Question re: Gen 1 failure

When Gen A Fails, Gen B is commandeered to power the ECU Bus to allow the engine to continue to operate.
This removes Gen B from the Airframe Bus and the house loads are then all dependent on the Battery for power.

Gen B has ~3X the ampacity that Gen A did.  So, While Ben B can easily power the ECU, it has a lot of capacity going unused.

The Sling POH Instruction is covertly referring to the backdoor procedure that makes it possible to reattach Gen B to the Airframe Bus - - - with Conditions.

The BACKUP Power switch connects the AIrframe Bus directly to the ECU Bus allowing the Battery to power the ECU in the event of a DUAL Gen Failure.
However, this connection works in Both Directions.

It allows the surplus power available from Gen B to be used to Power the Airframe Bus and "Maintain" the battery charge.
After reducing any unnecessary electrical loads from the Airframe Bus, the BACKUP Power Switch can be activated.
NAV Light, Strobes, Landing Lights, and other equipment not essential to flight and should be turned OFF.
It is important that if you are going to utilize BACKUP Power in reverse, you do it soon after GEN A fails.
If you delay, and the battery becomes significantly depleted, it is possible to overtax GEN B in the attempt to "Recharge" the Battery.
Lightly Charging and "Maintaining" a fully charged battery is possible.
Trying to recharge a nearly dead battery that you have been draining for a half-hour will be a problem,

Thanks Bill!

Can I please ask a question @Bill

Do you know how the ECU Backup Switch works in the Sling TSI. I want to know if it is switched on all the time if the engine ECU unit will report to the EFIS in the plane if Gen1 and Gen2 both go off. Or on a much worse note, if nothing happens at all, and you fly the plane unbeknownst to the pilot and then the battery dies 30 minutes later and then you have more problems.

In the Sling TSi owners manual, it states to switch off the ECU Backup after the engine is on, but I am merely asking because I wish to understand what the ECU backup switch does and how it works with the EFIS and batteries in the plane.

Thank you!

The BACKUP Switch connects the Battery directly to the ECU Master Bus.
It should NEVER be ON unless you are dealing with a Generator Failure.
It is the Backup Power supply of Last choice.
If the Backup switch is ON and the plane has no problem, The A and B Generators and the Battery will ALL be in parallel.

I can not comment with any certainty if the Lane warning Lights would illuminate.
Easy enough to test.
Turn ON the BACKUP Switch and then unplug the Generators.
What happens?

And Yes!, If you had no lane lights, the first warning would be 30 minutes later when the engine stopped.
On a positive note, you will be the first person EVER to have a double Generator Failure.
Go worry about something else ... and always keep the BACKUP Switch OFF !!!

The START Power Switch should be used for Starting the engine.
The START Power Switch should be turned OFF after starting.
If it remains ON During a normal Flight,  there will be No problems.
However, in the event of a crash, if the START Power Switch were still energized. The fuel Pumps would continue to run even after the engine stopped;  Feeding fuel to any fire that may have started.

Will, you asked if you would get a warning on the EFIS if Gen1/Gen2 failed. You may want to see this post on the Sling Builder's forum, which included this text from Steve O'Connor of Midwest Panel Builders:

"As for your concern that the Engine ECU will not warn if the 30amp generator fails. Not to worry, the G3X system can alert you to this failure. First of all , by monitoring your volt meter you can see a failure, as your voltage starts to drop below 13.8v you can suspect the system is not properly charging. Also we can set a warning for the ammeter to turn on the master warning light if the battery sees an excessive draw. If the system is working properly the battery shunt should show 0 amps which means the battery is not charging or discharging, as soon as we see a discharge we know you have either exceeded the capacity of the main generator or it’s not charging. A small amp draw is typically from exceeding the capacity and a large amp draw is a sign of complete failure of the generator. Back this up with looking at the voltage reading and you can learn quickly what has happened.

Another thing that could warn you is the back up batteries we install. All of our IFR systems get 2 backup batteries that will power all of the essential avionics. The avionics wired to them are wired as a passthrough and the batteries have logic that if the main bus voltage drops below approximately 11.5V they automatically kick in to keep your avionics running uninterrupted. When this happens the batteries send an alert to the G3X and shows a CAS message on the screen that you are running on the backup batteries."