AeroElectric-List Digest Archive

Mon 05/11/09


Total Messages Posted: 19



Today's Message Index:
----------------------
 
     1. 07:20 AM - Relays (Robert L. Nuckolls, III)
     2. 11:18 AM - Battery Charger as Ground Power (Craig Winkelmann)
     3. 11:26 AM - Re: Battery Charger as Ground Power (woxofswa)
     4. 11:44 AM - Re: GPU - 24V System - Crowbar Needed (woxofswa)
     5. 12:23 PM - Re: Re: GPU - 24V System - Crowbar Needed (George, Neal E Capt USAF ACC 605 TES/DOA)
     6. 12:24 PM - Comm & Nav audio with SPA 400 (Gilles Thesee)
     7. 01:09 PM - Re: Comm & Nav audio with SPA 400 (Patrick Hildebrand)
     8. 01:12 PM - Re: Comm & Nav audio with SPA 400 (Patrick Hildebrand)
     9. 02:00 PM - Re: Battery Charger as Ground Power (Robert L. Nuckolls, III)
    10. 02:22 PM - Re: Re: GPU - 24V System - Crowbar Needed (Robert L. Nuckolls, III)
    11. 03:11 PM - Re: Re: Ground Power (Walter Fellows)
    12. 03:33 PM - Re: Battery Charger as Ground Power (Matt Dralle)
    13. 05:11 PM - Re: Re: GPU - 24V System - Crowbar Needed (Ed Holyoke)
    14. 05:55 PM - Ground Power Receptacle? ()
    15. 06:43 PM - Re: Re: Battery Charger as Ground Power (David L.)
    16. 07:16 PM - Re: Battery Charger as Ground Power (Craig Winkelmann)
    17. 07:47 PM - Wonky Ammeter Redux (Kevin Jones)
    18. 08:42 PM - Re: Re: Battery Charger as Ground Power (Robert L. Nuckolls, III)
    19. 08:44 PM - Re: Re: Battery Charger as Ground Power (Robert L. Nuckolls, III)
 
 
 


Message 1


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    Time: 07:20:20 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Relays
    Subject: Re: relays Bcc: nuckolls.bob@aeroelectric.com At 11:06 AM 5/10/2009 +0100, you wrote: >Hi Bob, > > >I m really struggling to understand how to wire a relay. Whilst I >understand in principle the wiring, I m struggling to get it to work >and no amount of reading schematics is sinking into my head! > > >This is what I understand about the relay so far; > >Pin 30 is power in > >Pin 87 goes to the item to be powered - (let s say fuel pump) > >Pin 86 goes to ground > >Pin 85 is to the switch. The numbers you're referring to are artifacts of a European terminal identification system commonly used in automobiles and probably other vehicles for decades. It's not uncommon today to find off-the-shelf relays with terminal markings molded into the housings that conform to this convention. The numbering convention is illustrated in the drawing cited below. Think of the relay as a big, fat, remotely operated push- button. Continuity through the push-button in the "relaxed" state is through terminals 30 and 87a. Power can go either way through these contacts. The push-button is remotely operated by a magnetic motor with coil terminals 85 and 86. It doesn't matter how you apply 12v to this coil . . . terminal 85 OR 86 can be (+). When you apply power to the coil, the "push-button" contacts move to break continuity between 30/87a and make contact between 30/87. This state is maintained until you remove power from the coil. > > >At the moment this switch is wired directly to the unit and for me >that is easy to understand. The fuel pump 12v + is wired to the >switch on the panel and then into the bus, fuel pump 12v is to >airframe ground. Press the switch and it works. But put a relay >in the midst of this and nothing happens apart from frying my brain! Relays are used to shorten the distance you might need to run "fat wires" and/or to add functionality. For example, the switch needed to control the relay is a simple single-pole, single-throw device but the relay effects a single-pole, double-throw functionality. >Is pin 30 the power supply from the bus that would normally go to >the switch ? I m struggling to understand how to wire the switch >into this circuit. Whilst this might sound elementary to you Bob, >I just cannot get my head around it !! > >I need an verbatim explanation on how to wire the pump to the bus, >the switch and the relay. Once I see it in practical terms, i.e. >this wire goes to this, this wire goes to that, I m sure the penny >will drop, just as it has on all other problems I ve hit! There's a drawing on my website at . . . http://www.aeroelectric.com/PPS/Engine/Fuel/Fuel_Pump.pdf . . . that describes one way to implement the wiring you've asked about. Of course, the 10A fuse and 18AWG wires may need to be resized for your specific fuel pump . . . I will invite you to join us on the AeroElectric List to continue this and similar discussions. It's useful to share the information with as many folks as possible. A further benefit can be realized with membership on the list. There are lots of technically capable folks on the list who can offer suggestions too. You can join at . . . http://www.matronics.com/subscribe/ Ask your question again on the List. I check the List several times a day and attempt to be responsive as time will allow. Further, there are 1800 or so subscribers that include many technically capable teachers. This is the best venue for assisting you in your studies. Bob . . . Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------


    Message 2


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    Time: 11:18:31 AM PST US
    Subject: Battery Charger as Ground Power
    From: "Craig Winkelmann" <capav8r@gmail.com>
    Bob: I've been reading some posts on ground power and noted that some people are using a battery charger as a ground power unit. From what I remember about the output voltage of almost all battery chargers, there is a significant potential to overvoltage the aircraft isn't there? The voltage from most chargers is not filtered and is not as clean as you'd want for powering avionics, etc. Am I right, Craig Read this topic online here: http://forums.matronics.com/viewtopic.php?p=243567#243567


    Message 3


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    Time: 11:26:37 AM PST US
    Subject: Re: Battery Charger as Ground Power
    From: "woxofswa" <woxof@aol.com>
    I'm no expert, but I think you are right. I think a 12.5 volt "maintainer" would make much more sense. They can be had at Harbor Freight for $5 For ground tests and assembly, I plan on using a cheapo lawn tractor battery with a maintainer hooked up to it. The battery would then serve as a sink if there is a problem with the maintainer. -------- Myron Nelson Mesa, AZ Emp completed, legacy build fuse in progress Read this topic online here: http://forums.matronics.com/viewtopic.php?p=243569#243569


    Message 4


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    Time: 11:44:24 AM PST US
    Subject: Re: GPU - 24V System - Crowbar Needed
    From: "woxofswa" <woxof@aol.com>
    Can I ask a neophyte question in the quest for further light and knowledge? Why is a contactor, and/or switch needed for ground power? It seems to me that the very act of plugging in the plug could serve as "activating" the power, and pulling the plug out would deactivate it. What am I missing? -------- Myron Nelson Mesa, AZ Emp completed, legacy build fuse in progress Read this topic online here: http://forums.matronics.com/viewtopic.php?p=243572#243572


    Message 5


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    Time: 12:23:10 PM PST US
    Subject: Re: GPU - 24V System - Crowbar Needed
    From: "George, Neal E Capt USAF ACC 605 TES/DOA" <Neal.George@hurlburt.af.mil>
    Myron - Switching the ground power connection allows the pilot full control of the circuit. Over-voltage warning enhancements provide the opportunity to monitor and verify that the lineboy has indeed plugged in 12v instead of 24v - before you light up the internal circuits. Neal ================== Can I ask a neophyte question in the quest for further light and knowledge? Why is a contactor, and/or switch needed for ground power? It seems to me that the very act of plugging in the plug could serve as "activating" the power, and pulling the plug out would deactivate it. What am I missing? -------- Myron Nelson Mesa, AZ Emp completed, legacy build fuse in progress


    Message 6


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    Time: 12:24:21 PM PST US
    From: Gilles Thesee <Gilles.Thesee@ac-grenoble.fr>
    Subject: Comm & Nav audio with SPA 400
    Hi all, A buddy is trying to install a KX 155 with a Sigtronics SPA 400 in a two seater. He is trying to devise a way to hook up the Nav audio output. Any suggestions as to how to mix or hook up Comm AND Nav audio ? Thanks in advance Best regards, -- Gilles http://contrails.free.fr


    Message 7


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    Time: 01:09:57 PM PST US
    From: "Patrick Hildebrand" <equinav@interbaun.com>
    Subject: Comm & Nav audio with SPA 400
    Usually, there is a audio input or "aux" input for the coms. This is designed to mix the audio for a variety of devices. You could try hooking pins 10 and L of connector A1 (Nav high and low) to Pins H and F of connector A2 (Aux high and low in). This would mix the Nav audio output into the comm audio input. Probably accomplish what you need to mix the audio prior to the SAP400. Patrick -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Gilles Thesee Sent: May 11, 2009 1:20 PM Subject: AeroElectric-List: Comm & Nav audio with SPA 400 <Gilles.Thesee@ac-grenoble.fr> Hi all, A buddy is trying to install a KX 155 with a Sigtronics SPA 400 in a two seater. He is trying to devise a way to hook up the Nav audio output. Any suggestions as to how to mix or hook up Comm AND Nav audio ? Thanks in advance Best regards, -- Gilles http://contrails.free.fr


    Message 8


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    Time: 01:12:30 PM PST US
    From: "Patrick Hildebrand" <equinav@interbaun.com>
    Subject: Comm & Nav audio with SPA 400
    Usually, there is a audio input or "aux" input for the coms. This is designed to mix the audio for a variety of devices. You could try hooking pins 10 and L of connector A1 (Nav high and low) to Pins H and F of connector A2 (Aux high and low in). This would mix the Nav audio output into the comm audio input. This would probably accomplish what you need to mix the audio prior to the SAP400. Patrick -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Gilles Thesee Sent: May 11, 2009 1:20 PM Subject: AeroElectric-List: Comm & Nav audio with SPA 400 <Gilles.Thesee@ac-grenoble.fr> Hi all, A buddy is trying to install a KX 155 with a Sigtronics SPA 400 in a two seater. He is trying to devise a way to hook up the Nav audio output. Any suggestions as to how to mix or hook up Comm AND Nav audio ? Thanks in advance Best regards, -- Gilles http://contrails.free.fr


    Message 9


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    Time: 02:00:19 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Battery Charger as Ground Power
    At 01:11 PM 5/11/2009, you wrote: ><capav8r@gmail.com> > >Bob: > >I've been reading some posts on ground power and noted that some >people are using a battery charger as a ground power unit. From >what I remember about the output voltage of almost all battery >chargers, there is a significant potential to overvoltage the >aircraft isn't there? The voltage from most chargers is not >filtered and is not as clean as you'd want for powering avionics, etc. "Battery Charger" is non-qualified. Technically, any source of energy that is capable of reversing current flow into a battery is a 'charger'. The quality of output power from chargers can be all over the map. The very first charger I owned was a 6v Tungar rectifier electro-whizzy. Emacs! The output quality of this thing would have been REALLY noisy, ZERO voltage regulation, hideously inefficient, but entirely suited to keeping my '41 Pontiac straight-6 ready to start on a cold morning. By the way, anyone interested in exploring/reliving some of the history of lead-acid battery technology, feel free to download this item. (Caution 9+ MB) http://tinyurl.com/owad89 45 years later and at the other end of the spectrum, we can purchase light, relatively inexpensive, high quality switch-mode power supplies that will serve as both ground power supplies for system operations but battery chargers as well. Unfortunately, devices tailored to serve as "smart" chargers (quick recharge, indefinite storage) probably don't make good ground power supplies because their internal battery-pampering software gets confused when the "battery" being maintained keeps changing terminal voltage and load. A few years ago, we made a great buy on a quantity of Samlex 1223 power supplies. http://www.universal-radio.com/catalog/hamps/2423.html We offered these as "alternator simulators" with the suggestion that they could be used to make the ship's systems believe that a 23A alternator was running. This would allow the ship's battery to be charged and ship's systems of up to 20A draw (about anything but pitot heat) to be tested in the shop. The short answer is that not all battery chargers are suited for use as ground power supplies perhaps due to their particular noise/voltage-regulation characteristics. However, you can hook any charger across a battery and give it a try. Make sure you know how it behaves in the long term (watch bus voltage) and know it's specific limits. With a modicum of due-diligence, the experiment offers minimal risk to system components. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------


    Message 10


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    Time: 02:22:29 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: GPU - 24V System - Crowbar Needed
    At 01:38 PM 5/11/2009, you wrote: > >Can I ask a neophyte question in the quest for further light and knowledge? > >Why is a contactor, and/or switch needed for ground power? The implementation of ground power connectors published on my website and discussed on the forums grew out of the following design goals: (1) protection from 28 volt ground power being applied to a 14v airplane. (2) pilot control of ground power from the left seat. (3) reverse polarity protection. (4) convenience of an industry-common connection to the aircraft relatively free of hazard to ground crew from spinning props. Twice in my experience, I've had 28v connected to my 14v airplane. In one case, the line-boy caught the error and flipped the switch before I could even react. In the other case he couldn't hear me over the roar of the ground power cart engine and he had his back to me watching the gages on the cart. I had to unbuckle, slide over, open r.h. cabin door and yell at him while stuff in the airplane suffered. >It seems to me that the very act of plugging in the plug could serve >as "activating" the power, and pulling the plug out would deactivate it. Making and breaking a high current load during mate/de-mate operations is hard on the connector. But if you plan to exercise absolute and personal control over how and under what conditions external sources of power get hooked to your airplane, then it might be as simple a task as hooking up the jumper cables. But standing in a stream of wet, wind-driven snow this winter, I got a pair of jumper cables reversed to my son's van . . . didn't hurt anything but it sure COULD have. The degree of risk you're willing to shoulder is up to you. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------


    Message 11


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    Time: 03:11:44 PM PST US
    Subject: Re: Ground Power
    From: Walter Fellows <walter.fellows@gmail.com>
    Thanks for the post, your installation is nicely documented. On Sat, May 9, 2009 at 6:21 PM, Matt Dralle <dralle@matronics.com> wrote: > At 05:42 PM 5/9/2009 Saturday, you wrote: > > > >I am bumping this after a search. > > > >I am in the process of putting together a ground power receptacle for my > RV10. > > > >I have ordered a piper receptacle from A. Spruce, and the crowbar and > contactor from BandC. > > > >My primary goals are: > > > >1. To be able to come up to a dead airplane, start it from ground power, > and go fly. > > > >2. To be able to charge a dead or weak battery without having to remove > access panels. > > > >3. to be able to provide power during construction/testing with a cheapo > spare battery. I don't want to buy my ship's battery until the day before > my first start. > > > >I don't necessarily need to be able to switch the ground power on or off. > I'm okay with the act of putting the plug in as switching it on. However, > I would like the circuit to die once I pulled the plug out if that makes > sense. > > > >Does the Aero'lectric diagram meet my needs or do I need changes? > > > >Anyone have pictures of an installation, preferably in an RV10? > > > >-------- > >Myron Nelson > >Mesa, AZ > >Emp completed, legacy build fuse in progress > > > Hi Myron, > > Attached are some pictures of my GPU power installation in the RV-8. Works > great and allows me to charge the battery, run the avionics, or start the > engine. I also included the backbone wiring schematic. I'm using the > Vertical Power VP-200 electrical system, but the GPU wiring should be fairly > common. The GPU wiring is shown in the lower right hand side of the > diagram. I haven't updated the diagram yet, but you might need to add a > connection between the Sense input on the GPU plug through a Normally Open > push button to the EBus (and through a small fuse or polyfuse). What I > found was that the late-model chargers won't turn on their output unless > they see about 4-5 volts. So, they won't pull the GPU relay down when you > plug the GPU plug in. The button allows you to pull the relay in and make > the charger think there is voltage. The only catch is that your aircraft > battery has to have enough juice to pull the relay down. > > Let me know if you've have any questions. > > Matt Dralle > RV-8 #82880 N998RV > Laying Carpet Out in CAD... > >


    Message 12


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    Time: 03:33:57 PM PST US
    From: Matt Dralle <dralle@matronics.com>
    Subject: Re: Battery Charger as Ground Power
    At 01:58 PM 5/11/2009 Monday, you wrote: >At 01:11 PM 5/11/2009, you wrote: >> >>Bob: >> >>I've been reading some posts on ground power and noted that some people are using a battery charger as a ground power unit. From what I remember about the output voltage of almost all battery chargers, there is a significant potential to overvoltage the aircraft isn't there? The voltage from most chargers is not filtered and is not as clean as you'd want for powering avionics, etc. > > Unfortunately, devices tailored to serve as "smart" > chargers (quick recharge, indefinite storage) probably > don't make good ground power supplies because their > internal battery-pampering software gets confused when > the "battery" being maintained keeps changing terminal > voltage and load. > > A few years ago, we made a great buy on a quantity > of Samlex 1223 power supplies. > > Bob . . . I've got one of these Black and Decker BC40EB units that has adjustable charge output limits in addition to a 110amp starter booster. I'm plugging it into my GPU plug and use it to run the avionics, charge the battery, and I'm hoping eventually to jump start the engine when the battery is on the low side. The only downside seems to be that the unit has to see 4-5volts on the "battery" before it will turn on its output. This means that it won't flip the GPU relay and you have to have an external switch to do that. Bob, does this seem like a good charger/GPU product for aircraft systems? http://www.blackanddecker.com/ProductGuide/Product-Details.aspx?ProductID=17925 Matt Dralle RV-8 #82880 N998RV Carpet CAD Drawings... (1200+ Hours Build Time...)


    Message 13


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    Time: 05:11:02 PM PST US
    From: Ed Holyoke <bicyclop@pacbell.net>
    Subject: Re: GPU - 24V System - Crowbar Needed
    Besides keeping the wrong voltage from hitting your battery and buss, a ground power contactor keeps the fat wire running to the receptacle from being hot all the time and being a potential shorting hazard. Pax, Ed Holyoke woxofswa wrote: > > Can I ask a neophyte question in the quest for further light and knowledge? > > Why is a contactor, and/or switch needed for ground power? > > It seems to me that the very act of plugging in the plug could serve as "activating" the power, and pulling the plug out would deactivate it. > > What am I missing? > > -------- > Myron Nelson > Mesa, AZ > Emp completed, legacy build fuse in progress > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=243572#243572 > > >


    Message 14


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    Time: 05:55:22 PM PST US
    From: <bakerocb@cox.net>
    Subject: Ground Power Receptacle?
    5/11/2009 Hello Ian, You wrote: 1) "Having spent the last couple of weeks needing to repeatedly recharge my RV-9A battery,........" What is abnormal about either your system or your mode of operation that causes this repeat problem? If there is a fundamental fault in either of those two areas maybe a fault correction approach rather than an external charging receptacle band-aid should be considered. 2) "......I can say that an external charging receptacle would have made my life a lot easier." Realize that external charging receptacles can come in two different flavors: A) A simple low amperage connection system going directly to the battery that is suitable for connecting a 120 volt input, low amperage output battery charger / maintainer for just the purpose of recharging / maintaining the battery. B) A more elaborate high amperage system that would facilitate cranking the engine as well as recharging the battery with maybe some additional features such as reverse voltage protection. 3) "Can anyone tell me the best receptacle to use, that would be the most standard?" You would have to decide whether you wanted an A or a B solution in order to answer the "best" question. If an A solution satisfies your needs then there are dozens of choices -- it only requires two wires with some simplistic polarity protection. I have operated for several years now with just two wires coming directly from my battery up to the cockpit area. One wire is terminated with a female, fully insulated, Faston type connector, the other wire is terminated with a male, fully insulated, Faston type connector. The wires are just tucked out of the way when not in use. See: http://www.terminaltown.com/Pages/Page9.html My battery charger clip ons have been modified with the appropriate stub wires and Faston type connectors added. One benefit of this system is that I can connect it up and then attach a volt meter to the charger clips. It tells me what the battery voltage is. Then I can plug in the charger and monitor the charging voltage -- very handy. If only a B solution will satisfy you then look to Bob Nuckoll's published material on this subject. The most commonly found receptacle and plug arrangement found at FBO's is the three prong. See here: http://www.aircraftspruce.com/catalog/elpages/extpowerrect.php The next most commonly found is the Piper receptacle and plug arrangement.** See here: http://www.aircraftspruce.com/catalog/elpages/piperplugsock.php BUT there is a major "gotcha" that you must be aware of if you have a 12 volt aircraft electrical system and you install one of the above receptacles -- some ground power carts with the above plugs will only put out 24 volts. If you zap your 12 volt system with 24 volts you will suffer damage. 'OC' Says: "The best investment we can make is the effort to gather and understand knowledge." **PS: There is also a single center post receptacle and plug system similar in apprearance to the Piper system, but not compatible, that is found on some Beechcraft airplanes. Very unlikely to find a ground power cart with a plug compatible with this odd ball receptacle. ======================================================== Time: 12:24:10 PM PST US Subject: AeroElectric-List: Ground Power Receptacle? From: Ian <ixb@videotron.ca> Having spent the last couple of weeks needing to repeatedly recharge my RV-9A battery, I can say that an external charging receptacle would have made my life a lot easier. Can anyone tell me the best receptacle to use, that would be the most standard? Can you also suggest a good source? While not planning to fly away on an almost dead battery, I do envisage moments when it would be useful to start from ground power, and then do some charging direct from the alternator. I'd imagine that flying locally would be fairly safe while the battery is being topped up, as long as your whole panel doesn't shut down if you lose battery. Ian Brown Bromont Quebec


    Message 15


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    Time: 06:43:30 PM PST US
    From: "David L." <skywagon@charter.net>
    Subject: Re: Battery Charger as Ground Power
    The little, cheap Harbor Freight "maintainers" work quite well. I have used several. One key point however, ...many of them come set a tad too high in their fixed "float" voltage, to my thinking. I have seen them as high as 13.9 v. The good news, is they can be adjusted to the float voltage that you want. The little controller box should have a back lid that is lightly glued in place. Carefully work a very narrow blade screw driver or other tough, but thin device into the glued seam and work it until the back pops off. Inside is a small circuit board and potentiometer. It may have a spot of RTV on it. Work this loose. Turning the pot CW lowers to float voltage. I like about 13.2 v. Others may want a slightly different setting. I usually locate where the pot slotted screw adjust hole is located next to the little case and drill a 3/16 hole. That way, it can be adjusted from the outside. The little unit is quite stable after you get the setting where you want it. David ---- woxofswa <woxof@aol.com> wrote: ============ I'm no expert, but I think you are right. I think a 12.5 volt "maintainer" would make much more sense. They can be had at Harbor Freight for $5 For ground tests and assembly, I plan on using a cheapo lawn tractor battery with a maintainer hooked up to it. The battery would then serve as a sink if there is a problem with the maintainer. -------- Myron Nelson Mesa, AZ Emp completed, legacy build fuse in progress Read this topic online here: http://forums.matronics.com/viewtopic.php?p=243569#243569


    Message 16


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    Time: 07:16:57 PM PST US
    Subject: Re: Battery Charger as Ground Power
    From: "Craig Winkelmann" <capav8r@gmail.com>
    Bob: Thanks, BUT some GPUs bypass the battery because they are not meant to be a port for charging the battery. In these cases, whatever comes out of the charger goes on the main bus. I suspect the right thing is to see how conditioned and stable the output voltage is prior to plugging the unit into a plane full of expensive avionics. Craig Read this topic online here: http://forums.matronics.com/viewtopic.php?p=243643#243643


    Message 17


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    Time: 07:47:37 PM PST US
    From: "Kevin Jones" <kmjone2@comcast.net>
    Subject: Wonky Ammeter Redux
    Hello Folks, I have a problem that is very similar to the Aeroelectric Connection issue of the same subject from 2001. I've got a Vans -40,0+40 ammeter (load meter) connected to a 40mV @40A shunt wired exactly (minus the fuselinks) as Figure Z-13 in the Connection. I also have a 10mV shunt wired to read the aux SD-8 alternator loads. The signal wires from the two shunts are controlled by a switch on the panel. Main is wired to show negative, aux is positive ammeter deflection. The following is my scenario: 1. Ground operation with engine off; power supplied to main alternator feed through a radio shack 13.8V 3A supply. 2. Ammeter power is on the E-Bus, with alternate feed switch off. 3. Power supply is providing ~3A and I measure 3.8mV across the shunt. Shunt voltage to ground is 13.08V. 4. Instrument reads ~3.5mV at the sense wire connections 5. Instrument power voltage is ~12.2 volts 6. Ammeter shows full-scale discharge (negative). If I turn power supply off, this doesn't change??? If I switch on the E-Bus alternate feed, the ammeter returns to zero. Instrument voltage increases to 12.6V. If I power the alternate alternator feed, ammeter shows slight positive deflection, but nothing near the 35% deflection expected. I first started running this problem down after seeing large ammeter deflections with the strobe on without any load applied to the shunt. How robust are the Vans ammeters and should I invest in a new one or re-wire the system? Why would opening the E-Bus alternate path cause a change in ammeter reading? Do I need to feed the ammeter with the same voltage as the shunt? Many thanks. KJ


    Message 18


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    Time: 08:42:32 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Battery Charger as Ground Power
    >I think a 12.5 volt "maintainer" would make much more sense. They >can be had at Harbor Freight for $5 > >For ground tests and assembly, I plan on using a cheapo lawn tractor >battery with a maintainer hooked up to it. The battery would then >serve as a sink if there is a problem with the maintainer. Actually, the ideal maintainer voltage is just above 100-200 millivolts the battery's open circuit voltage 24 hours or so after taking it off the charger. Lead-Acid batteries, this is 13.1 to 13.2 volts. The idea is that you want to hold the battery at or just above it's own chemistry voltage . . . thus any and all tendencies to self-discharge are supported by the external energy source. I.e. self-discharge currents do not tax the chemistry. See: http://www.aeroelectric.com/Pictures/Curves/Battery_Tender_Recharge.pdf http://www.aeroelectric.com/Pictures/Curves/Ideal_Recharge_Protocol.jpg Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------


    Message 19


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    Time: 08:44:50 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Battery Charger as Ground Power
    At 09:13 PM 5/11/2009, you wrote: ><capav8r@gmail.com> > >Bob: > >Thanks, BUT some GPUs bypass the battery because they are not meant >to be a port for charging the battery. In these cases, whatever >comes out of the charger goes on the main bus. I suspect the right >thing is to see how conditioned and stable the output voltage is >prior to plugging the unit into a plane full of expensive avionics. It's the system integrator's task to decide whether or not the battery is on line during ground power connection. I've heard the stories for both cases for BIG airplanes with BIG batteries and BIG ground power carts. For our purposes and considering relative sizes of our hardware, it's best to have a battery on line during ground power ops . . . especially if the power quality of the power source has not been fully qualified to the task. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------




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