E-mag / P-mag

[mahlon_r]

John,
Why not just do the check with the power to the Pags off? That way you check back up electric function and spark plugs, ignition leads, etc all in one check. You do need an active aircraft electrical system to get the engine started, so your check for the aircraft electric system/pmag integrity would be checked by the fact the engine started.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts
are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

[Captain_John]

Originally Posted by mahlon_r

John,
Why not just do the check with the power to the Pags off?

Well, yes indeed!

What I am pondering is where to locate (if at all) the switch for the power lead.

If I make it independently switched, it becomes a possible point of failure.

If I put it on the main bus, I can't check it during runup without shedding the main. This resets the GPS, flight plan, radio programming and ummmm, stuff.

I suppose a PM check would be fine.

Thoughts?

CJ

[mburch]

For what it's worth, Bob Nuckolls the electrical system guru recommends you connect each P-Mag to the main battery bus through a three-position switch: OFF-ON-BAT.

With the switch in the OFF position, the the P-Mag is disconnected from aircraft power. Its orange "switch" lead is also grounded, which disables the ignition module even if the P-Mag's generator is turning.

With the switch in the ON position, the P-Mag is still disconnected from aircraft power, but it is allowed to self-power if the engine is already turning.

With the switch in the BAT, position, the P-Mag is connected to aircraft power and will draw current either from the aircraft's battery bus or from its internal generator, whichever is providing greater output.

So I guess you'd start up with both P-Mags on BAT, then make sure the engine will still run with #1 set to ON and #2 set to OFF, then again with #1 set to OFF and #2 set to ON. That will tell you that both P-Mags' generators are working before takeoff.

Yes each P-Mag has a single point of failure, but you still have what seems to me like an excellent amount of redundancy with a setup like this. (Use a good switch and change it out every X years if you really want to!)

Click here for Bob's recommended diagram.

mcb

[Captain_John]

Hmmmm, That sounds reasonable!

After looking at Bob's diagram and thinking it over... I like it!

One switch with 3 positions for each P-Mag.

Start engine on Bat, Taxi to runup area and...

Brakes set
Mixture full rich
RPM 1,800
Alt Air Check
Exercise Prop (check oil pressure)
Left P-Mag On, then Off (125 RPM max drop) return to Bat
Right P-Mag On, then Off (125 RPM max drop) return to Bat
Max. difference 50 RPM
Pitot on (check amps)
Engine to Idle, then 1,000 RPM
Controls free and correct
Lights, Camera, Action!

Good practices?

CJ

[mburch]

Originally Posted by mburch

Yes each P-Mag has a single point of failure

Actually, I take that back. Each P-Mag has a single point of failure that might prevent it from starting the engine, but unless the switch fails shorted (which seems unlikely to me) then once the engine is running the P-Mags are on the case for good. Pretty cool setup.

I should add that, from looking over the archives of the AeroElectric email list, Nuckolls seems pretty bullish on the P-Mags. That alone is enough to make me seriously consider them, once I get to that stage.

mcb
RV-7, emp done, QB fuse/wings in two weeks

[Davepar]

In order to be in trouble with a dual P-mag system, you would need the following to occur:
Alternator failure AND
Battery failure AND
Both P-mags fail

Seems unlikely. That's what I like about the P-mags. They are independent, self-contained and self-powered (above a certain RPM). Even if one gets completely fried for some reason, the other one should keep going.

I've been fairly conservative on my project, sticking with time-tested stuff. But the P-mags have too many advantages to pass up. Mine should be arriving soon, to be installed on my engine by Mattituck next month.

Dave

[Davepar]

Where's Bob's diagram for the switch? That sounds like a good idea.

[vlittle]

I ended up with conventional mags. I prewired my RV-9A to support emag/pmags in future should I decide to upgrade.

The emagair products were not available due to development delays, and I needed my engine (Aero Sport/Superior O-320 A1AC2 - roller lifters). So, I decided that I'll let someone else be the guinea pig(s), while I use the old, proven technology.

I developed an electrical system design and reviewed it with emagair. They had some tips which were beneficial. Whatever electrical design you choose, have them give it the once-over.

I'm rooting for these guys. In a few years when my mags need rebuilding, I'll give them another look.

Vern Little RV-9A

[N941WR]

Originally Posted by Davepar

In order to be in trouble with a dual P-mag system, you would need the following to occur:
Alternator failure AND
Battery failure AND
Both P-mags fail

Seems unlikely. That's what I like about the P-mags. They are independent, self-contained and self-powered (above a certain RPM). Even if one gets completely fried for some reason, the other one should keep going...

What about a single E-mag/P-mag setup? I don't hear much about that.
It seems with this setup you would have to have two failures before you started gliding. The electrical system and the P-mag would both have to fail. Two failures is what traditional mags require before an engine stoppage.

With a duel P-mag setup you have triple redundancy because both P-mags would have to go down before you did. Is this over kill?

I ask because I'm thinking of using the E-mag/P-mag setup. Which, BTW, is what they recommend. This also makes me wonder if they will stop building the E-mag because most customers seem to be installing duel P-mags.

Thoughts?

[Davepar]

P-mag + E-mag should be perfectly fine. However, the difference in price between a P-mag and an E-mag is "only" $250. Heck, that's like $.50 in airplane-dollars (kind of like dog-years). The other choices for additional redundancy were more hassle (extra battery) or more dollars (like the very pricey B&C SD-8 back-up generator).