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Author Topic: Kill switch recommendations and wiring  (Read 94 times)

Jimr1999

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Kill switch recommendations and wiring
« on: 08 May 2022, 08:26:27 am »
Electrickery is not quite a dark art to me but I know when I need advice on it. After watching a CK video where the back of the kill switch was sparking when runnning I am asking for advice on.
1 which switch is a good un
2 Which wire it should interrupt

Any pointers welcome  :)
... You can lead a horse to water, but a pencil must be lead.

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StefanN

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Re: Kill switch recommendations and wiring
« Reply #1 on: 08 May 2022, 12:31:43 pm »
The kill switch on the engine, connects the low voltage side of the ignition to "ground" (ie the engine).   There's a connector that goes to the low oil safety cut-out and that does the same thing - it connects the ignition to ground when the oil is too low.   We disconnect the low oil system, the cyclekart motion and in particular, corners, make the oil move and trigger the cutout.   This means we can take a wire from the now unused connector, put it through a switch and then back to ground on the engine.

It's very easy to test.  Poke a wire into the connector, run your engine.  Touch the other end of the wire onto your engine and it should stop.

This way you can kill the engine with either switch.

It's worth having a heavier duty toggle switch because they look good.  Don't forget to mark it clearly.

If you have a metal chassis you could use the chassis as the return path to ground, but it's really not worth it given how little wiring there is in cyclekarts.

Would be interested to see the video with the sparking switch if you can remember where you saw it.

Jimr1999

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Re: Kill switch recommendations and wiring
« Reply #2 on: 08 May 2022, 12:59:49 pm »
Thanks again Stefan, I have just got rid of all the oil sensor stuff and I will need to run a return wire to the engine to ground it as I have too much wood in between.
The switch I have ordered is this...
https://www.ebay.co.uk/itm/313824236361?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
And is labeled as heavy duty.
I was wondering if it was on the low voltage side, I can't find the video but below is a report of this on the U.S CK site....
... You can lead a horse to water, but a pencil must be lead.

synthpunk

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Re: Kill switch recommendations and wiring
« Reply #3 on: 08 May 2022, 02:28:47 pm »
Most big toggle switches have a hefty AC current rating, but can skimp on their DC current rating.

If the switch is interrupting a DC line with a reasonable amount of power flowing through it, then the contacts will arc. All switches will do it. If you do it enough times then the contacts within the switch will build up extra carbon and probably flash over.

Switching an AC line makes much smaller sparks, as there’s a reasonable chance the switch will break at a zero crossing as the AC goes through 0 volts 50 times a second, so the sparks are much much smaller. So the switch can switch a higher rated AC current. In most electronics, it makes more sense to switch the ac side of a power supply than the DC side, as the switches are much cheaper.

I don’t think cyclekart electrics will have an ac side, it’s DC or nothing.

So in this application, look for a switch that can handle a large DC current. It will be much more expensive than a normal (AC) switch, due to being built much more robustly.

That’s probably a fairly shonky explanation but hopefully it might make things a bit clearer as to why some switches might fail. A switch that has a 6Amp rating at 250 AC volts  might well fail in a DC setting, as it might only be rated for 0.5 amps DC…

Jimr1999

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Re: Kill switch recommendations and wiring
« Reply #4 on: 08 May 2022, 03:12:28 pm »
Thanks Synthpunk, the one I ordered is 12v, 32A and in the photos it has 250v 16A on the side. It says heavy duty so am I on the safe side?
... You can lead a horse to water, but a pencil must be lead.

StefanN

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Re: Kill switch recommendations and wiring
« Reply #5 on: 08 May 2022, 07:10:04 pm »
Yep you'll be fine.

The voltage on that lead is fairly low and also goes to zero between sparks, so will have the same effect that Synthpunk was describing for switching ac.

On some older engines (eg lawnmowers) you stopped the engine by earthing the high tension lead at the spark plug.  I wonder if the person who had the sparking switch was doing something similar.

synthpunk

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Re: Kill switch recommendations and wiring
« Reply #6 on: 12 May 2022, 07:51:12 pm »
Technically speaking- DC going to zero between sparks is definitely not the same as AC. Going *through* zero out the other side into negative voltage land with a similar amplitude excursion but in the other direction is AC. Going to zero between pulses is at best maybe pulse width modulated DC, or ‘Dc with a square wave AC component superimposed on top’, or at at stretch DC biased AC, but basically simply still just DC…

The ‘through zero’ bit is important.

But your 12V 32A switch should be perfect.

Jimr1999

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Re: Kill switch recommendations and wiring
« Reply #7 on: 12 May 2022, 08:02:34 pm »
The switch arrived today and has a most pleasing and positive action... I will endeavour to wire it this weekend. Thanks for all the help and reassurances all :-)
... You can lead a horse to water, but a pencil must be lead.

synthpunk

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Re: Kill switch recommendations and wiring
« Reply #8 on: 12 May 2022, 09:28:54 pm »
Post a pic!
I won’t be getting round to my ‘lectrics for a while but I love a good switch.
;c)