Voltage needed to drive a relay.

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=43836
Printed Date: July 12, 2025 at 3:32 PM

Topic: Voltage needed to drive a relay.

Posted By: riggz
Subject: Voltage needed to drive a relay.
Date Posted: November 26, 2004 at 4:01 PM

I am curious if 4.8v will be enough to drive a standard SPDT 12v 30amp relay. The reason is, i have a 5spd tranny and in order to have the remote start function ONLY when the vehicle is NOT in gear is to use a wire that reads 4.8v when the vehicle is in gear and 0v when it is not. The remote start input looks for a negative ground for the 'Park-Neutral".

Thanks

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-=riggz

Replies:

Posted By: greermodela
Date Posted: November 26, 2004 at 9:06 PM

not sure but this seems like a signal return circuit to pcm. may cause trouble.

Posted By: riggz
Date Posted: November 26, 2004 at 10:56 PM

i was under the impression that using a relay didnt draw any current or very little at most.

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-=riggz

Posted By: D'Ecosse
Date Posted: November 27, 2004 at 11:17 AM

Surely you would want to use the 0V (neutral condition) to enable the remote start?

I think you will find that the neutral switch is really closing to ground when in the neutral condition; however the "in gear" position is simply that the switch is "open" and the voltage you are seeing is likely the floating voltage at the ECU - you can't use this to drive a relay! You need to use a realy with 12V constant to one side of the coil and hook your neutral switch feed to the other side. It will only energize when your switch is at 0V. Then have your contacts do whatever you need it to do.

For an example of how to wire up a neutral switch to enable the remote start, check out

https://www.nsxprime.com/forums/showthread.php?t=41381

I'm not sure if you have a clutch switch interlock for the starter in your case.