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How would I wire 2 mag switches like a starter?

blueflyer

blueflyer

Well Known Member
If I was to use 2 toggle switches (left mag switch would have momentary position for starter) for my magnetos, how could I wire it so that it would operate like a keyed ignition switch, i.e., shut the right mag down during start, but automatically come online after I release the starter?

Any wiring diagrams out there to show this? I checked Bob's Aeroelectric book, but I didn't see any Z diagrams that showed this.
 
If you could find a 3-pole double throw ON-OFF-(ON) switch you could do this. 2 poles would be the two mags with the down-on position grounding the Mag. The 3rd would be power to the starter solenoid when in the momentary up position. You could also run ground to the right Mag on its pole when in the momentary up position to kill it for start. I don't know where you would get a switch like this, but it would do he trick.
 
Jesse said:
If you could find a 3-pole double throw ON-OFF-(ON) switch you could do this. 2 poles would be the two mags with the down-on position grounding the Mag. The 3rd would be power to the starter solenoid when in the momentary up position. You could also run ground to the right Mag on its pole when in the momentary up position to kill it for start. I don't know where you would get a switch like this, but it would do he trick.
Click to expand...

Mouser has a reasonably priced NKK 633-S39 at just a little under thirteen bucks. 3PDT ON-OFF-(ON). Not sure why you'd need a 3PDT though, if he wants to use two mag switches...
 
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Carling switches available at Mouser or Digikey
6GM5B-78 DPDT ON-OFF-(ON)
B and C part number S700-2-5 (ON)-OFF-ON

Wire per Z-11 as suggested by BigD.
When the mag is on, the switch is off (open)
It would not be automatic though. Right mag switch must be off to enable starter. After starting, the right mag needs to be turned on. Not a problem, as the start switch is released, snap the adjacent switch on.
 
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To make both mag switches look the same when in the on position, they should both be DPDT ON-OFF-(ON). The parentheses means momentary.
 
3PDT

Jesse/Dale, thank you! I am good with using one switch for both mags....I just didn't think about having that option when I made my original post.

Any drawbacks to this solution other than switch failure issues?
 
On aeroelectric site, Bob Nuckolls has a paper in the references regarding "Shower of Sparks". In that paper, he has several different diagrams on how to wire magnetos with toggle switches if you are using the shower of sparks.
Jerry
 
blueflyer said:
Jesse/Dale, thank you! I am good with using one switch for both mags....I just didn't think about having that option when I made my original post.

Any drawbacks to this solution other than switch failure issues?
Click to expand...

The main drawback to what I suggested is that you don't have a way to do a magneto check. You could have two separate momentary switches, even hidden, that you could use one at a time to ground a Mag to do a check.

Another system that I have used in lieu of a typical key switch is a momentary toggle and a push button. You had to lift the toggle and hold it while you mashed the button. It worked really well and I think it would have been unlikely for someone that wasn't really clever to figure out how to start unless they were shown how. With the switch I mentioned, you could use that in the momentary position to kill one Mag and to energize the start push button. When in the momentary position with the engine running, you could kill one Mag to test, but not the other. On a mag check where you can only kill one mag, you want to make sure the mag drop is over a certain number to verify both mags are good.
 
Here is exactly what you asked for: 2 mag switches, both switches up momentary to start,
automatic both mags turned on when released.
Two independent mag switches have no common failure point. (except starter)
Starting requires that both switches be operated to the spring loaded up position.
Accidentally (or intentionally by kids) moving one switch fully up will not start engine.
Mag%252520Switches.jpg

Download PDF version.
Hover mouse in black area above PDF and click the down arrow.
 
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The typical way I have seen this is done is a bit different. If the right mag switch is on, it should disable the starter.
 
The typical way I have seen this is done is a bit different. If the right mag switch is on, it should disable the starter.
Click to expand...
Yes, that is the way that my circuit works, if the right mag switch is on (center position), the starter is disabled. And when the right switch enables the starter (full up position), the mag is disabled. It is confusing because we normally think that turning a switch on completes a circuit and turns something on. But when a mag switch closes (is on), it actually shorts out the mag, turning the mag off.
 
I want to make sure I understand what I'm looking at correctly (The Schematic pdf).

Going with this you remove the need for any push button start and instead use two toggle switches with momentary (ON) positions.

Starting the plane you push both toggles into their momentary positions which engages the starter while simultaneously ungrounding the left mag to make it hot, and keeps the right mag grounded and therefore dormant?

Once the engine is going you release the momentary switches which put them in their middle position which is the starter not engages and both magnetos ungrounded.

Going this method you can still check each mag as needed with the engine going just by turning a mag off at a time?

For extra accidental start protection you could just put a covered switch or something in series with the line to the starter if you want correct?
 
You could easily use a Bosch 12 volt SPST relay connected to the started button to energize the relay on when you push the start button. The relay poles, 1 to ground and the other to the mag P-lead. When you push the starter button it will ground the P-lead on the mag you don't want on when starting. You can use two SPST locking toggle switched for L & R mags.
 
Justin, everything that you wrote is correct.
BandC.aero DPDT switch part number S700-2-5 (ON)-OFF-ON
 
Starter on stick

Mich48041 said:
Here is exactly what you asked for: 2 mag switches, both switches up momentary to start,
automatic both mags turned on when released.
Two independent mag switches have no common failure point. (except starter)
Starting requires that both switches be operated to the spring loaded up position.
Accidentally (or intentionally by kids) moving one switch fully up will not start engine.
Mag%252520Switches.jpg

Download PDF version.
Hover mouse in black area above PDF and click the down arrow.
Click to expand...

I did something close to this, as an alternate idea for tail wheel guys who want the starter on the stick. Change the left mag to a ON-OFF-ON and use it as a starter 'arm'. Wire the stick starter button across the existing right On-Off-(ON) and move the right mag disable to a relay across the starter....
Allows the safety of a 'arm' switch and hand on stick during cranking for tail wheel guys.
 
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