0
\$\begingroup\$

I'm trying to build a kill switch in my car so that when I turn the ignition, a button also has to be held down. When the power goes through, the button can be let go and the system stays closed until the car shuts down, then you have to repeat the process. I came up with this diagram:

https://i.sstatic.net/AcvVN.jpg enter image description here

What kind of parts does it take to build this? I drew logic gates but I have no idea how that translates to real components. Is a button and relay from an electronics store enough? I'm worried about 1) splitting the ignition wire like that and 2) how much power actually loops back, would things over heat?

\$\endgroup\$
7
  • \$\begingroup\$ Does your car use a starter motor to turn over the engine? Because, if it does, all you need to do is buy a momentary switch capable of handling the required current to the starter motor and wire it in series. (Or use a relay and a smaller momentary switch.) \$\endgroup\$
    – jonk
    Commented Aug 21, 2018 at 7:24
  • 1
    \$\begingroup\$ @jonk cranking current is pretty high. I wouldn't want to put my thumb on that switch. \$\endgroup\$
    – Oliver
    Commented Aug 21, 2018 at 7:59
  • 1
    \$\begingroup\$ Starters in all cars (except BMC mini's) is switched by a solenoid. The key current is only a few amps. \$\endgroup\$
    – Henry Crun
    Commented Aug 21, 2018 at 8:21
  • \$\begingroup\$ I've put my thumb on a starter switch, (it was the back end of the starter pull in a morris 1100). the engine cranked. nothing exciting happened. \$\endgroup\$
    – Jasen Слава Україні
    Commented Aug 21, 2018 at 9:12
  • 1
    \$\begingroup\$ Starter motors are used with both gas and diesel engines - they crank the engine. Both types of engine do their own compressing of the air or air/fuel mixture. You stop a gas engine by turning off the electric ignition system. You stop a deisel by stopping fuel delivery from the fuel injection pump. \$\endgroup\$
    – Peter Bennett
    Commented Aug 21, 2018 at 17:19

1 Answer 1

Reset to default
2
\$\begingroup\$

Typically you use a relay wired so that the live side of the switch powers the relay coil. the button used should be capable of powering the whole switched load

schematic

simulate this circuit – Schematic created using CircuitLab

by adding a diode the load can be isolated fronm the button allowing the use of a smaller button that only needs to pass the relay coil current (about 0.1A)

\$\endgroup\$
3
  • \$\begingroup\$ Thank you. I saw the first pic and thought OK I have no idea what's going on this looks legit, after understanding the diode that makes even more sense. Thank you \$\endgroup\$
    – Dzenis Zigo
    Commented Aug 21, 2018 at 12:44
  • \$\begingroup\$ So you also mention automotive relays, would you recommend those over one I get in a Fry's or Micro center? \$\endgroup\$
    – Dzenis Zigo
    Commented Aug 21, 2018 at 12:58
  • \$\begingroup\$ the quick connect terminals and mounting tab on automotive relays mean you can use them without using a PCB or an enclosure \$\endgroup\$
    – Jasen Слава Україні
    Commented Aug 22, 2018 at 10:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.