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MMiller
Joined: 07 Jul 2016
Posts: 8
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 Posted: Sat Jul 09, 2016 3:24 pm Post subject: Re: Z-13/8 Questions |
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Bob
Here are the details of about a dozen Rotax regulator failures. Draw your own conclusion(s).
First some background. There are several versions of the Rotax 912/Ducati regulator. Older versions include Rotax PN 965-345/Ducati 383475, I believe this is the version examined on the http://contrails.free.fr/elec_ducati_en.php website. This was replaced by Rotax PN 965-347/Ducati 343620. This version was manufactured until late 2009 and was replaced by the current version, Rotax PN 965-349/Ducati 362001. I believe this change was driven by component obsolescence, the button case diode was no longer produced. My findings show there are two failure modes, depending on the version of the regulator.
The older pre 2010 regulators fail from the inability to adequately transfer heat from the diode assembly to the case. This causes the diodes to unsolder themselves from the assembly. Both diodes show signs of unsoldering, but, If look closely, the inboard diode always shows more heat damage then the outboard diode. This asymmetrical failure is likely caused by the asymmetrical geometry of the enclosure/heat sink. This is the only failure I have seen in this version regulator. This includes regulators with melted supply terminals (G pin,) the solder connections on these diodes show the same failure mode. I have not seen any component fail out of spec in any regulator examined.
Here a schematic/assy for this version
https://drive.google.com/open?id=0ByPxADyU-DwPdTQ3NWp5LW9iOHc
Typical failure mode
https://drive.google.com/open?id=0ByPxADyU-DwPTnlXcUVEQTdfcVU
Current production since 2010 uses a different diode package. This resolved the internal heatsinking issue of the older regulator versions. Unfortunately, at this time they changed to gel type potting compound. All the examined failures of this version are likely caused by vibration. This failure is unique to the regulators with the new gel potting compound, this failure mode is nonexistent on the older version regulators.
Here a schematic/assy for this version
https://drive.google.com/open?id=0ByPxADyU-DwPWTBBcGlUeENTcHc
Here are some failure photos
https://drive.google.com/open?id=0ByPxADyU-DwPYm1rYUVsbUJyQ3M
Heat is often the cause of failure in electronics, but these regulators fail from poor mechanical design and poor material choices, long before heat would kill them.
| nuckolls.bob(at)aeroelect wrote: | At 06:37 AM 7/5/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew>
Mike Miller has done autopsies on several failed Ducati regulators and he attributes the failures to poor manufacturing and vibration, |
vibration in a potted assembly?
Has he published a teardown report?
| Quote: | | Some RV-12 owners have reported a gradual failure where they get low voltage alarms at RPMs where they used to have normal voltage. Each regulator could fail differently. |
Color me skeptical . . . these regulators have
been in production for decades. There must have
been thousands sold. Over that period of time
and numbers of examples, I find it curious that
a constellation of failure modes would emerge.
.....
Bob . . . |
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ceengland7(at)gmail.com
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| Posted: Sat Jul 09, 2016 4:13 pm Post subject: Z-13/8 Questions |
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FWIW, I spent a lot of years doing electronics repair, first on consumer
products and then industrial products. The post-2010 failure pics all
look like what electronics techs call 'cold solder joints'. Either bad
prep (dirty contacts or leads), or inadequate heat when soldering. I've
seen joint failures on circuit boards from TV sets that never move after
installation to industrial equipment valued at 6-7 figures. Every time I
dealt with it, cleaning the lead either mechanically (scraping) or by
using a good electronics grade flux during the re-soldering process,
cured the problem.
I have no reason to doubt your word that the components can move if
embedded in 'soft' potting compound, but.... in my opinion, a properly
soldered joint on a pc board pad like that would not fail due to
vibration. The pad/trace would peal up from the substrate, or the lead
would break, before the solder joint to the lead would fail. Properly
executed solder joints are much stronger than most people think.
Charlie
On 7/9/2016 6:24 PM, MMiller wrote:
| Quote: |
Bob
Here are the details of about a dozen Rotax regulator failures. Draw your own conclusion(s).
First some background. There are several versions of the Rotax 912/Ducati regulator. Older versions include Rotax PN 965-345/Ducati 383475, I believe this is the version examined on the http://contrails.free.fr/elec_ducati_en.php website. This was replaced by Rotax PN 965-347/Ducati 343620. This version was manufactured until late 2009 and was replaced by the current version, Rotax PN 965-349/Ducati 362001. I believe this change was driven by component obsolescence, the button case diode was no longer produced. My findings show there are two failure modes, depending on the version of the regulator.
The older pre 2010 regulators fail from the inability to adequately transfer heat from the diode assembly to the case. This causes the diodes to unsolder themselves from the assembly. Both diodes show signs of unsoldering, but, If look closely, the inboard diode always shows more heat damage then the outboard diode. This asymmetrical failure is likely caused by the asymmetrical geometry of the enclosure/heat sink. This is the only failure I have seen in this version regulator. This includes regulators with melted supply terminals (G pin,) the solder connections on these diodes show the same failure mode. I have not seen any component fail out of spec in any regulator examined.
Here a schematic/assy for this version
https://drive.google.com/open?id=0ByPxADyU-DwPdTQ3NWp5LW9iOHc
Typical failure mode
https://drive.google.com/open?id=0ByPxADyU-DwPTnlXcUVEQTdfcVU
Current production since 2010 uses a different diode package. This resolved the internal heatsinking issue of the older regulator versions. Unfortunately, at this time they changed to gel type potting compound. All the examined failures of this version are likely caused by vibration. This failure is unique to the regulators with the new gel potting compound, this failure mode is nonexistent on the older version regulators.
Here a schematic/assy for this version
https://drive.google.com/open?id=0ByPxADyU-DwPWTBBcGlUeENTcHc
Here are some failure photos
https://drive.google.com/open?id=0ByPxADyU-DwPYm1rYUVsbUJyQ3M
Heat is often the cause of failure in electronics, but these regulators fail from poor mechanical design and poor material choices, long before heat would kill them.
nuckolls.bob(at)aeroelect wrote:
> At 06:37 AM 7/5/2016, you wrote:
>
>>
>>
>> Mike Miller has done autopsies on several failed Ducati regulators and he attributes the failures to poor manufacturing and vibration,
> vibration in a potted assembly?
>
>
>> not from heat.
> Has he published a teardown report?
>
>
>> Some RV-12 owners have reported a gradual failure where they get low voltage alarms at RPMs where they used to have normal voltage. Each regulator could fail differently.
> Color me skeptical . . . these regulators have
> been in production for decades. There must have
> been thousands sold. Over that period of time
> and numbers of examples, I find it curious that
> a constellation of failure modes would emerge.
>
> .....
>
> Bob . . .
|
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MMiller
Joined: 07 Jul 2016
Posts: 8
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| Posted: Sun Jul 10, 2016 3:24 am Post subject: Re: Z-13/8 Questions |
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Charlie, Yes I agree with you, that was my first thought also. But the more I looked at these, the more my opinion evolved. I lean towards vibration on this version for several reasons;
1). Sample 1 of the post 2010 version photos had many failed solder joints but the ultimate failure was lead stress that sheared the gate pin at the body of the SCR. The same logic would suggest " how can this happen in a potted device."
2). This failure mode is nonexistent on the older versions without the gel type potting compound.
3). These don't fail out of the box, they run about 125 hours before failure...on average for these samples.
| ceengland7(at)gmail.com wrote: |
...The post-2010 failure pics all look like what electronics techs call 'cold solder joints'. ...
...
I have no reason to doubt your word that the components can move if
embedded in 'soft' potting compound, but.... in my opinion, a properly
soldered joint on a pc board pad like that would not fail due to
vibration. The pad/trace would peal up from the substrate, or the lead
would break, before the solder joint to the lead would fail. Properly
executed solder joints are much stronger than most people think.
Charlie
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