Mag Check With E-mag?

[rv7guy2]

I'm on the verge of ordering an EMS system for my RV-7 project and I was wondering how the units detect RPM drops during Mag checks. Do the systems (VM-1000c, AFS 2500, and/or Dynon EMS-120) show the left-right mag drop as would a mechanical tach, or is "special" wiring needed? I take itt the systems use an RPM generator on one of the mags so how do they "read" RPM drop during mag checks?

Dave
C-GCPD..ready to build the panel

[gmcjetpilot]

I'll tell you what I did. I have two electronic ignitions and a GRT EIS 4000 (I recommend for bang for the buck).

To get around the loosing a Tach signal during Mag check (or EI box and spark plug check), I went with a Tach sender on the engines mechanical drive. Its a hall effect unit and sends out a 5v pulse once per rotation (two pulse per crankshaft rotation). It does not matter what the mags or EI's are doing, I always have Tach as long as the engine is rotating and there's power to the sender and EIS. It works and is simple, however cost of a Tach drive is the negative (I recall only about $30-$40).

What I recall about the way other folks did it is they pick directly off only one of the Mags or EI box's as the case may be. They just deal with the loss of tach signal with a "check". Especially with EI, the RPM drop is Nil when you shut the MAG off (if running one Mag one EI). Apparently they go by ear. Not ideal but what the heck.

The other way is wire up switching to flip the Mag or EI Tach signal between left or right. You could sync the switching up with what mag you have selected (or de-selected). I see some relays involved. I have not thought that through but seems doable, however I do not like the complication. Also when it comes to ignition I don't want to go crazy with experimental switching (if there is any chance it could affect the spark makers).

In the end I did not like loosing the Tach signal with single ignition Ops and did not like the complication of switching the Tach signal; therefore I ended up with the mechanical/electro solution (tach sender). I used a UMA sender. I don't care for the one Van's sells, which looks like something off a Bicycle.
G

PS: I got this off Lightspeeds FAQ, and apparently the new Plasma III (A) allows both tach leads to be tied together in parallel:

"13.) Does the Plasma CDI work with my electronic tachometer?

All Plasma CD Ignitions have a pulse output (on the input connector) for an electronic tachometer. The pulse characteristics are shown in the manual and most tachometers will respond to that signal. If you have two Plasma systems and you want to have a tach reading from either Plasma CDI, you need to run the signals through a selector switch.

If you are using Plasma III versions "A" (available after 12/05), you can connect the tach pulses from two systems together to one tach terminal.

Plasma III and Plasma II Plus CD ignitions also have a built in tach which provides a voltage output for a millivolt meter on the output connector. See the wiring diagrams for details."

[penguin]

4 methods

1. Install a switch to swop over which mag drives the tach function
2. Use a tacho sender on the tach drive output from the engine
3. Use an E-mag or P-mag that keeps sending the tach output when the sparks are turned off.
4. Drive from one ignition only and use your ears to compare the mag drop.

Pete

[gmcjetpilot]

Originally Posted by penguin

4 methods

1. Install a switch to swop over which mag drives the tach function
2. Use a tacho sender on the tach drive output from the engine
3. Use an E-mag or P-mag that keeps sending the tach output when the sparks are turned off.
4. Drive from one ignition only and use your ears to compare the mag drop.

Pete

Copy cat George ( you left off dual LS plasma III's)

[penguin]

Sorry George, didn't have time to read everything that you wrote

[Ironflight]

I was worried about the same thing - only reading the RPM on one mag - until I really got thinking hard about it. Over all my years of flying, I have never had a mag check failure that wasn't 100% obvious by listening to the engine. The old "difference of 75 rpm" rule is good, but if you have a fouled plug, you're going to see a whole lot more drop than that, and the missing will be really apparent. I suppose that a subtle mis-timing between mags might be a little less noticable, but since you're going to be flying your own plane, and know what and when the maintenance has been done, you'll probably find that those kinds of problems won't crop up.

You can certainly do the switch thing if you're worried about it, but it's really low on my worry list, based on experience.


Paul

[gmcjetpilot]

Originally Posted by penguin

Sorry George, didn't have time to read everything that you wrote

I understand G

PS I just came across a post about tying two P-leads (dual mags) together with a capacitor? Don't know how that works or if its a good/bad idea. George

[gmcjetpilot]

Originally Posted by Ironflight

I was worried about the same thing - only reading the RPM on one mag - until I really got thinking hard about it. Over all my years of flying, I have never had a mag check failure that wasn't 100% obvious by listening to the engine. The old "difference of 75 rpm" rule is good, but if you have a fouled plug, you're going to see a whole lot more drop than that, and the missing will be really apparent. I suppose that a subtle mis-timing between mags might be a little less noticeable, but since you're going to be flying your own plane, and know what and when the maintenance has been done, you'll probably find that those kinds of problems won't crop up.

You can certainly do the switch thing if you're worried about it, but it's really low on my worry list, based on experience. Paul

I think the most obvious (or NO rpm change) is when you have one Electronic ignition and one regular MAG. Turning the mag off results in no RPM change. So even with out a tach reading, if you go to EI only (Mag off) and you hear any change, than that would be unusual.

Also as you point out, dual traditional Mags is more subtial and having RPM on both Mags is more important to evaluate the quality of the spark for each Mag. I guess you than need to do the switch solution or the solution I mention above.

Some claim that you can tie the two p-leads of traditional mags together and isolate them with a capacitor? Don't know how that works, but it would be nice if it worked. Is there a danger of taking one Mag down with the P-leads tied? I would not do it unless I understood it better. May be some one can explain this idea?

George

[stewartj]

Don't make this so difficult, The VM1000 or 1000c both come with a RPM sensor. The sensor style is determined by the type of mags you are using (slick or bendix). The sensor is installed in ONE magneto. The sensor counts the RPM of the internal working parts of the engine and displays the RPM on the indicator on the panel. A mag check is very simple. As RPM decreases the internal parts RPM decrease and the drop of RPM is shown on the Indicator. No switches, fancy wiring, etc. are necessary. You simply remove the vent plug on the magneto, install the included mag sensor, plug in the two included connectors, and you are finished. The computer does the rest. The only way the system could fail is if... 1- you would lose your battery voltage, 2-the internal gears in the engine broke (causing the mag to stop turning), or 3-a system component failure. I have one mag and one EI on my RV-6A and during runup it works fine. I have 2 mags on my RV-10 with excellent results. I think what is confusing is the fact that the sensor senses the RPM of a gear turning in front of it. When you switch from one mag to the other the mags still turn. The sensor does not care where you have the switch positioned. As long as the gear is rotating in front of it, it will show you the RPM.I hope I have better described this for you. If not I would be happy to try again. GOOD LUCK!!!


John
RV-6A 800 hrs
RV-10 100hrs

[MelJordan]

The Dynon Engine Monitors have two mag inputs, so no switch or other arrangements are needed. The unit will automatically switch between the two as you do the mag check.

Regards,
Mel Jordan
RV-6A Tucson