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New single Pmag on an O-320

cojaken

Active Member
I am going to replace the right Slick magneto on the O-320 in my 9A with a Pmag.

I plan to replace the right magneto which only has 120 tach hours on it since new, but is 14 years old and has therefore already exceeded Slick's recently introduced 12 calendar year overhaul requirement.

I chose to replace the right magneto because I wanted to retain the starting capability of the left magneto which has an impulse coupling, in case the Pmag should fail in flight.

I have bought a Klixon 3 amp circuit breaker/switch to put in the power supply line to the Pmag, to function as both the circuit breaker and test switch.

I plan to wire a DB9 female plug in the cockpit to enable use of the EICAD program to customize the B curve to set the Max RPM to 2816 since my fixed pitch prop is limited to 2600, the Advance Shift to -1.4 degrees and the Max Advance to 33.6

I am about to order the Pmag, HT leads, plug adapters and plugs, and would be grateful for any constructive criticism of my plan so far.
 
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O-360 Pmag on the right

Your set up is just like mine, except I put in a second toggle switch to handle the test function. I mounted the test switch just below the P-lead switch for the P-Mag.
 
I was kind of thinking about a single three position mag switch .....Off-On-(On) where the last position is spring loaded and removes ship power from the P-mag. Switches are lighter and cheaper than a CB, and the CB life cycle of CB that gets cycled often is a consideration to me.
 
The cb/switch I chose is a Klixon 7270-1-3

The left Slick also has 120 hours on it and is 14 years old. I am not intending to overhaul it at this time, but maybe replace it with a Pmag next year.
 
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I was kind of thinking about a single three position mag switch .....Off-On-(On) where the last position is spring loaded and removes ship power from the P-mag. Switches are lighter and cheaper than a CB, and the CB life cycle of CB that gets cycled often is a consideration to me.

I like this idea of the spring loaded switch!

My only concern is that I like to have all switches in the UP position when on/operation. From a visual standpoint / ergonomics it is a better to have all switches in the same UP position so that at a quick glance, you know they are on. That said, I have caught myself flying with one switch in the middle position, which for me is Ungrounded and Unpowered (running off of the P-mag's internal generator). So, maybe the spring loaded switch is the better option.

With regard of using a pullable breaker for your test switch, they really aren't designed for that. I would either add a switchable breaker or a three position switch, as discussed.

If you have a key switch, your other option is to put a push button switch that drops the power to the P-mag when pressed. You can position that pushbutton switch close to your key switch, so you aren't moving your hand all around your panel.
 
3 position switch ?

Where does the spring loaded 3 position switch come from ? Bill makes an excellent point about regarding ?UP means GO?. I am faced with the same dilemma because killing master power to check Pmags screwed up some tach time in my electronic device. One more contact , whether in a switch or a NC button IS another failure point. I am voting for the button.
 
Three position switches OFF/ON/(ON)

I have this exact setup with my dual p-mags on my -4. I have two DP three position switches. Off/ON/(ON). They also have a lockout between the on and off position so that I can?t inadvertently turn them off and it forces me to pull the levers up to put them in the off position.

So, my normal opinion is to flip both switches up to the middle/on position and then start the engine. Then, while idling, pull one lever up and put it in the down/off position while leaving the other switch in the middle/on position. I do this maneuver to both switches and this is to confirm ship power.

Then, with both switches back in the middle position, I bring up the engines RPM?s. I then pull one lever up and pull it down to place it in the off position and then push the other switch up into the up momentary position. This operation checks the self generating power of the p-mag. I do this to both switches and this confirms that both p-mags are making their own power.

So, with two, three position switches, with a lockout and a momentary position, I can do my full p-mag check in about ten seconds and it?s impossible for me to inadvertently kill the power while in flight. Oh, BTW, I also have the same three position switch for the main power/starter....OFF/ON/(ON). This is a very simple and efficient setup.
 
What you don't want to do is set up your P-mag switches (no one on this thread has suggested it, but I have run into it before) as Test-Off-Run. With that setup you have to pass through Off to perform your check.

With one ignition grounded and the other temporarily being grounded (shut off) as you move to the Test position, unburned fuel will be pumped into the exhaust for the few milliseconds that both ignitions are off. When the one ignition comes back online, the unburned fuel in the exhaust will light off with a bang!
 
A 14 year old Slick mag is definitely an item of concern. Mine were manufactured in 2005. Prior to our first flight in 2017 I pulled the left (impulse) mag and sent it out for IRAN. The list of Service Bulletins accomplished on the magneto was as long as your arm. Importantly, the SB for soft carbon brushes was required on this brand new, zero time (but old stock) mag. I was out of pocket more than CAD$500 by the time the Slick impulse mag was back on the engine. Hard to believe a brand new mag needed five hundred bucks worth of repairs as a result of manufacturing / design defects.

I've been in your position and believe I made the wrong choice. If I had it to do over again I would not spend a penny on performing the (necessary) IRAN on your Slick impulse mag. Pull it now, install the second P-Mag, sell the Slick, and never look back.
 
I have this exact setup with my dual p-mags on my -4. I have two DP three position switches. Off/ON/(ON). They also have a lockout between the on and off position so that I can?t inadvertently turn them off and it forces me to pull the levers up to put them in the off position.

Mark, do you have a diagram how these are wired. I'd like to copy this when I wire up my pmag.
 
I was kind of thinking about a single three position mag switch .....Off-On-(On) where the last position is spring loaded and removes ship power from the P-mag. Switches are lighter and cheaper than a CB, and the CB life cycle of CB that gets cycled often is a consideration to me.
Beside the things Bill has mentioned, consider that the three position switch will either require both hands to be involved (one to hold the switch and one to work the p-lead switch) or turn the p-lead to your other mag to off and work the power on your PMAG. Not that this is not doable but I would want my test to be as simple and straight forward as possible.
Here is what I have done, which does not mean is the correct/best way to do it but it has been working well for me.
I have a two position switch (ON-ON) which one leg is connected to the PMAG and the other leg feeds a LED warning light above the switch. The function of the LED is 1- to visually warn me if I have left the switch to OFF for the PMAG, 2- if for any reason my fuse to the PMAG is blown and there is no power on the wire.
 
Mark, do you have a diagram how these are wired. I'd like to copy this when I wire up my pmag.

I don?t have an actual diagram but basically all I?m doing is using the middle (#2) position as ?on?. Then I?m grounding ?killing? the ship/battery power in the (#1) (off position). Then grounding ?killing? the self generating power lead in position (#3)...the momentary position. So here?s the sequence:

1. Flip both switches from the (#1/off) position to the (#2/on) position.

2. Start the engine.

3. At engine idle move one of the switches back down to the #1/off position while leaving the other switch in the #2/on position. This is checking ship/battery for the opposite mag. If the engine keeps running you?ve now confirmed that the engine will run on one mag/ship power on that one particular mag. Repeat this step with the other switch in the off position. You?re now confirmed that the engine will run on each individual mag/ship/battery power.

4. Now, with both switches in the middle (on/run) position, run your RPM?s up to about 1500. Move one of the switches to the (#1/off) position and move the other switch into the (#3/off/momentary) position. You?ve now killed the battery power lead on one mag and kill the p/lead (self generating power) on the other mag. The engine is now running on one mag/self generating power. Now, move both switches back to the middle position and repeat with the opposite switches. You?ve now confirmed that the engine will run one only one mag while generating its owner power...(no ship/battery power).

5. Finally, confirm that both switches are back in the middle/on positions and you?re now ready for flight. It takes less than 10 seconds to perform a complete test.

Like I?d mentioned in my previous post, my switches have a lockout between the #1/off and #2/on positions. This prevents me from inadvertently moving either switch back into the #1/off position. If one or both switches were to accidentally be moved into the #1/off position, it would continue to run just fine while your flying, but when you slow down for landing, and if both switches were in the #1/off position, the engine would die because you?re not generating self power and you?ve killed your battery power. If I were to accidentally bump a switch up into the #3/momentary position while maybe flying through turbulence, it?s not a big deal because it?ll immediately return to the #2/on position on its own. In your case I think you?d said that you?re planning to use only one p/mag, but you?d basically go through the the same sequence to check the one p-mag while killing power to your regular mag.

I hope this helps you out a little bit.
 
Wiring

I wired my P-Mag as their manual suggests with a separate switch. Here is an image of that setup.

118g51e.jpg


It is easy to use and test the P-Mag.
 
The 3 position OFF/ON/(ON) toggle switch is available from Stein. Look for ?Pmag switch?. My two Pmag 3 position toggle switches are guarded with those loop guards, which make them look different than the other similar looking toggle switches on my two row switch panel, so the fact they are standing up in the on position verses forward like the rest of the switches, isn?t unusual looking.
 
Thought ... initial adjusting via EICAD should not be a repetitive thing. Rather than installing a Dsub9 in the cockpit, I?m thinking of making up a harness to be connected directly to the Pmag temporarily when needed.

Comments?
 
I made that harness. Although I could have done two harnesses; one for the P-Mag to D-sub and one a D-sub to the laptop,as I did not intend to change the advance once it was set that seemed a lot of work for a once or twice use.

So I made a long harness to reach the laptop. It works fine.

If I had plans to install EI Commander product I would have run the wires to the panel.
 
I?ve got to the point where I?m ready to time the Pmag. If I understand correctly, it doesn?t matter whether cylinder number one is on the compression or exhaust stroke since the plug fires on both. The timing mark just needs to be on TDC.

Am I correct?
 
Why not wire a three position switch as OFF-ON-ON, with the TEST mode in the middle? That way you move through TEST to ON when starting and running, but can drop to TEST briefly to TEST. If you forget to move back to ON, a glance will show that switch isn't UP along with the others that are UP when ON.
 
Thought ... initial adjusting via EICAD should not be a repetitive thing. Rather than installing a Dsub9 in the cockpit, I?m thinking of making up a harness to be connected directly to the Pmag temporarily when needed.

Comments?

You'll want to leave the harness connected. Mine are just tie wrapped under the cowling for easy access through the oil door. I've adjusted mine a few times for Adv Shift and Max Adv and happy with Adv shift = 0, Max Adv = 33.6 (or was it 32.2?). I wrote the settings down on my laptop at the hangar for future reference.
 
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