Basic description of Generator and Lane system operation

OK Jeff I think you are saying that if Both Lane lights start blinking, you have lost Generator A since Generator B has moved over to run the engine so in the table you need to  "rely on alternate power supply system" rather than "rely on alternate system" meaning Lane B to A or A to B as all the others read. Yes this makes sense with some speculation. Next chance I get I am going to disconnect Generator A and see what happens, maybe someone has done this? Pretty easy test....

Rotax Wizard wrote:

Hi all, thanks both for bringing this up, many are lost on the logic of the system.  I would like to point out one very real problem we see from time to time with users.  To start the engine most use some type of switch or relay to draw power from the battery for the initial start.  This is because until the engine turns there is no power to fire the spark plugs or injectors.  Once the generators have started to spin (it takes 2 full turns of the crank just for the crank bias to register the correct firing order and sort out the power flow, then we are good to shut off the power from the battery.  The engine is then generating its own energy and independent of the battery.  

The major problem we have in the field is leaving the battery power on once the engine is running and generating power on its own.  If you do this for sustained time it can fail the generators internally, yes both of them.  I have seen this now in at least 2 aircraft and can confirm it was due to the pilot leaving the battery connected in normal flight.  In both cases they decided not to turn off the backup power, they soon found that the only thing keeping them in flight was the battery and it ran until the power was drained in the system.  ( depending on your battery you should get 30 to 45 mins on battery alone if it is the correct size and you do not load it too much) 

Just be sure after engine startup that that switch is not used unless you have a total failure of the generators. 

Cheers

This is interesting, the last 912iS aircraft I bought was down a while since both generators were bad. I could not understand how this could happen. Well maybe this is it.

It has been promoted by some, that if generator A fails and Generator B takes over to turn on the battery feed switch and use Generator B to run the engine and charge the battery to get home rather than let the battery die in 15 to 45 minutes. Any speculation as to how long connecting all three Generator A, B and battery together would burn out the generators and more importantly, why it would burn them out. Maybe if one generator is out this would be OK? Maybe with both generators connected their interaction to each other creates a problem? You do see in my initial thoughts above that any one flying, if trained properly should be able to fly home safely with no instruments so maybe turning on the battery to ECU might not be the best advice? 

I do remember picking up an airplane and figuring out after about 45 minutes of flight that I did not turn off the battery connection...... 

Paul Hamilton wrote:

OK Jeff I think you are saying that if Both Lane lights start blinking, you have lost Generator A since Generator B has moved over to run the engine so in the table you need to  "rely on alternate power supply system" rather than "rely on alternate system" meaning Lane B to A or A to B as all the others read. Yes this makes sense with some speculation. Next chance I get I am going to disconnect Generator A and see what happens, maybe someone has done this? Pretty easy test....

Paul,

If you are going to do that test, I would unplug alternator A before starting the engine. Disconnecting it during operation may cause a voltage spike.  I’ve often thought of doing that, just never got around to it.  

RW
I too am curious about how leaving the start power switch on can burn out the alternators. This would essentially connected the output of the two regulator/rectifiers in parallel, which is not that uncommon in similar systems in order to combine the power output. This connection would be on the DC (rectified) output of the regulator and would also be connected to the battery. All I can think of is that the load may end up being carried more by one generator than the other during low load conditions. So that may load one alternator more and cause the other to shunt more of its power. But with any significant load, the voltage would equalize.  

The 912iS installation manual states:

Load distribution: Due to slightly different output voltages of the regulators (alternator and regulator A/B of the Fuse box) the power is drawn by the generator with the higher output voltage at low load.

I’m not saying that leaving the start power switch can’t damage the alternators, but I’m skeptical and would like to understand why this can happen. Maybe one of our electronics specialists will chime in on this.  

Hi Jeff

I will make an inquiry, however everyone is off until Jan 5th at the factory right now so it may take a few weeks to get some feedback from them.  This question came up a few times in the past few months with some warranty issues and the common thread between the cases was the flights being done with the backup power switches left on and the total failure of the stator as a result.  (engines were almost new and very low hours in new aircraft) The analysis from the factory was the use of the backup power failed the stators.  

In one case the owner thought it was just the fact that his battery was dead so he installed a new battery and did it once more resulting in a emergency landing at about 35 mins after the new battery installation.  One case was a gyro and one was a fixed wing, so 2 different installation types.  

I will ask for more details as to the exact mechanism, how it could occur, when they are back to work.  

Cheers

picture for effect only