COMPLETE UPDATE.
With all the greatly appreciated comments from the industry experts, four pages now, I have completely updated and expanded my first attempt to this which I feel is now accurate. This is not for experts but for pilots trying to understand the complicated Generator and Lane situation. Additionally, I want to provide who ever reads this with the best information to avoid confusion.
Here it is updated version 2:
Describe the operation of the Rotax fuel injected generators for normal operation and startup.
The Rotax fuel injected engine has two internal generators. These operate from the flywheel on the back side of the engine opposite the propeller side.
Generator A three wire alternating current goes into regulator A on the fusebox, regulates the power to direct 12 volt and into the fusebox. From the fusebox, power is sent out to each fuel pump and to the Engine Control Unit (ECU). The ECU supplies power to the engine, interprets sensors and controls all engine functions. Alternator A is 12/14 volts DC, 16 amps/about 240 watts, and the ECU/engine and fuel pumps use around 150 watts to run the engine. This power is supplied from the fuse box to the Engine Control Unit (ECU) and fuel pumps.
From Generator A, through the fuse box, to the Engine Control Unit (ECU), two separate systems called Lanes, A and B come out of the ECU which operate two completely separate systems/lanes. These separate Lane systems have two separate sets of spark plugs, two separate sets fuel injector valves, two separate manifold pressure readings, and two separate air manifold air inlet temperature probes, etc.. Additionally, shared feedback sensors (for ambient pressure/temperature, throttle position, engine speed/position, EGT) are additionally fed back to the ECU. All the feedback information to the ECU allows the ECU to adjust the spark advance and fuel injected mixture for the engine for optimum operation. In summary, for normal operation, all engine electrical power, operation and fuel pump power is from Generator A, using Lane A and B as separate systems.
The second Generator B three wire alternating current goes into regulator B on the fusebox, regulates the power to direct 12 volt and into the fusebox. Generator B has about twice the power output of Generator A. Generator B output is 30 amps/about 420 watts output. Generator B powers/charges the battery, main electric buss thus airframe power systems. Typically, the master switch, sometimes with a relay, powers the main aircraft power buss from the battery. This airframe buss supplies the panel, avionics, lights, autopilot and all aircraft electric systems (minus the engine and fuel pumps powered by Generator A). In summary for normal operation, Generator B powers the battery and airframe electrical system (minus the engine which is powered by Generator A).
Typically, before you start the aircraft, with the master on, you should be reading airframe battery voltage which should be around 12. 5 volts. When you start the engine, the starting sequence is to connect the battery to the Engine Management System (EMS)/ECU with the “Start Power” switch which should be momentary and hit the starter to engage and turn the engine. This engine rotation activates generator B to provide power to start the engine. Immediately after the engin starts, not just the propeller rotates, immediately release the start power switch and starter engage switch. Now Generator B is powering/feeding the engine EMS/ECU/fuel pumps. After the engine starts, MAKE SURE to disconnect the Start Power/battery connect switch from the EMS/ECU/fuel pumps. Typically this is a momentary switch so releasing everything accomplishes this. Your airframe/panel/buss voltage is still reading battery voltage, about 12.5 volts since Generator B is running the engine and not charging the battery. In this phase of starting you are simply checking the operation of Generator B as it runs the engine. You increase the RPM to 2500 for five seconds which tells the ECU to switch the engine power to Generator A, and now Generator B connects to the battery so you should read above 13 volts indicating your battery is being charged by Generator B. Simply, a charged battery is about 12.5 volts and when ther battery is being charged the charging voltage is 13.5 volts. Note the engine has gone through a sequence to check Generator B first and Generator A during startup. Now it is in normal operation. Generator A feeding the engine/fuel pumps, Generator B feeding the battery/airframe. Both the temporary start power and ECU backup switches should be turned off so everything is fed with the generators. Since the Generator B is feeding/charging the battery the system voltage should read about 13.5 volts.
It should be noted that the fuel injected Rotax likes a little throttle to start, well above low idle for initial startup, about 2200 RPM is a guideline that can be marked on the throttle lever.
Too summarize so there is no misunderstanding, during normal operation, Generator A provides the power to run the engine including both Lane A and Lane B. Generator B supplies the power to run the airframe (minus engine/fuel pumps) and charge the battery.
Describe the generator failure modes of the Rotax fuel injected generators?
Overall strategy: In any case if you suspect and/or have a generator failure, indicated by decreasing panel voltage, at or below 12.5 volts, you should turn off all non-essential items such as lights and other systems with minimum radio transmissions to minimize draining your battery. Some modern Electronic Flight/Engine Information Systems (EFIS) systems have backup batteries if your electric system fails.
If generator A fails, the ECU recognizes this failure and commends the fuse box relay to immediately and automatically feed the power from Generator B to the output/system of Generator A at the fuse box output. This way the fuel pumps and the engine/ECU now have power and the engine keeps running on Lane B. Both Lane A and Lane B lights will start blinking as immediate warning there is this specific problem. Now with Generator B power diverted to the Engine/ECU and fuel pumps, to run the engine, there is no power going to the battery/airframe so the airframe system must run off the battery and the battery voltage should be 12.5 volts since it is not being charged and start to decrease from the 12.5 volts as the battery is drained. Some systems can go 30 minutes in this situation but this depends our your aircraft.
If generator B fails, the engine will keep running since it is running off Generator A, but the power to the battery/airframe will not be functioning so this system must run off the battery and the battery voltage should start to decrease from 12.5 volts as the battery is drained. No Lane lights will come on and no warning. Some systems may have a low voltage warning that could be an indication when the battery goes below the programmed low voltage threashold.
Either way, with Generator A or Generator B failing, you will see a reduction in voltage as the lead/acid battery starts getting drained. With the new lighter weight Lithium battery many use, it is said they stay at a reasonably high voltage, rather than slowly dropping voltage, until they drain than a more dramatic drop and they are dead, less warning.
What happens in the remote event that both generators fail at the same time, the engine dies. The battery backup or emergency power stitch, what ever you call it on your aircraft, switch is moved to on and connects the battery to the ECU and fuel pumps and you can start and run the engine directly off the battery rather than the generators. This battery backup or emergency power switch is a third item that can be used to power the engine. Depending on your battery and other loads, the battery might go for 15 to 30 minutes running the engine.
So the battery backup or emergency power stitch connects both generators on the 12 volt side and the battery together in parallel. All are connected as one. If you knew that your generator A failed and you were running the engine on just Generator B, and you see your voltage start to go down, if you turn on the battery backup or emergency power stitch, you connect the generator B with the battery system, you can power your battery and keep it charged. Does generator B have enough power to run the engine, charge the battery and run the airframe/avionics? Probably if you do this right away and the battery voltage has not drained and you have shed most of your loads and minimize radio transmissions. However, this scenario depends on how long you were running off the battery and how discharged it is and your electric load after you shut down essential items such as lights. Note Generator B has significantly more power 30 amps than Generator A 16 amps. It has been known that connecting all three sources with the emergency power switch is not advised since there have been some known cases of both generators failing running with the ECU backup switch turned on, so this is not advised.
If Generator B fails, and you turn on the battery backup or emergency power stitch, then that could be a bigger problem since Generator A does not have that much excess power to power the engine and now the additional load to charge the battery and power the aircraft. So with Generator A failing (both Lane lights blinking), do not use the battery backup or emergency power stitch to charge the battery. The last thing you want to do is not have enough power to keep the engine running and/or burn out both generators.
For most situations, simply running the battery out, losing your panel, instruments, communications, airspeed, altitude, etc… and keeping that engine running is the best option. If you were trained properly as a pilot, you simply fly the aircraft and land it without any electricity as long as that engine keeps running. Each situation is unique but understanding the generator systems helps make good decisions while flying.
With a fuel injected engine, what is the purpose of the Lanes and the associated Lane lights. What do you do if a lane light starts blinking or comes on solid?
The lanes are two separate systems coming from the Engine Control Unit (ECU) each having 4 spark plugs, four fuel injector nozzles, a manifold pressure sensor, manifold temperature sensor and shared Exhaust Gas Temperature (EGT), ambient temperature/pressure, RPM, engine position sensors. These are two completely separate systems which are called Lane A and Lane B. The aircraft can fly if one system is not operating so it can fly with just one Lane in case one Lane fails in flight. However, for safety/redundancy, both systems are checked to make sure both Lane systems are operational before takeoff so you are flying with two systems for reliability.
On startup, if there are any Lane lights on after 5 seconds, you can reset the Lane by cycling it (turning it off for 5 seconds and back on). If that does not work, shut EVERYTHING down and restart. It is a computer and resetting is sometimes needed just like your computer.
Generally speaking, blinking lane lights indicate some sort of sensor error. Solid lights indicate a more severe system failure.
As an example, if you are doing a long descent at idle in cold weather, the EGT probes in front of the engine have more cold air blowing on them and cool faster than the rear ones. If you continue, the temperature split from the front to the back EGT can get past the alarm level determined by the ECU and give a flashing Lane light, a sensor error. This is irritating since it will stay blinking even after you fix the problem. Giving it some throttle to equalize the EGT probes and resetting the Lane can clear the blinking Lane light. If you were situationally aware as you were descending and saw the EGT’s start to split, you could give it some throttle and avoid the EGT’s splitting and the blinking/warning Lane light coming on in the first place.
Generally, if you are flying and a lane light comes on solid or blinking, you should immediately check engine systems, battery voltage and see if there is anything indicated as to what the problem might be.
Generally, with any solid or blinking light, you can shut that Lane off, wait for 5 seconds and turn it back on and it may clear itself. If it does not, then fly to your airport and figure out what you need to do to clear that light on. Sometimes it is just a loose connection. So, wiggling/pressing on the electric connections may temporarily fix the problem. If the problem persists, you need to down load the data with the Rotax/Buds/dongle and have the information analyzed to find the problem.
