what kind of relay do I need?
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=33459
Printed Date: August 25, 2025 at 12:07 PM
Topic: what kind of relay do I need?
Posted By: casnj
Subject: what kind of relay do I need?
Date Posted: June 07, 2004 at 12:06 PM
what kind of relay do I need for this and how do I wire it? i have two wires one that goes positive and the other is 0 when the door is locked. then they both go to positive at unlock. well if the 1st condition exist I want the positive voltage to flow to my device.
Replies:
Posted By: markcars
Date Posted: June 07, 2004 at 3:54 PM
I don't know what exactly you're wanting but I you can accomplish any switching requirement with a spdt relay. If there is 2 simultaneous switching that you need the go for a dpdt relay or 2 spsts will do too.
Posted By: casnj
Date Posted: June 07, 2004 at 5:23 PM
markcars wrote:
I don't know what exactly you're wanting but I you can accomplish any switching requirement with a spdt relay. If there is 2 simultaneous switching that you need the go for a dpdt relay or 2 spsts will do too.
what i want to do is simple. im just not explaining it fully :) i have two wires. one is positive and one is negative during lock both are positive during lock when the 1st condition exist I want the power to go to a pin when the 2nd condition exist i want te power to go to another pin I need the 1st condition. the 2nd is optional
Posted By: CHaseHeadrick
Date Posted: June 08, 2004 at 10:51 PM
i don't understand how they can both be positive during lock, or at unlock? if they rest a ground, then when one wire changes to 12v+ it is the function (lock/unlock) wire. if they rest at 12+, then its the same way, the wire that stays at 12v+ is the function wire.
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Posted By: markcars
Date Posted: June 09, 2004 at 4:49 PM
You could use a single pole double throw relay(SPDT) available at any electronics stores. Even Radio Shack has them if you don't have it already.
Connect pin 85 to ground (-ve)
pin 86 to the wire that gives +ve at lock
pin 30 to a constant +ve
pin 87a to the wire that you want power during lock
pin 87 to the wire you want power during unlock
Posted By: casnj
Date Posted: June 10, 2004 at 7:56 AM
so pin 85 is connected to the wire that shows ground when locking right? pin 85 is not a chasis ground?
Posted By: casnj
Date Posted: June 10, 2004 at 8:46 AM
Posted By: markcars
Date Posted: June 10, 2004 at 4:10 PM
casnj] wrote:
so pin 85 is connected to the wire that shows ground when locking right? pin 85 is not a chasis ground?
Pin 85 goes to direct chassis ground.
Posted By: markcars
Date Posted: June 10, 2004 at 4:18 PM
casnj] wrote:
also will this relay work
https://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F013%5F000&product%5fid=275%2D240
This won't work, and if it does it will burn out! Get yourself a BOSCH automotive relay or a similar one. They're for autos and can handle the high amperage if you need it, plus they get energized by 12v. The one on this link is a 5 Volt so I'd say don't get this.
At the Shack, the part number is
30A Automotive Relay
Catalog # 275-226
If you just walk by to a Radio Shack nearby where you live, you can just pick one up from their parts section. They're in a tray marked "Automotive Relays" or "Relays"
Posted By: casnj
Date Posted: June 10, 2004 at 6:49 PM
this wont work then. wire 1 is positive at lock and wire 2 is negative wire 1 is positive at unlock and wire 2 is positive
Posted By: markcars
Date Posted: June 10, 2004 at 10:22 PM
Sorry, by this wont work, I meant the relay wont last. The circuit and pins are ok. I meant the relay. Sorry about that. Get the right relay (12V Automotive relay) and it will work just like you want! I apologize again.
Posted By: casnj
Date Posted: June 11, 2004 at 8:56 AM
markcars wrote:
Sorry, by this wont work, I meant the relay wont last. The circuit and pins are ok. I meant the relay. Sorry about that. Get the right relay (12V Automotive relay) and it will work just like you want! I apologize again.
im lost. the schematic you gave me wont work right? I cant have it check chasis ground. it has to check ground of a wire!
Posted By: markcars
Date Posted: June 11, 2004 at 9:51 AM
Ok here's a drawing I made up for you. It will work. Just get the automotive relay.
About the chassis ground, thats only for the relay coil. Your +ve during locked status is going to be the switching signal for the relay. If thats not what you want, can you please explain more clearly waht you want? Maybe I'm not understanding exactly what you need. Here's the drawing though:
Posted By: casnj
Date Posted: June 11, 2004 at 10:18 AM
markcars wrote:
Ok here's a drawing I made up for you. It will work. Just get the automotive relay.
About the chassis ground, thats only for the relay coil. Your +ve during locked status is going to be the switching signal for the relay. If thats not what you want, can you please explain more clearly waht you want? Maybe I'm not understanding exactly what you need. Here's the drawing though:
Thanks for your help. but since the lock wire also displays +ve at unlock the above wont work?! Yesterday I used a digital volt meter and tested alittle further. i hooked the red led off the DVM to the cigarette lighter and the lock motor wire showed these conditions showed 12.5 volts when I touched it showed 0 when I hit the lock button showed 7 when I hit the unlock button
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