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Push Button Start and Mag Toggle Switches

transientair

Active Member
I know that this topic has been addressed before, but I'll be the first to admit that when it comes to wiring, I start scratching my head near immediately. So the searches I've done (Google and VAF) have offered some diagrams, but nothing I've been able to successfully figure out.

I have a push button start and two toggle switches (NKK S-6AL) and I'd like to wire them in such a way that with both switches up, the right mag (non-impulse coupling) grounds. I'll have two conventional mags.

From what I understand, this should be possible with the switches I have.

But as soon as I look at all of the connections on the back of these switches, my brains turn to water.

Does anybody have a kindergarten-level explanation or drawing that would help?

Thanks all
 
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I have a push button start and two toggle switches (NKK S-6AL) and I'd like to wire them in such a way that with both switches up, the right mag (non-impulse coupling) grounds. I'll have two conventional mags.

Having both switches up but the right mag grounded would be unconventional. You don?t want your switches ?lying? to you. Here?s what most would do:
Notice each mag switch is really two switches (?double pole, double throw?). Pick one switch on the left mag switch. Bring the left P lead to the center connection. Use an ohmmeter to see which connection (top or bottom in the photo) is connected to the center terminal, when the switch is down (off). Connect that terminal to ground, leave the other one unconnected. Repeat for the right switch. Now look at the two remaining switches. On the right mag switch, bring a wire connected (fuse or CB) to 12 volts to the terminal next to the grounded one. Connect a short wire from the middle terminal, over to the left switch, but to the terminal opposite the one connected to ground. Connect a wire from the middle terminal, to the starter switch. And from the opposite terminal on the starter switch, to the start relay. Now, 12 volts will flow to the starter switch only when the left mag switch is up (on), and the right mag is off. After start, turn the right mag on (up).
 
Clarification

Trying to understand your instructions:

When you say to connect a short wire from the middle of the second right mag switch to the terminal of the second left mag switch ?opposite the grounded terminal? do you mean the terminal on the second left mag switch which is connected to the middle when the switch is ?on?? This confused me because the ?off? terminal of the second left mag switch is not connected to anything according to your instructions. Only the first switch on the left and right mag is grounded.

Thanks for the clarification!

Leonard Westermeyer
Newman Lake, WA
RV-7A waiting for an engine
 
Try one of these

I installed an ElectroAir electronic ignition switch panel:
https://www.aircraftspruce.com/cata...erm=4580977758698486&utm_content=All Products

Looks fantastic, performs exactly the way you want it to. I just covered over the ElectroAir label with my own label. Be careful with the wiring: You'll have to invert one of the switches for it to work properly with your mags.

It costs. But I love the professional non-home-rolled look it gives that corner of my panel.
 
I think you got it. Use an ohmmeter. The wire which is going to go to the 12 volts should flow thru the mag switches when the right mag is off (down) and the left mag is on(up), and on to the start switch. All 4 center terminals should have a wire on them. Of the remaining 8 terminals, 4 are not connected. Draw out a schematic, it should be clearer.
 
Here is a picture showing how to connect the wires.
Without having the parts in hand, I had to make assumptions.
I know that is risky.
I assume that the top of the picture is up.
Anyone feel free to correct me if wrong.
enhance
 
Hi Cody,

I?ll send you a PM with my email attached and if you?ll send me a return email I?ll attach a simple, easy to understand circuit schematic of a DPDT toggle switch. The one I?ll send you is for a Honeywell toggle switch, but I?m sure all DPDT switches work the same. One thing to keep in mind when trying to figure out which terminal is hot at any particular time is to think about the switch as actually being two separate switches in one. What I mean by that is to picture each three rows of terminals as two totally separate switches from one another. So for example, if you were to connect a hot wire to the center terminal (common) on a particular row, you would only have power to the top and bottom terminals (depending on the position of the switch) on that one row of three. The other row of three terminals wouldn?t have any power going to any of them. To have power going to that row of three you?d have to put a jumper wire going over to the other side. That?s what makes a DPDT switch so useful. You just have to decide which terminal(s) you want powered (or no) in any particular position. Once again, just think about the switch actually being two separate switches in one. It takes a little while to wrap your head around what you want the switch to do in a particular position and what terminal(s) you want hot and that?ll tell you where to bring the power in to and then where to put your jumper wire to power the other row of terminals. Once you study it a little bit, it becomes clear.
 
Here's a schematic version of what I did. Left on-start (up); right off-start (down) .. that permits the pushbutton starter to activate the starter contactor. Once started, flip the right to the on (run) position.

i-K99MQqv-L.jpg
 
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I was thinking that one of the good features of the push-button start is the capability to crank the engine independently from whether either or both of the mags are 'on'. This puts the onus on the pilot to select left mag only to start, then select the right mag once the engine starts. But it enables engine cranking with both mags off - that can be handy.

Question for Bill -- if I understand your schematic, you are 'grounding' your mags into the shield conductors of the leads. But I don't see where the shields are connected to real ground.

Also, is there a special reason for putting the momentary contact start switch between the two mag switches? Or could it be 'upstream' of both mag switches?
 
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If you want to be able to crank the engine:

L1 Common - Ground
L1 Up ON - Not Connected
L1 Down ON - L Mag P-Lead

L2 Common - Not Connected
L2 Up ON - Not Connected
L2 Down ON - Not Connected

R1 Common - Ground
R1 Up ON - Not Connected
R1 Down ON - R Mag P-Lead

R2 Common - 12V Supply
R2 Up ON - Not Connected
R2 Down ON - To Starter Button

Starter Button Supply - From Right Mag
Starter Button Load - To Starter Relay

Disadvantage is that if you forget to put on the left mag for start .... well, it won't start! Also the Start Button is "Live" with the mags off so "Curious" fingers could cause issues ......

The ground does not have to go to the shield - it's just a schematic...... You can ground at any convenient point.

Note that on most double throw switches, the "live" terminal is normally opposite the switch position. So up powers the bottom terminal and vv.

If you choose this route, you could simplify things by changing the left switch to a SPST (OFF-ON) with OFF being UP. Right switch could be a DPST (OFF-ON) with OFF UP.
One side GND/P-lead and other side 12v/Starter Button
 
I used two SPST switches for the Mags. I used a switch for start on an Infinity control stick. I used a Master Switch to control the use of the starter and so no accidental start.
Worked for me.
 
I originally had my switches set up so that the starter was disabled when the right mag is on.
Later I got a deal on a new impulse mag and installed it on the right. Now start on both mags. Problem solved.
 
to each their own, but i dont see the need to complicate two switches and a push button.

bob burns
RV-4 N82RB
 
I wiring my push button start though a relay that grounds the right mag anytime the starter solenoid is powered. Basically the same thing a 3 position keyed switch would do. I like to keep things simple.
 
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Summary: There are lots of ways to do this. Do you want to be able to spin the starter, mags off, for maintenance? Do you want the starter switch locked out when flying? Your choice.
 
Summary: There are lots of ways to do this. Do you want to be able to spin the starter, mags off, for maintenance? Do you want the starter switch locked out when flying? Your choice.

+1

I went back to SPST switches so that I had more options in an emergency. If you can't remember to keep the right mag off during start, you have other issues to address. I can think of many things that will harm you in aviation if you don't remember them. This is why we have checklists. You don't have a switch or relay to insure you have gas in the tank before takeoff, right.

Larry
 
DPST Starter Switch

It looks like you have a double pole starter button there. You could easily use one pole to engage the starter and the other to ground the left mag (even when it's "on"). That way, all you have to do is flip both mags on for start, hit the button to engage the starter (which also grounds left mag). When the engine fires, release the button and both mags are live, just like a key switch.
 
I have two toggles for mags, and a pushbutton starter (plus keyed master). L mag is impulse coupled, right is not.

I have a schematic I can send you that shows how I wired it so that

a) no matter what the mag toggle switch positions are, if the master (keyed) is not on, the starter will not engage (starter pushbutton is disabled) and
b) when the start button is pushed, the right mag is grounded

I think this is what you're after. I'll dig it out and send it later tonight.

Oh, and once started, failure of the keyed master will not cause the engine to stop. I did a whole fault tree on this circuit to ensure safety (both personnel on the ground and safety of flight).
 
Schematic

Here's a schematic showing one way to wire individual mag toggle switches with a push button starter (DPST) and a key switch for just the starter circuit. Working great for over 350hrs and 2 Atlantic crossings :D

i-Rzj2Q46-XL.jpg
 
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Switches

Merely my opinion, I would have the toggle switches
With guards over them in the down position. Engine
?On? guards up engine ?off?. Right mag up, it?s off.
If backwards.... Flying along and and soda falls off,
you almost catch
It... oops as you reach for it you knock the switches
Down, oops throw them back up and boom, backfire!!
Hope you didn?t just blow your intake hoses off.
Same goes for a nice roll or slow loop, you fell through
And your iPad falls off and makes contact. Turbulence
Etc. only down side is canopy open and someone pushes
Down mags ?hot??
 
Merely my opinion, I would have the toggle switches
With guards over them in the down position. Engine
?On? guards up engine ?off?. Right mag up, it?s off.
If backwards.... Flying along and and soda falls off,
you almost catch
It... oops as you reach for it you knock the switches
Down, oops throw them back up and boom, backfire!!
Hope you didn?t just blow your intake hoses off.
Same goes for a nice roll or slow loop, you fell through
And your iPad falls off and makes contact. Turbulence
Etc. only down side is canopy open and someone pushes
Down mags ?hot??

Locking toggle switches solves that. Then up can be on as usual.
 
Toggle Switches

Locking toggles for Mags in this application. Push button bezel lights up and starter switch becomes active when key on and engine <600rpm. Once engine starts and exceeds 600rpm, bezel light goes out and switch becomes inactive, preventing accidental starter engagement while the engine is running. Engine restart required in flight and rpm <600; bezel lights up to prompt the pilot to engage the starter. The key switch is just there to stop kids and assorted curious types from hurting themselves while I'm not looking...

i-rpWrZ4L-L.jpg
 
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Question for Bill -- if I understand your schematic, you are 'grounding' your mags into the shield conductors of the leads. But I don't see where the shields are connected to real ground.

Also, is there a special reason for putting the momentary contact start switch between the two mag switches? Or could it be 'upstream' of both mag switches?

Hi Steve ... my understanding about grounding the mags is to short the points that would otherwise open and generate the spark. This will do that. The shield is grounded to the engine case through the mag body -- so there's your ground connection (good for RFI suppression from the HV in in the mags). All that really matters is that the points don't open electrically. I didn't totally dream this up, though, it's also a common pattern in the AeroElectric connection.

There's no special reason why the switch is in between the two mag switches .. it can go anywhere in line with that circuit. On my panel, it's a super easy connection, right next to the mag switches, so it caused no complications.
 
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Mags_zpsumt7kcqq.jpg


Apologies for the watermark. Looking for a better hosting site for pics, but all the free options suck.
 
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Thanks for the good info offered. Believe me, it's nice to know so many folks have such a wealth of knowledge.

I'm getting closer to having a handle on how to proceed, but I'm not ashamed to admit (mostly) that I still don't have it all together in my head.

I used a multi-meter to test the switch connections in the hopes of knowing with certainty how they operate. I used my crude skills to work up the below drawings. Remember I said kindergarten level, right? :eek:

There's a chance that I'll never quite understand fully the reasoning behind how everything is supposed to connect up, so the most helpful thing for me may be a very simple drawing that shows which wire connects to a specific switch connection. I have to admit that the wiring diagrams still leave me scratching my head!

https://1.bp.blogspot.com/-h1PgT8C5Q8U/XcGnzfXLeLI/AAAAAAAAAZo/wH8PK0Onj4U2vT7802VEWCbMhSjwxmulgCLcBGAsYHQ/s1600/Mag%2BSwitch.png

https://1.bp.blogspot.com/-0sdZnEnhUSA/XcGnzZzjP4I/AAAAAAAAAZs/tjkWHYxY-usLafVw0jILFZxTwEkYIrTRwCEwYBhgL/s1600/Start%2BSwitch.png

Thanks again

So the first thing is to use standard symbols...that way, you know what they mean, we know what they mean, Joe Schmoe EE knows what they mean, etc.

Second, get ahold of a good book (Nuckolls' Aerolectric Connection book is a good one) and learn the meaning of those symbols. Then get some of those switches, stick a multimeter on them and see for yourself how they work when flipped one way or t'other.

These are all really simple circuits, but they can be a little overwhelming at first sight.
 
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