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Using switches for starter - two 2-5's for mags?

Fearless

Fearless

Well Known Member
I am doing preliminary wiring on my 9A. I bought two 2-5 switches to use for my mag setup to start the plane. It appears to me that the 2 -5 switch is setup for OFF-On-(ON). Per the Z-11 diagram in AeroElectric Connection it is showing the two switches. If I understand things correctly then for the left mag the Mag Off -Mag On - (Starter engaged). For the Right Mag the diagram has Mag Off - Start -mag grounded - (Mag On). I don't think the switch is correct because the On mode is on the momentary setting.

Am I understanding this right and if so what switch type would I use for the right mag if the 2-5 isn't correct? My left mag would be the impulse one.

Thanks in advance for replies.
 
I have the same set up on my -6. The switch for the right mag is off for start (the lower position) and on (the middle position) to run. The top spring loaded position isn't used for the right mag.
 
You can use two 2-5's.

For the left it is wired where the lower position is off (mag is grounded), middle position is on (mag not grounded), and the momentary up position is on (mag not grounded) and the starter is energized when the right mag switch is down (mag grounded).

For the right, it is wired where the lower position is off (mag grounded), and the middle position is on (mag not grounded), the momentary position is not used. Also interlocked on the other pole is the starter contactor circuit that is only enabled when the switch is in its down position.

I think your understanding of the right switch may be wrong...

Left Switch Down = mag off (mag grounded)
Left Switch Middle = mag on (mag not grounded)
Left Switch Up (momentary) = mag on (mag not grounded and start)

Right switch Down = mag off (mag grounded and start enabled)
Right Switch Middle = mag on (mag not grounded and start disabled)
Right Switch Up (momentary) = not used

See :

http://www.aeroelectric.com/PPS/Engine/Ignition/TogMagSw.pdf
 
Why not just use two on off switches and a push button? What will you do if you just want to crank the motor over without starting it? How do you keep the mag grounded.
 
gasman said:
Why not just use two on off switches and a push button? What will you do if you just want to crank the motor over without starting it? How do you keep the mag grounded.
Click to expand...

You can but this leaves it up to the pilot to know that he should keep the non impulse coupled mag off until the engine is started. To know it and to do it.

Not really sure why one would ever want to crank the engine over with the starter without intending to start the engine so this thought never occurred to me.

How does one achieve this feat with a standard key switch?
 
Brantel said:
How does one achieve this feat with a standard key switch?
Click to expand...

My "Standard Key Switch" does not have a "start" position - it is Mags only. I have a spring-loaded toggle switch (under a cover) for the starter. My checklist says to start on the Left Mag only, and that is what I do. this was how my Grumman was set up, so I learned the habit pattern over 23 years....

Paul
 
Ok... Key switch with and wired for OFF/L/R/Start positions. One might say that this one is more "standard" than most :p
 
Brantel said:
You can but this leaves it up to the pilot to know that he should keep the non impulse coupled mag off until the engine is started. To know it and to do it.

Not really sure why one would ever want to crank the engine over with the starter without intending to start the engine so this thought never occurred to me.

How does one achieve this feat with a standard key switch?
Click to expand...

If you were going to use switches, a good way to wire them to start only on the impulse mag is to use a DPST switch for the right mag. One side will short the mag, and the other side will pass power to the starter button. This way, the only way the starter will crank is if the right mag is off. You will need the left mag on to start the motor.
Remember, you must mount the switches up side down for the mags to be HOT when the switch is in the up position.

As far as cranking without starting with a standard key switch, you leave the mixture control in cut off position. When would you do this? If the aircraft was parked for a long time without running, you might want to crank to get oil pressure and fill the lifters before power is applied to the pistons etc.

The main problem with key switches is they have had failures and leave the left mag hot if the key is turned too far to the left and it does not spring back before you take the key out............:eek: It has happened to me!
 
Thanks - I misread what the right switch was doing

Thanks gang,

I was indeed misunderstanding what the diagram was telling me for the right switch: off - start/on. I didn't recognize that the momentary setting wasn't being used. But I do wire it as shown on the diagram so they are grounded and not grounded at the proper times. I can count on you guys to keep me straight.
 
If your push button switch...

Brantel said:
You can but this leaves it up to the pilot to know that he should keep the non impulse coupled mag off until the engine is started. To know it and to do it.

Not really sure why one would ever want to crank the engine over with the starter without intending to start the engine so this thought never occurred to me.

How does one achieve this feat with a standard key switch?
Click to expand...

...has two poles, one of the poles could short out the non-impulse magneto while the starter is activated - just wire it in parallel with the appropriate (usually R) magneto switch.

This is exactly what happens inside the R-L-BOTH-START ignition switches.

Both magneto switches would now be straight ON/OFF switches.

This would also allow cranking with both magnetos off if you must...:)
 
How about this?

gasman said:
If you were going to use switches, a good way to wire them to start only on the impulse mag is to use a DPST switch for the right mag. One side will short the mag, and the other side will pass power to the starter button. This way, the only way the starter will crank is if the right mag is off.
Click to expand...

Another way might be to use standard switches for the mags and a DPDT switch for the starter that grounds the non-impulse mag whenever the starter is engaged? A little more automatic.
 
NOT GOOD!

lucky333 said:
Another way might be to use standard switches for the mags and a DPDT switch for the starter that grounds the non-impulse mag whenever the starter is engaged? A little more automatic.
Click to expand...

The problem with this is that as soon as you let off of the starter button, (and the motor did not start) the non impulse mag is hot and might fire and cause a kick back. Turning on the right mag after the motor is running will eliminate this problem.

So the DPST mag switch is more automatic......:D
 
But a standard...

gasman said:
The problem with this is that as soon as you let off of the starter button, (and the motor did not start) the non impulse mag is hot and might fire and cause a kick back. Turning on the right mag after the motor is running will eliminate this problem.

So the DPST mag switch is more automatic......:D
Click to expand...

...key start switch doesn't do this, does it?...
 
Would there be a issue with using switches with both mags if they were both impulse coupled as in my Superior XP?
 
No issues...

Tbone said:
Would there be a issue with using switches with both mags if they were both impulse coupled as in my Superior XP?
Click to expand...

...with two impulse magnetos you could start on either left or right, but preferably on both.

You would not need any of the switch wiring interlocks previously mentioned.
 
Tbone said:
Would there be a issue with using switches with both mags if they were both impulse coupled as in my Superior XP?
Click to expand...

No problem at all. You could just switch them both on and hit the starter.

I have a LSI and an impulse and can start with either or both.
 
Source for (2-5) Switches

Greetings,

I have seen a lot of postings referring to the (2-5) switch used for the mags/starter. Can anyone please tell me which manufacturer is preferred and where I can find them? Also, a photo of one of the switches would be most helpful.

Thanks in advance.

-= Brian Norris =-
 
sources

Brian,

The switch referred to is an On-Off-(On) and can be purchased through any reputable dealer in electronics. Newark and Mouser are two. The specific 2-5 switch being referred to is sold by B&C Electrical : http://www.bandc.biz/index.aspx
 
Last edited:
(2-5) switches

Thanks! I have decided to get the Honeywell NT series, # 2NT1-5 from Allied Electronics.

-= Brian =-
 
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