ad A:
Don't agree. The only stress would be somewhat higher reverse voltage.
The Ducati R/R is not a shunt regulator.
ad B:
Agree, but the thyristors are more stressed than the diodes. They drop a
little more voltage and dissipate more heat.
On the other hand, the custom fitting of the diode pills could be more
uncertain than the standard fitting of the thyristors (TO220 I believe).
Parallelling the diodes with external ones is possible. They would
require a heat sink. Are the failure statistics clear about the diodes?
I think it would be better to get an R/R without issues.
Regards,
Jan
On 1/21/2014 6:30 PM, Greg Fuchs wrote:
>
>
> Well, since the generator is not a two-legged 'phi' connection (i.e. the
> midpoint of the generator coil connected to the ground of the system or
> vehicle, then 'dumping to ground' may not be the term to use after all. Yes,
> I think that is correct.
>
> Here are the two main failure modes of the Ducatti regulator as I see it..
>
> A) If the aircraft has a very low load usage (i.e. no lights, no
> instruments, etc.), the scr's are stressed and 'may' fail eventually. If
> this happens, the Ducatti is unrecoverable.
>
> B) If the aircraft has a very high load usage (using up most of its 15-18
> amps), the output diodes are stressed and probably will fail eventually,
> which is backed up by historical data gathering (they fail a lot at high
> loads per many forum users). The Ducatti would then be recoverable by
> placing 25 Amp or higher diodes on the external terminals as referenced
> earlier.
>
> Scenario (A) is unlikely, since everyone likes power-hungry instruments and
> the like, where scenario (B) is the most likely for the same reason.
>
> Thus, if someone wants to 'beef up' their ducatti, then they have the option
> to place the external diodes. I guess it doesn't matter what kind, as long
> as they can withstand the current from the generator. They will either help
> the internal diodes survive almost forever, or take over for them when they
> fail (It depends on the turn-on points between the internal and external
> diodes).
>
> Jan, do you agree with this?
>
> Best Regards,
> Greg
>
> -----Original Message-----
> From: owner-europa-list-server@matronics.com
> [mailto:owner-europa-list-server@matronics.com] On Behalf Of Jan de Jong
> Sent: Tuesday, January 21, 2014 4:59 AM
> To: europa-list@matronics.com
> Subject: Re: Europa-List: Re: Ducati rectifier/regulators
>
> Equally respectfully - "dumping to ground" is not dumping, but connection to
> the negative DC output terminal.
> I attach a little OpenOffice drawing that hopefully clarifies (I hope that
> works).
>
> Regards,
> Jan
>
> On 1/20/2014 11:21 PM, Greg Fuchs wrote:
>> --> <gregoryf.flyboy@comcast.net>
>>
>> Respectfully, I believe that the circuit configuration that you are
>> thinking of is incorrect, Jan de Jong.
>>
>> The SCR's do EXACTLY 'dump' the AC output DIRECTLY to ground.
>> When one end of the thyristor connects to the alternating current
>> output of the coil, and the other end to ground...then that is all
>> they can do but short the AC output to ground. It is not acting as a
>> PWM-like device at all, simply a grounding device. Call it a
> direct-connect.
>>
>> You mention heat. The direct-connect method is the best way to deal
>> with the heat. The forward voltage drop of the 'dumping' device is
>> low, and the current does not need to go through the diodes at all,
>> which are bypassed...hence your lowest heat output.
>>
>> Since the 'dumping device' connects the alternator output directly to
>> ground, without going through the diode, what is the power dissipated?
>> While in the dumping mode, lets say the current to dump was 10
>> amps(I'll use your generously supplied information, so I don't have to
>> look up specs) it would be 1.1V * 10 amps. That's it. 11 watts. That
>> is much better than the 18 Watts in your configuration.
>>
>>> (
>>> a failure mode for the Ducati device is reportedly the loss of
>>> continuity
>> of a diode pill attachment through thermal >cycling; fitting external
>> parallel diodes has been proposed as a solution; replacing the whole
>> device seems more
>>> sensible
>>> )
>> Well, maybe so! However, if the failure mode is a loss in continuity,
>> that would mean the diodes are opening. That would also mean that
>> connecting the external diodes to the regulator would bring it back to
> life!
>> Regards,
>> Greg
>>
>>
>>
>> -----Original Message-----
>> From: owner-europa-list-server@matronics.com
>> [mailto:owner-europa-list-server@matronics.com] On Behalf Of Jan de
>> Jong
>> Sent: Monday, January 20, 2014 7:40 AM
>> To: europa-list@matronics.com
>> Subject: Re: Europa-List: Re: Ducati rectifier/regulators
>>
>>
>> Re two-phase bridge rectifier/regulator.
>> The 2 thyristors in the rectifier bridge do not short the AC input or
> "dump"
>> anything.
>> On the contrary, they disconnect the DC output from the AC input when
>> the output voltage threatens to exceed the set voltage.
>> All output current passes through one branch of one diode and one
>> thyristor in series half the time and through the other identical
>> branch also half the time.
>> Heat development is proportional to the output current and the voltage
>> drop across a branch.
>> Voltage drops increase somewhat with current, so heat development
>> increases more than linearly with output current.
>> In the Ducati device the diode is reportedly a MR2510 pill (typically
>> 0.75V at 10A, 0.8V at 20A), the thyristor can be a 2N6504 (typically
>> 1.1V at 10A, 1.3V at 20A).
>> So at 10A the two branches of the bridge are each expected to generate
>> 0.5 x (7.5 + 11) = 9.25W (total 18.5W) of heat.
>> And at 20A the two branches of the bridge are each expected to
>> generate
>> 0.5 x (16 + 26) = 21W (total 42W) of heat.
>>
>> (
>> a failure mode for the Ducati device is reportedly the loss of
>> continuity of a diode pill attachment through thermal cycling; fitting
>> external parallel diodes has been proposed as a solution; replacing
>> the whole device seems more sensible
>> )
>>
>> Cheers,
>> Jan de Jong
>>
>
>
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