---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 08/16/19: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:15 AM - Re: TC wire and dsub (Robert L. Nuckolls, III) 2. 03:30 PM - Revmaster PM alternators (dj_theis) 3. 05:48 PM - Re: Flaky EGT Probe (fidot) ________________________________ Message 1 _____________________________________ Time: 07:15:00 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: TC wire and dsub At 08:36 AM 8/15/2019, you wrote: > >Theoretically, extending thermocouple wires using a dsub connector >(with, say, gold over bronze contacts) should be ok provided any >temperature gradient across the connector is ignored. The >thermocouple voltages across the connector cancel out to 0. > >In practice there could be a problem with corrosion of a >thermocouple wire where it meets gold. Gold is electrolytically inert. I think most thermocouple alloys are similarly resistant to oxidation. I've run TC wires though d-subs for decades with good success . . . with one caveat: My tasks were temporary instrumentation installations so I've not personally observed/demonstrated longevity in field service. But given the low reactivity of the alloys involved, I'm pretty confident that they'll last a long time. Bob . . . ________________________________ Message 2 _____________________________________ Time: 03:30:12 PM PST US Subject: AeroElectric-List: Revmaster PM alternators From: "dj_theis" The subject of the Revmaster PM alternators has come up in the past, regarding the regulators used and the nature of how best to wire them. In summary, I think Professor Nuckolls declared there was not enough detail to offer significant, specific advice. I have a little more detail of a failure that was posted on the SonexBuilders forum and would like to toss this to the AeroElectric group and see what wisdom I might extract. My interest is related to the fact that I have a Revmaster (R2300), the same design as what is noted in the following story. The Revmaster has a dual PM alternator setup as part of the flywheel assembly. Two separate failures with very similar circumstances go as follows: Dual PM alternators with the default, dual regulators. Both planes had both alternators wired to charge full time. One engine did not have any method of shutoff of either regulator (hardwired) and the other may have chosen to always run with both (even though switches may have allowed for single PM operation) One engine had 160 hours running with this configuration and the second had 450 hours. Both had Odyssey PC680 batteries. The 160 hour plane experienced a difficult time starting the engine while exiting KOSH a few weeks back and after wearing down the battery significantly (my assumption, as it was reported that it took 30 minutes of cranking to finally get started with no note of any ground recharging once is started). Once the plane was started and after about 10 minutes in the air, the pilot noticed a smell of smoke and promptly returned to KOSH. I think the plane was eventually trailered back home (to TX) and upon disassembly, the stator(s) were/ was diagnosed as "fried." Please review the included drawing. I've added the relays and selection switches but for the sake of this discussion, imagine the switches for PM selection are both left in the "ON" state. I also have the patent of what I think the 2 wire regulator details include and will dig it out but I think it was posted in the past. I've simplified the regulator in my sketch as an SCR controlled by a black box. An interesting note, the two (20 amp) auto fuses were not blown. I need to verify if one or both of the stators were destroyed and likewise, if all 4 of the PM regulator fuses were OK. The second plane had 450 hours running both alternators full time during those hours. As noted, same battery (PC680). I don't know if this failure had fuse failures for the regulator, I don't believe so. I'll double check the report but the pilot smelled smoke about 6 minutes after takeoff and once he landed and had everything apart he identified that the stator was toast. Again, I'm not sure if both sides had failed or just one. I'll follow up and check. The manufacturer (Remaster) recommended not running both alternators at the same time and pointed to this as a likely contributing factor. He also indicated that the PC680 was partially to blame. His comment was that the RVLA batteries draw too much current. Hmmm, why did the fuses not blow then..... I think I know what the consensus will be regarding the PC680 (not likely a contributor to the debacle). My sense, because the 20 amp inline fuses did not blow, that the stators were not overloaded (else they have the wrong fuse selection)..I've heard that each alternator is capable 18 amps but the detailed specifications are very limited. I plan on checking my engine alternators for open circuit voltage curves and short circuit current. I'm just a little ways away from that... The alternators are (as can be seen) single phase. I believe the two alternators are in phase (I need to verify if it's possible to wire them so they charge out of phase, i.e. the regulator is half wave so it might be that each alternator could provide a half wave charge pulse, out of phase with the other. My theory (aside from agreeing that only one system can run at a time) is that running both on a heavily discharged battery allowed both regulators to operate. At some point, the battery reached a "closer to" full voltage level and as might be expected, one of the regulators started opening the charge circuit from the alternator. If this occurred at the wrong time, with the other regulator running, the inductive voltage spike(s) burned a hole in the stator winding insulation at one or more spots. the result, a fried stator. What do you guys think? I look forward to hearing opinions. Dan Theis Sonex 1362R -------- Scratch building Sonex #1362 Read this topic online here: http://forums.matronics.com/viewtopic.php?p=490910#490910 Attachments: http://forums.matronics.com//files/revmaster_regulators_111.pdf http://forums.matronics.com//files/revmaster_regulators_880.pdf ________________________________ Message 3 _____________________________________ Time: 05:48:45 PM PST US Subject: AeroElectric-List: Re: Flaky EGT Probe From: "fidot" Art, For what it's worth, when I had a similar problem on my EI Engine Monitor, it turned out to be the bad input channel rather than probe. I'd start with trying to move it to another channel (ie, swap two probes) and seeing what happens... unless you've already done that... Read this topic online here: http://forums.matronics.com/viewtopic.php?p=490911#490911 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.