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Circuit for a keyless ignition switch.

Discussion in 'General Electronics Discussion' started by Rob_K, Sep 20, 2013.

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  1. Rob_K

    Rob_K

    59
    0
    Sep 20, 2013
    Dear All,

    I have a little project going on here. Since my motorbike was stolen and then recovered, it is clear that a key ignition for my particular rather ratty cafe racer of a bike is not particularly useful, I lock it with a sturdy lock now.

    As a result, I am not really that bothered to buy another ignition switch for it and have come up with an idea for a keyless ignition system. At the moment, I have a 30 A switch as my key and I plug it into the two wires that energise the system on a 30 A circuit (Starter motors take a lot of umph).

    My plan, is to put a relay in instead, this will be activated with a main on off switch and another small latching relay and instead of a push to make switch to latch it, I want to use a reed switch placed into the main wiring loom so that I can just run a magnet over it. This is just to prevent anyone riding off into the sunset when I go into shops or just stop for 10 minutes or so. The idea is that a chancer will be completely foxed as to how the bike is started.

    The thing I am trying to learn about at the moment is this. The main relay I am using is a 30 A relay from an automotive shop, the type that is used for radiator fans or the like. That bit is fine. But what I need to know is the rest of the circuit, ie the smaller relay activated by the reed switch will be on a separate feed (all be it from the main 12 V battery) and I wanted to make it into a small PCB that I can stick in a project box an then just fill with resin and mount under the seat with the other little brains that make up the electronics of a vehicle.

    For the smaller circuit, the main load is the coil of the main relay, am I right in assuming that the current through this side of the circuit is milliamps? If not, what do I need to do to prevent the reed switch from being destroyed as I have only a 1 A rating for it?

    Also, are there any solid state type of relays that could be used as the latching relay that could make this little circuit smaller and maybe more reliable also.

    There are two main concerns involved in this project and they are both safety issues, the circuit can not catch fire and also the system needs to be reliable, or if it is to fail, fail in th on position. I don't want my bike to suddenly cut all power whilst on the motorway.

    Please let me know your thoughts on this.

    Kind regards

    Rob
     
  2. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    The Safety side worries me.

    First note: Are you sure your starter pulls less than 30A? This seems low to me (360W is not much). Moreover, your starter should already have a contactor or relay, so your ignition switch should only be driving it, not the starter directly.

    Second note: Alarm systems typically use magnetic switches that are "normally open" but in the presence of a magnet are closed. Typical ignition systems "ground" the ignition in the "off position". This suggests that to turn the motor "off" you might place an Alarm switch to ground the ignition. As long as there is a magnet on the magnetic switch, the bike won't start, remove the magnet to start the motor.

    I MUST state that I have not messed with a motor bike in several decades, so I could be wrong about how the ignition system works in modern bikes.

    Fish
     
  3. Rob_K

    Rob_K

    59
    0
    Sep 20, 2013
    Thank you for your reply, I think i need to clarify, but you have given me some interesting ideas. This is a circuit in place of the ignition switch. In cars and motorbikes, the main fuse is usually 30 A and this circuit goes from the battery to through the main fuse to the ignition switch and then through all the various processes to energise the system.

    The circuit I am building purely takes the place of that ignition switch, not the starter circuit which you are quite correct is a rather hefty affair. That is usually fed straight from the battery as a large thick cable and an equally large earth strap. No not that, I am literally replacing the ignition switch with a relay, and the circuit I am trying to design is just a simple push to make switch to latch a relay that will energise the coil in the relay that is acting as the ignition switch which is part of the 30 A harness of the wiring loom.

    So we have a 30 A loom being switched by what I was hoping was a much smaller input circuit that is completely separate except that it comes from that battery as say the indicator circuit or the dashboard lights do.

    Where I am unclear, is how a particular loom is rated, how do know what gauge wire you need. I was assuming that the amount of amps through a circuit is governed by the amount of power the load uses, which in this case, is a 12 V relay.

    I have a picture of the schematic that I made, it has a couple of led's on it but that is inconsequential, as I was just playing around with ideas, this circuit is complete though, minus the freewheeling diodes to protect the relay coil's. I hope I uploaded it right.
     

    Attached Files:

  4. Rob_K

    Rob_K

    59
    0
    Sep 20, 2013
    Was my post too long?
     
  5. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    Hrmmm, Your ignition switch serves three purposes: 1) Disable the motor 2) Enable the motor 3) energize the starter contactor. This is typically done with a three position switch with the third position being "momentary", and the second position being "enable the motor". This could easily be replaced with two switches, one a simple "on"/"off" and the other a momentary "on" for the starter. If you wanted to make the "on"/"off" switch a magnetic reed switch that doesn't really change anything. Likewise, if you want to have the magnetic reed switch engage a relay that's fine as well. Without seeing a wiring diagram I can't begin to guess how the bike is wired, but I would guess that the ignition switch when in the "on" position already simply engages a relay; you can verify this by touching the two wires together and listening for a "click". That would be the sound of a relay closing. Assuming this is the case, I don't see any reason to add a relay or relays.

    As far as the current carrying capability of wires used....assuming the main power is already connected via a relay, the ignition wires would carry very little current, so likely 16ga-20ga should be plenty. You can verify this by placing an amp-meter across the ignition wires, but I suspect it will be in the mA range.

    hehe, no. I just have a real life that occupies most of the daylight hours, lol.

    Fish
     
  6. Rob_K

    Rob_K

    59
    0
    Sep 20, 2013
    Yes, that's how an ignition for a car works, not a bike. Bikes have the on/off ignition and then a starter button.

    But this is just what I needed to know, thank you Fish4Fun. I'll post back to let you know how well it works.
     
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