bobmarkert

bobmarkert

Well Known Member
I blew way too much time (hours) trying to figure out the design for a switching circuit for my P-mags. I need to qualify that?. to design it so it will work the way I want. I?m hoping someone with more electrical smarts than me (I?) can help. Part of the problem is I?m also trying for a certain aesthetic as well as function. My design point is that each P-mag will have its own switch:
Military locking 3 positions
Up position (Fly Position) ?P? lead open & Ship?s power closed
Mid position (Mag Test) ?P? lead open & Ship?s power open
Down position (Mag Off) ?P lead Closed (grounded) & Ship?s power open
To complicate it even further I would like to add a warning light whenever the switch is in the mid (test) position to prevent me from inadvertently flying in the mid ?test? position. Does that mean I need a 3 pole triple throw?. and is there a mil type locking lever switch that will do all this?
I have the switch below which is a double pole ?On-On-On? switch which may be part of the problem.
Thanks for your feedback

 
Can't help with the circuit, sorry, but if it were me, I'd far prefer a momentary test position instead of a fixed one, and then get rid of the light.

The thing with the light is that a person could get into a behavior pattern where you go to test, check the light - ignoring the functional effect of the test - and then are satisfied.

Plus, it's more wiring, more weight, all to simply remind you that yes, indeedy, you've got the switch in the wrong position.

Perhaps you can find a switch that has these positions:
Momentary up = test
Middle = on
Down = off

But wouldn't the normal on - off kind of switch work just fine, with off testing the other side of the system like a magneto switch would?

Like I said, I can't help with the electrical end of it and the "on - off" idea might be wrong for P mags.. But just like other pilots, I know what functionality I like.

Dave

Dave
 
Dave, I considered all that and .... And still would like a solution for my original post..... If there is even a switch that will fit the bill.
Cheers
Bob
 
Bob,

You could wire it like this using your existing switch (EDIT: See corrected drawing in later post):

PmagSw_zps22a8a1d5.png


Edit: Of course you would need the necessary circuit breaker or fuse per the Pmag installation manual, etc.
 
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Now if I just knew how to decipher the schematic......sigh
Thanks. PM sent
 
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I guess my schematic would not work with your existing switch (double pole double throw or DPDT). The schematic shows a double pole triple throw (DPTT). Sorry.
 
Have a look at page 6 of the following link. http://www.aeroelectric.com/articles/Progressive-Xfr_Split-Rocker_Switches.pdf

I think your switch is similar to a 10-2. If so, I believe you can accomplish what you want by connecting the terminals as follows:
1) Idiot light Ground
2) Ground
3) P Lead
4) Pmag Power
5) Bus Power
6) Idiot light positive.


There is a very good chance I don't know what I am taking about, so make sure you test first.

John
RV6A C-FNLY
 
Bob,

John (J CRATE) has it right. It should work if you connect it up as he posted. As he said, test it first.

I will post a corrected schematic tomorrow.

EDIT (12/27/2012) - Here's the corrected drawing for DPDT ON-ON-ON switch:
PmagSw_zps85b8263a.png
 
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Bob,

You will need a 2-10 type switch, ON-ON-ON, see AeroElectric Connection, Chapter 11. Wire it like this:

scan0025_zpsf38c873d.jpg


Use the numbered terminals as shown. I don't have a P Mag but I'm assuming it is set up as shown (the P Mag may be grounded by its case mounted to the engine). If so, you may not have to ground the P Mag. Wired as shown, it should work as you described in your post.
 
John's solution will work with the keyway on the switch facing up.

Pat's solution will work with the keyway on the switch facing down.
 
I am once again deeply thankful for the expertise and willingness to share by members of this forum. Paul, John, and Pat came through quickly. I breadboarded (is that a word?) a quick test and have a workable solution. Thanks guys.
 
Paul, I agree! I know it is Bob Knuckoll's convention to show switches with the keyway up, however, I think there is a case for the other way: one, mechanically the switch toggle works opposite of the internal switches as would seem logical; two, it is often easier to drill the required hole for the anti-rotation keyway on the bottom (especially if you are doing it after the panel is mounted in the airplane--poor planning!). But to each his own! :)
 
Something I forgot to mention on my initial post......I believe when timing the Pmag (Setup Mode), it has to be powered at the same time the P lead is grounded. With your proposed switching, that is not possible. As such, you will have to attach some kind of jumper or other secondary ground to the P Lead when timing the Pmag and then remove it when you are finished.


John
 
I also am confused. This seems way to complex.
I am running two p/e mags on my O-320.
Mags have a key right, left start ACS ignition switch. Both side of the mag have individual circuit breaker and wiring. When I want to test whether they are power independent I just go right mag, pop the right circuit breaker or/and then go repeat on the other side. Added advantage is I have a popped cb staining me in the face.
Simple and it works for me.
 
The fun of this affliction is we get to build it exactly like we want. Besides, I don't have an ignition switch with a key
 
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As John says above, by combining what is usually 2 separate functions [4 binary combinations] into a single 3 position switch, you remove one combination. and also restrict transition between combinations into set paths.

P-Lead....Pwr.......Function

GND.......ON........Testing Mag Drops, Timing
Open......ON........Fly
GND.......Off.......Safe [can use to Test Mag Drops > self sustain RPM]
Open......Off.......Testing Self Sustain

Your switch removes the 1st option, and removes the ability to go from 2nd to/from 3rd direct.

As an aside, at a guess you introduce 2 operational limitations I can think of:
  1. You cannot test the Mag Drops @ < Self Sustain RPM
  2. If the Self Sustain generator fails, say in 1 P-Mag, one might suggest the aircraft is safe to fly provided the other works. However, you cannot now test the Mag Drop on that P-Mag (adding Pwr with Engine running is not advised on a P-Mag)
I'll leave others to comment on whether this causes potential issues, but would run your idea past Brad as well - he will know better than any hidden pitfalls in your proposal. Or if Brad says fine, go ahead, you have it on probably better authority than any on here you are good to go ;) My personal opinoon is it is a neat idea, with some ingenious wiring suggestions here, but not for me for the above reasons.
 
Decision made and update

An update. I sent diagrams of the switching circuit and then had a phone conversation with the great folks at e-mags. I can?t say enough about the great customer service I received!
Here is the bottom line for my instillation:
It?s safe and it will work
I will need to use a jumper wire for maintenance functions to enter set-up mode
It?s safe
Thank you for all your help and thoughtful feedback
Now on to the next decision?.

P.S. this set-up will not work if you plan to use the e-mag RMSD function. If you don?t know what that is you don?t need it (VERY seldom used).
 
I remain a strong believer in keeping basic controls as simple and conventional as possible, but I am convinced that the ability to remove ships power from the PMag and run on internal power should be a flight option for the pilot. While I would rather see a "conventional" ON/OFF switch for the main user interface (P-lead) and a resettable CB for power (serves double duty as a "test" position), your scheme does allow flight in the internal power (test) mode if you need it.
 
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Just doing some research and found this old thread.

I went a different route and wired mine like this:
Pmag%20wiring%203.jpg


This allows me to do the following for my pre-flight:
pmag%20preflight.jpg
 
Personally I think you are making it too complicated. I plan on using one switch for each pmag power. These switches will normally be on except for when running a test of the pmag. I then plan on using a standard ACS keys witch for the mag kill wires. You can use separate switches instead of the keyswitch if you prefer.

I don't feel the need for an indicator in my simple arrangement but if you wanted one it would be simple to wire up using a dpdt switch for the pmag power switches.
 
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