---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 10/02/23: 10 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 10:09 AM - Re: OVM14 MkIII, rev P3 (Robert L. Nuckolls, III) 2. 11:46 AM - Re: OVM14 MkIII, rev P3 (user9253) 3. 01:35 PM - Re: OVM14 MkIII, rev P3 (Eric Page) 4. 01:58 PM - Re: Official AeroElectric-List Usage Guidelines (John Bright) 5. 02:31 PM - Re: Official AeroElectric-List Usage Guidelines (Jeff Holdridge) 6. 02:49 PM - Re: Re: OVM14 MkIII, rev P3 (Robert L. Nuckolls, III) 7. 07:26 PM - Re: PVC Conduit in Certificated Aircraft (Alec Myers) 8. 07:28 PM - Re: PVC Conduit in Certificated Aircraft (Alec Myers) 9. 10:02 PM - Re: Re: OVM14 MkIII, rev P1 (Robert L. Nuckolls, III) 10. 10:34 PM - Re: PVC Conduit in Certificated Aircraft (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 10:09:41 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: OVM14 MkIII, rev P3 At 01:42 PM 10/1/2023, you wrote: > >Bob, I can't argue with your logic. However, airplanes are toys for many of >us. And builders like to equip their toys with more toys. Take for instance >the VP-X Electronic Circuit Breaker System. It has lots of nice >features. But a >builder could install fuses for much less money than the sales tax >on the VP-X. >Even so, many builders elect to install the VP-X because they want the >extra features. It is the same with the over-voltage module. Some pilots >want the extra feature of an over-voltage indicator light. Others >might elect >to not install the light or reset button. No argument there my friend. Certainly everyone here on the list is encouraged to fabricate the airplane of their dreams. I hope that what I bring to the List is several decades of experience in keep it simple, light as possible, low cost as possible, absolute conformance to a well stated design goal, more than passing homage to lessons learned and human factors. Yeah . . . the VPX system is a good case study. I'm recalling conversations with pilots while working the GP180 project at Lear. Over lunch one day, we were discussing the features of the latest EFIS/Navigation system being integrating into the proposed new airplane. One fellow opined that he was really pleased with some of our proposals, "Yeah, all that stuff gives us something to pass the time during hours of watching the ground crawl slowly below." I was tempted to suggest a pocket video game but I kept my mouth shut. I may come off as curmudgeonly in these discussions. For every one participating there are 10x present and future readers perhaps not so confident/capable of sorting out the issues. Some of these readers might be better served by crafting an airplane that behaves very much like their grandpa's C170. Not trying to be a hard-ass . . . just encouraging everyone to achieve personal goals with a foundation of understanding. Speaking of the test switch 'option', I have incorporated it onto the ECB as a maintenance aid. Latest iteration of the schematic attached. Also did a real estate survey. I think I can get this critter assembled and packaged it only 1/4" longer than the legacy design. Further, it has retained the simple, two wire integration feature of the older offerings. One can ignore the switch and have it work just like the first few hundred examples did. Opps, already spotted a 'bug'. R10 calculated value is 56.2K Bob . . . //// (o o) ===========o00o=(_)=o00o======== < Go ahead, make my day . . . > < show me where I'm wrong. > ================================ In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ________________________________ Message 2 _____________________________________ Time: 11:46:43 AM PST US Subject: AeroElectric-List: Re: OVM14 MkIII, rev P3 From: "user9253" Suggestion: Instead of having a wire or wires exiting the over-voltage module for an external switch, use an internal solid state switch that is magnetically operated. These devices are small like a transistor and go by various names: digital magnetoresistive sensors, Unipolar Hall-effect sensor ICs, unipolar switches, Hall effect IC, Hall switch. Some of these devices require either a north or south magnetic pole. Others are bipolar. They cost from less than a dollar on up. For the annual OVM test, a magnet is held near a certain spot on the OVM. The OVM could be mounted on one side of aluminum skin and the magnet held on the other side. No external wires or switch required -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=511540#511540 ________________________________ Message 3 _____________________________________ Time: 01:35:04 PM PST US Subject: AeroElectric-List: Re: OVM14 MkIII, rev P3 From: "Eric Page" Bob, did my questions about your Rev P1 schematic slip by unnoticed? See the second post in this thread: http://forums.matronics.com/viewtopic.php?t=16781079 My 2nd question is resolved by Rev P3 but I'm still curious about questions 1, 3 and 4. Please ignore my last question, below the dashes. I found the answer. -Eric Read this topic online here: http://forums.matronics.com/viewtopic.php?p=511541#511541 ________________________________ Message 4 _____________________________________ Time: 01:58:54 PM PST US From: John Bright Subject: Re: AeroElectric-List: Official AeroElectric-List Usage Guidelines Thanks Matt... question... any way to get my account fixed so I can post on the Aeroelectric List website? Thanks, John Bright Newport News, VA cell: 757-812-1909 john_s_bright@outlook.com ________________________________ From: owner-aeroelectric-list-server@matronics.com on behalf of Matt Dralle Sent: Monday, October 2, 2023 02:00 Subject: AeroElectric-List: Official AeroElectric-List Usage Guidelines Dear Listers, Please read over the AeroElectric-List Usage Guidelines below. The complet e AeroElectric-List FAQ including these Usage Guidelines can be found at the following URL: http://www.matronics.com/FAQs/AeroElectric-List.FAQ.html Thank you, Matt Dralle Matronics Email List Administrator *************************************************************************** *** AeroElectric-List Usage Guidelines *************************************************************************** *** The following details the official Usage Guidelines for the AeroElectric-Li st. You are encouraged to read it carefully, and to abide by the rules therein. Failure to use the AeroElectric-List in the manner described below may resu lt in the removal of the subscribers from the List. AeroElectric-List Policy Statement The purpose of the AeroElectric-List is to provide a forum of discussion fo r things related to this particular discussion group. The List's goals are to serve as an information resource to its members; to deliver high-quality content; to provide moral support; to foster camaraderie among its members; and to support safe operation. Reaching these goals requires the participation and cooperation of each and every member of the List. To this end, the following guidelines have been established: - Please keep all posts related to the List at some level. Do not submit posts concerning computer viruses, urban legends, random humor, long lost buddies' phone numbers, etc. etc. - THINK carefully before you write. Ask yourself if your post will be relevant to everyone. If you have to wonder about that, DON'T send it. - Remember that your post will be included for posterity in an archive that is growing in size at an extraordinary rate. Try to be concise and terse in your posts. Avoid overly wordy and lengthy posts and responses. - Keep your signature brief. Please include your name, email address, aircraft type/tail number, and geographic location. A short line about where you are in the building process is also nice. Avoid bulky signatures with character graphics; they consume unnecessary space in the archive. - DON'T post requests to the List for information when that info is easily obtainable from other widely available sources. Consult the web page or FAQ first. - If you want to respond to a post, DO keep the "Subject:" line of your response the same as that of the original post. This makes it easy to find threads in the archive. - When responding, NEVER quote the *entire* original post in your response. DO use lines from the original post to help "tune in" the reader to the topic at hand, but be selective. The impact that quoting the entire original post has on the size of the archive can not be overstated! - When the poster asks you to respond to him/her personally, DO NOT then go ahead and reply to the List. Be aware that clicking the "reply" button on your mail package does not necessarily send your response to the original poster. You might have to actively address your response with the original poster's email address. - DO NOT use the List to respond to a post unless you have something to add that is relevant and has a broad appeal. "Way to go!", "I agree", and "Congratulations" are all responses that are better sent to the original poster directly, rather than to the List at large. - When responding to others' posts, avoid the feeling that you need to comment on every last point in their posts, unless you can truly contribute something valuable. - Feel free to disagree with other viewpoints, BUT keep your tone polite and respectful. Don't make snide comments, personally attack other listers, or take the moral high ground on an obviously controversial issue. This will only cause a pointless debate that will hurt feelings, waste bandwidth and resolve nothing. - Occasional posts by vendors or individuals who are regularly subscribed to a given List are considered acceptable. Posts by List members promoting their respective products or items for sale should be of a friendly, informal nature, and should not resemble a typical SPAM message. The List isn't about commercialism, but is about sharing information and knowledge. This applies to everyone, including those who provide products to the entire community. Informal presentation and moderation should be the operatives with respect to advertising on the Lists. ------- [This is an automated posting.] do not archive ________________________________ Message 5 _____________________________________ Time: 02:31:06 PM PST US From: Jeff Holdridge Subject: Re: AeroElectric-List: Official AeroElectric-List Usage Guidelines Same here.=C2- Can't log into my newly approved account. Sent from Yahoo Mail on Android On Mon, Oct 2, 2023 at 3:09 PM, John Bright wr ote: Thanks Matt... question... any way to get my account fixed so I can post on the Aeroelectric List website? Thanks, John Bright Newport News, VA cell: 757-812-1909 john_s_bright@outlook.com From: owner-aeroelectric-list-server@matronics.com on behalf of Matt Dralle Sent: Monday, October 2, 2023 02:00 Subject: AeroElectric-List: Official AeroElectric-List Usage Guidelines=C2 om> Dear Listers, =C2- Please read over the AeroElectric-List Usage Guidelines below.=C2- The co mplete AeroElectric-List FAQ including these Usage Guidelines can be found at the following URL: =C2- =C2-=C2- http://www.matronics.com/FAQs/AeroElectric-List.FAQ.html =C2- Thank you, =C2- Matt Dralle Matronics Email List Administrator =C2- =C2- *************************************************************************** *** =C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2 -=C2-=C2-=C2-=C2-=C2-=C2-=C2- AeroElectric-List Usage Guide lines *************************************************************************** *** The following details the official Usage Guidelines for the AeroElectric-Li st. You are encouraged to read it carefully, and to abide by the rules therein. Failure to use the AeroElectric-List in the manner described below may resu lt in the removal of the subscribers from the List. AeroElectric-List Policy Statement The purpose of the AeroElectric-List is to provide a forum of discussion fo r things related to this particular discussion group.=C2- The List's goals are to serve as an information resource to its members; to deliver high-quality content; to provide moral support; to foster camaraderie among its members; and to support safe operation.=C2- Reaching these goal s requires the participation and cooperation of each and every member of the List.=C2- To this end, the following guidelines have been established : =C2-- Please keep all posts related to the List at some level.=C2- Do n ot submit =C2-=C2- posts concerning computer viruses, urban legends, random humor , long =C2-=C2- lost buddies' phone numbers, etc. etc. =C2-- THINK carefully before you write.=C2- Ask yourself if your post w ill be =C2-=C2- relevant to everyone.=C2- If you have to wonder about that, DON'T send it. =C2-- Remember that your post will be included for posterity in an archiv e =C2-=C2- that is growing in size at an extraordinary rate.=C2- Try to be concise and =C2-=C2- terse in your posts.=C2- Avoid overly wordy and lengthy post s and =C2-=C2- responses. =C2-- Keep your signature brief.=C2- Please include your name, email ad dress, =C2-=C2- aircraft type/tail number, and geographic location.=C2- A sh ort line =C2-=C2- about where you are in the building process is also nice.=C2 - Avoid =C2-=C2- bulky signatures with character graphics; they consume unneces sary =C2-=C2- space in the archive. =C2-- DON'T post requests to the List for information when that info is =C2-=C2- easily obtainable from other widely available sources.=C2- C onsult the =C2-=C2- web page or FAQ first. =C2-- If you want to respond to a post, DO keep the "Subject:" line of =C2-=C2- your response the same as that of the original post.=C2- Thi s makes it =C2-=C2- easy to find threads in the archive. =C2-- When responding, NEVER quote the *entire* original post in your =C2-=C2- response.=C2- DO use lines from the original post to help "t une in" the =C2-=C2- reader to the topic at hand, but be selective.=C2- The impac t that =C2-=C2- quoting the entire original post has on the size of the archiv e =C2-=C2- can not be overstated! =C2-- When the poster asks you to respond to him/her personally, DO NOT =C2-=C2- then go ahead and reply to the List.=C2- Be aware that click ing the =C2-=C2- "reply" button on your mail package does not necessarily send your =C2-=C2- response to the original poster.=C2- You might have to activ ely address =C2-=C2- your response with the original poster's email address. =C2-- DO NOT use the List to respond to a post unless you have something =C2-=C2- to add that is relevant and has a broad appeal.=C2- "Way to go!", "I =C2-=C2- agree", and "Congratulations" are all responses that are bette r sent =C2-=C2- to the original poster directly, rather than to the List at la rge. =C2-- When responding to others' posts, avoid the feeling that you need t o =C2-=C2- comment on every last point in their posts, unless you can tru ly =C2-=C2- contribute something valuable. =C2-- Feel free to disagree with other viewpoints, BUT keep your tone =C2-=C2- polite and respectful.=C2- Don't make snide comments, person ally attack =C2-=C2- other listers, or take the moral high ground on an obviously =C2-=C2- controversial issue.=C2- This will only cause a pointless de bate that =C2-=C2- will hurt feelings, waste bandwidth and resolve nothing. =C2-- Occasional posts by vendors or individuals who are regularly =C2-=C2- subscribed to a given List are considered acceptable.=C2- Po sts by =C2-=C2- List members promoting their respective products or items for sale =C2-=C2- should be of a friendly, informal nature, and should not resem ble =C2-=C2- a typical SPAM message.=C2- The List isn't about commerciali sm, but =C2-=C2- is about sharing information and knowledge.=C2- This applies to =C2-=C2- everyone, including those who provide products to the entire =C2-=C2- community.=C2- Informal presentation and moderation should b e the =C2-=C2- operatives with respect to advertising on the Lists. ------- =C2- [This is an automated posting.] =C2- do not archive =C2- =C2- ric-List Email Forum - Electric-List">http://www.matronics.com/Navigator?AeroElectric-List p;=C2-=C2- - MATRONICS WEB FORUMS - ums.matronics.com p;=C2- - NEW MATRONICS LIST WIKI - matronics.com p; - List Contribution Web Site - p;=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- =C2-=C2-=C2-=C2-=C2- -Matt Dralle, List Admin. ps://matronics.com/contribution ________________________________ Message 6 _____________________________________ Time: 02:49:20 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: OVM14 MkIII, rev P3 At 01:46 PM 10/2/2023, you wrote: > >Suggestion: Instead of having a wire or wires exiting the over-voltage module >for an external switch, use an internal solid state switch that is >magnetically >operated. > No external wires or switch required Hadn't considered that but it could probably work. Perhaps a reed switch. They'll operate on either magnetic polarity. Opted for the dip-switch. Gold, low-level contacts, environmentally robust. No external 'tools' needed. Bob . . . //// (o o) ===========o00o=(_)=o00o======== < Go ahead, make my day . . . > < show me where I'm wrong. > ================================ In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ________________________________ Message 7 _____________________________________ Time: 07:26:24 PM PST US From: Alec Myers Subject: Re: AeroElectric-List: PVC Conduit in Certificated Aircraft I have a small certified aircraft with PVC tubes. I just read the 3000 hour inspection checklist that requires them to be inspected. Theres a cable conduit under the cabin floor that Im pretty sure is PVC, although Im not sure if thats one that needs inspecting. Some of the control surfaces have PVC tubes in. Searching through the maintenance manual, I see that the entire structure of the aircraft is described variously as "GRP skins [AND] a rigid PVC foam core, and theres a lot of rigid PVC foam too. On Oct 1, 2023, at 12:37, Jeff Luckey wrote: Bob and others, I want to summarize ... Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules. Right on the money, as usual. However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe. If an A&P/IA completes a 337 and gets it approved by their local FSDO, a piece of PVC could be used in a Certificated airplane. It is really up to the FSDO and the relationship that A&P has with them. I understand that the approval process might be challenging, but there is no reg that prohibits the use of PVC as a conduit. Over the past few years, I have come to discover that what is dis-allowed by one FSDO might be approved by another. I was surprised to find out just how capricious and inconsistent the application of the rules is from district to district across the country. For the record, I am not considering using PVC for a conduit in a Certificated or Experimental aircraft. Based on my understanding of the toxic properties of PVC, I would not consider it. I had overheard a conversation with an IA who suggested using a piece of PVC in the tail of an Experimental and he went on to say that "he had done it in a Cessna". And I thought that was odd and I also thought: "I wouldn't let this guy work on MY airplane". -Jeff On Saturday, September 30, 2023 at 06:37:37 PM PDT, Robert L. Nuckolls, III wrote: At 11:57 AM 9/30/2023, you wrote: > Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft? A TC aircraft left the factory configured per approved drawings. Substituting any part not on that drawing requires an approval via one-time field approval (Form 337) or an STC. I can't imagine any licensed technician attempting to 'sell' such a deviation to the local FSDO. What kind of 'mod' are we talking about? If the wires were not part of the original TC then one is advised to rely on legacy practices when submitting a Form 337. To be sure, PVC plumbing would not fall in that category. Bob . . . //// (o o) ===========o00o=(_)=o00o========= < Go ahead, make my day . . . > < show me where I'm wrong. > ================================ In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ________________________________ Message 8 _____________________________________ Time: 07:28:07 PM PST US From: Alec Myers Subject: Re: AeroElectric-List: PVC Conduit in Certificated Aircraft Sorry - that should say a lot of rigid PVC honeycomb too. On Oct 2, 2023, at 22:25, Alec Myers wrote: I have a small certified aircraft with PVC tubes. I just read the 3000 hour inspection checklist that requires them to be inspected. Theres a cable conduit under the cabin floor that Im pretty sure is PVC, although Im not sure if thats one that needs inspecting. Some of the control surfaces have PVC tubes in. Searching through the maintenance manual, I see that the entire structure of the aircraft is described variously as "GRP skins [AND] a rigid PVC foam core, and theres a lot of rigid PVC foam too. On Oct 1, 2023, at 12:37, Jeff Luckey wrote: Bob and others, I want to summarize ... Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules. Right on the money, as usual. However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe. If an A&P/IA completes a 337 and gets it approved by their local FSDO, a piece of PVC could be used in a Certificated airplane. It is really up to the FSDO and the relationship that A&P has with them. I understand that the approval process might be challenging, but there is no reg that prohibits the use of PVC as a conduit. Over the past few years, I have come to discover that what is dis-allowed by one FSDO might be approved by another. I was surprised to find out just how capricious and inconsistent the application of the rules is from district to district across the country. For the record, I am not considering using PVC for a conduit in a Certificated or Experimental aircraft. Based on my understanding of the toxic properties of PVC, I would not consider it. I had overheard a conversation with an IA who suggested using a piece of PVC in the tail of an Experimental and he went on to say that "he had done it in a Cessna". And I thought that was odd and I also thought: "I wouldn't let this guy work on MY airplane". -Jeff On Saturday, September 30, 2023 at 06:37:37 PM PDT, Robert L. Nuckolls, III wrote: At 11:57 AM 9/30/2023, you wrote: > Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft? A TC aircraft left the factory configured per approved drawings. Substituting any part not on that drawing requires an approval via one-time field approval (Form 337) or an STC. I can't imagine any licensed technician attempting to 'sell' such a deviation to the local FSDO. What kind of 'mod' are we talking about? If the wires were not part of the original TC then one is advised to rely on legacy practices when submitting a Form 337. To be sure, PVC plumbing would not fall in that category. Bob . . . //// (o o) ===========o00o=(_)=o00o========= < Go ahead, make my day . . . > < show me where I'm wrong. > ================================ In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ________________________________ Message 9 _____________________________________ Time: 10:02:58 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: OVM14 MkIII, rev P1 Eric: My 2nd question is resolved by Rev P3 but I'm still curious about questions 1, 3 and 4. Ach!!! Sorry 'bout that! At 02:50 PM 9/22/2023, you wrote: > >A few things that I noticed... > >1. Absolute maximum cathode-to-anode voltage on >the LM431 is 37V (see TI and onsemi >datasheets). A significant OV event could >exceed that limit until the crowbar brings bus >voltage under control. This might not be an >issue with a lead-acid battery, but the OV >behavior of the BMS in lithium batteries is >unknown. If a lithium BMS disconnects pronto, >bus voltage could rise farther and more quickly than with lead-acid on the job. > >Q: Should there be a 33V Zener in parallel to protect the LM431? The LM431 IS a zener. It's biased up thru 392 ohm R1. So the 10V Vcc rail is rigid. If anything is at-risk from a bus voltage excursion, it's probably R1. >----- > >2. The recommended maximum voltage on LM293 >inputs is Vcc minus 2V (see table 6.2 in the TI >datasheet). In this case Vcc is 8V, so the max input voltage is 6V. >- The 7V reference exceeds 6V on the inverting inputs of both comparators. >- Any bus voltage >13.64V will exceed 6V on the non-inverting input of U16A. >- Timing capacitor C11 on the non-inverting input of U16B will charge to 8V. Yeah, raised Vcc to 10V. Changed trip reference to 2.5V. The Non inverting input to U16B will not exceed 8V 'cause that's where the SCR trips. >Q: Should the comparator reference be adjusted >downward (perhaps delete R4, adjust R3/R5, and >use the LM431's 2.5V reference for the comparators)? Yup. >Q: Should the non-inverting inputs be protected with 5.1V Zeners? Nope . . . >----- > >3. In recent discussion of the OVM task you >mentioned your intent to make the trip delay >500mS +/- 50mS. This schematic provides ~200mS. > >Q: Have you reconsidered the 500mS trip delay? Not necessarily. Legacy OVM management devices were oblivious to the 20V for 1 second qualification requirements under DO160. Powers that be were fond of the 50mS value for step response from 14.2 to 20V. I think I mentioned having offered a very similar configuration and running the delay out further. Early days solid-state latches for OV management were plagued with nuisance trips very short, low energy noises on the bus that would do a dv/dt trigger of the scr. Ultimately managed with the 0.1 uF cap right across the SCR combined with low value resistor gate to cathode (which drives up required trigger current). This design now ties the gate to ground through the open collector output of U11B. I'm anticipating dv/dt issues to be irrelevant. AS to selection of time delay certainly much longer than 50mS and much smaller than 1 second. 500mS seems like a happy medium but given the self-resetting nature of the comparator/timer, 200mS is probably comfortable too. Either value honors design guidance of DO160/Mil-Std-704 The current proposal offers a way to select ov trip, maintenance trip and trip delay values with a simple adjustment of resistors. >----- > >4. Schematic Note 1 contemplates a crowbar >current of 100-200A DC for 25mS. The BT139-600E >SCR datasheet shows a peak non-repetitive >on-state current of 155A, but that specification >assumes an initial junction temperature of >25degC (unlikely under an engine cowling), a >pulse duration =89=A420mS and a full-sine-wave AC pulse, not DC. Those have been proven conservative . . . especially in later years of SCR offerings. Beech had a qualification requirement to effect 50 shutdowns in a row, each about 2 seconds apart, with the 51st still in spec. That protocol arose from the fact that the weakest link in contemporary ov RELAY designs was relay CONTACTS failing to break the inductively stabilized ARC. Powers that be assumed that no airplane would every experience 50 OV events, hence the BIG HAMMER test. It was during development of the prototype Beech Lightning (single engine turboprop) that not a single OV relay in Beech inventory would pass the test including those we sold at Electo-Mech. When Jack Thurman called to tell me the sad story, I told him I'd be in his office in an hour. I modified one of our stock regulator/ov relay products to a CrowbarSCR configuration and took it out to try on the bench test. When Jack hit the OV initiate button, he thought something was broke. No squawks from the alternator, no great flashing of panel lights. The chart recorder showed a rather un-impressive rise to 32 volts whereupon the system was quietly shut down. "Yeah says Jack, will it do it 50 times?" "You bet says I". The previously stressed devices was a relay trying to break an inductively driven ARC. Now, major stress was on a circuit breaker qualified for thousands of operations doing the job it was designed for . . . clear a faulted feeder. Had the Lightning project continued to production, I have no doubt that the crowbar ov management system would see it's first application in a TC aircraft. Unfortunately, volume production of crowbar ov management had to wait until it appeared in the B&C LR series regulators which eventually made it onto TC aircraft. Lamar, PlanePower and others picked up on the idea . . . tens of thousands of crowbar ov sytems are flying today. Indeed, the 50x tests were no problem. Only time we lost SCRs was when someone tried to crowbar a fatter breaker . . . or one with a particularly long operate time. Typically, our favorite style of miniature breaker opens in 25mS or less. >Q: Can the BT139-600E handle this crowbar >task? If not, could you swap U16B's inputs and >interpose a P-FET to trigger a beefier SCR? Don't think this will be necessary. All of our OVM-14 versions used SCR's with rather benign single cycle ratings. But just for grins and in honor of Jack Thurman's skeptical testing protocols, I'll do the 50x test at 100A. I'll go rescue my environmental chamber from a lab in Wichita so I can test it at temperature . . . say -20 to +150F. Bob . . . //// (o o) ===========o00o=(_)=o00o======= = < Go ahead, make my day . . . > < show me where I'm wrong. > ======================== ======== In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ________________________________ Message 10 ____________________________________ Time: 10:34:47 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: PVC Conduit in Certificated Aircraft >Bob and others, > >I want to summarize ... > >Bob - I understand, agree with, and appreciate your cogent and >concise explanation of the rules. Right on the money, as usual. > >However, as far as anyone who responded knows, there is no FAR or >other regulation that would prohibit the use of a PVC conduit in a >Certificated airframe. Didn't say there was . . . only that deviations from the airplane's type certification is to be discouraged without overriding approval lest lightning from on high come down and smite thee. Now, if some manufacture has achieved certification with ANY particular material, then that TC becomes "approved data" but only for that particular application. PVC approved in one place doesn't say okay to use anywhere. >If an A&P/IA completes a 337 and gets it approved by their >local FSDO, a piece of PVC could be used in a Certificated >airplane. It is really up to the FSDO and the relationship >that A&P has with them. I understand that the approval >process might be challenging, but there is no reg that >prohibits the use of PVC as a conduit. I recall rules that speak to flammability of any material used on the airframe. The topic got really hot after Swissair 111 suffered some soft fault ignition of insulation in the overhead. Something about flaming drips, self extinguishing times, fumes, proximity to critical systems, etc. Yup, here 'tis: https://www.faa.gov/documentlibrary/media/advisory_circular/ac%2023-2a.pdf >Over the past few years, I have come to discover that what is >dis-allowed by one FSDO might be approved by another. I >was surprised to find out just how capricious and inconsistent >the application of the rules is from district to district across the country. You got that right! In years past seekers of royal permission would FSDO Shop . . . Back then Ft. Worth and Seattle were popular shops. Last I heard, the practice was halted with a directive, "Tho shalt seek blessings only from thy local FSDO." I think the Teterboro office got miffed 'cause nobody ever asked them for permission/guidance . . . wonder why. >I had overheard a conversation with an IA who suggested using a >piece of PVC in the tail of an Experimental and he went on to >say that "he had done it in a Cessna". And I thought >that was odd and I also thought: "I wouldn't let this guy work on MY >airplane". I wonder if he jumped the hoops for paperwork. There's nothing inherently hazardous for incorporation of PVC . . . depends on application and exacerbation of risk. But the absolutely minimal risk solutions call for consideration of better materials first. I suspect PVC conduit in the tailcone is not a significant elevation of risk. Bob . . . //// (o o) ===========o00o=(_)=o00o======== < Go ahead, make my day . . . > < show me where I'm wrong. > ================================ In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ------------------------------------------------------------------------------------- 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.