P-Mag installation - Help

[erich weaver]

Originally Posted by rwtalbot

I am happy as long as I can rotate the prop to a position where both P-Mags show a green light at the same time even if it looks like one is very slightly ahead.

I don't understand what this means. How would it "look like one is very slightly ahead"?

Erich

[MississippiJim]

Erich,
I think he means that while slowly rotating the prop by hand to TDC, one mag lights up green very slightly ahead of the other one. I'm sure this could be caused by lash in the gears in the mag drive train, or some magnetic jump as the armature in the built in generator turns, or maybe the sensor resolution? I'm not an expert on this by any means, but it is starting to make sense to me.
I cranked mine again today and ground-ran it. I set the idle speed (very smooth, I might add) down to about 625 rpm. While testing the system with the P-mag power shut off and running on one P-mag only at a time, my engine quit at exactly 800 RPM on each one........good thing to know. This way I know that on my particular airplane, it will self-support right down to 800 RPM.
I hope this helps.
Jim

[erich weaver]

Got it. Thanks

Erich

[N941WR]

What we have discovered during the development of the EICommander is that the gear lash allows the ignition to swing a good bit. This also applies to standard mags, not just P-mags. Because of this, we do not report on any timing discrepancy below two degrees. That coupled with the P-mags timing resolution is probably what caused Jim to display the yellow LED.

Truth is, he probably could have flown that way and not seen a difference and his engine wouldn?t have known the P-mag was off just a bit. However, by bumping the mag just a 1/2 a degree or so allowed both P-mags to display a green LED when at TDC.

I seriously doubt there is any dual magneto setup running as close tolerance as a pair of P-mags. Remember, the P-mags are independent, same as a standard magneto and they will fire at slightly different times, same as a traditional mag.

(Jim, good to hear all is working with your installation!)

[Brantel]

The timing resolution on the P-mag is 1.40625 degrees between steps. This is due to the fact that the hardware/firmware does not truly support floating point and the timing is constrained to 1 byte of data. In practical terms, this is no problem at all. Most other ignitions have no idea what the crank angle is except once or twice per rev. The P-mag knows 256 times per rev where it is.

[N941WR]

Originally Posted by Brantel

The timing resolution on the P-mag is 1.40625 degrees between steps. This is due to the fact that the hardware/firmware does not truly support floating point and the timing is constrained to 1 byte of data. In practical terms, this is no problem at all. Most other ignitions have no idea what the crank angle is except once or twice per rev. The P-mag knows 256 times per rev where it is.

This is correct and is another reason why there is some minor timing differences. Still it is less than with regular mags.

[mfshook62]

You mentioned that you set one Pmag and than the other.

Both of my Pmags are attached to the same MAP tube, so I blow into the tube, and watch both led's to set the timing for both PMags at the same time. Ignition timing for both mags takes less than one minute. Occasionally one led looks orange, but less than a 1 degree prop rotation will turn it green. Next time this happens, I will rotate one PMag to get 2 greens, and see if this improves the timing.