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Z101 with Rotax 915iS
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m.whiting(at)frontier.com
Guest

Posted: Fri Jun 12, 2020 2:48 pm Post subject: Z101 with Rotax 915iS

This is my first post to the mailing list so hopefully I get it reasonably right.  I am not sure if this best fits this list or the Rotax engine list, but will start here.



For context, I am a retired CS/EE and about to start my first home built project.  My RANS S-21 is scheduled to ship in July.  I plan to use a Rotax 915iS engine and am looking now at electrical system and avionics.



I have read the Connection book and perused some of the newer Z architectures at the web site.  I am leaning towards a Z101 configuration as the baseline, but the problem is that the Rotax comes with only one generator (I know it has two, but I believe the small one is only available to run the engine and not available for shipâ€™s power).  Rotax sells an external alternator kit, but a quick tally of the parts shows the cost to be north of $2,000 and I see nothing yet in the aftermarket.



So, I am curious as to whether anyone here has installed a 915iS and, if so, what electrical system architecture did you choose.  And, is anyone aware of alternative way to add a second alternator/generator to a 915iS or is the Rotax option the only game in town?



My second choice is a second battery to back up the avionics and engine should the unthinkable happen and both alternators fail and the primary battery not have enough reserve to get to a safe landing site.  Iâ€™d much rather have a second alternator than a second battery, but $2,000 seems a little steep for an alternator that likely will never get used and a second battery at least has the advantage of extra starting reserve on our cold winter days in northern PA.



Regards,

Matt Whiting



Sent from my iPad

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Fri Jun 12, 2020 4:19 pm Post subject: Re: Z101 with Rotax 915iS

The Rotax 912iS engine has two generators.

Generator A 16 Amp is for engine only.

Generator B 30 Amp is for aircraft electrical system.

If generator A fails, generator B automatically takes over engine duties,

 but no longer supplies the aircraft electrical system.

If generator B also fails, the pilot may operate a switch to

operate the engine using aircraft battery power.

_________________
Joe Gores

kenryan

Joined: 20 Oct 2009
Posts: 424

Posted: Fri Jun 12, 2020 4:25 pm Post subject: Z101 with Rotax 915iS

It seems to me that, even though it does not allow you to strictly follow the new and improved Z101, the standard Rotax 915iS (two alternatorsÂ + battery) offers good redundancy. What is it about that set up that you find lacking?



Ken





On Fri, Jun 12, 2020 at 2:54 PM Matthew S. Whiting <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Matthew S. Whiting" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>

 

 This is my first post to the mailing list so hopefully I get it reasonably right.Â  I am not sure if this best fits this list or the Rotax engine list, but will start here.

 

 For context, I am a retired CS/EE and about to start my first home built project.Â  My RANS S-21 is scheduled to ship in July.Â  I plan to use a Rotax 915iS engine and am looking now at electrical system and avionics.

 

 I have read the Connection book and perused some of the newer Z architectures at the web site.Â  I am leaning towards a Z101 configuration as the baseline, but the problem is that the Rotax comes with only one generator (I know it has two, but I believe the small one is only available to run the engine and not available for shipâ€™s power).Â  Rotax sells an external alternator kit, but a quick tally of the parts shows the cost to be north of $2,000 and I see nothing yet in the aftermarket.

 

 So, I am curious as to whether anyone here has installed a 915iS and, if so, what electrical system architecture did you choose.Â  And, is anyone aware of alternative way to add a second alternator/generator to a 915iS or is the Rotax option the only game in town?

 

 My second choice is a second battery to back up the avionics and engine should the unthinkable happen and both alternators fail and the primary battery not have enough reserve to get to a safe landing site.Â  Iâ€™d much rather have a second alternator than a second battery, but $2,000 seems a little steep for an alternator that likely will never get used and a second battery at least has the advantage of extra starting reserve on our cold winter days in northern PA.

 

 Regards,

 Matt Whiting

 

 Sent from my iPad

 

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kenryan

Joined: 20 Oct 2009
Posts: 424

Posted: Fri Jun 12, 2020 6:34 pm Post subject: Z101 with Rotax 915iS

All accurate Joe. But I think there is a wrinkle. It is my understanding that if Gen A fails, AND the Emergency Power Switch is closed, THEN Gen B will operate both Engine and power the Bus. At least that's my understanding.



On Fri, Jun 12, 2020 at 4:31 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 The Rotax 912iS engine has two generators.

 Generator A 16 Amp is for engine only.

 Generator B 30 Amp is for aircraft electrical system.

 If generator A fails, generator B automatically takes over engine duties,

 Â but no longer supplies the aircraft electrical system.

 If generator B also fails, the pilot may operate a switch to

 operate the engine using aircraft battery power.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=496806#496806

 

 

 

 

 

 

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m.whiting(at)frontier.com
Guest

Posted: Fri Jun 12, 2020 6:34 pm Post subject: Z101 with Rotax 915iS

Yes, that is my understanding.  My desire though is to have two alternators available for the aircraft electrical system.  The question is: is there an economical way to do that? The Rotax way appears to cost at least $2,000.  Which I probably will suck it up and do if there is no other way as I plan to fly IFR and I like to have good backup not just for a comm radio and transponder, but also pitot heat at least and that generally takes some juice.  Although, I think the Garmin regulated pitot should be a fair bit more efficient unless it is really cold out.



Sent from my iPad



 	  Quote: 	
		   On Jun 12, 2020, at 8:31 PM, user9253 <fransew(at)gmail.com> wrote:

 

 ï»¿

 

 The Rotax 912iS engine has two generators.

 Generator A 16 Amp is for engine only.

 Generator B 30 Amp is for aircraft electrical system.

 If generator A fails, generator B automatically takes over engine duties,

 but no longer supplies the aircraft electrical system.

 If generator B also fails, the pilot may operate a switch to

 operate the engine using aircraft battery power.

 

 --------

 Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jun 13, 2020 4:22 am Post subject: Z101 with Rotax 915iS

At 07:38 PM 6/12/2020, you wrote:

  	  Quote: 	
		  All accurate Joe. But I think there is a wrinkle. It is my understanding that if Gen A fails, AND the Emergency Power Switch is closed, THEN Gen B will operate both Engine and power the Bus. At least that's my understanding. 	


   You need to start your project planning with

   a load analysis: A comparison of system energy

   demands with energy supplies (gen a, gen b, bat a,

   etc) under the various phases of flight (taxi/t-o,

   day vfr cruise, night cruise, ifr cruise, and

   then decide what items will be shut off under

   which failure condition).



   Z101 is NOT applicable to the Rotax. That

   engine's design and energy supplies are pretty

   much cut in stone by the engine manufacturer.

   But your need to quantify and then organize

   your energy requirements is still the same.



   There are examples of load analysis in

   both Excel and paper forms at:



  https://tinyurl.com/9rt6ymn



   You first need to KNOW that there's energy

   available to power up your planned suite

   of electro-whizzies . . . you mentioned

   pitot heat . . . do you plan to poke holes

   in clouds? Each phase of flight has its

   own energy budget.



   The electrical section (24) of the Rotax

   manual is not very clear as to what the engine's

   energy needs are. I didn't find any mention

   of what power (if any) is available from

   the PM alternator-A under alternator-B

   failure conditions. Without that kind of

   information, you're not going to be able

   to define the 'dual alternator' opportunities

   of this engine.

   



 



 

 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jun 13, 2020 4:24 am Post subject: Z101 with Rotax 915iS

At 07:19 PM 6/12/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 The Rotax 912iS engine has two generators.

 Generator A 16 Amp is for engine only.

 Generator B 30 Amp is for aircraft electrical system.

 If generator A fails, generator B automatically takes over engine duties,

  but no longer supplies the aircraft electrical system.

 If generator B also fails, the pilot may operate a switch to

 operate the engine using aircraft battery power. 	


   . . . if the PM alternator fails, engine

   ops revert to the pad mounted alternator

   leaving NO power for other needs?



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sat Jun 13, 2020 8:18 am Post subject: Re: Z101 with Rotax 915iS

Both Generator A and generator B are permanent magnet type integrated with the engine.  The magnets are embedded in the flywheel.  Other than the magnets, there are no moving parts.  The two generators are just two stationary sets of coils.  Generator A is for engine only.  If "A" fails, Generator B will automatically take over engine duties and automatically disconnect from the aircraft electrical system.  However as pointed out in previous posts, the pilot can cheat and flip the backup switch which will reconnect generator B to the aircraft electrical system.  Doing that could jeopardize electrical power that is available to the engine.

  According to above posts, an optional external alternator is available for $2000.

_________________
Joe Gores

kenryan

Joined: 20 Oct 2009
Posts: 424

Posted: Sat Jun 13, 2020 10:13 am Post subject: Z101 with Rotax 915iS

Thanks for confirming Joe, and clarifying that "cheating" opens up the risk of starving the engine of necessary electrical power. While $2k for the THIRD approved (but not certified) alternator is tough to swallow, it's peanuts compared to the $37k price of the engine itself.

I just couldn't believe it when Bob said he couldn't find any info on what the electrical current requirements are for running the engine, so I scoured the Installation, Line Maintenance and Heavy Maintenance manuals and I too couldn't find any information at all in that regard. Pretty hard to make intelligent decisions about important things like best battery size without that essential information. Also, if one is unlucky enough to suffer dual alternator failure, wouldn't it be good to know how long before the engine quits? What is Rotax thinking?

Ken





On Sat, Jun 13, 2020 at 8:27 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 Both Generator A and generator B are permanent magnet type integrated with the engine.Â  The magnets are embedded in the flywheel.Â  Other than the magnets, there are no moving parts.Â  The two generators are just two stationary sets of coils.Â  Generator A is for engine only.Â  If "A" fails, Generator B will automatically take over engine duties and automatically disconnect from the aircraft electrical system.Â  However as pointed out in previous posts, the pilot can cheat and flip the backup switch which will reconnect generator B to the aircraft electrical system.Â  Doing that could jeopardize electrical power that is available to the engine.

 Â  According to above posts, an optional external alternator is available for $2000.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=496818#496818

 

 

 

 

 

 

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 eferrer" target="_blank">http://forums.matronics.com

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ceengland7(at)gmail.com
Guest

Posted: Sat Jun 13, 2020 10:15 am Post subject: Z101 with Rotax 915iS

On Sat, Jun 13, 2020 at 11:48 AM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

 	  Quote: 	
		  On Fri, Jun 12, 2020 at 5:54 PM Matthew S. Whiting <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "Matthew S. Whiting" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>

 

 This is my first post to the mailing list so hopefully I get it reasonably right.Â  I am not sure if this best fits this list or the Rotax engine list, but will start here.

 

 For context, I am a retired CS/EE and about to start my first home built project.Â  My RANS S-21 is scheduled to ship in July.Â  I plan to use a Rotax 915iS engine and am looking now at electrical system and avionics.

 

 I have read the Connection book and perused some of the newer Z architectures at the web site.Â  I am leaning towards a Z101 configuration as the baseline, but the problem is that the Rotax comes with only one generator (I know it has two, but I believe the small one is only available to run the engine and not available for shipâ€™s power).Â  Rotax sells an external alternator kit, but a quick tally of the parts shows the cost to be north of $2,000 and I see nothing yet in the aftermarket.

 

 So, I am curious as to whether anyone here has installed a 915iS and, if so, what electrical system architecture did you choose.Â  And, is anyone aware of alternative way to add a second alternator/generator to a 915iS or is the Rotax option the only game in town?

 

 My second choice is a second battery to back up the avionics and engine should the unthinkable happen and both alternators fail and the primary battery not have enough reserve to get to a safe landing site.Â  Iâ€™d much rather have a second alternator than a second battery, but $2,000 seems a little steep for an alternator that likely will never get used and a second battery at least has the advantage of extra starting reserve on our cold winter days in northern PA.

 

 Regards,

 Matt Whiting 	
Have you been able to take a close look at the hi-$ Rotax option? If it's a belt driven alternator, then the only high barrier to rolling your own might be the flywheel pulley. Brackets aren't that difficult to fabricate, and an alternator is an alternator. Integrating it into the a/c systems should be a simple matter of consulting an appropriate Z diagram here. Â 

Charlie





	
Followup; if this is the right option, looks like you could buy all the Rotax drive & mounting bits, and still save about $1000 on the alternator itself, by using an off the shelf automotive model. The image in that parts breakout looks like a very common Nippon Denso internally regulated alternator that's available in output levels from around 35A to over 55A. They're all basically the same external dimensions.

Charlie

ceengland7(at)gmail.com
Guest

Posted: Sat Jun 13, 2020 10:17 am Post subject: Z101 with Rotax 915iS

On Fri, Jun 12, 2020 at 5:54 PM Matthew S. Whiting <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "Matthew S. Whiting" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>

 

 This is my first post to the mailing list so hopefully I get it reasonably right.Â  I am not sure if this best fits this list or the Rotax engine list, but will start here.

 

 For context, I am a retired CS/EE and about to start my first home built project.Â  My RANS S-21 is scheduled to ship in July.Â  I plan to use a Rotax 915iS engine and am looking now at electrical system and avionics.

 

 I have read the Connection book and perused some of the newer Z architectures at the web site.Â  I am leaning towards a Z101 configuration as the baseline, but the problem is that the Rotax comes with only one generator (I know it has two, but I believe the small one is only available to run the engine and not available for shipâ€™s power).Â  Rotax sells an external alternator kit, but a quick tally of the parts shows the cost to be north of $2,000 and I see nothing yet in the aftermarket.

 

 So, I am curious as to whether anyone here has installed a 915iS and, if so, what electrical system architecture did you choose.Â  And, is anyone aware of alternative way to add a second alternator/generator to a 915iS or is the Rotax option the only game in town?

 

 My second choice is a second battery to back up the avionics and engine should the unthinkable happen and both alternators fail and the primary battery not have enough reserve to get to a safe landing site.Â  Iâ€™d much rather have a second alternator than a second battery, but $2,000 seems a little steep for an alternator that likely will never get used and a second battery at least has the advantage of extra starting reserve on our cold winter days in northern PA.

 

 Regards,

 Matt Whiting 	
Have you been able to take a close look at the hi-$ Rotax option? If it's a belt driven alternator, then the only high barrier to rolling your own might be the flywheel pulley. Brackets aren't that difficult to fabricate, and an alternator is an alternator. Integrating it into the a/c systems should be a simple matter of consulting an appropriate Z diagram here. Â 

Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jun 13, 2020 6:42 pm Post subject: Z101 with Rotax 915iS

 	  Quote: 	
		  On Sat, Jun 13, 2020 at 8:27 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

  Both Generator A and generator B are permanent magnet type integrated with the engine.Â  The magnets are embedded in the flywheel.Â  Other than the magnets, there are no moving parts.Â  The two generators are just two stationary sets of coils.Â  Generator A is for engine only. 	
 

   They managed to squeeze a pretty healthy set of

   stators in there! Would be interesting to see the

   maintenance/overhaul data on those parts . . . but

   unable to locate same in documents downloaded so

   far.



   If generator-B is un-dedicated except in case of

   emergency, then it just MIGHT fold into a variant

   of Z101/8 sans engine bus . . .



 	  Quote: 	
		    Â  According to above posts, an optional external alternator is available for $2000. 	
 

   Hmmm . . . wonder if its the same AND20000 drive pad common

   to vacuum pumps like the on the 912/914 engines. If so,

   the B&C pad-mounted alternators may well perform well

   there for perhaps less money. You guys need to talk

   to B&C (at) 316-283-8000 for confirmation/denial of

   compatibility.



   The Rotax documents are organized in ATA100 (Air

   Transport Association Spec 100) which speaks to

   subjects, formatting, language (many readers will

   not have English as their first language) and

   clarity of explanations.



   I've written numerous pages and sometimes whole

   sections destined to publish in a ATA100 documents

   intended for world wide consumption in the aviation

   disciplines. If I had submitted a work along the

   lines of section 24 of the Rotax installation

   manual, I think I would have reason to fear

   for my ongoing employment.



   After having read the thing a couple of times,

   I don't think I've got any more information about

   this engine's operations than I would get

   from their 4-color, marketing brochure.



   The wiring diagram is . . . well . . . I

   spent the day on the road and I need to UNwind . . .



   If these guys are aviation systems integrators,

   you sure couldn't tell it by their documentation.



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sun Jun 14, 2020 6:43 am Post subject: Re: Z101 with Rotax 915iS

Bob,

I agree that the Rotax documentation needs improving.

Something is lost in translation.

Here is a link to the Rotax iS engine heavy maintenance manual.

https://www.rotax-owner.com/pdf/MMH_915iASeries_ED0_R1.pdf

Section 24-20-00 page 6 says,

 "The two 3-phase AC generators are physically separate power supplies which are integrated in the engine."

But then in section 71-00-00 page 11 is says, 

"Integrated generator Permanent Magnet single-phase generator".  

So which is it, 3 phase or single phase.  Looking at the picture of cable plugs, 

there are 3 wires, so it could be 3 phase.  It looks like there are approximately 25 coils.

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sun Jun 14, 2020 6:48 am Post subject: Re: Z101 with Rotax 915iS

Oops, my mistake. The link I posted above is for the 915 engine, not the 912.

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sun Jun 14, 2020 7:50 am Post subject: Re: Z101 with Rotax 915iS

Here is the correct link to the 912iS heavy maintenance manual:

https://www.cps-parts.com/cps/pdf/d05973.pdf

It also has conflicting descriptions of the integrated alternator.

Section 24-20-00 Page 5 says three phase.

Section 71-00-00 Page 11 says single phase.

_________________
Joe Gores

m.whiting(at)frontier.com
Guest

Posted: Wed Jun 17, 2020 4:29 am Post subject: Z101 with Rotax 915iS

Yes, exactly what I was looking at.  I would probably spring a few hundred more for a B&C unit, but I suspect a car one would do the job as a second alternator.  I am attending the Lockwood installation course in August, assuming covid doesnâ€™t return and kill it, so I will know more then and be able to ask some questions, but it looks very doable with the Rotax pulley and mounting rings.  Although those pieces alone are about $1,000 as I recall.  Crazy expensive, but then I own a BMW motorcycle so I am used to parts that cost 3X what they should.  



Matt



 	  Quote: 	
		  On Jun 17, 2020, at 5:13 AM, Charlie England <ceengland7(at)gmail.com> wrote:

 	  Quote: 	
		  

	
Followup; if this is the right option, looks like you could buy all the Rotax drive & mounting bits, and still save about $1000 on the alternator itself, by using an off the shelf automotive model. The image in that parts breakout looks like a very common Nippon Denso internally regulated alternator that's available in output levels from around 35A to over 55A. They're all basically the same external dimensions.

Charlie

m.whiting(at)frontier.com
Guest

Posted: Wed Jun 17, 2020 5:31 am Post subject: Z101 with Rotax 915iS

I believe Joe is correct and this is the reason I desire an external alternator.  Even though the 915 has two alternators, it effectively only has one from the perspective of shipâ€™s power.  From page 3 of the Appendix to the Rotax 915iS installation manual.



â€œEngagement of the backup power supply system Generator B is done by the Engine Control Unit (ECU) in the case of over voltage and under voltage. If the voltage of power supply system Generator A decreases signifi- cantly or at all, the control transition of the power supplies is additionally done per mechanical means (relays drop out). These mechanism allow engagement of backup power supply under every probable circumstance.



If power supply system Generator B is used to supply the aircraft electrical system (possible in common opera- tion mode) it must be noted that in case of failure this power supply system B is disconnected from the aircraft to serve as the backup to the EMS.â€œ

 	  Quote: 	
		   On Jun 17, 2020, at 5:15 AM, Ken Ryan <keninalaska(at)gmail.com> wrote:

 

 ï»¿

 All accurate Joe. But I think there is a wrinkle. It is my understanding that if Gen A fails, AND the Emergency Power Switch is closed, THEN Gen B will operate both Engine and power the Bus. At least that's my understanding.

echristley(at)att.net
Guest

Posted: Wed Jun 17, 2020 8:36 am Post subject: Z101 with Rotax 915iS

$1,000?!  For a pulley and some brackets?

For those prices, you could have a machine shop design and custom build the pieces.  Does no on in your EAA chapter own a lathe?  No one around you does aluminum casting?



I mean, c'mon Rotax.  I understand you've got to make a profit.  But, you don't have to make it all off of one sale.



                  

                                                                    On Wednesday, June 17, 2020, 8:30:21 AM EDT, Matthew S. Whiting <m.whiting(at)frontier.com> wrote:                 

                 



                 



                 Yes, exactly what I was looking at.  I would probably spring a few hundred more for a B&C unit, but I suspect a car one would do the job as a second alternator.  I am attending the Lockwood installation course in August, assuming covid doesnâ€™t return and kill it, so I will know more then and be able to ask some questions, but it looks very doable with the Rotax pulley and mounting rings.  Although those pieces alone are about $1,000 as I recall.  Crazy expensive, but then I own a BMW motorcycle so I am used to parts that cost 3X what they should.  



Matt



 	  Quote: 	
		  On Jun 17, 2020, at 5:13 AM, Charlie England <ceengland7(at)gmail.com> wrote:

 	  Quote: 	
		  

	
Followup; if this is the right option, looks like you could buy all the Rotax drive & mounting bits, and still save about $1000 on the alternator itself, by using an off the shelf automotive model. The image in that parts breakout looks like a very common Nippon Denso internally regulated alternator that's available in output levels from around 35A to over 55A. They're all basically the same external dimensions.

Charlie

kenryan

Joined: 20 Oct 2009
Posts: 424

Posted: Wed Jun 17, 2020 12:30 pm Post subject: Z101 with Rotax 915iS

If Gen A fails, the ECU will disconnect Gen B from the charging system (battery) and connect it to essential engine loads. Rotax does not want you to do it, but if you then close the Emergency Power switch, Gen B will also be re-connected to the charging system. In this condition, it would be possible to load the generator to the point where voltage drops to a level where the essential engine equipment fails. Because Rotax does not publish how much current the engine requires, it is difficult to determine what is safely available for running non-engine equipment.

On Wed, Jun 17, 2020 at 5:37 AM Matthew S. Whiting <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "Matthew S. Whiting" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>

 I believe Joe is correct and this is the reason I desire an external alternator.Â  Even though the 915 has two alternators, it effectively only has one from the perspective of shipâ€™s power.Â  From page 3 of the Appendix to the Rotax 915iS installation manual.

 â€œEngagement of the backup power supply system Generator B is done by the Engine Control Unit (ECU) in the case of over voltage and under voltage. If the voltage of power supply system Generator A decreases signifi- cantly or at all, the control transition of the power supplies is additionally done per mechanical means (relays drop out). These mechanism allow engagement of backup power supply under every probable circumstance.

 If power supply system Generator B is used to supply the aircraft electrical system (possible in common opera- tion mode) it must be noted that in case of failure this power supply system B is disconnected from the aircraft to serve as the backup to the EMS.â€œ

 > On Jun 17, 2020, at 5:15 AM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

 > 

 > ï»¿

 > All accurate Joe. But I think there is a wrinkle. It is my understanding that if Gen A fails, AND the Emergency Power Switch is closed, THEN Gen B will operate both Engine and power the Bus. At least that's my understanding.

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Posted: Wed Jun 17, 2020 2:32 pm Post subject: Z101 with Rotax 915iS

They don't publish how much the engine requires, but would it be difficult to insert a meter between the generator and the engine bus?



    On Wednesday, June 17, 2020, 4:31:44 PM EDT, Ken Ryan <keninalaska(at)gmail.com> wrote:  

 

 If Gen A fails, the ECU will disconnect Gen B from the charging system (battery) and connect it to essential engine loads. Rotax does not want you to do it, but if you then close the Emergency Power switch, Gen B will also be re-connected to the charging system. In this condition, it would be possible to load the generator to the point where voltage drops to a level where the essential engine equipment fails. Because Rotax does not publish how much current the engine requires, it is difficult to determine what is safely available for running non-engine equipment.

On Wed, Jun 17, 2020 at 5:37 AM Matthew S. Whiting <m.whiting(at)frontier.com> wrote:






I believe Joe is correct and this is the reason I desire an external alternator.Â  Even though the 915 has two alternators, it effectively only has one from the perspective of shipâ€™s power.Â  From page 3 of the Appendix to the Rotax 915iS installation manual.



â€œEngagement of the backup power supply system Generator B is done by the Engine Control Unit (ECU) in the case of over voltage and under voltage. If the voltage of power supply system Generator A decreases signifi- cantly or at all, the control transition of the power supplies is additionally done per mechanical means (relays drop out). These mechanism allow engagement of backup power supply under every probable circumstance.



If power supply system Generator B is used to supply the aircraft electrical system (possible in common opera- tion mode) it must be noted that in case of failure this power supply system B is disconnected from the aircraft to serve as the backup to the EMS.â€œ

[quote] On Jun 17, 2020, at 5:15 AM, Ken Ryan <keninalaska(at)gmail.com> wrote:

 

 ï»¿

 All accurate Joe. But I think there is a wrinkle. It is my understanding that if Gen A fails, AND the Emergency Power Switch is closed, THEN Gen B will operate both Engine and power the Bus. At least that's my understanding

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