Toyota. We could leave dome lights on or door and trunks open and im pretty sure that the electrical system would shut off until you tried to start it or started messing with the light or whatever.

I was told by someone that when the electrical current drops below 12 volts it activates, Im just curious, thinking that would be neat to do in my project car. Thanks for any help!

Replies:

Posted By: i am an idiot
Date Posted: August 14, 2007 at 7:34 PM

Most of the newer vehicles allow the vehicle to go to sleep after a predetermined time. This process is not voltage sensitive.

Posted By: daveo1
Date Posted: August 14, 2007 at 8:25 PM

Is it possible to wire up on a 70's vehicle?

Posted By: hotwaterwizard
Date Posted: August 14, 2007 at 9:35 PM

You could build this circuit and drive a opto isolator with the output then drive a transistor to drive a relay with.

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: hotwaterwizard
Date Posted: August 14, 2007 at 10:28 PM

https://www.electronics-lab.com/projects/automotive/009/index.html

https://www.electronics-lab.com/projects/automotive/009/carbatterytester.gif

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https://www.electronics-lab.com/projects/automotive/001/index.html

https://www.electronics-lab.com/projects/automotive/001/car4f.gif

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https://www.reconnsworld.com/power_highlowbattmon.html

https://www.reconnsworld.com/power/highlowbattmon.gif

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https://www.reconnsworld.com/power_12vbattmon.html

https://www.reconnsworld.com/power/12vbattmon.gif

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: hotwaterwizard
Date Posted: August 14, 2007 at 10:41 PM

Here is one I modified fro the post above.

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: daveo1
Date Posted: August 16, 2007 at 12:42 PM

Thank You, that should keep me busy!

Posted By: dualsport
Date Posted: August 18, 2007 at 10:29 PM

Interesting project. I think there's a commercial product that does this; search for Battery Guard and a bunch of things will come up on google.

If you want to DIY, the thing to use is solid state components to do the load connect/disconnect, because having a relay coil turn on defeats the purpose of the circuit. You wouldn't want the circuit to draw any extra power off the battery, either above or below your 11V threshold.

It'd be easy enough to do with a voltage comparator, which then drives your transistor to turn on or off the power when the trigger conditions are met, and also bypass the cutoff when the ignition is on, to keep it from shutting down when cranking. Not much to it except to pick a transistor that will handle the current. It'd have to be a separate tap off your battery, not in line with your starter, but that shouldn't be a problem because you wouldn't expect your starter to draw anything when the car is off. The commercial item uses a mechanical latching relay that doesn't draw any power except when switching, which would be better since it could handle full current, but costs more.