Kill switch voltage/amperage

[Andrew 4CE]

Anyone know the approx voltage/amperage going through a kill switch? I need a relay connected to it and wondering what size to get.

[25xs]

Andrew, you should at least say what the engine is you are working on... An electronic ignition may be quite different from a magneto.

[Andrew 4CE]

Good point, omc 15a. But info from any stock racing motor would be good enough.

[dwhitford]

Voltage high (sparkplug voltage) amperage low, none of it lethal, but enough to get your attention and decide whether you really want to go out for that heat.

[ricmontoya]

Do you know an auto mechanic with a digital lab scope? Will also need the inductive amp meter for the lab scope too. Check voltage while the motor is running at full rpm's. Pull the kill switch and the digital amp meter will give the amperage.

[Andrew 4CE]

Do you know an auto mechanic with a digital lab scope? Will also need the inductive amp meter for the lab scope too. Check voltage while the motor is running at full rpm's. Pull the kill switch and the digital amp meter will give the amperage.

Nope, was hoping someone would have an idea. I'll start trial and error I guess.... I ordered a 40A automotive relay, I'll see if it fries or not.

[ricmontoya]

Automotive relays like the Bosch little square ones probably do not have enough air gap between the contact to prevent the high voltage from arcing across the air gap.Finding a high voltage, low amperage with 12 volt activation may be quit difficult to find. May be an electronic relay similar to the Hella Mini ISO Solid State Relay - 12V DC, 20 Amp might work.

[Andrew 4CE]

Interesting Ric. The one I bought says "Medium pressure resistance: 750VAC between contacts" I wasn't sure what it meant, but I'm guessing it what you are talking about and your explanation makes it more clear. I'll have to do some more googling and see if there are higher internally rated ones.

[foot_doctor]

I think we could be more helpful if you would describe the purpose for the relay, and what source you plan to use to energize the coil. You should not expect the ignition to operate the relay. You may use the relay to provide the open or closed circuit for your engines ignition. Typically the primary voltage in a magneto may rise to sever hundred volts for a short duration after the points open. The current is nominal if the switch is used to short the point circuit. If you are planning to use your setup with a CD ignition, things change. The kill switch lead from those ignitions ar typically used to discharge the capacitor, or prevent charging of same. Typically the voltage potential at CD kill switch circuits is several hundred volts, I have never measured the current. If you plan to enable the kill function in a racing boat by employing a relay, use only a completely water proof relay. If you would attempt to use a relay actuated kill circuit in a race that I were the inspector at, I would not allow it. It would reflect the reliability of the power for the relay, and all of the associated wiring in a marine environment. Just my opinions. R.T.

[Andrew 4CE]

First off, I'm not much of an electronics person... but can google pretty good, haha.
I've been working on a wireless kill switch for a couple years when I have a little spare time. I can operate it for about a 1/2 mile. The regular in boat kill switch works on it's own and the remote one works on it's own. It worked fine when tested on the raceboat without the motor running. Once the motor was running, and it was activated, it fried the small relay I was using. I replaced with a slightly larger one I had and it fried too. These were about 6a or something, can't recall. It's all mounted in a small waterproof box, with a battery pack to run things, that just connects between the standard 2 prong kill switch connector so it can easily be moved from boat to boat. I wanted this for our race school and J kids first few rides. I've seen a few people hit shore over the years coming in too hot on their first rides (not in our school), and others trying to get on plane while they drive a mile down the lake and everyone is cringing waiting for the motor to blow up. If i ever get it working properly, I'll post all the parts I used and the 3D print models for the housing so anyone can make one. It cost about $50-$60 or so.

[foot_doctor]

So your system would be used in parallel with the boat mounted, tether operated kill switch. Back-up, so to speak. I think it’s a great idea. Just don’t eliminate the main kill switch. R.T.

[Andrew 4CE]

Correct, has no impact on operation of the standard tethered kill switch.

[25xs]

I've been working on a wireless kill switch... ...for our race school and J kids first few rides.

Cool... I like it! Are you using a race radio system so you can talk to the drivers as well..? That might be a "verbal remote control" at first.

[Andrew 4CE]

I do have race radios, but was not planning to use with the school. An expensive tool, and setting up for each person to pass around would be a nightmare.