Last night and today I worked on wiring the E-Mag electronic ignition system. The wiring was straightforward, I just followed the installation manual and connected the wires to the plugs, then installed the plugs into the magnetos. The time consuming part was routing the wires, and figuring out where to ground the mags. I ended up using the accessory pad studs as the ground, because items nearby, has easy access, and I’m not planning to install a backup alternator at this stage.
I made the ground wires, routed them, then routed the other wires (power, switch, and tach reading). Once I was happy with the wiring, I trimmed the wires, labeled them, and then installed them into the plug.
The E-Mag magneto uses electronics to time the spark, vs. just a static timing as a traditional mag does. The advantage is that the spark timing can be dynamically adjusted based on manifold pressure (which is determined by throttle position and altitude), for a more efficient fuel burn.
The original electronic magnetos needed a backup power supply to continue to operate in an electrical failure scenario. This model has a built in alternator in each magneto, so it will keep running even if all power is lost, and/or manifold pressure is lost. That makes it way simpler to install, and more reliable.
The wiring includes a power wire to power the electronics from the electrical bus, a switch wire to immobilize the unit when activated, and a complimentary tach output which serves as a tech reading for the Garmin system, then there is a ground wire for local ground to the engine block.
The two ignition switches on the panel each have an “off”, “on” and “test” position. They control the left and right magnetos independently. When “off” the switch grounds the “kill” (lt/rt mag sw) wire, which immobilizes the unit. In that condition it is still “awake” and drawing power from the electrical bus, as long as the battery switch is activated. When the ignition switch is set to “on” the kill wire is ungrounded and the ignition will fire. When set to “test”, the power wire is disconnected. The test is to ensure the unit’s internal alternator runs and provides power to the unit. One important note: the internal power has a minimum RPM setting, something around 1100 RPM, below which the internal power will not function. This has several important implications:
- The engine can’t be started without external (to the E-Mag) power.
- The “test” function before flight should be performed above 1100 RPM, ideally at 1700 RPM. The engine RPM will drop if a magneto is in “test” and RPM is below 1100. The engine will quit if both magnetos are in “test” and RPM is below 1100.
- In an emergency if the battery buss is no longer supplying electrical power, and the engine were to quit for any reason, a restart is only possible if the prop is windmilling above 1100 RPM. An example of this condition could be an alternator failure, followed by a fuel starvation event. If switching tanks were to remedy the fuel starvation, the prop needs to be >1100 RPM for the magnetos to fire.
