Fitting a kill switch to a bike with 2 coils

D

devilishdesigner

Been Around the Block
Hi All,

This one has me a bit thrown. I am building up a Yamaha YL1 Twinjet. 100cc 2 cylinder 2 stroke. I need to fit a kill switch to it (they never same with one, only a key for on/off) and am not sure how to wire it. I have bought an aftermarket on(open) off(closed) kill switch and fitted it to the handlebars but am not sure where to wire it on a bike which has a separate coil for each cylinder?
 
The two separate coils can share the same wire for power. So your switch would have one wire for power going in, and then one wire for power going out. The "out" wire to the coils can then be spliced into a second wire and each coil gets one of those "out" wires. Splitting a single wire into multiples is more than acceptable (provided your single wire is thick enough gauge to handle the amperage requirements). A circuit with a single wire is called a series circuit, but when you split it, it becomes what's known as a parallel circuit.
 
Cutting the power between the battery and coils is fine, except that every kill switch I have encountered, including the ones I have, are designed to connect a circuit in the off position, rather than open one. I need a method of wiring the kill switch to a bike with 2 coils (1 per cylinder) which will stop the bike running when a circuit is closed.

The only method I've read so far is to put the switch between the 2 trigger wires on the coils, but I have heard that the motor can still run on (poorly) in this setup depending on revvs
 
hi
i have not tried this but from the diagram for your bike you could try two 1n2004 diodes , one on to the orange wire and one on ash green with the bar on the body of the diodes ends wired to your switch .
when made and the other terminal hooked to ground this should stop motor. switch needs to be momentary as your coils will get hot if left like this. if this fails still try mucking around with diode directions.

dont shoot me if this does not work..

on a single this works without the diodes, they are to stop flow of power between coils otherwise they will crossfire
 
suuscustoms said:
Cutting the power between the battery and coils is fine, except that every kill switch I have encountered, including the ones I have, are designed to connect a circuit in the off position, rather than open one. I need a method of wiring the kill switch to a bike with 2 coils (1 per cylinder) which will stop the bike running when a circuit is closed.
Click to expand...


So, just run the switch in reverse.
 
hillsy said:
So, just run the switch in reverse.
Click to expand...

Unfortunately as part of the race prep for the bike I am also fitting a dead-man-switch, where a lanyard from the riders wrist is attached to the bike and when the rider comes off the lanyard pulls off the bike and kills the motor. this is also designed to close a circuit when the rider comes off.
 
my idea should work for your lanyard too . as long as ignition is killed in an hour or so. same as points being closed when ignition is on
 
Thanks Orrible, missed your post before. The cross-flow was what I was concerned about, so if the diodes work to stop that then that could be suitable. I'm guessing the idea is to set it up so the diode allows OUT from the coil wire but not IN.
 
another way to do this ,but not as elegant , is with a relay. use the relay to break the positive feed to coils when activated.use your switch to earth the coil on relay and feed the coil with constant +ve when ignition is on.hence making your kill switch will cut power to coils..

diode solution is nicer..if i could find a drawing package on this apple(ex pc tech ) would draw both diagrams.

both are simple .if you have probs pm me...
with any luck i will see you at lake gardener

pete
 
Back this thread on up a few posts, guys. :p

The correct answer here is to use a five pin relay. This is not an uncommon issue and the solution is not an uncommon one, either.

First up, the kill switch types that complete a ground when switched off did not become common until the 80s, so that's why you see a lot of aftermarket controls that don't work as expected on these old bikes.

To make use of one of those types of kill switch on a vintage bike requires a five pin relay that is operated in the normally closed setting (see attached image for relay diagram). One side of your kill switch should be connected to +12V and the other wire connected to pin 85 of the relay. Pin 86 of the relay should be grounded. Pins 30 and 87 of the relay should also be connected to +12V. Pin 87A outputs to your coils.

So... when the kill switch is in the 'run' (or open) position, the relay's coil is not energized, and so power can flow from pin 30 to pin 87A (the ignition coils). In the 'off' (or closed) position, the relay becomes energized and breaks the flow of electricity to the coils.

Is your lanyard normally open or normally closed?
 

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Thanks guys.

Lanyard is normally open, so it matches the other switch and can be run parallel for simplicity.

The other question from this arises - If I go down the relay route, is it still possible to find a 5 pin in 6V?
 
The only ones I know of (in normally closed configuration) are going to be built for digital electronics. Something for 5V should do the trick if you protect the inputs from too much current by including a few resistors.

Something like this, probably:
http://www.ebay.com/itm/1-Channel-Isolated-5V-Relay-Module-Coupling-For-Arduino-PIC-AVR-DSP-ARM-/221358549533?pt=LH_DefaultDomain_0&hash=item3389ff6a1d

You might be able to track down a 6v "normally closed" relay if you shop around though.
 
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