As info.....
I opened up one of the Rotax regulators a friend gave me after a
failure. The two diodes were bad and were open so paralleling them with
external diodes does seem to be a viable option. Relatively cheap for
the cost of the diodes and a heat sink. No modification to the existing
regulator required. Attached is the fix I obtained from another
website. Just need to join the diodes to the B and two G terminals.
Just my two cents worth.....
Bill
A010 Classic Monowheel
Still building.
On 1/21/2014 3:02 PM, Jan de Jong wrote:
>
>
> 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:
>> <gregoryf.flyboy@comcast.net>
>>
>>
>>
>> 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
>>>
>>
>>
>>
>>
>>
>
>
|