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
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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