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[Thack]

Zippy, you wrote: "If you were to use a momentary off switch, then it is alot simpler. Split your poins wire and extend your wires back to the switch. Press and hold until your engine stops. release to restart. No power draining shorts - no fire risk ."



I've already explained the shortcomings of that idea. The switch is continuously in the ignition circuit so you need to make sure it is of sufficient quality. That means a high enough current rating, and definitely waterproof.



There is absolutely no "power draining shorts" and no "fire risk" using my method, which is just shorting out the points. No excess current will flow - only the current that normally flows when the points are closed. And the switch, being normally open, is no longer a critical component in the ignition circuit.



Anyway, I'm sure Count Johnny has enough advice to make up his own mind now!

[Adrian]

You could convert your Bullet to the later K/S model switchgear (post '99 Minda, as sold by our hosts), the throttle twist grip body (therefore right-hand) on these has an engine on/off switch built in. I have my Project bike with one of these wired as a kill switch hooked up to the magneto on one side and the bike's earth on the other. But for your set-up you could just use one of these to interrupt the 12v supply from whatever main ignition switch that may be on your bike to the supply to the coil. Simple. Regards, A.

[Norm]

Switchgear, you want him to fit switchgear Adrian? he doesn't even want to fit a decomp lever lol

[zippy]

Thack. Many motorcycle killswitches are wired up this way and have been for decades. I think you are overestimating just how many amps go through a points ignition coil, Its a small altenator and a small battery, not a power station. I put a similar setup on my works hack back in 1987,using a simple dolly switch. It's been used daily and has yet to play up.
Like I said, press it - it works. No shorts - it's open circuit. No fires. simple as it gets. As a clue to the amps it needs - look at the wire being cut It isn't a heavy duty cable by any means....

[Count Johnny]

Gentlemen



Many thanks for your replies.



The existing problem is that, currently (if you'll pardon the pun) shuffling the electrons around on my bike (Slo Poke) takes a big ugly Boyer Powerbox; an ignition switch (power off/power on/lights on) and the ubiquitous aftermarket dip/full beam switch - which is a nasty piece of tin that sits on the handlebars.






Over the winter, amongst many other things, I'm going full house on completely cleaning up the handlebars - fitting inverted levers and a Brown and Barlow straight pull throttle - and having aforementioned nasty piece of tin still sitting on my handlebar would task my eye.



So, I'm replacing my Boyer Powerbox with the much smaller and neater Pazon unit (which I can more easily tuck away out of sight); planning to fit the ignition key within a capped off Moon coil cover that will be mounted low to what's left of the rear mudguard; using the ignition key to switch the lights (lights off/dip on/full on) and would rather not be hunting around for the decomp within the bowels of the hot engine.



As Thack mentions, I had already worked out that a momentary off switch would need to live with the power, all of the time, so decided that a momentary on switch - that provided a momentary path to earth - might be the way to go.



So, yes. As has oft been mentioned in this thread, I AM trying to solve a problem that isn't there - unless, like me, you're not a fan of a half a mile of wire and big clunky switches.

[Count Johnny]

PS (Zippy)



In fact I have a BIG alternator and NO battery - but the math tells me that volts/ohms = 2 amps (all be they pulsing).

[simon]

Get rid of all the battery and coil gubbins and get a mag. an SR1 has a earthing lug to short the LT to earth but you will need an auto advance. You could go berserk and buy a new BTH one which looks like an SR1 and has the same mount but has rare earth magnets and a solid state advance. It would however be more valuable than the rest of the machine in all likelihood.

[Thack]

Zippy, you wrote: "Many motorcycle killswitches are wired up this way and have been for decades. I think you are overestimating just how many amps go through a points ignition coil......"



Actually I know exactly how many amps, as I've said earlier. Anyone can work it out for themselves by measuring the primary coil resistance. On mine the primary resistance is specified as 4 to 8 ohms. With a 12V supply that means the current will be 2 to 3 amps.*



But as we've already established, either approach will work just fine. All we are saying is that a switch which is permanently in-circuit needs to be more reliable than one that isn't.



*Actually the coil offers an inductive load, so the current starts off less than this, and builds up over a short period of time (measured in milliseconds).

[Thack]

Sorry!! 1.5 to 3 amps (too bloody early in the morning to think straight!)



For a switch permanently in circuit, I would scope the switch for the worst case of 3A.

[Count Johnny]

As I've mentioned in this surprisingly contentious thread, I have no battery, Simon, and my (Sparx rotor and 120 Watt stator) alternator does a spiffing job of running the ignition and 35W halogen bulb, so I don't feel the need for the trouble and expense of a magneto. This said, the thought that led to me posing this question, came to me when I was killing the ignition on my mate's (mag'd) A10.