Ernest , Todd and Group,
Self contained and redundant
electrical power system that will keep the engine running
without the battery after
start-up...........I presume our planned PM alternators
will keep our
engines running in the event our battery
dies or is switched out of the electrical system ??
What say the more knowledgeable EE
types of the group ??..........
http://www.eaa.org/experimenter/articles/2010-11_revmaster.asp
Accessory Case
This accessory housing package accommodates four items
critical to engine and aircraft operations. It contains
three major operating systems: the dual alternators, the
self-energized ignition source, and the electric starter.
And it also provides the physical mount to the airframe. The
R-2300 model is nearly identical to the proven unit
currently used on the R-2100 (more than 60 of those units
are now in use) and is yet another product made exclusively
by Revmaster. The three electrical subsystems are
independent but function as an integrated unit within one
compact aluminum case. Let’s look at each component
separately for the sake of clarity.
The precision-machined alloy casting fully encloses the
dual 18 ampere alternator package. Mounted to the interior
face is a stationary 12-pole stator ring. An aluminum
flywheel incorporates 12 neodymium iron-boron magnets that
are attached to the interior of the flywheel. These magnets,
the strongest magnets commercially available, rotate around
the 8½-inch-diameter stator. Any movement of the flywheel
sends its magnets orbiting in close proximity to the
stators, with 12 feet each of copper wire windings exciting
the electrons and creating electrical energy. There are two
groups of five alternator coils, each set functioning as an
independent 18 amp alternator. The current generated from
these coils is sent to solid state regulators and then to
the aircraft’s battery and operational power bus. In the
unlikely case of a failure in one system, the other would
remain unaffected.
Ignition
The two coils which make up the ignition power source are
located 180 degrees apart at the 12 and 6 o’clock positions
(see photo above), separating the previously mentioned
five-left and five-right alternator stator coil groups. The
ignition coils are also creating power whenever there’s
rotation of the flywheel, but their energy is dedicated
exclusively to the CDI (capacitor discharge ignition)
package.
The back side of the accessory case, showing the ignition
trigger sensors
A triggering sensor mounted to the center area of the
housing’s interior receives a signal from a device attached
to the end of the crankshaft, acting as the “distributor”
and telling the CDI when to transmit the power to the eight
mini coils which are positioned near the upper and lower
sparkplugs at each combustion chamber. Once the engine has
been started, the battery isn’t necessary to operate the
ignition.
With the accessory case installed, timing the ignition is
next on the list.
The ignition advance is set at a maximum of 25 degrees
before top center. This would normally be identified as a
fixed timing position, but in reality the “effective
advance” behaves as if the low rpm timing is at 15 degrees
BTC (before top dead center- sometimes BTDC). This desirable
situation is created by magnetic precession in the
self-energized design. Lower voltage exists in the system
when the engine is turning slowly, reducing the current flow
at the timing triggers.
The “brains” behind the brawn. Once the timing is set,
the electronics are wired up and bolted in place.
The engine likes 15 degrees BTC for easy starting and
comfortable idle. But as rpm rises so does the voltage and
the ability to “snap” the timing, and the advance moves
quickly to its maximum setting. Experience has proven that
25 degrees BTC, while possibly leaving a few horsepower
untapped, is a smart place to limit the spark advance
because it greatly reduces the possibility of destructive
detonation.