RPM off electric ignition

[tps8903]

Hello,

Has anyone tried driving a rpm reading off the trigger side of the secondary coils?

If you have, what was your setup for a MGL RDAC.

Alternately,

Has anyone driven rpm of the p-lead of the fixed ignition?
Again, what was you setup?

I installed a new VR for the Li Ion battery and I am getting weird readings from time to time reading RPM off the AC lead to the VR. Because I have the turbo, and RPM is a secondary indication for me, I'm okay with it turning off for a Mag check if it is accurate the rest of the time.

I contacted tech support, but they haven't tried either of these options and so could not advise.

[Bryan Cotton]

One of the terminals on the VR is grounded. On my instrument I got no signal there. The other one is not grounded and only gets lost below 500 RPM.

Maybe try the other terminal. It could be your instrument is sensitive enough to pick up the noise on the ground side.

[T41pilot]

I'm not using an MGL system but I've had no issues so far taking a tach input off one of my ignition coils and the other tach input off a p-lead for my GRT system. I have an Aerovee with turbo. The series resistors are needed to keep the input more stable.

[pappas]

Chris,

Glad to hear your turbo is running well and within specs. I was reading the traffic over the last couple of weeks.

I used the stock voltage regulator. I had two go bad on me and replaced them with other stock ones. They are the type of regulators that are used on lawnmowers. I believe the Aerovee charging system is a bit of a weak link. They can work but I had to develop an operating protocol. I took my RPM data per the plans from one of the VR leads without a problem.

On my first and second attempted flights with a mile-long taxi to the departure end, by the time the tower released me for departure, I had a dead battery and needed a tow back to the hangar. I finally determined that with all of my electronics, both mags, wig-wags, EFIS, strobes, nav lights, A/P, intercom, Ipad, radio, etc operating, the Aerovee charging system couldn't replace the battery loss caused by all the equipment load during taxi. The Aerovee system doesn't produce any usable charging below about 2300 rpm so everything was running off of the battery until take-off. It would take a long time in flight to replace the charge.

After that, I started getting my preflight ATIS info from a handheld radio prior to engine start. I started the engine on both mags and then shut one down for taxi. I turned the radio on but left the A/P, intercom, strobes, navs, Ipad, and any other electronic device not required for taxi in the off position. After run-up and clearance for departure, I would take the active runway and turn on the second mag and the devices I wanted for the flight immediately prior to applying take-off power. Also, don't run the turbo cooling system at any time other than after landing. Those changes seemed to solve my problem, mostly.

I was always monitoring the electrical system just because I believe it to be less than ideal. Additionally, I always had a charger in the plane and always left the battery charging on the Li-Ion charger when it was in the hangar.

I think Sonex should come up with a better charging solution. They need at least 30 amps available at idle for the Aerovee to be what it should be. Someone machined and installed a pully and bracket where the mag is now and ran a belt to a real alternator. You can find that thread and images on the forum.

Sonex should do something like that because we all put a lot more into these than John Monnet originally imagined. Even though he doesn't like all of the electronics we use in these now, we have changed the way his airplane is used from how he originally imagined it. So, I think, they should do the design changes and make them available to the Adrovee fleet. It is a convenience and safety matter now.

Of course, if you are flying Rotax or another motor with an alternator..... never mind!

Fly safe!

[daleandee]

FWIW, it seems that MGL products in general do not have a very good source input for a tach reading. I have a Corvair and I used several ways to try and get a steady reading and (at the recommendation of a MGL dealer) went through various resistors and different connections ... all to no avail.

Tiny tach anyone?

[Spaceman]

I had issues with getting the RPM from a voltage regulator terminal, so this is what I'm using now. This is totally different and a little bit of a project but it works well!

http://paegelow.blogspot.com/2021/10/rp ... 6.html?m=1