Lane A/B failure- what is powered by batt?

Hey Jeff - what is the Rotax CAN? Aaron

Hi Aaron,
CAN stands for Controller Area Network, and it’s the two wire network that the Rotax ECU uses to communicate with other components in the system.  If you are using the G3X as your EFIS, then the Rotax CAN is connected to a Garmin GEA24 (engine interface module) to convey instrument and FADEC information to the EFIS. Dynon has a similar architecture with different part numbers.

There is also a separate Rotax maintenance CAN, which is what you use to connect the BUDS dongle and software.  What’s more is the EFIS has its own CAN to communicate with other devices in its network.  Garmin calls these remote devices LRUs (line replaceable units). There are also serial connections to some Garmin components that are not CAN capable.  Complex yes, but this is the stuff that enables all the great features. 

Jeff Blakeslee wrote:

Great comments here by Maximo and Eric.

I would like to add a comment about generator failure notifications.  If generator A fails at any time, you will get a notification via the Rotax CAN to the EFIS. This failure message means that generator A has failed, and the engine has taken generator B. However, if generator B fails, and alternator A is working fine, you won't get a failure notification from the Rotax CAN. Your only notification will be a discharge shown on the airframe amp meter and a declining battery voltage.  If configured, this may cause an alarm on your EFIS.  Simply put, once the engine switches to generator A and assigns generator B to the airframe, the Rotax ECU no longer monitors generator B.  

Jeff,

When either generator fails, are we to assume "get a notification via the Rotax CAN" this would trigger the lane light coming on since that is the purpose on the lane light warning?

I had a suspected generator failure with various problems, traced it from the generator with the guidance from Brett now Advance Powerplant Solutions, back to the fuse box. After trying to mickey mouse around testing the relays, replaced the relays and the problem went away. Anyone know what the three relays do in the fusebox? They obliviously must help in these transfer somehow..... Who does what?

One last question, when you switch on the ECU backup or emergency switch, yes it switches the ECU power/fuel pumps power to the battery but does it disconnect the generator A and B from the battery system? On startup, you connect the battery to the ECU system  but what happens if you leave the ECU backup/emergency switch on or it does not switch back to off once the engine is running?

Paul,

1.  You will not be notified by the Rotax CAN if only generator B fails, provided it has already switched over to the airframe.  You may get an EFIS alarm if you have those set up for amps and/or volts. 

2.  Typically the emergency battery backup switch is used only after a totally failure of both generators…the engine stops and you tie in the battery and restart.  However, if only generator B fails and the airframe electrical bus shows declining voltage, you could use this same switch (or the start power switch) to tie the airframe electrical buss (and battery) to generator A.  (The start switch and emergency power switch do essentially the same thing, but the later bypasses some of the normal lane checks for a faster emergency restart). However, using the switches in this way risks overloading the one generator you still have to run the engine.  So you would need to be careful doing this and reduce the airframe loads to minimum first.  Alternator A is limited to 230 watts, and the engine and fuel pumps use around 150 watts.  Personally, I would not do this.  I would only use the emergency power switch if both alternators failed and the engine quit.  But discussing the possibility gives you a clearer understanding of how it works.  

3.  Yes, the relays in the Rotax Fusebox handle the alternator switching. I think someone posted the exact description of each relay but I don’t remember.