Maybe not so fast about waste/dump conclusions..
When I built my motorcycle regulator about 5 years ago, I made it in the
shunt configuration, or the simple waste/dump. It still works great to this
day. It is very similar to the example in Nigel's document (which I plan to
go over in more detail about the Mosfet versions of regulators), except I
used an actual programmable shunt regulator IC to control the high-power
stage (a simple thing..it modeled like a zener with an amazing amount of
math to come up with the programming resistors, for what it is).
Unfortunately in this case, I didn't pay attention to the orientation of the
scr's in the Ducatti regulator.
When I went to prove to myself that they were shorting out the windings of
the generator to itself (similar to connecting the two outputs together), I
could only prove what Jan de Jong has been saying all along..that they
weren't. Thus, seems to not be a shunt configuration after all.
One downfall in this configuration..with no load on the generator, its AC
potential may have the ability to climb quite high. In hindsight, I guess
that was talked about in this thread ..30 volts...(42 volts peak?), but I
assumed probably incorrectly, that the measurement was made without a
regulator connected.
I wouldn't prefer those high voltages flying around...increasing the danger
of getting zapped and the dielectric needs of the components, but it is what
it is. In this configuration, the diode AND the scr are conducting at once,
to carry current to the load...increasing the needs on the heat sink.
Still, if the output diodes are a common failure mode, and with the cost of
replacements...it would be nice to see some of these things come back to
life. Stick it to the man..or the overpriced dealer, heehee.
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Pete
Sent: Tuesday, January 21, 2014 1:42 PM
Subject: Re: Europa-List: Re: Ducati rectifier/regulators
>From that schematic, it is indeed a simple waste/dump regulator,with the
two failing diodes being there to prevent battery from reverse feeding
during the dumps. It is pretty silly that they undersized them for rated
alternator generating current capacity. "Certified". Wow.
Cheers,
Pete
> On Jan 21, 2014, at 4:12 PM, Bill Henderson <europa10@bellsouth.net>
wrote:
>
> 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:
>> --> <jan_de_jong@casema.nl>
>>
>>
>> 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
>>>>
>>>> --> <jan_de_jong@casema.nl>
>>>>
>>>> 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
>
> <Rotax Regulator Fix.doc>
|