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Rotax 912ULS Voltage

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lgold(at)quantum-associat
Guest

Posted: Wed May 20, 2009 10:17 am Post subject: Rotax 912ULS Voltage

I am a sport pilot and don't fly at night, but took my Zenith 701 /Rotax

912ULS up a few evenings ago just to see how hard it would be to land in the

dark. No problem landing, but with all the extra night time stuff on

(strobes, 55watt landing light, & cabin lights) plus my normal stuff

(intercom, 2GPS's, Dynon 180, ICOM radio, transponder, and intercom) the

voltage went down to 11.9 at 3500-rpm and 12.3V at my 4900-rpm cruse. The

blinding low voltage light (from aeroelectric's Z16 diagram, which I used

for my aircraft) came on for the first time and gave me a scare. 

My question; is this low voltage situation normal or do I have voltage

regulation issues? 

Without the extra load during daylight flight my voltage runs about

12.9-13.0 V and my battery holds a 12.8V charge. I don't have an extra

alternator and just use the internal Rotax coils for power. One guy already

told me that what I am getting is the norm with the extra stuff on, and that

the Rotax voltage regulator heats up a lot and should not be expected to

last very long. Are these things true?  

Thanks for your advice.

Les

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 20, 2009 10:56 am Post subject: Rotax 912ULS Voltage

At 01:08 PM 5/20/2009, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Les Goldner" <lgold(at)quantum-associates.com>



 I am a sport pilot and don't fly at night, but took my Zenith 701 /Rotax

 912ULS up a few evenings ago just to see how hard it would be to land in the

 dark. No problem landing, but with all the extra night time stuff on

 (strobes, 55watt landing light, & cabin lights) plus my normal stuff

 (intercom, 2GPS's, Dynon 180, ICOM radio, transponder, and intercom) the

 voltage went down to 11.9 at 3500-rpm and 12.3V at my 4900-rpm cruse. The

 blinding low voltage light (from aeroelectric's Z16 diagram, which I used

 for my aircraft) came on for the first time and gave me a scare. 

 My question; is this low voltage situation normal or do I have voltage

 regulation issues? 	


   If the low votlage light is on (bus less than 13.0 volts)

   then the alternator is not producing sufficient energy to

   carry all of the ship's loads AND maintain a battery.



  	  Quote: 	
		  Without the extra load during daylight flight my voltage runs about

 12.9-13.0 V and my battery holds a 12.8V charge. 	


   This is TOO LOW. No load and engine running should produce

   a bus voltage of 14.0 MINIMUM, 14.2 to 14.4 is better. With

   a 13.0V set-point, your alternator is not replenishing the

   energy used to get the engine started. It's also maintaining

   your battery in a very low state of charge, probably less

   than 50% of capacity.



  	  Quote: 	
		   I don't have an extra

 alternator and just use the internal Rotax coils for power. One guy already

 told me that what I am getting is the norm with the extra stuff on, and that

 the Rotax voltage regulator heats up a lot and should not be expected to

 last very long. Are these things true? 	


   Not quite. That voltage level is too low. You need to

   add up the real current draw for all accessories that

   might be on at the same time. These cannot exceed

   the rating of the alternator (assuming the battery

   is charged) for the operating RPM . . .



 [img]cid:.0[/img]

   . . . and should not be more than 75% of that rating if

   you want the alternator to replenish energy removed

   before cruising flight RPMs are achieved.



   The stock rectifier/regulator is marginal for the

   way we use them. I wish they were a bit more robust.

   It would add very little to the cost of the product.

   John Deere has some single phase rectifier/regulators

   rated in the 30A class. It would be interesting to

   see how well these might substitute for the

   stock regulator.



 

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

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franz(at)lastfrontierheli
Guest

Posted: Wed May 20, 2009 2:20 pm Post subject: Rotax 912ULS Voltage

Hi Bob,

 Could you please help me with a low voltage problem that I am having in my RV7. Voltage indicators on the Dynon and engine monitor both show fluctuations between 12.5V and 11.5V while in flight. This is something that just started during the last few flights, I have 300h on the airplane with this being the first problem. I have had the ND 60A internally regulated  alternator form Vans in the shop and it checked out fine, I also have put in a new battery with no improvements. Airplane wired as per Z11 with an added electronic ignition on the top side

 Thanks for any suggestions you may have

 Franz

 

 

 

 

  [img]cid:3325677364_135572[/img]

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lgold(at)quantum-associat
Guest

Posted: Mon May 25, 2009 9:40 pm Post subject: Rotax 912ULS Voltage

Thank you for the information Bob.

 

   

I am trying to trouble shoot my low voltage problem to determine its cause (i.e.; the regulator, wiring, or the internal engine alternator) so I can take corrective action.  

There is nothing in the Rotax 912 manuals to assist in doing this. I checked the internal engine coil resistance reading and found it to be .7-ohms. The DC voltage at the regulator is the same previously reported (still under 13-volts). Finally I measured AC voltage coming from the coils. The voltage varied as follows:  

Idle   (1900-RPM) was 12.8 volts  

            2500-RPM   was 16.0 v

             3000-RPM   was 19.0 v

             4000-RPM   was 24.5 v

 cruse(5000-RPM)was not measured.  

Bob, Am I correct to think that the AC voltage looks adequate and the problem is likely a faulty Rotax voltage regulator?  

Thanks again for your help.  

Regards,

 Les    

       

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert L. Nuckolls, III

 Sent: Wednesday, May 20, 2009 11:54 AM

 To: aeroelectric-list(at)matronics.com

 Subject: Re: Rotax 912ULS Voltage  

  

  

   

At 01:08 PM 5/20/2009, you wrote:

 

   

--> AeroElectric-List message posted by: "Les Goldner" <lgold(at)quantum-associates.com>

 

 I am a sport pilot and don't fly at night, but took my Zenith 701 /Rotax

 912ULS up a few evenings ago just to see how hard it would be to land in the

 dark. No problem landing, but with all the extra night time stuff on

 (strobes, 55watt landing light, & cabin lights) plus my normal stuff

 (intercom, 2GPS's, Dynon 180, ICOM radio, transponder, and intercom) the

 voltage went down to 11.9 at 3500-rpm and 12.3V at my 4900-rpm cruse. The

 blinding low voltage light (from aeroelectric's Z16 diagram, which I used

 for my aircraft) came on for the first time and gave me a scare. 

 My question; is this low voltage situation normal or do I have voltage

 regulation issues?   



   If the low votlage light is on (bus less than 13.0 volts)

   then the alternator is not producing sufficient energy to

   carry all of the ship's loads AND maintain a battery.

 

 

   

Without the extra load during daylight flight my voltage runs about

 12.9-13.0 V and my battery holds a 12.8V charge.  



   This is TOO LOW. No load and engine running should produce

   a bus voltage of 14.0 MINIMUM, 14.2 to 14.4 is better. With

   a 13.0V set-point, your alternator is not replenishing the

   energy used to get the engine started. It's also maintaining

   your battery in a very low state of charge, probably less

   than 50% of capacity.

 

 

   

 I don't have an extra

 alternator and just use the internal Rotax coils for power. One guy already

 told me that what I am getting is the norm with the extra stuff on, and that

 the Rotax voltage regulator heats up a lot and should not be expected to

 last very long. Are these things true?   



   Not quite. That voltage level is too low. You need to

   add up the real current draw for all accessories that

   might be on at the same time. These cannot exceed

   the rating of the alternator (assuming the battery

   is charged) for the operating RPM . . .

 

 [img]cid:image001.jpg(at)01C9DD87.8BF1C190[/img]

   . . . and should not be more than 75% of that rating if

   you want the alternator to replenish energy removed

   before cruising flight RPMs are achieved.

 

   The stock rectifier/regulator is marginal for the

   way we use them. I wish they were a bit more robust.

   It would add very little to the cost of the product.

   John Deere has some single phase rectifier/regulators

   rated in the 30A class. It would be interesting to

   see how well these might substitute for the

   stock regulator.

 

 

   

       Bob . . .

 

        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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