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Ducati Regulator (too little load)

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kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Tue Jun 12, 2018 12:57 pm Post subject: Ducati Regulator (too little load)

There is a respected member of a popular Rotax list asserting that the Ducati regulator can be harmed by too little load. I don't believe this to be true, and it interests me directly because my wiring architecture has the regulator, under normal conditions, supplying only my primary fuel pump (it can be tied to the main bus if necessary). To those of you familiar with the Ducati regulator, is there any truth in the assertion that a light load is bad for it?



Ken Ryan

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Tue Jun 12, 2018 3:25 pm Post subject: Re: Ducati Regulator (too little load)

I am on your side Ken.  Roger should should reference the schematic and the laws of physics to explain why too little of a load can damage the rectifier/regulator.  The greater the current, the greater the heat.  A small load will result in less heat.

_________________
Joe Gores

echristley(at)att.net
Guest

Posted: Tue Jun 12, 2018 3:39 pm Post subject: Ducati Regulator (too little load)

Some regulators "regulate" by dumping the excess power generated by the generator.  They dump the power by shorting it to ground.  A direct short would be a weld, so the regulator stands in the middle and acts as a heater.  If there is no load on the electrical system, the regulator is being heated by everything the generator can put out.

But, really, it is a poor engineer that could not have anticipated and and properly designed for that eventuality.  Of course, the proper design may have been to install it in the exact position on the motorcycle that they designed it to be install in (with its accompanying blast air). 

 

    On Tuesday, June 12, 2018 7:27 PM, user9253 <fransew(at)gmail.com> wrote:



  



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



I am on your side Ken.  Roger should should reference the schematic and the laws of physics to explain why too little of a load can damage the rectifier/regulator.  The greater the current, the greater the heat.  A small load will result in less heat.



--------



Joe Gores



Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=480834#480834



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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Tue Jun 12, 2018 4:18 pm Post subject: Re: Ducati Regulator (too little load)

Agreed.  Some regulators regulate by adding a parallel resistance to short out excess current.

Some regulators regulate by adding a series resistance to limit the current.

Some regulators regulate by turning the output on and off rapidly.  The ratio between the on time and the off time controls the average current.  

The Ducati is the on-off type.  It does not waste as much heat as the first two types.  But it still gets very warm due to IR losses.  The greater the load, the greater the heat.

_________________
Joe Gores

gilles.thesee(at)free.fr
Guest

Posted: Tue Jun 12, 2018 4:34 pm Post subject: Ducati Regulator (too little load)

Le 13/06/2018 à 01:25, user9253 a écrit :

 	  Quote: 	
		   



 I am on your side Ken.  Roger should should reference the schematic and the laws of physics to explain why too little of a load can damage the rectifier/regulator.  The greater the current, the greater the heat.  A small load will result in less heat.




	


Hi all,



I'll second that.

In the 15-18 past years we have been seeing lots of opinions about the 

Rotax rectifier/regulator, but unfortunately very few hard data by 

people who actually conducted experiments.

To date I am not aware of any data in addition to those we obtained 

during our build, a short report of which can be seen here on Contrails !

http://contrails.free.fr/elec_ducati_en.php



More accurate versions of my schematics have been published since, but 

no further bench tests have been reported.



FWIW

kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Tue Jun 12, 2018 5:13 pm Post subject: Ducati Regulator (too little load)

Thank you Joe and Ernest.



On Tue, Jun 12, 2018 at 3:32 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)>

 

 I am on your side Ken.  Roger should should reference the schematic and the laws of physics to explain why too little of a load can damage the rectifier/regulator.  The greater the current, the greater the heat.  A small load will result in less heat.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=480834#480834

 

 

 

 

 

 

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lyleapgmc

Joined: 19 Feb 2014
Posts: 57

Posted: Tue Jun 12, 2018 5:28 pm Post subject: Ducati Regulator (too little load)

Thinking, and that for me is dangerous.     

The alternator in a Ducati or similar system is not controlled.        It's output is dependent on its RPM.  I have two Honda motorcycles       that use the same type of system.  To test the alternator one       checks the output voltage from each of three windings.  The       expected voltage is in the range of 45 to 70 volts on each       winding.  When the vehicle system is not demanding any output from       the rectifier/regulator the alternator output must go somewhere.        It is converted to heat.  Heat is the enemy of electronics.  

          

I may be way out in left field on this but it makes some sense to       me.     

I have one failure of the charging system on my Hondas.  It was       the regulator.  My wonderful wife brought the car so we could put       a little charge in the battery.  It took two or three charges to       get home.  I miss that lady so much.  This would be hard to do       with an airplane.

          

Lyle 

          

     On 6/12/2018 8:12 PM, Ken Ryan wrote:

     

      	  Quote: 	
		         Thank you Joe and Ernest.

       

                On Tue, Jun 12, 2018 at 3:32 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)>

           

           I am on your side Ken.  Roger should should reference the           schematic and the laws of physics to explain why too little of           a load can damage the rectifier/regulator.  The greater the           current, the greater the heat.  A small load will result in           less heat.

           

           --------

           Joe Gores

           

           

           

           

           Read this topic online here:

           

           http://forums.matronics.com/viewtopic.php?p=480834#480834

           

           

           

           

           

           

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 12, 2018 8:56 pm Post subject: Ducati Regulator (too little load)

At 07:18 PM 6/12/2018, you wrote:

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



 Agreed.  Some regulators regulate by adding a parallel resistance to short out excess current.



   nobody does that any more . . . VERY inefficient. The

   silicon controlled bridge rectifier, series control

   rectifier=regulator is teh gold standard. Ducatti is

   but one example.



   https://goo.gl/yYYeM5

 

 Some regulators regulate by adding a series resistance to limit the current.



   Not even sure how that would be done . . . ever see a

   schematic?



 Some regulators regulate by turning the output on and off rapidly.  The ratio between the on time and the off time controls the average current.  The Ducati is the on-off type.  It does not waste as much heat as the first two types.  But it still gets very warm due to IR losses.  The greater the load, the greater the heat.



   This kind-of describes the full-wave bridge

   circuit cited above. The 'duty cycle' management

   is rather coarse. The SCR's are triggered on the

   UPswing of the AC waveform any time the bus is

   perceived to be below setpoint. But unlike series

   switches controlled by precision comparators, the

   silicon controlled rectifier or triac will not . . .

   indeed cannot be shut off until the AC waveform

   goes to zero. So while there is some discrimination

   for siwtch-on delay after zero crossing, the critter

   stays 'locked' on until the next zero crossing

   irrespective of instantaneous bus votlage.



   Since this can happen as rapidly as every few

   milliseconds, any raggedness in regulation value

   is small and insignificant. Here are some typical

   ripple profiles off an SD8 Dynamo under various

   conditions.



 

   https://goo.gl/tLDCSu

 

   Except for the more 'advanced' full wave bridge

   rectifier-regulators using MOS-Fets, I believe

   that any rectifier-regulator rated for more than

   5A or so will be VERY similar to the Ducatti

   schematic cited.



 



 

 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 12, 2018 8:59 pm Post subject: Ducati Regulator (too little load)

At 08:27 PM 6/12/2018, you wrote:



  	  Quote: 	
		  Thinking, and that for me is dangerous.



 The alternator in a Ducati or similar system is not controlled. 	


   Agreed . . . the alternator output is proportional

   to engine rpm but the rectifier-regulator is

   a 'gated' device that disconnects the alternator

   from the bus on a cycle-by-cycle basis, hence

   its output IS managed for the purpose of charging

   batteries and running electrowhizzies . . .



 

 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 14, 2018 4:30 am Post subject: Ducati Regulator (too little load)

At 11:55 PM 6/12/2018, you wrote:

  	  Quote: 	
		  At 07:18 PM 6/12/2018, you wrote:

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



 Agreed.  Some regulators regulate by adding a parallel resistance to short out excess current.



   nobody does that any more . . . VERY inefficient. 	


   Hmmmm . . . seems I was half right. The shunt regulator

   is horribly inefficient but no . . . there ARE some

   individuals pursuing the shunt style regulation

   topology. For example, I found this article out

   there on the web:



 https://goo.gl/ofvHSe 



   It took a bit to noodle through the functionality

   of this design. If one studies the wiring of

   the bridge rectifiers, you see that they are

   set up to be classic, three phase rectifiers

   essentially UNCONTROLLED. This means that if

   the SCR's were left out of the circuit, the

   alternator's three phase output is simply

   rectified and pumped directly to the bus.



   The ONLY time an SCR would be capable of conducting

   current is during the OFF or reverse-voltage

   interval on the companion rectifier leg. Any

   time the SCR is in conduction, there is a SHORT

   across the windings of the alternator . . . 



   

   



   Note the boss-hog heat sink recommended in this

   design. As long as system demands are a substantial

   percentage of the alternator's output, the ON-

   time for SCRs is low. But during normal ops with

   low system loads, the SCRs will be working hard . . .

   as will the alternator.



   One could argue that this design is thermally

   robust and may indeed last longer than 

   the stock or aftermarket devices tried . . . but

   as noted elsewhere in this thread, beefing up

   the 'weakest link' in the chain may well move

   the failure to some other component in the system.



   Not sure that the first and follow-on authors

   of the DIY thread will report their long term

   experiences with alternator failures . . . and

   who knows, maybe the heat rejection profile

   of the alternator is robust enough to handle

   this mode of operation.



   I have to believe that there must be SOME

   off-the-shelf designs out there that subscribe

   to the shunt regulation philosophy. As seen

   above, it's hard to beat the simplicity!

   So I'll walk back my earlier assertion but

   with a sense of . . . well . . . don't

   need to go there.



   We do know that the Ducatti design is not

   a 'shunt regulation' topology . . . 



 



 

 

   Bob . . .

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