---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 09/27/09: 11 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:20 AM - Re: Why have a switch on ALT Field? (rvg8tor) 2. 03:16 AM - Re: Re: Why have a switch on ALT Field? (Jay Hyde) 3. 06:47 AM - Re: Why have a switch on ALT Field? (rckol) 4. 06:50 AM - Why have a switch on ALT Field? () 5. 07:41 AM - Re: Re: Welding cable (Robert L. Nuckolls, III) 6. 07:47 AM - While on the topic of alternators (Robert L. Nuckolls, III) 7. 08:07 AM - Re: Why have a switch on ALT Field? (Joe) 8. 08:57 AM - Re: Re: Why have a switch on ALT Field? (Kelly McMullen) 9. 11:27 AM - Re: Re: Why have a switch on ALT Field? (Tony Babb) 10. 02:18 PM - Re: Why have a switch on ALT Field? (Robert L. Nuckolls, III) 11. 02:26 PM - Re: Re: Why have a switch on ALT Field? (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 12:20:59 AM PST US Subject: AeroElectric-List: Re: Why have a switch on ALT Field? From: "rvg8tor" Bob, I know you are trying to help but, this last post does not seem to help me, it actually confuses me. I respect your experience but I am not trying to design an electrical system from scratch, much like I did not design my RV-8A from scratch. I picked a plane from a good designer (Van's). While building I study the plans and try to understand how the parts relate to be a better builder, if I have a question I call builder assistance and I ask questions on the forum. When it came to the electrical system, I went with a design from an expert in the field, in studying the design I asked a simple question, 'why is the alternator field switch needed". There have been a lot of words written, much of which my little brain doesn'tunderstand how it relates to the very simple question. The possible answers I was expecting were: 1. It has always been done that way 2. It doesn't matter the non-switch method will work but has these limitations (fill in the blanks) 3. You need the switch because if you don't have one it will cause XYZ. Some of what you wrote I get but I really just need the simple short answer, not a run down on design philosophy. Since you designed the systems I thought of all people you could provide the best explanation. I thank you for attempting to answer my questions, if nothing else you have convinced me not to deviate from the Z diagram. I can't say that I understand fully why the alternator field switch is a requirement other than to provide a convenient way to turn off the field. I look forward to the simple answer if there is one. -------- Mike "Nemo" Elliott RV-8A QB (Fuselage) Read this topic online here: http://forums.matronics.com/viewtopic.php?p=265184#265184 ________________________________ Message 2 _____________________________________ Time: 03:16:58 AM PST US From: "Jay Hyde" Subject: RE: AeroElectric-List: Re: Why have a switch on ALT Field? Hi there Mike, Perhaps I can shed a bit of light on your questions. The switch is used as it switches a smaller current than would be required on the B-lead; thus you can use a switch and not a contactor. By switching off the field you have effectively switched off the alternator in its entirety, not just its output. Now its just a spinning mechanical device. If you switch the output (B lead) then you have a live spinning device and if the fault is inside the alternator then you're still feeding it... Utilising the field to switch the alternator also allows you to fit in overvoltage protection that will quickly detect and clear any overvoltage fault that would fry all your avionics leaving you with a damaged alternator AND no instruments (electrically powered ones in any case); whereas, if the overvoltage fault is detected and cleared you can still run the instruments on the battery. If you have an internally regulated alternator then you need to switch the output by using a contactor close to the alternator, because you cannot access the field winding wire. Protecting the alternator by using a panel mounted CB means that you lead a fat wire into the cockpit to the breaker in your panel, which in turn means that there is a long bit of fat wire that is unprotected- that long bit from the alternator to the CB. Personally I don't like that. If you use a contactor that is close to the source (alternator or battery) then the only unprotected bit of fat wire is that bit between the source and the contactor. A short bit of fat wire is unlikely to fault, or has a higher reliability because it is short and mechanically robust. The closer a contactor is to the voltage source the better your chances of removing the power source from a fault. Jay -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of rvg8tor Sent: 27 September 2009 09:15 AM Subject: AeroElectric-List: Re: Why have a switch on ALT Field? Bob, I know you are trying to help but, this last post does not seem to help me, it actually confuses me. I respect your experience but I am not trying to design an electrical system from scratch, much like I did not design my RV-8A from scratch. I picked a plane from a good designer (Van's). While building I study the plans and try to understand how the parts relate to be a better builder, if I have a question I call builder assistance and I ask questions on the forum. When it came to the electrical system, I went with a design from an expert in the field, in studying the design I asked a simple question, 'why is the alternator field switch needed". There have been a lot of words written, much of which my little brain doesn'tunderstand how it relates to the very simple question. The possible answers I was expecting were: 1. It has always been done that way 2. It doesn't matter the non-switch method will work but has these limitations (fill in the blanks) 3. You need the switch because if you don't have one it will cause XYZ. Some of what you wrote I get but I really just need the simple short answer, not a run down on design philosophy. Since you designed the systems I thought of all people you could provide the best explanation. I thank you for attempting to answer my questions, if nothing else you have convinced me not to deviate from the Z diagram. I can't say that I understand fully why the alternator field switch is a requirement other than to provide a convenient way to turn off the field. I look forward to the simple answer if there is one. -------- Mike "Nemo" Elliott RV-8A QB (Fuselage) Read this topic online here: http://forums.matronics.com/viewtopic.php?p=265184#265184 ________________________________ Message 3 _____________________________________ Time: 06:47:47 AM PST US Subject: AeroElectric-List: Re: Why have a switch on ALT Field? From: "rckol" Mike, Here is a response without embellishment. You need the alternator field switch because there is no alternator field breaker in Z-12. A fuse is used instead. You could substitute a breaker for the fuse and use it instead of a switch, but I wouldn't because: 1. You will be switching the field on and off at least once on every flight and a normal breaker is not designed to be a robust switch. 2. You could use a "switch-breaker", but I have heard so many stories about these having short life spans (at least the reasonably priced ones) that I would not put one in my aircraft. 3. I don't think you will save any money or weight using a breaker instead of the more reliable switch and fuse. Regards -------- rck Read this topic online here: http://forums.matronics.com/viewtopic.php?p=265200#265200 ________________________________ Message 4 _____________________________________ Time: 06:50:46 AM PST US From: Subject: AeroElectric-List: Why have a switch on ALT Field? 9/27/209 Hello Ian, Thanks for reading my post and responding. Please let me make an attempt at reducing your confusion. You wrote: 1) "As I understand it, the switch is on the alternator field low-current 12V line (called IGN on my alternator) ........" Can you both turn ON (activate) and turn OFF (deactivate) your alternator's electrical output with this alternator field switch?** This is generally considered a desireable design goal. There are some internally regulated alternators that, once activated, draw their field current from inside the alternator and it is not possible to deactivate those alternator's electrical output by turning OFF an external field switch. While this subject has been hotly debated several times on the aeroelectric list it is generally considered that the feature of not being able to shut down the alternator's electrical output with an external field switch is an undesirable design goal. 2) "..........the circuit breaker protects the output side (B lead)." The primary purpose of a CB or fuse in the B lead is to protect the wiring in the B lead. This wiring normally goes from the positive terminal of the battery to a main battery contactor and then onto the B output terminal of the alternator. If this wiring should encounter a short to ground the BATTERY could dump a huge amount of amperage into the wiring and cause a fire. Therefore the primary purpose of the CB or fuse in the B lead wiring is to protect the wiring from BATTERY electrical output. But since there are alternators that could "run away" and not be shut down by a switch in the circuit providing electricity to the alternator's field some people who have those kinds of alternators look upon the CB in the B lead as a means of cutting off the excess electrical flow from the alternator. Depending upon the manual pulling of a circuit breaker in the B lead as the only means of terminating an over voltage situation or a "run away" alternator is generally not considered a desirable design goal. Does this help? 'OC' Says: "The best investment we can make is the effort to gather and understand knowledge." **PS: I'd be interested in knowing how your alternator field switch does work and if you have an externally or internally regulated alternator? ====================================================== Time: 10:45:24 AM PST US Subject: Re: AeroElectric-List: Why have a switch on ALT Field? From: Ian OK, now here's one more vote for "confused". I thought the circuit breaker was supposed to be rated at the output amperage of the alternator because it's that current that one wants to limit. My 40A circuit breaker would do nothing for me on the alternator field circuit. As I understand it, the switch is on the alternator field low-current 12V line (called IGN on my alternator) and the circuit breaker protects the output side (B lead). Mine is wired this way because it made sense. Ian Brown, RV-9A, Bromont, QC ________________________________ Message 5 _____________________________________ Time: 07:41:04 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: RE: AeroElectric-List: Welding cable At 06:22 PM 9/26/2009, you wrote: >Well I guess you see why I asked, I spent some time googling and >didn't find much whioch actually called out the epdm >insulation. Guess I should have mentioned that. I did find >this place and I sent an email to ask what brand it is they carry, >hopefully they will respond Monday and I'll report back. Its >finding that EPDM insulation that seems tricky, I had some stuff >locally but it had a paper inner liner and I didn't find the outer >stuff to be very tough, it seemed easy to nick and penetrate. I looked at some wire in the junk box that I think came from an installation kit for an automotive super-sound system. The insulation was decidedly plastic looking (shiny) and also had a paper liner. > > >http://www.wesbellwireandcable.com/Welding.html Hey, good find on the web-source! Looks like their prices are really good too. As you can see from their offerings, there are MANY different kinds of insulation . . . EPDM is not the magic material, just one of many that would be suitable. I didn't intend that one zero in on EDPM in that manner. The fact that a reel of wire (or a catalog page) cites EDPM says that you KNOW what's being offered. That reel of shiny stuff with unknown and/or questionable insulation material MIGHT be okay. Without identification or other qualification data like materials or temperature ratings, it's good to move on and consider other sources. Looks like the WesBell folks are an excellent source of wire suitable for use as fat wires in your airplane. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 6 _____________________________________ Time: 07:47:29 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: While on the topic of alternators I've had a number of private e-mails on the alternator field switch thing. I want to thank those who have joined the discussion with lucid and accurate offerings of their own. I recalled an article that was sent to me about spring time of last year where the author attempted to explain the simple-ideas upon which the battery/alternator power system works in our airplanes. Seems that many folks on the 'net were citing this article as a valuable reference. http://www.aeroelectric.com/articles/Know_Your_Charging_System.pdf Those who are interested in expanding their understanding of what alternators do (and don't do) are encouraged to review this piece wherein I've endeavored to screen out the 'chunks' of misinformation. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 7 _____________________________________ Time: 08:07:20 AM PST US From: "Joe" Subject: Re: AeroElectric-List: Why have a switch on ALT Field? This is the way I understand it. Please correct me if I am wrong. The alternator output current does not need to be limited by a circuit breaker because the alternator output is self-limiting. If one were to add more loads to a fully loaded alternator, the voltage would drop, thus limiting the current automatically. It is not desired to unnecessarily run the alternator B lead into the cockpit. The B-lead circuit breaker is not necessary, and adds weight, cost and complexity. The purpose of an ANL fuse on the alternator output is not to protect the alternator or to prevent it from producing more than its rated current. The purpose of the ANL fuse is to protect the wires between the battery and alternator from 400+ amps of battery current in the event that the alternator shorts out, most likely from shorted diodes. In the event that an over-voltage condition occurs (due to a faulty regulator), an over-voltage module will short out the supply voltage that goes to the alternator field. If that happens, an alternator-field circuit breaker will trip, thus protecting the wires from excessive current resulting from this short circuit. Joe ________________________________ Message 8 _____________________________________ Time: 08:57:54 AM PST US From: Kelly McMullen Subject: Re: AeroElectric-List: Re: Why have a switch on ALT Field? rckol wrote: > > > 1. You will be switching the field on and off at least once on every flight and a normal breaker is not designed to be a robust switch. Why?? Is there a need to turn the alternator on/off separate from the master if it is functioning correctly? > 2. You could use a "switch-breaker", but I have heard so many stories about these having short life spans (at least the reasonably priced ones) that I would not put one in my aircraft. The Klixon switch breakers in my Mooney are almost all OEM from 45 years/6000 hours ago. A couple have been replaced from springs getting weak. ________________________________ Message 9 _____________________________________ Time: 11:27:49 AM PST US From: "Tony Babb" Subject: RE: AeroElectric-List: Re: Why have a switch on ALT Field? Jay, Thank you so much. Spelling out what may be obvious or intuitive to experienced hands is a great assistance to us neophyte electron herders. Tony Velocity SEFG 62% done, 78% to go www.alejandra.net/velocity -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Jay Hyde Sent: Sunday, September 27, 2009 3:04 AM Subject: RE: AeroElectric-List: Re: Why have a switch on ALT Field? --> Hi there Mike, Perhaps I can shed a bit of light on your questions. The switch is used as it switches a smaller current than would be required on the B-lead; thus you can use a switch and not a contactor. By switching off the field you have effectively switched off the alternator in its entirety, not just its output. Now its just a spinning mechanical device. If you switch the output (B lead) then you have a live spinning device and if the fault is inside the alternator then you're still feeding it... Utilising the field to switch the alternator also allows you to fit in overvoltage protection that will quickly detect and clear any overvoltage fault that would fry all your avionics leaving you with a damaged alternator AND no instruments (electrically powered ones in any case); whereas, if the overvoltage fault is detected and cleared you can still run the instruments on the battery. If you have an internally regulated alternator then you need to switch the output by using a contactor close to the alternator, because you cannot access the field winding wire. Protecting the alternator by using a panel mounted CB means that you lead a fat wire into the cockpit to the breaker in your panel, which in turn means that there is a long bit of fat wire that is unprotected- that long bit from the alternator to the CB. Personally I don't like that. If you use a contactor that is close to the source (alternator or battery) then the only unprotected bit of fat wire is that bit between the source and the contactor. A short bit of fat wire is unlikely to fault, or has a higher reliability because it is short and mechanically robust. The closer a contactor is to the voltage source the better your chances of removing the power source from a fault. Jay -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of rvg8tor Sent: 27 September 2009 09:15 AM Subject: AeroElectric-List: Re: Why have a switch on ALT Field? Bob, I know you are trying to help but, this last post does not seem to help me, it actually confuses me. I respect your experience but I am not trying to design an electrical system from scratch, much like I did not design my RV-8A from scratch. I picked a plane from a good designer (Van's). While building I study the plans and try to understand how the parts relate to be a better builder, if I have a question I call builder assistance and I ask questions on the forum. When it came to the electrical system, I went with a design from an expert in the field, in studying the design I asked a simple question, 'why is the alternator field switch needed". There have been a lot of words written, much of which my little brain doesn'tunderstand how it relates to the very simple question. The possible answers I was expecting were: 1. It has always been done that way 2. It doesn't matter the non-switch method will work but has these limitations (fill in the blanks) 3. You need the switch because if you don't have one it will cause XYZ. Some of what you wrote I get but I really just need the simple short answer, not a run down on design philosophy. Since you designed the systems I thought of all people you could provide the best explanation. I thank you for attempting to answer my questions, if nothing else you have convinced me not to deviate from the Z diagram. I can't say that I understand fully why the alternator field switch is a requirement other than to provide a convenient way to turn off the field. I look forward to the simple answer if there is one. -------- Mike "Nemo" Elliott RV-8A QB (Fuselage) Read this topic online here: http://forums.matronics.com/viewtopic.php?p=265184#265184 ________________________________ Message 10 ____________________________________ Time: 02:18:45 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Why have a switch on ALT Field? At 09:58 AM 9/27/2009, you wrote: >This is the way I understand it. Please correct me if I am wrong. > > The alternator output current does not need to be limited by a > circuit breaker because the alternator output is self-limiting. correct > If one were to add more loads to a fully loaded alternator, the > voltage would drop, thus limiting the current automatically. yes > It is not desired to unnecessarily run the alternator B lead into > the cockpit. yes > The B-lead circuit breaker is not necessary, and adds weight, > cost and complexity. > The purpose of an ANL fuse on the alternator output is not to > protect the alternator or to prevent it from producing more than > its rated current. The purpose of the ANL fuse is to protect the > wires between the battery and alternator from 400+ amps of battery > current in the event that the alternator shorts out, most likely > from shorted diodes. Yup . . . > In the event that an over-voltage condition occurs (due to a > faulty regulator), an over-voltage module will short out the supply > voltage that goes to the alternator field. If that happens, an > alternator-field circuit breaker will trip, thus protecting the > wires from excessive current resulting from this short circuit. Yes . . . this is a property unique to the crowbar philosophy for opening the alternator's field supply after an ov condition is detected. There are other designs that do not open the field supply breaker . . . and can be considered as a potential player in your design goals. The reason that Z-figures featuring crowbar ov protection -AND- fuseblocks have a field supply breaker is to accommodate the crowbar ov control philosophy. If non-crowbar shutdown products are considered, then one could easily supply alternator field through one of the fuses and leave the circuit breaker out. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 11 ____________________________________ Time: 02:26:33 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Why have a switch on ALT Field? Why?? Is there a need to turn the alternator on/off separate from the master if it is functioning correctly? Depends on your architecture. Does the MASTER control the alternator too? Is the MASTER a progressive transfer two-pole switch or classic "split rocker". Then indeed, the alternator field breaker may never need to be touched. But if the MASTER is a simple two-pole switch that controls alternator and battery at the same time, then you could use the field breaker to shut the alternator down for battery-only ground-ops. 2. The Klixon switch breakers in my Mooney are almost all OEM from 45 years/6000 hours ago. A couple have been replaced from springs getting weak. But the Potter-Brumfield W31 style breakers installed in many other airplanes for about the same length of time have been identified has having a safety of flight failure mode that is prompting an AD to replace about 80,000 of the critters. Not all switch breakers are alike. All are much more expensive than the fuse/switch architecture featured in the Z-figures. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ------------------------------------------------------------------------------------- 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.