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How does the Ducatti rectifier/regulator work?

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 20, 2014 12:08 pm Post subject: How does the Ducatti rectifier/regulator work?

At 13:51 2014-12-20, you wrote:

 	  Quote: 	

A fellow RV-12 builder asked me this:

 > From the the little that I have read concerning dynamos, they 

 operate at full output all the time as they have no field current 

 controlling them.

 > Does that mean that if one runs the strobes and landing light all 

 the time, the Ducati reg/rectifier will have less heat to dissipate 

 through the cooling fins, and perhaps stay cooler and last longer?

I do not know the answer, thus am asking the experts on the 

AeroElectric List.  How does the Rotax 912 rectifier/regulator 

work?  Does it short out the dynamo output to control voltage?  Or 

does it add a series resistance to drop the output voltage?  Or what?

Thanks, Joe

--------

   Back 'in the day' when pm alternators were first being

   added to small bikes, the electrical output on the order

   of 5 amps did not offer a very challenging energy management

   problem. Earliest regulators simply used an SCR triggered

   on each of the alternator's half-cycle to simply short the

   AC output when the waveform was 'high enough' . . . this

   crude regulation philosophy caused the alternator to operated

   in a max-power-output mode all the time . . . with excess

   power being dissipated in the alternator's windings and

   the SHUNT mode, rectifier/regulator's heat sink.

   As the alternators go bigger and consumer design goals

   for more sophisticated electrical systems grew, there

   was a pretty popular shift to SERIES mode regulation.

   The B&C R/R products have always used this philosophy.

   The Ducatti regulators favored by Rotax were of this

   general design as well . . .

http://aeroelectric.com/Pictures/Regulators/Rotax-Ducati_Rectifier-Regulator.jpg

   There are more modern versions of this design that

   use MOSFET transistors in the power control loop . . .

   designs that dissipate much less power as heat.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 20, 2014 2:21 pm Post subject: How does the Ducatti rectifier/regulator work?

At 13:51 2014-12-20, you wrote:




A fellow RV-12 builder asked me this:



. . . From the the little that I have read concerning dynamos, they 

operate at full output all the time as they have no field current 

controlling them.

   True, FULL output voltage, but not necessarily full

   output POWER. It's the job of the rectifier regulator

   to tailor the wild-frequency, wild-voltage AC into

   some reasonably stable output at the desired voltage.

   Bob . . .

user9253

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

Posted: Sun Dec 21, 2014 8:43 am Post subject: Re: How does the Ducatti rectifier/regulator work?

I assume that the SCRs conduct at low voltage and shut off when the voltage on terminal "C" reaches the set-point.  And heat is generated due to the forward voltage drop across the SCRs.

  The battery symbol in the Rotax regulator/rectifier schematic looks upside down.

According to this forum:

http://www.edaboard.com/thread67699.html

The "E" in resistor values stands for ohms.  Thus I interpret 2E2 to be 2.2 ohms.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 27, 2014 7:57 am Post subject: How does the Ducatti rectifier/regulator work?

At 09:15 2014-12-27, you wrote:

 	  Quote: 	
		  

<electronic.powertuning(at)yahoo.com>



Merry Christmas to all of you !

What is the maximum frequency of the output voltage generator ?


	


   Good question! I've never had occasion to 'scope

   the 912/914 internal alternator's electrical

   'innards'.  The SD-8 at 4KRPM is about 500 Hz.



   But without actually measuring the frequency

   on a running engine, you'll have to count the

   magnets on the flywheel. Each pair of magnets

   would produce one a.c. cycle as they pass an

   stator pole piece. So 8 magnets would give

   you 4 cycles per rev, 6000 rpm is 100 rev/sec

   so the output would be 400 Hz at 6000 rpm.

   Scale from there. That's the WAG, your own

   discoveries may vary . . .



   Let us know what you find out!

   Bob . . .

merlinspitfire

Joined: 26 Dec 2014
Posts: 3
Location: CLUJ_NAPOCA, ROMANIA

Posted: Sat Dec 27, 2014 8:55 am Post subject: Re: How does the Ducatti rectifier/regulator work?

Thank You .So not exceed 600Hz frequency

No one checked with an oscilloscope ?

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 27, 2014 9:32 am Post subject: How does the Ducatti rectifier/regulator work?

At 10:55 2014-12-27, you wrote:

 	  Quote: 	
		  

<electronic.powertuning(at)yahoo.com>



Thank You .So not exceed 600Hz frequency

No one checked with an oscilloscope ?


	


   Where does the 600Hz number come from?



   Bob . . .

merlinspitfire

Joined: 26 Dec 2014
Posts: 3
Location: CLUJ_NAPOCA, ROMANIA

Posted: Sat Dec 27, 2014 3:52 pm Post subject: Re: How does the Ducatti rectifier/regulator work?

We considered a maximum value for the choice of components in case I want to design a regulator

user9253

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

Posted: Sun Dec 28, 2014 9:02 am Post subject: Re: How does the Ducatti rectifier/regulator work?

Using Bob's formula and Gilles webpage info

http://www.aero-hesbaye.be/circuit_elec.htm

5 pair of magnets x 6000 RPM / 60 seconds = 500 Hz maximum

BTW, Gilles' webpage is interesting.  It is written in German.  Google Chrome translated it.  But much is lost in translation, making some of it difficult to understand.  During the short circuit test, the Rotax dynamo put out 21 amps without overheating.

  The 22,000 microfarad capacitor improves the output waveform, but is it required by avionics? (Not that I intend to remove mine.)

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Dec 29, 2014 7:48 am Post subject: How does the Ducatti rectifier/regulator work?

At 11:02 2014-12-28, you wrote:

 	  Quote: 	
		  



Using Bob's formula and Gilles webpage info

http://www.aero-hesbaye.be/circuit_elec.htm

5 pair of magnets x 6000 RPM / 60 seconds = 500 Hz maximum

BTW, Gilles' webpage is interesting.  It is written in 

German.  Google Chrome translated it.  But much is lost in 

translation, making some of it difficult to understand.  During the 

short circuit test, the Rotax dynamo put out 21 amps without overheating.

   The 22,000 microfarad capacitor improves the output waveform, but 

 is it required by avionics? (Not that I intend to remove mine.)

Joe


	


    I'd forgotten about the work that Gilles and friends

    had accomplished on the Rotax 912/914 alternator system.

    The text of the article cites 200Hz (at) 2400 rpm which

    confirms your extrapolation above.



    Experiments I conducted some years ago on the SD-8

    and companion R/R failed to demonstrate much value

    for having the capacitor in place.



    I'll be doing some work on PM alternators and next

    generation rectifier/regulators over the next few

    months. I'll take a look at the value for including

    the large capacitor beyond the need to operate the

    system sans battery.



    "Back-in-the-day" . . . a rule of thumb for brute-

    force (single cap) filters was 1000uF/Amp of load

    downstream of a 60Hz rectifier. Effectiveness of

    filtering would be about 5x better at the operating

    frequency of the Rotax pm alternator. It seems likely

    that the capacitor was originally included to offer

    smoother output given the really trashy performance

    of phase-switched SCR's as regulators.



    We'll see . . .

   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Dec 31, 2014 7:39 am Post subject: Re: How does the Ducatti rectifier/regulator work?

I hesitate to inject my questions about the schematic of the Ducati dynamo regulator. But what is that little unlabeled zener diode feeding the base of the BF493S?



And why does this look like an alternator regulator instead of a DC dynamo regulator? What am I missing?

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

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