P-MAG adapter and tach problem

[Racegunz]

Well, I was one of the first to put a P-mag on a C-85 and now (that engine went south and parted out) since I couldn't stand to have a 1200.00 ignition laying around while my O-235 was using slicks , I milled an adapter to line up the gears E-mag thought it was feesible and even offered to replace my faceplate with a Lycoming model at cost I forged ahead and it works wonderfully, starting is so much nicer and now with no prime! But.....another issue has arisen with my engine monitor (MGL E-1) won't see the tach pulse from the P-mag but still works fine hooked to the p-lead of the right side slick???? MGL says the combo has worked but so far I haven't had success. anyone on here have this combination?

[cub builder]

http://www.mglavionics.com/E1.pdf, page 23 for tach installation. Fromt he drawings, the E1 unit likes to be connected to the switched side of the coil. P-mag doesn't supply you with that. I believe the P-mag can supply switched tach pulses at either 5V TTL level or 12V, so you need to check the setup on the P-mag. While they don't say so in the MGL-E1 set up, you may need to remove the noise filter on the input of your E1 unit. On the EI units, the isolators need to be removed when you switch from using the P-lead on a magneto to the tach signal on a P-mag. The same *MAY* be true for the MGL-E1. You may also want to turn up the sensitivity on your MGL-E1 unit. An email to MGL might also be helpful.

-CubBuilder

[Racegunz]

I know of no "filter" on the E-1, unless you mean the software settings, I've tried every combination, they recommend a 10k resistor if it's hooked to the p-lead ,I've tried it with and with-out, also tried the sensitivity pot. The output from the P-mag is verified at 12vlt but shouldn't matter the e-1 can use from 5-100 vlt pulses so says the manual. I have talked to both manufacturers and the Man at E-mag air told me how to check the wiring and 12 vlt signal circuit and it checked out, MGL has documentation that this combo works with no "special" measures. I am going to borrow the scope from work to verify the square wave at the E-1 is indeed 12 vlts and drops to zero if this checks out then it has to be the E-1. Perplexing! OH I also hooked it up to the primary on the - side of the coil and nothing that really made me think it was/is wiring (my fluke says the grounds are tied togetherthough) and it works on the P-lead??? When it's a little warmer I'll really tear into this.

[Racegunz]

Well I got a scope and the nice square wave pulse measured at the MGL engine monitor's connectors is 12vlts but only 2ms in duration, MGL said 3ms minimum, so problem identified and apparently just isn't going to work.

[WLIU]

If you know how to use a 'scope, do you have other electronics skills? They make chips that easily turn a short pulse into whatever length that you want. Look up the "555". A chip and a couple of resistors maybe on a small "perfboard" in a small box should get the job done if you are so inclined. This can be the educational part of homebuilding......

Best of luck,

Wes
N78PS

[1600vw]

I kinda had the same problem. The seal went bad in my mag. Being this mag was getting old I decided to replace it with a new mag. After installing my new mag my tach would not work. The tach worked just fine before removing the mag.
I eneded up putting a digital tach on my airplane. I never liked the tach hooked to the P-lead anyway. it may not be a problem hooked up that way but I never liked it. I ground that lead to stop the engine, seems to me nothing should be hooked to that lead but the on-off switch.

[Racegunz]

I know how to use the scope (industrial electrician/maintenance) but no electronics engineer here, and I was pretty sure there are many ways to condition the signal. I'm using the P-lead hook up on the Slick mag as I have from the start, works good but someday I want to put electronic ignition on the right side also, before then I'll have a solution. Which tach brand wouldn't work 1600vw? I have had my MGL E-1 working off either of my slick mags before I switched the left side to the P-mag I had laying around.

[WLIU]

From the depths of my hazy middle-aged memory I recall at least one incident where an electronic tach that was connected to the P-leads of both magnetos failed, shorting both mags out and leaving the pilot to try out his glider flying skills. The systems that put a hall effect sensor into one of the mag's side vent ports don't have that failure mode....

Best of luck,

Wes
N78PS

[1600vw]

Racequnz:
That is a 0-3500 rpm Westach
I replaced my Mag with the same brand and style mag that come off my engine. After the mag replacement the tach would worked but would only read about 800 rpm at WOT.

I went with a digital Mini tach. The lead wraps around the sparkplug wire. It works great.

[cub builder]

Sounds like you found the problem. If you can use a scope, you can set up a 555 timer. A web search will get you all the info you need. Radio Shack used to carry them as well as a little booklet that tells you how to configure them. Won't cost but a few bucks to give it a try. Pretty simple to have a 2 ms pulse trigger a longer 4 or 5 ms pulse that should make your tach happy.