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Thread: Home made immobiliser question

  1. #1
    Spanner Monkey Kmp's Avatar

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    Home made immobiliser question

    Hi all,

    I would like to make my cigarette lighter into a home made immobiliser, I know of some one who does it but I don't know him well enough to ask him how he did it. He does it so that when you push the lighter in it triggers the starter, so i guess he has taken the feed from the ignition. How ever it also means that when you take the car to a show or our somewhere, you can take the lighter out and the car can't be started so easily. I know it won't entirely stop the person but in my mind, it makes the job harder for them.

    What I would like to know is, how can run I this sort of setup? Can I literally take the starter feed off of the ignition and put it onto the cigarette lighter or would I have to run it though a relay?

    I am not sure what a standard pinto starter draw is for the switch wire, so not entirely sure what fuse relay to use if I need one too. Auto electrics is something I am interested in and this is something to help me learn a few things.

    if anyone has any help or advice, that would be appreciated.

    thanks
    kris
    Last edited by Kmp; 07-12-2017 at 19:38.

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    Re: Home made immobiliser question

    its quite possible he has wired the cig lighter to a relay which energizes the starter. starter solenoid will draw around 20A

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    Spanner Monkey Kmp's Avatar

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    Re: Home made immobiliser question

    Thanks so much for the reply, that's great :-)

    Thanks
    Kris

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    Re: Home made immobiliser question

    Not sure how ciggy lighters work but I guess there is some bi-metalic strip that cuts the circuit and pops the unit out so if the guts are stripped out / re configured the 'lighter' will become a simple link in any circuit connected either side of it. I'd think it'd be more benefit in the ignition circuit rather than the starter - a bumped car with ign on will start whereas no ign. - no run. It would certainly not be a obvious anti theft measure - quite neat actually!

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    Re: Home made immobiliser question

    I had a battery kill switch-the one with the red key that you see on the scuttle panel of escorts-mounted behind the dash of a Capri and accessed by a longer aluminium version of the red key. The key fitted through where a choke cable would have been fitted and was totally hidden.

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    Spanner Monkey Kmp's Avatar

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    Re: Home made immobiliser question

    If the solenoid draws about 20 amps, would a 25 amp relay be good enough? If I am running it through a relay, would any of the other live's from it need an inline type fuse?

    Thanks
    Kris

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    Re: Home made immobiliser question

    just wire a hidden switch....or use an existing switch (heated rear window...wired to relay instead) you might loose the lighter when your out... cheers mark

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    Re: Home made immobiliser question

    25A relay would be ok, yes you would still use fuses in the circuit to protect wiring in case of a short circuit, all the relay is doing is is handling the high current switching

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    Home made immobiliser question

    All a bit academic now you have informed the world it's there 😄😄


    Sent from my iPhone using Tapatalk

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    Spanner Monkey Kmp's Avatar

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    Re: Home made immobiliser question

    Sorry to keep asking questions but could someone please explain how I work out what size inline fuse I would need for the 25a relay circuit. I have been googling and reading up from my autoelectrics book but I can't seem to find any info which would help. A relay switches from a light amperage circuit to a heavy amperage circuit and if the starter solonoid draws 20a, i assume this means I need a 20a blade fuse inline on the power source cable. I have read online that cold light bulbs draw more current when cold, so for a lighting circuit fuse you should add 30% more amps to cover the cold initial amp draw. Do I have to allow the 30% extra for all applications?

    I know the fuse has to be the weakest link of the circuit, so to me - having a 25a relay and a 25a inline fuse doesn't seem to make sense.... would I be better with a 30a relay and a 25a fuse?

    I would like to know how you work this out for all applications not just for a starter switch because I would like to wire my driving lights up myself, so I can practice more and more. I understand that for lighting, amps = watts divided volts, so is it right to assume the relay has to always be a higher amperage than what the load device draws?

    I am sure I will read this back in a few months and realise I was being a moron, how ever I love to learn :-).

    Thanks
    Kris

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    Re: Home made immobiliser question

    just about every circuit draws more current on start up, ordinarily allow 50%, so if you starter draws 20A use 30 A fuse. a relay would be rated at a constant current so a 20A relay should be able to handle a continuous 20A in your case if your only engagauing the starter its only short periods of load so your really not going to stress the relay

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    Re: Home made immobiliser question


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    Re: Home made immobiliser question

    Not knocking the 'belt & braces' approach but the starter solenoid is a form of relay so in effect you will have a switch powering a relay driving a relay switching a motor! That is a lot of wiring and connections (failure points) to reproduce the OEM switch to starter soli via a fuse! 20A sounds an awful lot for a starter soli bearing in mind the usual control wire fitted - IMO 10A wire with 15A fuse would be ok.

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    Spanner Monkey Kmp's Avatar

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    Re: Home made immobiliser question

    Thanks for the replies again, buying a pre made alarm isn't what I was after tbh but thanks though. Part of my thoughts behind wiring up things is to know how things are powered and to be able to sort out electrical problems/gremlins.

    Thanks
    Kris

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