Build a Constant to Momentary relay circuit

**siliconkibou** · 10-05-2005, 11:54 PM

Hello all,

Wonderful forums...I've learned so much.

However, being completely lame with analog electronics and soldering, etc, I'm having a great deal of trouble building a constant to momentary relay circuit.

For example:

http://www.the12volt.com/relays/page5.asp#ctm

The purpose, as has been often discussed in these forums, is to take the ACC ignition of starting the car and momentarily "press" a laptop momentary switch to power it up on car crank.

I've already got the laptop power button wired up with a long bit of wire that works great.

However, I'm completely buggered on building the relay circuit necessary.

I'd be willing to pay some reputable person a reasonable sum to build one for me.

Any takers?

Thanks,

-Paul

**SPDOSND** · 10-06-2005, 12:34 AM

How about taking another approach to what you are trying to do. Remember there are several things that happen when you start your car every morning. Several things give a momentary pulse to begin certain sequences. In your case since you don't have extensive knowledge with electronics just tie a relay in to your starter wire. The starter on your car is simply activated with a momentary switch. This will fix your problem but also install a toggle switch to the relay so you can turn off that function when you don't want it to work. (i.e. when you send your car in for service and they are starting your car to test for problems.)

Hope this helps

**pRoFiT** · 10-06-2005, 12:35 AM

All you need is: Relays, wire, Spade wire crimps that connect to the relay, A crimper and a stripper. No need to solder if you suck at it. And when your done i could use the stripper, for obvious reasons.

**siliconkibou** · 10-06-2005, 01:00 AM

Hey thanks for the thoughts guys...

Can you give some more specifics and perhaps a diagram?

What sort of relay would I use and where would I tie it into, specifically?

An automotive relay? Tied into the starter part of the fuse box?

Thanks,

-P

**SPDOSND** · 10-06-2005, 01:35 AM

A standard 10amp Bosch SPDT relay is all you need (you can get a bigger one too it won't matter). If you tell me what car you have I can tell you the color and location of the starter wire. This link should fill in the rest of the blanks for you. http://www.bcae1.com/relays.htm. When you are done with your reading you should find that you will tie in the Starter wire to 85 and ground 86 or the other way around it doesn't matter. Then 30 and 87 will replace your momentary switch. tie the toggle switch inline with the ground wire. Good Luck!! If the explanation is short or incomplete it is because I am tired and for that I apologize.

The relay is a standard relay you should be able to find it anywhere. But if you have problems I can ship you one for $12. But the install bay at your local car audio shop will have tons of them.

**siliconkibou** · 10-06-2005, 01:49 AM

Thanks SPDOSND,

I think I can track down one of those Bosch relays...my old volvo seemed to throw them everywhere, and I got real used to replacing them years ago.

Currently, I'm driving a 2005 Nissan Altima.

Any further tips you have would be appreciated.

Thanks again,

-Paul

**SPDOSND** · 10-06-2005, 01:54 AM

There are two starter wires. You can use either one. BLACK/YELLOW or BLACK/RED in the ignition harness. Look for the harness running out of the back of the key cylinder under the dash and grab it where you can. Make sure you use a DMM (digital multi-meter- Test Lights are dangerous!!)to test the wires. They will read 12V-14V when you are cranking the vehicle.

Tell me how it comes out.

**siliconkibou** · 10-06-2005, 09:39 AM

Thanks,

Should I run an inline fuse on this? 10 amp or something else?

Also, is there anyway to wire this up without cutting the starter wires?

Perhaps using some wire taps or following the wires to a solder point?

Finally is the wire gauge an issue, or will nearly any gauge do?

Thanks for all the help...

-P