AeroElectric-List Digest Archive

Wed 03/03/10


Total Messages Posted: 16



Today's Message Index:
----------------------
 
     1. 05:07 AM - Re: This switch OK? (johngoodman)
     2. 06:31 AM - Re: Z13/20 (user9253)
     3. 06:58 AM - Re: Battery charging (Speedy11@aol.com)
     4. 07:08 AM - Re: Questions (Robert L. Nuckolls, III)
     5. 07:13 AM - Re: Battery charging  (Speedy11@aol.com)
     6. 07:13 AM - Loadmeter Shunt 10 amp ()
     7. 07:25 AM - Re: Questions ()
     8. 08:03 AM - Re: Battery charging (rampil)
     9. 08:03 AM - Re: Loadmeter Shunt 10 amp (Tom Barter)
    10. 12:15 PM - Re: Z8 (Noah)
    11. 03:09 PM - Re: Re: Z13/20 (Gerald Giddens)
    12. 03:28 PM - Re: This switch OK? (jerb)
    13. 04:46 PM - Re: Re: Z8 (Robert L. Nuckolls, III)
    14. 04:55 PM - Re: Re: This switch OK? (Robert L. Nuckolls, III)
    15. 06:22 PM - Re: This switch OK? (user9253)
    16. 09:47 PM - Re: Re: This switch OK? (B Tomm)
 
 
 


Message 1


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    Time: 05:07:40 AM PST US
    Subject: Re: This switch OK?
    From: "johngoodman" <johngoodman@earthlink.net>
    > The picture does not specify 250V AC or DC. I will assume that it is AC. I think it should be safe to use this switch to handle up to 5 amps at 14VDC. A switch will not immediately self-destruct if operated slightly above its rating. But its life will be shortened. How much current do you want to control with this switch and what type of load is it? > Joe I want to use it for Coil Power for a GearedDrives LS1 V8 engine in an RV-10. I'm not sure what the Coil actually draws but the wire is protected by a 15 amp fuse. The wire from the engine looks like a 14 or 16awg. I'll have to look into the actual draw, but this switch will probably not work since I need reliability. Thanks for the reply, John -------- #40572 QB. Engine on, wing attach coming soon. Panel delivery soon. N711JG reserved Read this topic online here: http://forums.matronics.com/viewtopic.php?p=289034#289034


    Message 2


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    Time: 06:31:05 AM PST US
    Subject: Re: Z13/20
    From: "user9253" <fran4sew@banyanol.com>
    David Lamb, I agree with rck that a relay is better than a switch between the battery and the E-Bus. RCK mentioned the current handling abilities of the switch. There is another issue: In case of smoke in the cockpit, there is no way to shut off power to the E-Bus switch. A relay will give you the ability to open the circuit on the engine side of the firewall. The ANL fuse is on the wrong end of the #10 wire. A fuse and a fuselink are not both needed, although having both does not hurt anything. The protection device should be as close as practical to the battery contactor. The intent is to prevent excessive battery current in case of a short circuit. No fuse is required to protect the alternator output because the alternator current is self limiting. Is there over-voltage protection for the main alternator? Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=289041#289041


    Message 3


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    Time: 06:58:32 AM PST US
    From: Speedy11@aol.com
    Subject: Re: Battery charging
    Ira, Good points, all. If I'm going to ask an opinion of someone on the list, then I certainly must provide accurate information - or expect no answer. I'm using Odessey and happy with it so far. I have no intention of changing at this time. But, I was interested in the answer to the proposed question. I am always interested in a less expensive, but adequate replacements for equipment. Perhaps changing a battery each year is a waste of money. And I've been called an old FUDdy before, but it is certainly not out of fear, uncertainty, or doubt. I change a battery a year because: 1. It is recommended by an expert in the field - Electric Bob 2. My ignorance dictates that I listen to the experts 3. It establishes a reasonable means to avoid failure 4. It is not overly expensive 5. The batteries are used in other equipment and not wasted 6. The oldest battery at any moment in my RV is 2 years. 7. I don't have to bother with capacity checks I also change my tires before they fail. Anyone who wants the old ones just let me know. I change my hoses before they fail. Anybody want the old ones? I don't like being stranded in remote locations because I tried to stretch the life of consumables such as batteries. Just call me an old fuddy. Ira, thanks for researching the correct info on the battery and providing your opinion. I appreciate it. It appears from your comment that you prefer Panasonic batteries. Which model do you use? Why do you believe that battery is better than an Odessey? Does it have more AH capacity? Does it have faston tabs or screw on terminals? Your suggestion of replacing a battery every two years seems like a reasonable thing to do - especially if one charges the batteries to capacity periodically. Regards, Stan Sutterfield Possibly the reason no answer was given was because M&B sells lots of different batteries, but one of us who have to expend some effort to figure out what kind of battery it is. I did so, just because of all the chatter. It is not a M&B battery, it is a CSB sealed Lead Acid battery Does not say gel vs immobilized in the little ad. Its probably ok but I have no experience with the CSB brand, so you will be a test pilot! After you use it a year let us know what you found. Half price off an Odessey is not bad unless there is a reason for the cheapness. As for swapping out batteries every year: what a waste of money! Driven by FUD, as the IBMers used to say: Fear, Uncertainty, and Doubt. If you learn a bit about batteries, then maybe you can still use premium quality Pana batteries and only swap them every other year!


    Message 4


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    Time: 07:08:12 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Questions
    At 12:42 AM 3/3/2010, you wrote: Thanks Bob I get the freedom that "expecting things to break" brings. That is very helpful, so thanks. We all must make a call between no backup and the backup of the backup to the Nth order. Many years ago I was a tech working on the Perth Airport ILS system. All I can remember is that it was the arbiter that decided which system was functioning correctly and which was failing, was most often the part that failed and took the ILS system offline! What level of redundancy does one go to before the backups defeat the original purpose and intent. Yeah. I had an opportunity to craft and install the cockpit mounted controller for a series of explosively deployed recovery parachutes in flight test aircraft. In fact, I'm presently tasked with doing the 4th such installation for Hawker-Beech. The design I replaced was horribly complex made so by some desire to monitor all features of a redundant and sometimes quad redundant system. Failures were displayed on an LCD screen. Over a year into the design, the system could not be made to work because of the monitoring system kept raising alarms . . . and the control system ultimately glitched one night and launched the 'chute in the hangar. The guys in the Targets group got together and built one in two weeks. http://aeroelectric.com/Pictures/Misc/Recovery_Parachute_Controller.jpg Simple array of relays, solid state sequencer, failure tolerant, preflight testable, very low comparative parts count. A little brother to that controller is on my bench right now awaiting a modern AC mains powered battery maintainer. A review of the service history of past installations revealed a lot of replaced batteries. Seems the crews were pulling the breaker from ship's DC power when the system was being "disabled". Then when needed next time, the internal battery wasn't fully charged. I'm building a battery maintainer into the controller with a placard that it be plugged in at least 1 hour in the 48 hours preceding a flight where the parachute will be armed. I suppose where I am still pondering is, given your systems make sense for aircraft batteries, alternator/generators and starters (I understand to be technologically challenged but may be miss informed), how would they change (if any) given modern alternators, starters etc? (My question predicates (foolishly) that all modern equipment is equal in reliability!!!???) It's an absolute fact that modern vehicular DC power components of all stripes are longer lived and more robust than their ancestors. So yes, one can comfortably state that reliability of components has increased . . . in virtually all technologies and brands. Perhaps, even if the mean time between failures has quadrupled in modern equipment the risks still demand your backup systems. Absolutely. It's been my observation that the vast majority of electrical systems unhappiness in OBAM aircraft (and a substantial number of TC aircraft) DOES NOT originate in ABILITY OF ANY PART TO DO ITS JOB. Most problems arise from mis-application of parts and poor process. Of course, all parts have service lives and will ultimately cease to function. From a systems perspective, reliability arguments that focus on parts are academic and non-productive. Resolution of such arguments depends heavily on statistical data derived from laboratory tests that may or may not accurately mimic service conditions. This is ESPECIALLY true when service conditions are defined by the knowledge, resources and skill sets of the designer/installer. That's why I started focusing on SYSTEM reliability through failure mode effects analysis and designs tolerant of failures. Once this relatively simple skill was mastered, it mattered little where one purchases parts. We're now free to concentrate on the weakest links the OBAM aircraft fabrication chain . . . knowledge, resources and skill set of the builder. This is one area where process trumps science every day. Again, thanks for the help on the journey and the decision making that lies at every turn. My pleasure sir . . . Bob . . .


    Message 5


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    Time: 07:13:19 AM PST US
    From: Speedy11@aol.com
    Subject: Re: Battery charging
    David, Thanks for your detailed and informative response. Superb info and analysis. Stan Sutterfield Do not archive This thread piqued my curiosity, so I did a little research. The Panasonic & CSB batteries have similar specs apart from the 17/20 AH rating curve. Their operating range has a lower limit of -15 C (5 F), and an internal resistance of 12-13 mOhms. Internal resistance and temperature range will have a large impact on cold-weather starting. The CSB is limited to a max of 230 A for 5 sec. The Panasonic specs do not provide this information, but I suspect it is similar to CSB due to the internal resistance. At the other end of the battery spectrum is the Osyssey 680. It has a -40 C (-40 F) lower temperature limit, and 7.5 mOhm internal resistance. They claim a 680 A discharge rate for 5 sec. and 400 A for 30 seconds. The longer time AH capacity is typical for a 16 AH battery. EnerSys (parent company) also produces the Genesis product line at the same plant as Odyssey in Warrensburg, Missouri. The Genesis G12V16EP happens to have the same case design/dimensions, terminals, and electrical specs as the Odyssey 680, but at a somewhat lower price. They may not be identical, but it's hard to tell any difference. Aviation is on the Genesis application list, so this might be a good value. http://tnrbatteries.com/geg11.html Odyssey and Genesis batteries also have a two year replacement warranty rather than the typical one year. Spec sheets (note that Odyssey & Genesis have every detail): Panasonic: http://www.panasonic.com/industrial/includes/pdf/Panasonic_VRLA_LC-PD1217P.p df CSB: http://www.csb-battery.com/upfiles/dow01242375277.pdf Odyssey: http://www.odysseybatteries.com/files/techbook.pdf Genesis: http://www.enersysreservepower.com/documents/US_GPL_SG_001_0303.pdf If you're looking at the Panasonic and/or CSB batteries, there are plenty of other batteries with similar specs that are even lower cost. Among other things, I'd pay close attention to the terminal style. Make sure that vibration won't weaken the terminal over time. Many of these batteries differ only by the label on top. If starting current isn't an issue with you, the lower cost batteries may well be the best value. If you don't want to be stranded with a dead battery in a cold climate or after a failed hot start, cranking amps will be a large part of your decision process. YMMV David Barrett


    Message 6


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    Time: 07:13:50 AM PST US
    Subject: Loadmeter Shunt 10 amp
    From: <longg@pjm.com>
    Can you folks recommend (a link to) a loadmeter shunt for a 10 amp application (SD-8)? I see B & C has from 20 and up. I tried digi-key but that place is like sorting through my attic. I prefer the closed type so I can use it inside my panel. Thanks, Glenn


    Message 7


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    Time: 07:25:03 AM PST US
    From: <stevei@carey.asn.au>
    Subject: Re: Questions
    Once again, thanks Bob, these fundamentals will steer the required decision s in the right direction. Steve Izett Perth WA On 3/03/10 11:07 PM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.c om> wrote: s.bob@aeroelectric.com> At 12:42 AM 3/3/2010, you wrote: Thanks Bob I get the freedom that "expecting things to break" brings. That is very helpful, so thanks. We all must make a call between no backup and the backup of the backup to the Nth order. Many years ago I was a tech working on the Perth Airport ILS system. All I can remember is that it was the arbiter that decided which system was functioning correctly and which was failing, was most often the part that failed and took the ILS system offline! What level of redundancy does one go to before the backups defeat the original purpose and intent. Yeah. I had an opportunity to craft and install the cockpit mounted controller for a series of explosively deployed recovery parachutes in flight test aircraft. In fact, I'm presently tasked with doing the 4th such installation for Hawker-Beech. The design I replaced was horribly complex made so by some desire to monitor all features of a redundant and sometimes quad redundant system. Failures were displayed on an LCD screen. Over a year into the design, the system could not be made to work because of the monitoring system kept raising alarms . . . and the control system ultimately glitched one night and launched the 'chute in the hangar. The guys in the Targets group got together and built one in two weeks. http://aeroelectric.com/Pictures/Misc/Recovery_Parachute_Controller.jpg Simple array of relays, solid state sequencer, failure tolerant, preflight testable, very low comparative parts count. A little brother to that controller is on my bench right now awaiting a modern AC mains powered battery maintainer. A review of the service history of past installations revealed a lot of replaced batteries. Seems the crews were pulling the breaker from ship's DC power when the system was being "disabled". Then when needed next time, the internal battery wasn't fully charged. I'm building a battery maintainer into the controller with a placard that it be plugged in at least 1 hour in the 48 hours preceding a flight where the parachute will be armed. I suppose where I am still pondering is, given your systems make sense for aircraft batteries, alternator/generators and starters (I understand to be technologically challenged - but may be miss informed), how would they change (if any) given modern alternators, starters etc? (My question predicates (foolishly) that all modern equipment is equal in reliability!!!???) It's an absolute fact that modern vehicular DC power components of all stripes are longer lived and more robust than their ancestors. So yes, one can comfortably state that reliability of components has increased . . . in virtually all technologies and brands. Perhaps, even if the mean time between failures has quadrupled in modern equipment the risks still demand your backup syste ms. Absolutely. It's been my observation that the vast majority of electrical systems unhappiness in OBAM aircraft (and a substantial number of TC aircraft) DOES NOT originate in ABILITY OF ANY PART TO DO ITS JOB. Most problems arise from mis-application of parts and poor process. Of course, all parts have service lives and will ultimately cease to function. From a systems perspective, reliability arguments that focus on parts are academic and non-productive. Resolution of such arguments depends heavily on statistical data derived from laboratory tests that may or may not accurately mimic service conditions. This is ESPECIALLY true when service conditions are defined by the knowledge, resources and skill sets of the designer/installer. That's why I started focusing on SYSTEM reliability through failure mode effects analysis and designs tolerant of failures. Once this relatively simple skill was mastered, it mattered little where one purchases parts. We're now free to concentrate on the weakest links the OBAM aircraft fabrication chain . . . knowledge, resources and skill set of the builder. This is one area where process trumps science every day. Again, thanks for the help on the journey and the decision making that lies at every turn. My pleasure sir . . . Bob . . . -- This message was scanned by ESVA and is believed to be clean. ________________________________ The contents of this email are confidential and intended only for the named recipients of this e-mail. If you have received this e-mail in error, you are hereby notified that any use, reproduction, disclosure or distribution or the information contained in this e-mail is prohibited. Please notify th e sender immediately and then delete/destroy the e-mail and any printed cop ies. All liability for viruses is excluded to the fullest extent of the law .


    Message 8


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    Time: 08:03:04 AM PST US
    Subject: Re: Battery charging
    From: "rampil" <ira.rampil@gmail.com>
    Hi Stan, Actually I have always used the Odyssey 680 in my Europa. I trust Pana in terms of general quality, but the specs for the Odyssey are better for me in the Northeast. Just changing batteries annually because you don't choose to learn about batteries (Not talking about anyone individually here) is a shame. Money is tight all around and frequent changes ignores the real possibility of infantile failure which is just as likely in the real world as premature failure if the products are made in the far, far east. Sometimes experts disagree. This is Bob's group and I respect that. I appreciate his public service in dealing with the underending series of questions. There are also other opinions formed on reasonably solid foundations of knowledge and experience that may differ however because some experts place different priorities on different aspects of a project. Look for example on the scrap between Nuckolls and Richter a few years ago. I was once an E.E., I spent 8 years in school and grad school, I try to keep up with the literature and I hand built my plane and panel. Ergo, I have opinions and they are not always the same as Bob's. Is is certainly not a dis at Bob when I think there are better places to spend money than changing out batteries that should be fairly fresh. (Of course some people know when they have intentionally abused a battery - that is a different story) -------- Ira N224XS Read this topic online here: http://forums.matronics.com/viewtopic.php?p=289060#289060


    Message 9


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    Time: 08:03:04 AM PST US
    From: "Tom Barter" <kesleyelectric@iowatelecom.net>
    Subject: Loadmeter Shunt 10 amp
    Glenn, I recently purchased a 10 amp shunt for my SD-8 load meter from B&C. It is the open style, but should be OK behind the panel. That is where mine is going. Tom Barter Kesley, IA Avid Magnum -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of longg@pjm.com Sent: Wednesday, March 03, 2010 8:48 AM Subject: AeroElectric-List: Loadmeter Shunt 10 amp Can you folks recommend (a link to) a loadmeter shunt for a 10 amp application (SD-8)? I see B & C has from 20 and up. I tried digi-key but that place is like sorting through my attic. I prefer the closed type so I can use it inside my panel. Thanks, Glenn


    Message 10


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    Time: 12:15:52 PM PST US
    Subject: Re: Z8
    From: "Noah" <sgninc@cox.net>
    Two questions regarding Z-8. 1. I assume this "new" Z-8 is different from the Z-8 published in 1999 in your document "All Electric Airplane on a Budget" at: http://www.matronics.com/aeroelectric/articles/allelect.pdf If this is the case, why not give the new Z-8 a new name to eliminate confusion? 2. What is the minimum practical battery capacity that would be recommended in a system as described above, on the bus with the smaller alternator (SD-20 in my case)? I am not asking from a battery-only loads & endurance standpoint, but rather from a battery-as-an-alternator-reservoir/voltage-stabilizer standpoint. I am loathe to install a second battery, contactor, and additional components when I think my requirements are met without them, but I will certainly have a long hard look at what is proposed and do some soul searching. Part of my question stems from the fact that my 16 A-Hr battery is already pretty much integrated into my platform. -------- Highest Regards, Noah Forden RV-7A Rhode Island Read this topic online here: http://forums.matronics.com/viewtopic.php?p=289084#289084


    Message 11


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    Time: 03:09:16 PM PST US
    From: Gerald Giddens <pruemotorgliders@cox.net>
    Subject: Re: Z13/20
    On Mar 2, 2010, at 7:54 PM, Robert L. Nuckolls, III wrote: > Might a switch be more efficient than a relay for the E bus load, assuming a ~10 > amp load? (I'm not refering to the brown out relay which I see is > necessary). > > Certainly more efficient since the switch does not > draw current to keep it closed. But the relay is > called for when it is functioning as a mini-contactor > located adjacent to the battery bus. If you can reach > a switch located there, then you could consider the > subsitution. > > What do these little Bosch type cube relays draw? > Thanks, Tim Andres > > About 100 mA depending on manufacturer and some > other details. These are not big energy hogs. > > Bob . . . > > >


    Message 12


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    Time: 03:28:21 PM PST US
    From: jerb <ulflyer@verizon.net>
    Subject: Re: This switch OK?
    John, Reading your reply to other folks replies I am concerned of your using this switch for your intended application. First off, the switch information you provided in the attachment does not designate if it is rated for AC or DC current. Note, an AC rated switch if used in an DC current application, the DC current capacity will normally be only a fraction of it's AC current rating. Second, I would point out that the reply by Joe saying that you could probably run 5 amps of current exceeds the switches current rating, if it turns out to be an AC application switch, you would be further outside the switches safe operating limits. Neither would be acceptable solution. I strongly recommend you determine your current needs for the circuit your controlling. Then determine if the switch your considering is AC or DC rated. If the switch is AC rated, find another switch appropriate for your application. Do it right the first time, you might not get the second chance to do it over again. jerryb >Attachments: > >http://forums.matronics.com//files/picture_1_380.png > >


    Message 13


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    Time: 04:46:46 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Z8
    At 02:10 PM 3/3/2010, you wrote: > >Two questions regarding Z-8. > >1. I assume this "new" Z-8 is different from the Z-8 published in >1999 in your document "All Electric Airplane on a Budget" at: >http://www.matronics.com/aeroelectric/articles/allelect.pdf >If this is the case, why not give the new Z-8 a new name to >eliminate confusion? Many moons ago, the z-figures went from Z-1 to 10 and somewhere around revision 8 or 9 were replaced with Z-11 and on as they were redrawn to be more consistent with each other. The suite of drawings was extended upward from Z-11. It was my plan at some time to fill the lower numbers back in later. Z-8 was the predecessor to Z-13/8. It only appears in the 1999 article and very old issues of the 'Connection which should have been updated several times over. >2. What is the minimum practical battery capacity that would be >recommended in a system as described above, on the bus with the >smaller alternator (SD-20 in my case)? I am not asking from a >battery-only loads & endurance standpoint, but rather from a >battery-as-an-alternator-reservoir/voltage-stabilizer standpoint. Technically, any size battery is adequate to the task of tickling an alternator to life. Batteries are of little value in noise abatement or voltage stabilization. Further, the smaller they get, the more they suffer the 'abuse' of short but heavy charge/discharge events. Having offered that, I have no idea what would be considered useful to your task. You'll need to put some sort of preventative maintenance program on it or (ugh!) throw a new one in ever so often. It may be that a tiny (6 a.h. or less) battery wouldn't support this application for a year . . . I just don't know. You can just pick one, check it from time to time and see how it goes. There some small products by Dekka that feature robust terminals indicative of an ability to source/sink the transients. >I am loathe to install a second battery, contactor, and additional >components when I think my requirements are met without them, but I >will certainly have a long hard look at what is proposed and do some >soul searching. The answer lies not with the soul but with calculated and considered assembly of ingredients into a recipe for success that meets your design goals. The task before you is the same that evolved the Z-figures over the years. You can look forward a sifting the details in search of the stable configuration. Bob . . .


    Message 14


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    Time: 04:55:04 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: This switch OK?
    >I want to use it for Coil Power for a GearedDrives LS1 V8 engine in >an RV-10. I'm not sure what the Coil actually draws but the wire is >protected by a 15 amp fuse. The wire from the engine looks like a 14 >or 16awg. I'll have to look into the actual draw, but this switch >will probably not work since I need reliability. Thanks for the reply, What coil? Ignition? The picture I saw appears to be a momentary push button. If it has 3 terminals, then I suspect it's a single-pole, double-throw device. Further, push-buttons of this style are slow-make, slow-break (no fast acting over-center mechanism). VERY poor technology for switching reactive DC loads. Bob . . .


    Message 15


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    Time: 06:22:59 PM PST US
    Subject: Re: This switch OK?
    From: "user9253" <fran4sew@banyanol.com>
    Looking at the picture of this switch (made in UK), the first thing that came to mind is that it was going to be used for a starter switch. It turns out that John intends to use it for a more critical application where a high quality switch should be used. So I take back what I said about the switch being ok to use. As a general rule, a 125VAC rated switch can handle the same current at 14VDC, even if the manufacturer does not publish the DC rating. Every AC switch has a DC ampacity. That ampacity might not have been determined by testing and thus is unknown. Jerry B. said, > "the DC current capacity will normally be only a fraction of it's AC current rating." That is true if the voltage remains the same: 250V in this case. But, generally speaking, a 125VAC rated switch can carry as much DC current at 14V as it can carry AC current at 125V. An example of this can be seen by reading the data sheet for another switch. http://www.nkkswitches.com/pdf/stoggleslowcap.pdf Notice that 125VAC rating is identical to the 30VDC rating. At 14VDC, this switch can handle even more. Also notice that this switch can handle 2 1/2 times the current at 30VDC than it can at 250VAC. Most good quality snap action AC switches are suitable for use in homebuilt aircraft as long as the 14VDC current does not exceed the 125VAC rating of the switch. Comments are welcome. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=289145#289145


    Message 16


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    Time: 09:47:14 PM PST US
    From: "B Tomm" <fvalarm@rapidnet.net>
    Subject: Re: This switch OK?
    Remember... Switches manufactured in the UK will not work in any north American aircraft (certified or amateur built) as the current flow requirement is OPPOSITE to what we consider normal. This is why many switch configurations in the UK call for switch orientation to be up to be OFF and down to be ON. :) Just trying to help. We're all in this together. Keep yur sticks on the ice. Bevan :) -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of user9253 Sent: Wednesday, March 03, 2010 6:21 PM Subject: AeroElectric-List: Re: This switch OK? --> <fran4sew@banyanol.com> Looking at the picture of this switch (made in UK), the first thing that came to mind is that it was going to be used for a starter switch. It turns out that John intends to use it for a more critical application where a high quality switch should be used. So I take back what I said about the switch being ok to use. As a general rule, a 125VAC rated switch can handle the same current at 14VDC, even if the manufacturer does not publish the DC rating. Every AC switch has a DC ampacity. That ampacity might not have been determined by testing and thus is unknown. Jerry B. said, > "the DC current capacity will normally be only a fraction of it's AC current rating." That is true if the voltage remains the same: 250V in this case. But, generally speaking, a 125VAC rated switch can carry as much DC current at 14V as it can carry AC current at 125V. An example of this can be seen by reading the data sheet for another switch. http://www.nkkswitches.com/pdf/stoggleslowcap.pdf Notice that 125VAC rating is identical to the 30VDC rating. At 14VDC, this switch can handle even more. Also notice that this switch can handle 2 1/2 times the current at 30VDC than it can at 250VAC. Most good quality snap action AC switches are suitable for use in homebuilt aircraft as long as the 14VDC current does not exceed the 125VAC rating of the switch. Comments are welcome. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=289145#289145




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