---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 07/15/14: 9 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:59 AM - Re: Re: Dual master solenoids (Sacha) 2. 07:53 AM - Re: Re: Dual master solenoids (Stein Bruch) 3. 11:56 AM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III) 4. 12:35 PM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III) 5. 01:34 PM - Re: Re: Dual master solenoids (Sacha) 6. 04:11 PM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III) 7. 06:59 PM - Re: Dual master solenoids (user9253) 8. 07:30 PM - Re: Re: Dual master solenoids (Sacha) 9. 07:42 PM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:59:49 AM PST US Subject: Re: AeroElectric-List: Re: Dual master solenoids From: Sacha It's also a safety issue with some starter configurations. For instance if you had a momentary push button for the starter instead of a key switch, even with the master off you would still be able to push the button and turn the prop. I have this configuration and as an added safety while the aircraft is stopped and the master needs to be on, I always pull the starter CB. Sacha > On 14 Jul 2014, at 14:06, "user9253" wrote: > > Having two contactors in series makes sure that the circuit can be opened. ________________________________ Message 2 _____________________________________ Time: 07:53:38 AM PST US From: "Stein Bruch" Subject: RE: AeroElectric-List: Re: Dual master solenoids Aside from some anecdotal references that are oft repeated at hangar flying sessions and on the interwebs, have you or do you know of a specific instance where a master contactor/solenoid of standard design failed repeatedly? All mechanical things have "been known to fail", but we build airplanes around the 99th percentile, not the 1th percentile. If you built a perfectly safe airplane, it would be one that wouldn't leave the ground....so to that end you design in for the 99th, but also take into account the 1th percentiles without doing crazy things like putting in two master contactors or two tachometers (unless of course you have two batteries, or two busses, etc..). If you are going to put in two of those, why not two starter buttons, or two circuit breakers for each circuit, or two throttle cables, or two rudders, or two elevator pushrods, (after all, those have also been known to fail)? You still do only have one camshaft and one propeller and one crankshaft and one carb/fuel injector, one brain, etc.. My point is that the probability of failure of that specific components is likely less than the probability of other equally as important mechanical things in your plane. There is no reason to randomly pick one particular component and focus on it over another when it has not proven to be a weak point in the entire aerospace vehicle system design. Just my 2 cents as usual, but one could come up with all sorts of 1th percentile "possibilities" that are really not worth expending energy, time, money, weight or complexity on as the return on all of that in actuality becomes a negative. Remember, adding things for "redundancy" does not necessarily and automatically translate into reliability - many times it has the inverse effect (increased complexity = decreased reliability). Cheers, Stein -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of user9253 Sent: Monday, July 14, 2014 7:07 AM Subject: AeroElectric-List: Re: Dual master solenoids > are heavy duty continuous service relays any less reliable than mechanical relays? If about the same reliability, what are the reasons that they aren't used more often for a master solenoid? There are several ways that a relay or contactor can fail. The contacts can develop a high resistance, the coil can burn open, springs or other mechanical parts can break, and etc. I do not know which type is more likely to fail. The current carrying capability determines which relay or contactor to use. Starters can draw a few hundred amps initially to get the engine rotating. A 30 amp automotive relay would not last very long carrying that much current. So why have the starter current go though the master contactor? The starter contactor could be wired directly to the battery. I think the reason is that contactors have been known to fail closed. Having two contactors in series makes sure that the circuit can be opened. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=426626#426626 ________________________________ Message 3 _____________________________________ Time: 11:56:28 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Dual master solenoids At 08:57 AM 7/15/2014, you wrote: > >It's also a safety issue with some starter configurations. For >instance if you had a momentary push button for the starter instead >of a key switch, even with the master off you would still be able to >push the button and turn the prop. Irrespective of the kind of switch that energizes the starter, I'm aware of no TC aircraft, or any OBAM aircraft wired per a Z-figure where this is the cased. The general rule of thumb for all airplanes is that opening the battery master contactor removes ALL power from the aircraft except for those items wired to a battery bus. Starters should be dead-in-place with the battery master off. >I have this configuration and as an added safety while the aircraft >is stopped and the master needs to be on, I always pull the starter CB. How was it that you came to wire your airplane this way? Bob . . . ________________________________ Message 4 _____________________________________ Time: 12:35:44 PM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Re: Dual master solenoids My point is that the probability of failure of that specific components is likely less than the probability of other equally as important mechanical things in your plane. There is no reason to randomly pick one particular component and focus on it over another when it has not proven to be a weak point in the entire aerospace vehicle system design. Precisely . . . When opening the seminar segment on reliability, I like to put a z-figure up on the screen, point to a component and ask, "What do you need to do if THIS part malfunctions?" At least one participant will suggest that it be replaced with a 'better part'. That's the segment where I pose the notion that the flight SYSTEM consists of an airframe, pilot, environment and expendable resources. From the time the wheels break ground until you're parked at the destination, the design goal is not break a sweat . . . irrespective of any component failure. The last few ideas offered at the end of the segment suggests that it doesn't matter if you buy electrical parts from Autozone, $high$ parts from Honeywell or TC aircraft parts from the Cessna warehouse . . . it is possible to ARCHITECTURE the electrical system such that no single component failure will induce an in-flight sweat. In the final analysis, you're more likely to have a bad day in the cockpit driven by events and conditions far removed from things electrical. #1 cause of engine stoppage is fuel starvation. #1 cause for unplanned arrivals with the earth are most often based on human factors for dealing with environment: weather, mountains, night ops, etc.) As we have studied many times here on the List . . . mishaps that included electrical issues were FIRST driven by lapses in assembly skills, failure tolerant design or poor maintenance. See: http://tinyurl.com/ky7szec In other words, "two parts" or a "better part" would not have produced a better outcome. Bob . . . ________________________________ Message 5 _____________________________________ Time: 01:34:20 PM PST US From: "Sacha" Subject: RE: AeroElectric-List: Re: Dual master solenoids >It's also a safety issue with some starter configurations. For instance >if you had a momentary push button for the starter instead of a key >switch, even with the master off you would still be able to push the >button and turn the prop. Irrespective of the kind of switch that energizes the starter, I'm aware of no TC aircraft, or any OBAM aircraft wired per a Z-figure where this is the cased. The general rule of thumb for all airplanes is that opening the battery master contactor removes ALL power from the aircraft except for those items wired to a battery bus. Starters should be dead-in-place with the battery master off. Hi Bob, I was referring to the hypothetical situation that Joe brought up where the starter contactor would be always hot, i.e. wired to the battery bus. >I have this configuration and as an added safety while the aircraft is >stopped and the master needs to be on, I always pull the starter CB. How was it that you came to wire your airplane this way? My apologies, I wasn't very clear... My electrical setup is essentially Z-16, but the starter button is a push button. So whenever I am tinkering around on the ground and the master needs to be on, I pull the starter CB just to be safe. Another situation is when my three year old wants to sit next to me in the a/c and see the panel light up and pretend he's flying the aircraft... :) ________________________________ Message 6 _____________________________________ Time: 04:11:22 PM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Re: Dual master solenoids My apologies, I wasn't very clear... My electrical setup is essentially Z-16, but the starter button is a push button. So whenever I am tinkering around on the ground and the master needs to be on, I pull the starter CB just to be safe. Another situation is when my three year old wants to sit next to me in the a/c and see the panel light up and pretend he's flying the aircraft... :) Understand . . . thanks! Bob . . . ________________________________ Message 7 _____________________________________ Time: 06:59:01 PM PST US Subject: AeroElectric-List: Re: Dual master solenoids From: "user9253" > I was referring to the hypothetical situation that Joe brought up > where the starter contactor would be always hot, i.e. wired to the battery > bus. I did not bring that up. I was referring to tomhanaway's post where he wrote, "the always hot side of the starter solenoid (always hot when master solenoid is hot)". It is much easier to understand each other when talking face to face compared to email or forum postings. :-) Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=426748#426748 ________________________________ Message 8 _____________________________________ Time: 07:30:26 PM PST US Subject: Re: AeroElectric-List: Re: Dual master solenoids From: Sacha Hi Joe Sorry for the confusion. Indeed it would be easier face to face. Sacha Do not archive > On Jul 16, 2014, at 3:57, "user9253" wrote: > > I did not bring that up. I was referring to tomhanaway's post where he wrote, "the always hot side of the starter solenoid (always hot when master solenoid is hot)". > It is much easier to understand each other when talking face to face compared to email or forum postings. :-) ________________________________ Message 9 _____________________________________ Time: 07:42:07 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Dual master solenoids > > It is much easier to understand each other when talking face to > face compared to email or forum postings. I'm wrestling with a similar phenomenon in crafting recommendations for crafting requirements documents. I use as many drawings and pictures as I can . . . a picture is worth 10,000 words. The flip side is not true . . . 10,000 words interpreted by ten different readers will NOT create identical images in the minds of the readers. My clients a loath to ask their charges to learn to draw . . . That's why I use my scanner, cameras and links to posted illustrations to augment the words . . . you can't have too many pictures but more words you have, the fuzzier the ideas become. Bob . . . ------------------------------------------------------------------------------------- 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.