automated 4-stroke kill switch using PIC

I wonder if anyone has any ideas, I am trying to use a microcontroller to stop a small 4-stroke engine. My plan was to use a relay and tap into the motors kill switch, when it is time for the motor to stop using a ground coming from the motor the relay will energize and short out the motor coil and stop the engine, which is the exact principal of any small engine kill witch. I measured the current when the short occurs at 800 mA which is fine they only problem is that I read online that some CDI voltages go as high as 30000 volts. What would be the best way to switch such a high voltage? I assume the amperage will always be lower than 1 A, do they make relays that can handle such high voltages, or even a triacs.

Any ideas would be appreciated.

The peak voltage can get high a feed resistor and a zener diode will do the trick I would think.

Most kill switches are connected to a separate winding on the coil, (or internally to the circuit), so the voltage on the kill switch contacts is not nearly as high as the normal plug voltage.

It would be good to know what you really have before you start.

Small magneto equipped engines kill switches work by shorting the<b> primary circuit</b>, and the voltage encountered will be several hundred volts, with enough amperage to give you a good hard shock, , I doubt if the voltage is high enough to have to worry about "flashover" of the relay contacts, snubber capacitor may be required.

Hi, Mitch

generally, the Kill switch of a CDI shorts the HV Winding ( 250-300 AC Volts ) without any fear ...

Now electronic ignition modules may have a special wire for that ...

I believe RELEASING the relay supply to stop would be a much safer practice ... but it's you to decide.

Alain

Quote:

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Originally Posted by Acetronics

Hi, Mitch

generally, the Kill switch of a CDI shorts the HV Winding ( 250-300 AC Volts ) without any fear ...


Alain

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Well Alain, at least we agree on the voltage range . . . Kettering (points type) ignition shorts the primary winding . . . CDI . . . I defer to Alain's experience.

Hi, Joe

YES, the HV winding !!! which is a special winding in the "generator", just dedicated to produce the "400vDC" to charge the CDI capacitor ...

Want to see ( and hear her roaring ... ) my Kawasaki KH500 tri-cylinder ???

Alain

Quote:

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Originally Posted by Acetronics

Hi, Joe

YES, the HV winding !!! which is a special winding in the "generator", just dedicated to produce the "400vDC" to charge the CDI capacitor ...

Want to see ( and hear her roaring ... ) my Kawasaki KH500 tri-cylinder ???

Alain

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NO No I believe you, but are we to assume it is a late model motorcycle? I think we should do as we did and present all possibilities since we do not know what he is working on. BTW 400v is high voltage compared to 5v, compared to 30,000 volts I would call it primary voltage. Anyway what matters is that we are helpful to the OP. Oh BTW, nice bike!

Thanks guys for all your info, every time i post a question you are always their with advice.

In my opinion their must be a secondary winding inside the motor that would step down the voltage to 400vdc because every kill switch uses normal 16 gauge wire rated for 600v. I will just take a chance and measure it

thanks alot guys here is the link i read that from ground to to the spark plug their is 30000 volts.

http://www.jetav8r.com/Vision/Ignition/CDI.html