Kill switch wiring

[Ebrownie]

So I bought some cheap toggle switches for my kart that have a little LED bulb in the switch that lights up when you flip the switch on. They look really slick and work great with my wiring from my battery to my headlights and tail light.

However, I am currently working on wiring up my kill switch for my predator. The LED in the switch lights up from the 12v power running through it. So, the power running through the kill switch on the engine isn’t regulated or constant 12v power, right? If so, what would happen if I hooked up the ground for the little switch LED? Would it just ruin the bulb, or not light up at all?

And is there any way that I could run 12v power to the bulb in the switch so it lights up when you turn it on, while still turning the engine on and off.

 

[Joe-405]

I’m suspecting you could do it through using a relay. I would have to try it To know for sure cause I’ve never tried it.

The majority of small engines shut off when grounded. It actually grounds out the coil.

 

[itsid]

I doubt you need a relay..
if I'm guessing right, the buttside terminals are the switch,
and the side terminal is to power the LED.
(likely grounded against the case therefor the chassis)

So it'd be a two position two line switch.. killswitch and LED do not share any common terminal,
I could be wrong and they share ground.. even if... doesn't matter since the switch will still work as intended.

The killswitch wire itself doesn't have any power running through for all I know,
it's essentially a bypass that stops the ignition coil from getting charged.
so it connects to ground and the ignition coil ..
if there is any power at all it'd be whatever the coil is magneto is generating;
a pulse, one revolution of the flywheel.. since once the LED lits up by that generated power it'd be grounded and the killswitch triggered anyways.

So you need a 12V line seperately (battery, lighting coil what have you)
and If I'm not mistaking that'd be isolated from the actual switch.

(just measure all terminals against each other in both switch positions, macke a simple table chart and you should see what's going on internall)

'sid

 

[Tpdingo]

The killswitch wire itself doesn't have any power running through for all I know,
it's essentially a bypass that stops the ignition coil from getting charged.
so it connects to ground and the ignition coil ..
if there is any power at all it'd be whatever the coil is magneto is generating;
a pulse, one revolution of the flywheel.. since once the LED lits up by that generated power it'd be grounded and the killswitch triggered anyways.

'sid

Nope. Killswitch when turning the motor off has a lot of power going through it. You are essentially shorting a few thousand volts to ground. Ohms law I=V/R, a few thousand volts divided by a few milliohms and your talking in the range of a few million amps. Now the joules of energy that come out is in the range of an static shock, maybe a few millijoules so the power is gone in a microsecond and the total heat energy produced is miniscule. This is also why touching the top of the plug hurts like **** but doesn't kill you.

 

[Karttekk]

Watch Red Beard install a kill switch.

Thanks

https://www.youtube.com/watch?v=DPORw5I9X1g

 

[itsid]

Nope. Killswitch when turning the motor off has a lot of power going through it. You are essentially shorting a few thousand volts to ground. Ohms law I=V/R, a few thousand volts divided by a few milliohms and your talking in the range of a few million amps. Now the joules of energy that come out is in the range of an static shock, maybe a few millijoules so the power is gone in a microsecond and the total heat energy produced is miniscule. This is also why touching the top of the plug hurts like **** but doesn't kill you.

Nahhh it's not on the discharge but on the charge side of things,
otherwise that flimsy wire would cook off in seconds

'sid

 

[Ebrownie]

I think I will need a relay if I am thinking about it right. The LED in the switch uses one of the positive terminals on the switch and the ground, which is the terminal on the side of the switch. So if I have the switch complete the ground to kill the engine, I will not be able to have a 12v positive wire on the switch because both of the butt terminals will be the engine ground. If I hooked up the 12v on one positive side, it would just short everything out because I have my battery grounded to the frame, and therefore the engine.

In addition, it would be backwards, so when you turn the switch on and complete the circuit, it would kill the engine, which is the opposite of what I want. So I believe that the only way to run 12v power to the switch and make it so that when the switch is ON, the engine is running, is to have a relay.

Now my other question is, if I was to have a relay, what type would I need for it to open a circuit when the switch circuit closes? It is the opposite of a lighting relay, where one closed circuit closes another. I need the switch to open the engine ground when the switch is on. Can a regular relay do that?

 

[itsid]

I think I will need a relay if I am thinking about it right. The LED in the switch uses one of the positive terminals on the switch and the ground, which is the terminal on the side of the switch. So if I have the switch complete the ground to kill the engine, I will not be able to have a 12v positive wire on the switch because both of the butt terminals will be the engine ground. If I hooked up the 12v on one positive side, it would just short everything out because I have my battery grounded to the frame, and therefore the engine.

In addition, it would be backwards, so when you turn the switch on and complete the circuit, it would kill the engine, which is the opposite of what I want. So I believe that the only way to run 12v power to the switch and make it so that when the switch is ON, the engine is running, is to have a relay.

Now my other question is, if I was to have a relay, what type would I need for it to open a circuit when the switch circuit closes? It is the opposite of a lighting relay, where one closed circuit closes another. I need the switch to open the engine ground when the switch is on. Can a regular relay do that?

So it's the Robinson K894 switch (A,G,B or R is color which I don't know)?

I assume blue.. but doesn't matter.

So the switch has ground on the side (likely to use chassis ground if possible)
that's good!

Well that is, if you have the battery grounded (as one would expect) if you have it Live (connected the positive to chassis)
I hope you insulated the engine, otherwise there will be issues

So let's assume a grounded chassis..

Then one of the two terminals will be the "incomming" signal line
that should not be grounded either way... (+) labelled

the other one (D) labelled [well a symbolised headlight] Is what that (+) line will get connected to.. when the switch is in it's "ON" position
and yes unfortunately that means if you conenct the killswitch to (+) and another ground to (D) the switch will work as intended but without any light!

I'm not sure which side powers the LED, is it always on, or is it only lit when the switch is in it's ON position?

if the latter you now only need a diode (a simple single diode!)
well and a 12V line from the battery...

attach it so that the 12V cannot interfere with the KillSwitch wire
and parallel the 12V and killswitch atatched to the (+) side of things, leave (D) unconnected)


(( In case it's permalit and you can have it lit only when 'ON', attach it to the (D) side and leave (+) unconnected))
To be sure.. again a multimeter and measuring the terminals helps .

The resistive ground through the lit LED should
a) be enough to trigger the engine shutdown (needs to be verified)
b) is resistive enough to not short out (it's a resistor and a LED in between )

'sid

PS I'm not sure if you even need the diode it's a safety measure in case the killswitch wire would get upset seeing a 12V signal .. so just to be sure... it's better to have one and don't need it .. right )

 

[Tpdingo]

So what prevents the 5KV from going right through that diode and killing the LED when you shut down the motor? The LED should be wired where the LED is completely isolated from the kill switch except for a common ground.

 

[itsid]

So what prevents the 5KV from going right through that diode and killing the LED when you shut down the motor? The LED should be wired where the LED is completely isolated from the kill switch except for a common ground.

Again.. there is NO 5KV on the killswitch wire! not even close,
if there's 12V that'd be impressive.

it's not the spark plug you're shorting out, it's the charge you prevent from building up if you close the killswitch!

Otherwise a few pulls with engaged killswitch would make that tiny wire melt!


'sid

 

[Ebrownie]

Ok that makes sense. Yes my frame is grounded, so that should work just fine. And the LED in the switch lights up only when the switch is ON. So what kind of diode would I want to put on it?

 

[Tpdingo]

Again.. there is NO 5KV on the killswitch wire! not even close,
if there's 12V that'd be impressive.

it's not the spark plug you're shorting out, it's the charge you prevent from building up if you close the killswitch!

Otherwise a few pulls with engaged killswitch would make that tiny wire melt!


'sid

I forgot that Magneto's aren't just a coil but a CDI unit. Without charging the cap nothing should happen.

 

[itsid]

Ok that makes sense. Yes my frame is grounded, so that should work just fine. And the LED in the switch lights up only when the switch is ON. So what kind of diode would I want to put on it?

IDK.. I think something like the SB540 makes sense
https://www.fairchildsemi.com/datasheets/SB/SB540.pdf

it's likely overkill already, but it's cheap and small.. so I don't see much of an issue.

you need 12V to protect against,
and in case there is at all noteworthy current flow from the killswitch wire,
it'd be no more than 20V and I doubt more than 500mA really
and only for a split second

So anything that's above those numbers is fine (30V 5Amp, 48V 10 Amp doesn't mater.. even 25V 2Amp should work)
but again, since the prices aren't any different really..
I'd get a beefy one just for added durability reasons

'sid

 

[Karttekk]

Does this help?

http://www.wiringdepot.com/blog/How-to-Wire-an-Illuminated-Rocker-Switch

 

[Ebrownie]

So I was thinking about it and I realized that even though that would work using the diode and running everything through the switch, it still would have been backwards, because when the circuit closed and the light turned on, the engine would have died.

So, I bought a relay that had both a normally closed(NC) and normally open (NO) output circuit. I hooked up my battery and switch to the first circuit, then hooked my killswitch up to the NC circuit on the relay. So when I have the switch on, it lights up and goes through the relay, which opens the kill circuit. When I turn the switch off, it closes the circuit and kills the engine.

It works great, and i also kept the original plug on the wire going to the engine so if my battery dies and cannot continue to function the relay, I can just disconnect the engine from the relay and use the switch that is on the engine.