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Magneto toggle switch

hcccs

hcccs

Well Known Member
Does anyone know where I can get a toggle magneto switch like this one? I have searched for one on eBay for several weeks and found nothing. Does these things exist on the market at all or are they vintage items? If only I could find a toggle switch with reasonably long shanks I could make one myself. Anyone ... ??

 
Is there anything special about *that* switch? I may be missing something.. but I just don't see anything obvious there that would make me want that one.. Two regular switches will do just fine..
 
Two toggles and a switch gard and you have it. Nothing special about a switch that makes it suitable for a mag switch. As long as it grounds the P lead when in the off position, you are good.
 
Hans,

That little panel looks pretty neat, and looks like it would be easy to fabricate the guard portion. You could probably adjust the size of the guard to fit most any toggle.

I used standard toggles, and then used guards from Perihelion Design

Here's what mine look like...colored toggle covers, courtesy Stein. The guards are what Perihelion calls the old NASA/X-plane guards, and come it bright aluminum, grey, black and unfinished:

switchesk.jpg


They are $6 a pair. Downside is you have to drill holes for each switchguard, but they work well. Perihelion also has Shuttle Toggle guards that cost $13.99 each, that the toggles would mount through, and thus fix the guard to the panel. They look like this:

spaceshuttleswitchguard.jpg


They also have rocker switch guards that are taller, squared off versions of mine that sell for $9.75 a pair. They are also on that link above.

Just some thoughts and ideas to pass your way.

Cheers,
Bob
 
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Magneto switch

Brantel said:
Two toggles and a switch gard and you have it. Nothing special about a switch that makes it suitable for a mag switch. As long as it grounds the P lead when in the off position, you are good.
Click to expand...

What is overlooked often on a magneto switch is that it is connected across the points, which are across the primary coil. The magneto coil works by a rapid change in the primary current to increase its voltage, and also that of the secondary winding which goes to the plugs. The peak voltage on the secondary is a function of the pressure in the cylinder. At WOT the voltage on the secondary, and on the primary, rise to very high values, so it is important that the switch have a voltage rating which will not arc at this voltage, as this would cause the engine to stumble. Along this same line, since the "P" lead has this high voltage pulse on it, it is important that it be in a shielded wire with the shield terminated at the magneto case and at the switch. The shield should NOT be attached to a metal airframe at the switch as that will cause some of the high frequency components of the "P" lead to flow through the airframe back to the source at the magneto and can radiate those annoying spark 'ticks' into the radio.
 
What would be a good example of a high quality toggle switch that could be used for the mags?
 
stein?

Maybe Stein could answer that question...I'd be interested too as I expect to be using toggle switches for mags too. I have been reading Bob Nuckols book and he discusses this option as well as adding a push button starter instead of a key starter..
 
miyu1975 said:
Maybe Stein could answer that question...I'd be interested too as I expect to be using toggle switches for mags too. I have been reading Bob Nuckols book and he discusses this option as well as adding a push button starter instead of a key starter..
Click to expand...

Mag toggles and pushbutton starter switch per 'Lectric Bob have worked flawlessly on my RV-6 for over ten years.

The only downside to this arrangement is the way it becomes easier to leave the master on when the airplane key isn't on your car key ring......... ;)

High quality switches are available here:

http://www.bandc.biz/electrical-supplies.aspx
 
that is exactly what I've done. Two locking toggles and a push button starter (on the throttle).
 
Mag Switches

Would this switch be acceptable to use for mags?

http://sensing.honeywell.com/index.cfm?ci_id=140301&la_id=1&pr_id=124574

I'm not sure I understand this note that is in the specs. If someone does, could you please explain what this means.

Application Note: Honeywell MICRO SWITCH
does not recommend the use of silver cadmium
oxide switch contacts in non-arcing loads. Non-arcing
loads are generally loads less than 12 volts
and/or 0.5 amp. TS switches use silver cadmium
oxide contacts.
 
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Specs

HT1 said:
Would this switch be acceptable to use for mags?

http://sensing.honeywell.com/index.cfm?ci_id=140301&la_id=1&pr_id=124574

I'm not sure I understand this note that is in the specs. If someone does, could you please explain what this means.

Application Note: Honeywell MICRO SWITCH
does not recommend the use of silver cadmium
oxide switch contacts in non-arcing loads. Non-arcing
loads are generally loads less than 12 volts
and/or 0.5 amp. TS switches use silver cadmium
oxide contacts.
Click to expand...

What they are saying is that you don't want to use silver cadmium oxide switches where the load is a low-level voltage or current signal that can't arc, such as a 5V logic-level signal or triggers to an EI. These contacts require an inductive or higher voltage circuit, since an oxide can form which will keep the contacts from making a low resistance connection. With these contacts you need to maintain enough voltage to break down the oxide layer, or enough current, that with wiring inductance, will cause a sufficient fly-back voltage to occur to again cause breakdown of the oxididation.
 
elippse said:
What they are saying is that you don't want to use silver cadmium oxide switches where the load is a low-level voltage or current signal that can't arc, such as a 5V logic-level signal or triggers to an EI. These contacts require an inductive or higher voltage circuit, since an oxide can form which will keep the contacts from making a low resistance connection. With these contacts you need to maintain enough voltage to break down the oxide layer, or enough current, that with wiring inductance, will cause a sufficient fly-back voltage to occur to again cause breakdown of the oxididation.
Click to expand...

Thanks for the clarification.....That makes sense.

elippse said:
At WOT the voltage on the secondary, and on the primary, rise to very high values, so it is important that the switch have a voltage rating which will not arc at this voltage, as this would cause the engine to stumble.
Click to expand...

So, how do I determine what voltage rating the switch needs to be?
 
Switch votage rating

HT1 said:
So, how do I determine what voltage rating the switch needs to be?
Click to expand...

That's a good question! I know that with the typical automotive coil-condenser-points system that the impedance of the coil circuit was about 60 ohms so that with a coil current of 4A the open-circuit voltage could rise to 240V pk. In a magneto the primary current is a function of the rpm and magnetic field, so that up to a point, the current increases with rpm. You are most likely to have arcing at the switch if at WOT at rated rpm and the plug gap is worn and open more than spec. If I had to make a guesstimate, I would say that if the contacts are rated for 240VAC that you have plenty of margin!
 
Paul - I have great respect for the depth of thought that goes into your posts here. While I would agree with your statements about switch rating for magneto useage, I would also state that using simple MS35059 or AN3027 switches from suppliers such as Spruce will produce a satisfactory result at a cost that is low enough to allow a builder to always keep a spare pair of switches on hand "just in case". Having experienced several ignition swtich failures in "certified" aircraft I can attest that ignition-specific switches often function reliably from an electrical perspective but frequently have some pretty dreadful mechanical shortcomings. Having the key fall out of the ignition switch with the engine running is "entertaining". Even more so when it's a float plane, with the door open, and you look down to see that key vibrating across the cockpit floor toward the open door. Thank goodness for floating keyfobs! *grin*

As a result of these little learning experiences my aircraft P-leads terminate on MS35059 toggle switches, mounted inside homemade Lexan guards. And my toolbox has an assortment of spare switches for that day when I might notice contact degradation on the mag switches. Four years of operation hasn't provided me any reason to second-guess the reliability of these switches. Perhaps a precautionary replacement of one switch (and subsequent dissection of the removed switch to inspect for contact erosion) will be the order of the day at next annual inspection...

Thanks again for making sure this important topic of switch ratings has been brought up for consideration.
 
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