Momentary Kill Switch Theory

[kMoto]

I'm planning on running an OEM CR style kill switch on my cb360. It's just a momentary kill switch that they run on the dirt bikes.


The CR style switch basically has two leads, one of which is grounded to the handlebars, and is closes the circuit to ground momentarily. I know the cb's original kill switch opens the coil (+) feed to kill the bike.


My question is, will it be safe to kill the ignition by grounding the coil (-) (basically grounding the points permanently until the engine dies, through the momentary switch)?


I would basically run the one lead of the switch to a ground, then split the other lead of the switch to the (R)/(L) point/condenser/coil (-) junctions.


I know this is how you would kill most small engines, such as lawn mowers, weed whips, go-carts. I think if you grounded the coils for and extended period of time they would overheat and fail, but would grounding them just for a second to kill the engine wear on them?


Thanks.

 

[kMoto]

Btw, my design intent for running the kill switch off of ground and not breaking the (+) feed is I want to maintain as few connections and components between the (+) supply and the coil. Basically the straightest shot there.


Also, I'm running Dyna 3ohms coils, have yet to add ballast resistors, but it's on the list.

 

[teazer]

Not a good idea to create a dead short. As you know, 2 stroke type kill switches work by shorting out the charge coil and that works with that type of ignition. 4 stroke kill switches work by breaking the circuit. You can buy 4 stroke type kill switches quite cheaply (relatively). I wouldn't risk blowing fuses or those DYNA coils

BTW, s/be 5 ohm for the street with most ignition systems. 3 Ohms draw too much power and can cause flat batteries and stalled bikes in traffic.

 

[kMoto]

Ok. I just didn't want to run power wires up to the bars. You just never know what can happen....bike falls over and curb pinches the wire.....something catches them. If a ground ground broke, then no problem, if a supply (+) breaks, now I at least have to have multi tool. Know what I mean? I understand though.

I will be adding ballast resistors to my coils the next order I place.

 

[kMoto]

So, thinking about this again. In my opinion, the best design for this circuit, is to run the ignition power through a normally closed relay, leave power at the relay coil, and switch the relay coil ground though a normally open handle bar switch (b/c most common kill switches are normally open).

That way, if there was ever an event that cause the handlebar mounted switch/wires to be damaged, the ignition would continue to fire.

Anybody care to comment/criticize?

 

[frogman]

So if the bike is in the OFF position then there will be a draw at that relay correct holding it open? You are using a battery right moto? Are you going to put any type of switch in the system that will shut off all battery power if the bike is sitting? Even with the switch in the run position, the coils will draw power if the points happen to be closed. Will cook one or the other or both after a while.

What I would do is get a normally closed switch. Run the MAIN power through a normally open relay and wire so when the switch is ON the relay is closed. Yes if the switch gets damaged you have to HOT WIRE the relay to make it work, if you use spade connectors you just pull them off the relay and plug them into each other.

Or just find a switch if you can that can handle at least 20 amps and wire it direct the system instead of a relay.

 

[kMoto]

Yeah, you got it. I currently have a 20a spst toggle that switches battery power to the ignition, while I complete the design. So, there would be no current draw. What I will do, if I have enough room, is run main power through a NO relay, ignition through NC relay, and lighting through another NO relay. I don't think I'll have room though.

 

[t71ford]

This seems overly complicated for something that should be pretty simple. Why not just fuse the power wire you are running to the bars if you are worried about a short in that area, and then use an idea similar to the stock one? Seems like it would be a lot simpler than three in circuit relays, and the additional power switch. For what it is worth, nealy all of these bikes run the power wires to the kill switch in stock trim, so I don't see why you can't still do it that way. Just fuse it and you would be fine.

So in essence, power from ignition switch "on"---> to fuse--->to handlebar switch---> across switch---> to coil. No relays needed, and circuit is protected. And if the fuse blows, you can repair the concern, stick a piece of wire across the fuse, and it will get you home. Way less moving parts, too.

 

[crazypj]

I'm running stock Honda switches at present, already re-wired bike for a single 15A fuse.
It's only done about 115miles since I 'finished' it though
Seems waaaaayyyyy complicated way to do things, orl they relays in there ;D
Eventually I'm going to re-wire different switch on left side and have a lanyard type grounding kill switch with a normally open relay
If I fall off, the engine will stop as there will be no power to coils, if anything goes wrong with relay, spare fuse will connect 2 spade connectors real good
Otherwise, I'm not using anything high enough amp draw to need more relays.
Shorting coils will overheat them and eventually they will split open

 

[kMoto]

Yeah, I here you guys. I was thinking about it the other day and thought, "Well, Honda didn't use any relays". So, I think I'll just keep it simple. Pretty much what ford said, but with a master switch to toggle the power, the switch on my bars will still be momentary.

 

[teazer]

Funny thing is that I just rewired a bike and fitted relays for headlights and ignition just to reduce the current through the switches.

 

[kMoto]

Well that is a valid design point. As my bike sits now, I have all of the power through one 20a SPST toggle. I hate to put all my eggs in one basket, if you will. I also like to remind myself K.I.S.S., in anything I'm designing. That is, Keep It Simple Stupid! I have a couple of micro relays on the way from Hella. So, I'll play with those some and see if I can come up with something that satisfies both design intents.

 

[kMoto]

So, I never got the micro relays. The store I ordered them from didn't actually have any. So all I got was a refund.

I did get my handlebar kill switch wired up last night though. What I ended up doing is using a very simple momentary push button switch off of a 4T motocross bike. This particular bike uses a NC push button contact. I just put the switch in line with the power wire I had running to my coils and it works just like it should.

Thanks for all the input guys.