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Rotax Charging System
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cluros(at)gmail.com
Guest

Posted: Wed Jun 13, 2018 12:41 pm Post subject: Rotax Charging System

Joe the Ducati has 6 pins instead of 5 for the John Deere. I believe the extra pin on the Ducati is for a large capacitor but the John Deere ones are MOSFET rectifiers which don't need the capacitor? So we could hook up the two AC wires, the B+, the L, and the IGN wires the same as on the Ducati and just remove the cap from the system?Â Am I making any sense?



On Mon, Jun 11, 2018 at 11:15 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)>

 

 Search eBay for AM101406 or MIA881279

 Chances are that the $20 ones are the same as the more expensive ones.

 Note that the terminals are arraigned in a different order than the Ducati.Â  The mounting holes are also spaced differently.Â  Be sure to use heat conductive grease on the mounting base to carry heat away.

 

 > Any luck on a part number or a way to determine an appropriate John Deere regulator? 

 

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Wed Jun 13, 2018 1:54 pm Post subject: Re: Rotax Charging System

Neither the Ducati or John Deere regulator has a terminal specifically for a capacitor, although some installers might connect a capacitor to Ducati terminal R.  Terminals B and R are connected together internally.  I believe the purpose of the R terminal is not for redundancy, but rather to reduce current through a single terminal.  A capacitor is required regardless of which regulator is used.  It can be connected to the main power bus.  I put a 10 amp fuse in series with mine.

  Splice the two wires together that were connected to Ducati terminals B & R and connect to John Deere terminal B+.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 13, 2018 6:39 pm Post subject: Rotax Charging System

At 03:41 PM 6/13/2018, you wrote:

  	  Quote: 	
		  Joe the Ducati has 6 pins instead of 5 for the John Deere. I believe the extra pin on the Ducati is for a large capacitor but the John Deere ones are MOSFET rectifiers which don't need the capacitor? So we could hook up the two AC wires, the B+, the L, and the IGN wires the same as on the Ducati and just remove the cap from the system?Â Am I making any sense? 	


   As long as you have a battery on line,

   the capacitor serves no demonstrable

   purpose.



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Thu Jun 14, 2018 3:18 am Post subject: Re: Rotax Charging System

Even if the battery is disconnected, I do not think that the capacitor does much good.  When my PC680 failed open, the alternator voltage was unstable.  However, Rotax documentation calls for a capacitor.  It is best to follow manufacturer's instructions.  They might know something that I don't.

 	  Quote: 	
		  As long as you have a battery on line, 

the capacitor serves no demonstrable purpose.

_________________
Joe Gores

wdaniell.longport(at)gmai
Guest

Posted: Mon Jun 18, 2018 1:07 pm Post subject: Rotax Charging System

Joe,

can you confirm wiring for the JD voltage regulator please.

B+ = DC + output to capacitor and system

AC = yellow wires from generator

L =Â  indicator light

IGW = master?

is that right?

thanks

Will



William Daniell



LONGPORT

+57 310 295 0744



 

On Sun, Jun 10, 2018 at 11:03 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)>

 

 Ken,

 While I have great respect for Mike M. and admire his knowledge, I do disagree with that ending statement.Â  Heat caused by high current can damage alternator windings.Â  But the total current is determined by the load, not by the regulator.Â  I do not think that the Silent Hektik regulator will stress the alternator any more than the Ducati regulator.

 Â  Two years ago I replaced the Ducati regulator in my RV-12 with a cheap John Deere regulator from eBay.Â  I made an adapter plate using 1/8" aluminum because the mounting holes did not line up.Â  I used heat conductive grease on both sides of the mounting plate.Â  A thermocouple attached to the John Deere regulator measured a maximum temperature of 157 degrees Fahrenheit on a 90+ degree day.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=480768#480768

 

 

 

 

 

 

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Mon Jun 18, 2018 2:37 pm Post subject: Re: Rotax Charging System

Will,

Yes, you are correct.

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Mon Jun 18, 2018 6:27 pm Post subject: Re: Rotax Charging System

Use heat conductive paste between the regulator and aluminum airframe or heat sink.  The regulator case should be well grounded.  Some installers connect a ground wire to one of the mounting bolts.  Forced air cooling will prolong regulator life.

_________________
Joe Gores

jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Thu Sep 13, 2018 8:56 pm Post subject: Re: Rotax Charging System

I don't believe I've ever seen a definitive answer to the question of what the exact purpose of the 22,000 mfd capacitor is in the 912 charging circuit.  Can anyone answer that question?  I apologize if the answer is buried somewhere in the archives of this forum, and I just haven't searched far enough to find it.



OK, I found where Bob said that as long as there is a battery connected in the system, there is no demonstrable need for a capacitor.  Is the capacitor there to protect something if the battery is disconnected?  I've seen all kinds of explanations offered by others, starting with "it's there to provide noise filtering", which I'm pretty sure is not the case.  I would just like to know.

_________________
John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Thu Sep 13, 2018 10:05 pm Post subject: Rotax Charging System

John,



Filtering.

Barry



On Friday, September 14, 2018, jrevens <jrevens(at)comcast.net (jrevens(at)comcast.net)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "jrevens" <jrevens(at)comcast.net (jrevens(at)comcast.net)>

 

 I don't believe I've ever seen a definitive answer to the question of what the exact purpose of the 22,000 mfd capacitor is in the 912 charging circuit.Â  Can anyone answer that question?Â  I apologize if the answer is buried somewhere in the archives of this forum, and I just haven't searched far enough to find it.

 

 --------

 John Evens

 Thorp T-18 N71JE (built &amp; flying)

 Kitfox SS7 N27JE (building)

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=483172#483172

 

 

 

 

 

 

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 ====================================

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 target="_blank">http://www.matronics.com/contribution

 ====================================

 

 

 

 	


-- 

Barry

"Chop'd Liver"

If you wash your hands before you go to the bathroom you may have the makings of a Crew Chief.

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 17, 2018 10:40 am Post subject: Rotax Charging System

At 11:56 PM 9/13/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jrevens" <jrevens(at)comcast.net>



 I don't believe I've ever seen a definitive answer to the question of what the exact purpose of the 22,000 mfd capacitor is in the 912 charging circuit.  Can anyone answer that question?  I apologize if the answer is buried somewhere in the archives of this forum, and I just haven't searched far enough to find it.

 	


   These capacitors have been included as part

   of many PM alternator systems with rectifier/regulators

   for a long time. Never got to talk with an original

   designer but the general consensus amongst those who

   have offered opinions is that it 'reduces noise' and/or

   'aids alternator-only operations'.



   Limited testing I've conducted on smaller systems

   (10 amp) showed no benefit with respect to noise

   levels on the bus . . . DC busses in vehicles are

   generally very noisy anyhow and everyone worth his

   salt as an appliance designer will know how to

   'live with it'.



   Here's a family of plots I took on an SD8 alterantor

   on B&C's drive stand about 15 years ago:



  https://tinyurl.com/cz7ekrf



   Page 1 is a picture of a fully loaded SD8 with

   capacitor installed.  Measured noise in the low

   frequency spectrum was about 250 millivolts peak

   to peak, 77 mV RMS.



   Page 2 shows what happens when the capacitor is

   removed . . .  760 mV pk-pk and 72 mV RMS.



   In other words, no significant change. Alternator

   noise on the bus in an airplane with a wound field

   is MUCH higher and broader spectrum . . . but still

   nothing that your electro-whizzies should care about.



   I fiddled with some no battery ops too on pages 7, 8 and

   9 . . . but didn't see how it performed with no capacitor.

   I'm thinking that planning for no battery ops is a

   capitulation to poor battery maintenance practices

   and/or errors of conducting FMEA in deciding architecture.



   Short answer is I don't think the capacitor adds

   any useful benefit. If anyone runs across some testing

   data that contradicts these findings, I'd be delighted

   to know about it. 



 

 

   Bob . . .

ceengland7(at)gmail.com
Guest

Posted: Mon Sep 17, 2018 2:04 pm Post subject: Rotax Charging System

On 9/17/2018 1:39 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                At 11:56 PM 9/13/2018, you wrote:

               	  Quote: 	
		  -->           AeroElectric-List message           posted by: "jrevens" <jrevens(at)comcast.net> (jrevens(at)comcast.net)

           

           I don't believe I've ever seen a definitive answer to the           question of           what the exact purpose of the 22,000 mfd capacitor is in the           912 charging           circuit.  Can anyone answer that question?  I apologize if the           answer is buried somewhere in the archives of this forum, and           I just           haven't searched far enough to find it.

         	
       

         These capacitors have been included as part

         of many PM alternator systems with rectifier/regulators

         for a long time. Never got to talk with an original

         designer but the general consensus amongst those who

         have offered opinions is that it 'reduces noise' and/or

         'aids alternator-only operations'.

       

         Limited testing I've conducted on smaller systems

         (10 amp) showed no benefit with respect to noise

         levels on the bus . . . DC busses in vehicles are

         generally very noisy anyhow and everyone worth his

         salt as an appliance designer will know how to

         'live with it'.

       

         Here's a family of plots I took on an SD8 alterantor

         on B&C's drive stand about 15 years ago:

       

                https://tinyurl.com/cz7ekrf

       

         Page 1 is a picture of a fully loaded SD8 with

         capacitor installed.  Measured noise in the low

         frequency spectrum was about 250 millivolts peak

         to peak, 77 mV RMS.

       

         Page 2 shows what happens when the capacitor is

         removed . . .  760 mV pk-pk and 72 mV RMS.

       

         In other words, no significant change. Alternator

         noise on the bus in an airplane with a wound field

         is MUCH higher and broader spectrum . . . but still

         nothing that your electro-whizzies should care about.

       

         I fiddled with some no battery ops too on pages 7, 8 and

         9 . . . but didn't see how it performed with no capacitor.

         I'm thinking that planning for no battery ops is a

         capitulation to poor battery maintenance practices

         and/or errors of conducting FMEA in deciding       architecture.

       

         Short answer is I don't think the capacitor adds

         any useful benefit. If anyone runs across some testing

         data that contradicts these findings, I'd be delighted

         to know about it. 

       

       

                

             Bob . . .                     	
     I wonder if that capacitor is an artifact from back when PM     alternators were operated in vehicles that were designed with no     battery. Not unlike the avionics master as a holdover from the     prehistoric germanium semiconductor days.

     

     Charlie

     	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 17, 2018 7:25 pm Post subject: Rotax Charging System

 	  Quote: 	
		    	  Quote: 	
		  	
I wonder if that capacitor is an artifact from back when PM alternators were operated in vehicles that were designed with no battery. Not unlike the avionics master as a holdover from the prehistoric germanium semiconductor days.



 Charlie 	


   An excellent hypothesis . . . but it seems

   it equally likely that somebody looked at that

   full wave rectifier downstream of an AC

   source and thought, "Gee, every circuit like

   that in the past has had a capacitor across

   the output . . . shucks . . . why not?"



   It's deceptively easy to buy into conventional

   wisdom. I was firmly in the camp followers for

   'the battery is your ship's best power filter.' I

   used to preach the doctrine myself. Then one

   day, I had to write a test report some sample

   batteries and the requester asked me to see if

   the samples were any 'better filters' than

   the products we were buying.



   No big deal . . . but the data gathered was

   a big deal. Totally blew the old saw into

   itty-bitty pieces. Intuitively, we all KNEW

   that batteries didn't take on serious charge

   below 13.5 nor would the deliver serious

   energy above 12.5. so what happens in that

   fuzzy area . . . very little.



   I was pretty stunned with that realization . . .

   and embarrassed that a MIL-STD-704  knowledge-nugget

   I'd worked with for decades was telling me the same

   thing . . .



 [img]cid:.0[/img]



   Noise levels to be EXPECTED in a normally operating

   28VDC system over the range of 1000 to 5000 Hz were

   1.0VRMS or 2.8V pk-pk . . . with fall-offs at

   each end.  In other words, as a normal state of

   affairs, pk-pk noise can be as much as 10% of

   system voltages. 



   

   We know that batteries stand off LARGE perturbations

   above 13.5 and below 12.5 but that would hardly

   qualify as a 'filtering' function.

    



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Sep 18, 2018 11:08 am Post subject: Rotax Charging System

At 10:24 PM 9/17/2018, you wrote:

  	  Quote: 	
		    	  Quote: 	
		  I wonder if that capacitor is an artifact from back when PM alternators were operated in vehicles that were designed with no battery. Not unlike the avionics master as a holdover from the prehistoric germanium semiconductor days.



 Charlie 	


   An excellent hypothesis . . . but it seems

   it equally likely that somebody looked at that

   full wave rectifier downstream of an AC

   source and thought, "Gee, every circuit like

   that in the past has had a capacitor across

   the output . . . shucks . . . why not?" 	


   Let's noodle some of the math that helps

   us figure out just how effective a capacitor

   might be for 'filtering' a PM alternator system:



   A fundamental quality of capacitors is described

   by this formula:



   Volts/Second = Amps/Farad



   meaning that if you apply 1 amp of constant

   current to a 1 Farad capacitor, you'll see

   voltage across the capacitor rise at a rate

   of 1 Volt per Second.



   How rapidly will the voltage change

   across at 22,000uF capacitor in a

   PM alternator system with 10A load

   assuming the positive excursion has just

   charged the capacitor to the expected peak

   voltage?



   V/S = 10/0.022 = 454 Volts/Second or let's

   say about 500 mVolts/mSecond.



   Adding a 500 mV/mS plot to the no-capacitor

   plot of SD8 performance we see



 [img]cid:.0[/img]



   By inspection we can deduce that the addition of

   22KuF to the output would have no appreciable effect

   on the voltage plot shown.  If we put a 47KuF cap

   on it (less than 1/2 the slope) we might see a reduction

   in pk-pk excursion to something on the order of 200mV

   . . . but why bother? We know that appliances qualified to run

   in aircraft EXPECT to see noises equal to or perhaps

   greater than what's depicted above with no capacitor.



   I might also add that automotive electrical systems

   are completely devoid of electrical system noise

   filters that address the spectrum of alternator

   ripple and switching.



   So if there is a reason based on physics for adding

   capacitors to the PM alternators, it's not intuitively

   clear.



 

   Bob . . .

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Wed Sep 19, 2018 8:08 am Post subject: Rotax Charging System

Bob et al, I've had three instances where I've added a capacitor to a charging system.Â The first time was when a friend asked me to rewire the Harley Sportster he was resurrecting. It had a magneto for ignition, a generator for power and was kick start only. He didn't want a battery added. At that time CCI (Custom Chrome Inc, or as I called it ChiCom Importers) had a kit with a capacitor, a spring mount and a couple of connectors. It simply provided a load for the generator. I remember the lights had a pronounced flikker at idle rpm.

The second was with the Rotax two stroke installation manual, page 18-3 where there is a wiring diagram for installing the 866 080 rectifier without a battery . Above the diagram is the note; "Attention, To avoid excessive voltage in conjunction with the rectifier regulator 866080 a constant minimum ballast load of 1 amp is required" On the next page there is a diagram for installing that same rectifier with a battery and there is no capacitor.

Third, was installing a Rotax 912. The Installation manual, section 24-00-00 page 7 says a capacitor of 22,000 uF at 25V is required to protect the regulator and flatten voltage, along with the warning that if the battery or the bus is disconnected from the system with the engine running the capacitor will safely dissipate the charge from the generator (Rotax term) and "otherwise the regulator will be damaged".

Whether it's an old pilot's tale or not I don't know, but the consistent theme is that the capacitor is there to dissipate a charge and protect the rectifier.

Rick Girard



On Tue, Sep 18, 2018 at 8:43 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 10:24 PM 9/17/2018, you wrote:

  	  Quote: 	
		    	  Quote: 	
		  I wonder if that capacitor is an artifact from back when PM alternators were operated in vehicles that were designed with no battery. Not unlike the avionics master as a holdover from the prehistoric germanium semiconductor days.



 Charlie 	


 Â  An excellent hypothesis . . . but it seems

 Â  it equally likely that somebody looked at that

 Â  full wave rectifier downstream of an AC

 Â  source and thought, "Gee, every circuit like

 Â  that in the past has had a capacitor across

 Â  the output . . . shucks . . . why not?" 	


 Â  Let's noodle some of the math that helps

 Â  us figure out just how effective a capacitor

 Â  might be for 'filtering' a PM alternator system:



 Â  A fundamental quality of capacitors is described

 Â  by this formula:



 Â  Volts/Second = Amps/Farad



 Â  meaning that if you apply 1 amp of constant

 Â  current to a 1 Farad capacitor, you'll see

 Â  voltage across the capacitor rise at a rate

 Â  of 1 Volt per Second.



 Â  How rapidly will the voltage change

 Â  across at 22,000uF capacitor in a

 Â  PM alternator system with 10A load

 Â  assuming the positive excursion has just

 Â  charged the capacitor to the expected peak

 Â  voltage?



 Â  V/S = 10/0.022 = 454 Volts/Second or let's

 Â  say about 500 mVolts/mSecond.



 Â  Adding a 500 mV/mS plot to the no-capacitor

 Â  plot of SD8 performance we see



 [img]cid:.0[/img]



 Â  By inspection we can deduce that the addition of

 Â  22KuF to the output would have no appreciable effect

 Â  on the voltage plot shown.Â  If we put a 47KuF cap

 Â  on it (less than 1/2 the slope) we might see a reduction

 Â  in pk-pk excursion to something on the order of 200mV

 Â  . . . but why bother? We know that appliances qualified to run

 Â  in aircraft EXPECT to see noises equal to or perhaps

 Â  greater than what's depicted above with no capacitor.



 Â  I might also add that automotive electrical systems

 Â  are completely devoid of electrical system noise

 Â  filters that address the spectrum of alternator

 Â  ripple and switching.



 Â  So if there is a reason based on physics for adding

 Â  capacitors to the PM alternators, it's not intuitively

 Â  clear.



 

 Â  Bob . . . 

  	




-- 

â€œBlessed are the cracked, for they shall let in the light.â€ Â Â Groucho Marx

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