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Permalink Reply by Bob Simmons 15 hours ago

I assume you're talking about the mag switches for ignition A and ignition B going to the electronic module, essentially P-lead switches. But I'm a bit confused by 'conventional keyed ignition'. Do you mean a RIGHT-LEFT-BOTH-START switch, or are you planning individual left and right toggle switches, with a separate momentary starter switch?

A standard aircraft  RIGHT-LEFT-BOTH-START switch should already be spec'd for what you need.

Individual left and right toggle switches don't have to be AC rated, but they're usually rated for both AC and DC. All they're doing is switching ground on and off to the electronic module. No special requirements for voltage, as long as it's at least 12 volts. But 250 volts certainly wouldn't hurt. And, as I said, it'll probably be rated for both anyway.

It's similar for a momentary starter switch. The starter switch itself does not spin the starter. It just sends a signal to trigger that action to happen elsewhere. In a typical application, that's the solenoid or starter contactor, but on the 914 it's the starter relay. The starter relay is what actually pulls the big current, so the starter switch itself does not have any major voltage or current requirements. 2 amps at 12 volts DC would be fine, but it helps to go a little over on specs, just to be on the safe side. The 914 install manual has some good diagrams for all this.

This might also help:

http://www.aeroelectric.com/articles/MagnetoSwitchOptions.pdf

This also has a couple of suggested part numbers for mil spec toggle switches if you want to go that route. I prefer mil spec for critical circuits if cost allows.

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Permalink Reply by Tony Renshaw 12 hours ago

Hi Bob,

firstly thanks for your detailed reply. You are correct, I did mean a RIGHT-LEFT-BOTH-START is what I currently  have, but what I wish to replace. I want to be able to swing the engine over without ignitions being ON.

I have read elsewhere that Rotax engines need switches that can cope with AC, as if the ignition circuitry generates AC….. it’s pretty obvious I don’t know, but I do know that a 250 Volt AC switch will cope with current demands of our switching, and you can get such rated switches from Spruce. 
Thanks for the Bob Knuckolls lead, I have been encouraged to buy his book and find the time to read it…. maybe I need to stump up the cash paying double to get it Downunder. 

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Permalink Reply by Bob Simmons 1 hour ago

I won't claim any expertise on the Rotax, but there's no AC on the starter momentary switch. It's on a 12 volt DC circuit that's fused for 2 amps. That's in the Rotax install manual. It's the starter relay that pulls the big voltage/current load, and you aren't changing that.

Bob Knuckolls' book is a fantastic resource. I recommend it for all homebuilders. Between his diagrams,. and the diagrams in the Rotax manual, you should be able to handle this easily. The MS24524-23 switch he mentions meets your specs with room to spare, but it's $56. Like I said, mil spec is more expensive. The 24-360 switch at Aircraft Spruce also meets your requirements, but it's not mil spec, so it's only $12. The other switch they have, the 44047/44053, gets crappy reviews. Apparently it's really hard to push. Either the MS24524-23 or the 24-360 at Spruce should work fine. The beauty of homebuilding is you get to choose what best suits you.

Love the t-shirt and the dog, by the way. We lost both our Labs in the last couple of years, and I really miss them.

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