momentary p/b start and stop 1st post

OK I am new to this site and only have enough electrical knowledge to make me dangerous! I have searched the forum for the answer to this question and have come close but could not find the solution.

Here is what needs to be done. 

1 momentary grounding switch that starts the car and turns it off

- 1st push and hold, ingition is turned on and starter engages until you let go of the button

No key will be used, power to the car will be controlled with a main latching solenoid in the trunk that is activated and deactivated with the alarm pad.

This system is available for around $130 from a comapny called Watson street works, but I was intersted in doing it myself and hopefully for a little cheaper. I called them and they told me that the system was made up of a bank of latching relays but did not tell me how it works or was wired exactly. (this does not suprise me)  

Here is a link to the system:  http://www.watsons-streetworks.com/ignition_switches.html

Can anyone help with the wiring of the relays for this application.

Thanks

You will need the following relay setup to turn the igniion on and then back off.  This will be performed by the single momentary button.

You will need an additional relay with a resistor/capacitor delay circuit.  The delay circuit will keep the relay from energizing for the first half of a second of the initial push of the button. 

The only thing that I am unsure of is if the latching relay setup below will chatter during an extended turn on pulse.  I will find the diagram for the delay relay this evening.

Latched On/Off Output Using a Single Momentary Pulse ( link)

Similar to the momentary to constant configuration above, we can engage and disengage the latched output with a single pulse from a switch or an output from an alarm or remote keyless entry. The first pulse from the switch will engage the latch. The next pulse from the switch will disengage the latch.

Thanks, I will check back for that diagram. Can you tell me is there any way to delay the starter relay any more than half a second? I do not mind having to hold the button down for a full second or two.

Also can you tell me the specifics on the items below circled in red. I assume they are diodes but are they as certain size and where would I purchase them...............Like I said - just enough knowledge to be dangerous!

Using a lataching relay as pictured for ignition is EXTREMELY dangerous.

Latched relays will not  stay latched if they exposed to a sudden shock.  If you are going to use relays you need a controller that keeps constant voltage on the relays.  Otherwise, if you hit a big bump there is a good chance your car will shut off.

The reason for this is simple and is based on the principle of how relays work.  When you latch one relay with either itself or another relay the only thing hold the relay in is the fact that current is still flowing through the contacts.  The only thing "holding" the contacts together is a small magnetic field.  If the relay is exposed to a shock that is greater then the magnetic field the contacts will start to seperate.  As soon as the current breaks the magnetic field will collapse and the entire circuit will drop out until it's relatched.

There is a # video I made about this a while back that shows how little force is needed on a relay to break the latch.

Now, if you have a controller of some sort that is constantly outputting voltage to the coil even if you hit a bump the current may stop flowing but will come right back on because the magnetic field won't be interuppted.  The "bouncing" of the contacts happens at a mS level and most likely wouldn't be noticed to the driver (or the car).

If you are stuck with using only relays try to find a real mechanical latching relay instead of one that uses magnetic energy for the latch.