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Ducati Regulator (too little load)

 
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kenryan



Joined: 20 Oct 2009
Posts: 284

PostPosted: Tue Jun 12, 2018 12:57 pm    Post subject: Ducati Regulator (too little load) Reply with quote

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


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user9253



Joined: 28 Mar 2008
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Location: Riley TWP Michigan

PostPosted: Tue Jun 12, 2018 3:25 pm    Post subject: Re: Ducati Regulator (too little load) Reply with 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.

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PostPosted: Tue Jun 12, 2018 3:39 pm    Post subject: Ducati Regulator (too little load) Reply with quote

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

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

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user9253



Joined: 28 Mar 2008
Posts: 1232
Location: Riley TWP Michigan

PostPosted: Tue Jun 12, 2018 4:18 pm    Post subject: Re: Ducati Regulator (too little load) Reply with quote

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.


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PostPosted: Tue Jun 12, 2018 4:34 pm    Post subject: Ducati Regulator (too little load) Reply with quote

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


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kenryan



Joined: 20 Oct 2009
Posts: 284

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

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lyleapgmc



Joined: 19 Feb 2014
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PostPosted: Tue Jun 12, 2018 5:28 pm    Post subject: Ducati Regulator (too little load) Reply with quote

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




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






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PostPosted: Tue Jun 12, 2018 8:56 pm    Post subject: Ducati Regulator (too little load) Reply with 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. 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 . . .


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PostPosted: Tue Jun 12, 2018 8:59 pm    Post subject: Ducati Regulator (too little load) Reply with quote

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 . . .


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PostPosted: Thu Jun 14, 2018 4:30 am    Post subject: Ducati Regulator (too little load) Reply with quote

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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