External Alternator - 2 Reasons why
Posted: Mon Mar 22, 2021 3:05 pm
Hey guys, here are 2 reasons why you may want to consider the optional External Alternator:
1. MINIMIZES AFT CG PROBLEM
For all those of you who have used the Excel Weight & Balance calculation file, you would see the huge benefit it provides. Again, if you want a copy of the Excel Weight & Balance file, shoot me an email (specify Imperial (inches) or Metric version) to mikesejourne@gmail.com.
2. FULL IFR ELECTRICAL LOAD REQUIREMENTS (from Steve OConnor @ Midwest Panel Builders)
"Hi Steve (Steve Wallace) and Mike (myself),
I would be happy to share my thoughts.
First of all, I would definitely opt for the external alternator and especially in your case. We have wired many of these onto Sling 4 aircraft and we are doing one for a TSi builder in Canada because of the extra equipment he plans to put into his plane.
When we do an electrical load analysis for our typical 2 screen advanced IFR system with lighting and a heated pitot, not only do we exceed the 80% that is required by the FAA in certified aircraft but we exceed the 30amps available from the Rotax generator. Having said that most people will not fly with the pitot on for real long periods and if they do, they are in a cloud and can shed some load by turning off their lights such as strobes since they won’t be seen anyway. This juggling act keeps them from drawing on the battery.
However, I would not bypass the 30 amp alternator. I would use it in conjunction and actually wire the external alternator to be optional by switching the field. You use it if needed such as the loss of your 30 amp generator or if your loads exceed 30 amps. After all you want redundancy and wiring them to work together will do just that. Also the generators in the Rotax system need to be used as the stored amperage in them can actually do harm if not being used. This is the reason we use the Rotax 30amp first and only use the alternator as needed.
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.
As for weight and balance. I think it will be negligeable as the external alternators are rather small but it certainly won’t hurt you.
I hope this helps
Steve"
=============================
Food for though....
Cheers!!
1. MINIMIZES AFT CG PROBLEM
For all those of you who have used the Excel Weight & Balance calculation file, you would see the huge benefit it provides. Again, if you want a copy of the Excel Weight & Balance file, shoot me an email (specify Imperial (inches) or Metric version) to mikesejourne@gmail.com.
2. FULL IFR ELECTRICAL LOAD REQUIREMENTS (from Steve OConnor @ Midwest Panel Builders)
"Hi Steve (Steve Wallace) and Mike (myself),
I would be happy to share my thoughts.
First of all, I would definitely opt for the external alternator and especially in your case. We have wired many of these onto Sling 4 aircraft and we are doing one for a TSi builder in Canada because of the extra equipment he plans to put into his plane.
When we do an electrical load analysis for our typical 2 screen advanced IFR system with lighting and a heated pitot, not only do we exceed the 80% that is required by the FAA in certified aircraft but we exceed the 30amps available from the Rotax generator. Having said that most people will not fly with the pitot on for real long periods and if they do, they are in a cloud and can shed some load by turning off their lights such as strobes since they won’t be seen anyway. This juggling act keeps them from drawing on the battery.
However, I would not bypass the 30 amp alternator. I would use it in conjunction and actually wire the external alternator to be optional by switching the field. You use it if needed such as the loss of your 30 amp generator or if your loads exceed 30 amps. After all you want redundancy and wiring them to work together will do just that. Also the generators in the Rotax system need to be used as the stored amperage in them can actually do harm if not being used. This is the reason we use the Rotax 30amp first and only use the alternator as needed.
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.
As for weight and balance. I think it will be negligeable as the external alternators are rather small but it certainly won’t hurt you.
I hope this helps
Steve"
=============================
Food for though....
Cheers!!