---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 12/06/16: 6 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:49 AM - Re: Avionics Master (donjohnston) 2. 08:25 AM - Re: Re: Avionics Master (Robert L. Nuckolls, III) 3. 10:39 AM - Re: Avionics Master (donjohnston) 4. 10:54 AM - Re: Re: Avionics Master (Sebastien) 5. 01:17 PM - Re: Ballasting Dsub connectors (Robert L. Nuckolls, III) 6. 06:54 PM - Alternator Field Circuit Fuse Blow (Valin Thorn) ________________________________ Message 1 _____________________________________ Time: 05:49:03 AM PST US Subject: AeroElectric-List: Re: Avionics Master From: "donjohnston" Not to poke a sleeping bear... I've got an avionics master not because I'm worried out spikes. My concern is with the opposite. Sags. I also have remote avionics (no power switches on the devices) with a VPX power distribution system. When I'm starting up the EFIS will reboot if the voltage gets too low (I'd have to check the doc's but I think it gets unhappy below 18 or maybe 20v). The radios are a bit more tolerant as they will handle much lower voltages. Not sure about the GPS or audio panel. The greater issue is that when the EFIS power sags, sometimes it won't reboot and just goes into limbo. Then I have to go in to the VPX, shut off the breaker, wait, and then reactivate the breaker to get the EFIS back up. The EFIS doesn't reboot on every start. But if I've been fighting a stubborn hot start then the battery can get a little tired. For the primary EFIS, I have a small backup battery that powers the EFIS that during engine starts. I could have put in a second backup battery for the other EFIS, or a switch for the second EFIS. But it seems like the simplest solution is an avionics master. This also allows me to power up the electrical system if I want to work on the gear retract system, lights, etc., without powering up the avionics. Just my .02 Read this topic online here: http://forums.matronics.com/viewtopic.php?p=463750#463750 ________________________________ Message 2 _____________________________________ Time: 08:25:14 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Avionics Master At 07:47 AM 12/6/2016, you wrote: > >Not to poke a sleeping bear... > >I've got an avionics master not because I'm worried out spikes. My >concern is with the opposite. Sags. > >I also have remote avionics (no power switches on the devices) with >a VPX power distribution system. When I'm starting up the EFIS will >reboot if the voltage gets too low (I'd have to check the doc's but >I think it gets unhappy below 18 or maybe 20v). The radios are a bit >more tolerant as they will handle much lower voltages. Not sure >about the GPS or audio panel. Low voltage is generally not a stress to be 'handled' beyond the ability to make a graceful recovery after the brown-out event. This shortcoming is generally limited to devices with micro-controllers that are not fitted with brown-out protection features . . . Failure to design such features into a modern appliance is something akin to forgetting to include a filler-spout on a fuel tank. Pretty elementary. In 50+ years of designing and fabricating electro-whizzies for aircraft from Hawker 4000 to ultra-lights, I've never been challenged by the notion that brown-outs of any magnitude, rate and duration are a special force to be wrestled with. > > >The greater issue is that when the EFIS power sags, sometimes it >won't reboot and just goes into limbo. Then I have to go in to the >VPX, shut off the breaker, wait, and then reactivate the breaker to >get the EFIS back up. > >The EFIS doesn't reboot on every start. But if I've been fighting a >stubborn hot start then the battery can get a little tired. For the >primary EFIS, I have a small backup battery that powers the EFIS >that during engine starts. > >I could have put in a second backup battery for the other EFIS, or a >switch for the second EFIS. But it seems like the simplest solution >is an avionics master. This also allows me to power up the >electrical system if I want to work on the gear retract system, >lights, etc., without powering up the avionics. > >Just my .02 Unfortunately, there are numerous products offered to the aviation markets that are not designed to the spirit and intent of legacy rules-of-the-road for aviation appliances. Brownout mitigation has been discussed numerous times over the years here on the List with a variety solutions offered. They all have the disadvantage of increased weight, system complexity and potential electro-magnetic compatibility issues (radio noise). Do these affected systems not have their own power switches? If not, then you're not really adding an avionics master but simply a power control switch to a device that does not already have one. In such cases, it seems prudent to have a separate switch for each device . . . this gets around the issue of generating single points of failure for multiple appliances. Cost of ownership for adding switches will be lower than for adding more batteries that need to be maintained throughout the life of the aircraft . . . but only serve a useful purpose for a few tens of milliseconds every flight cycle. Bob . . . ________________________________ Message 3 _____________________________________ Time: 10:39:35 AM PST US Subject: AeroElectric-List: Re: Avionics Master From: "donjohnston" nuckolls.bob(at)aeroelect wrote: > At 07:47 AM 12/6/2016, you wrote: > Do these affected systems not have their own power switches? Nope. These devices have no external controls. > If not, then you're not really adding an avionics master but simply a power control switch to a device that does not already have one. In such cases, it seems prudent to have a separate switch for each device . . . this gets around the issue of generating single points of failure for multiple appliances. I thought about doing that. But I felt the additional wiring and switches to be an added complication. Besides, each device can be powered on or off through the VPX so that is my "individual device" switch. And my "Avionics Master" switch can be bypassed from the VPX as well (should it fail). So to me, that seems like a win-win. :D Read this topic online here: http://forums.matronics.com/viewtopic.php?p=463754#463754 ________________________________ Message 4 _____________________________________ Time: 10:54:32 AM PST US From: Sebastien Subject: Re: AeroElectric-List: Re: Avionics Master All the Beech products I flew had a NC relay opened by turning the avionics master switch off. If the switch failed and the avionics went dark, you just pulled the breaker for the switch and the avionics came back on. Seems like a simple solution to me. Sebastien > On Dec 6, 2016, at 10:38, donjohnston wrote: > > > > nuckolls.bob(at)aeroelect wrote: >> At 07:47 AM 12/6/2016, you wrote: >> Do these affected systems not have their own power switches? > > Nope. These devices have no external controls. > > >> If not, then you're not really adding an avionics master but simply a power control switch to a device that does not already have one. In such cases, it seems prudent to have a separate switch for each device . . . this gets around the issue of generating single points of failure for multiple appliances. > > I thought about doing that. But I felt the additional wiring and switches to be an added complication. Besides, each device can be powered on or off through the VPX so that is my "individual device" switch. And my "Avionics Master" switch can be bypassed from the VPX as well (should it fail). > > So to me, that seems like a win-win. :D > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=463754#463754 > > > > > > > > > ________________________________ Message 5 _____________________________________ Time: 01:17:59 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: Ballasting Dsub connectors At 11:14 AM 12/6/2016, you wrote: >Bob > >For the illiteratti among us, please explain the concept behind the >12 inch pigtails a bit more. My takeaway from the article was that >12 inches of wire act as a "resistor" in series with the pin. Would >you not need to tailor each pigtail to attain the correct >resistance? Or, just by having this increased resistance, within a >range, does it drive the pins to share current? Correct. And thank you for that question. I should have described that effect in the article. I've edited it to include that explanation. >The final takeaway was that, without the pigtails, one pin would hog >the load, overload and fail, causing a cascade failure of the entire >connector under load. Yes, no or should I go back to my corner? Not at all . . . in fact, you've spotlighted the need for further elaboration. Bob . . . ________________________________ Message 6 _____________________________________ Time: 06:54:05 PM PST US From: "Valin Thorn" Subject: AeroElectric-List: Alternator Field Circuit Fuse Blow Hello Bob, First, let me say a big thank you for all your help over the years during the design and build of the electrical system of our Lancair Legacy airplane. We've been flying now for 14 months, have about 140 hours of flight time, and the airplane received EAA's Kit Built Grand Champion Award this year. The electrical system has been working very well. It's based on your Z-12 single battery, dual alternator architecture. We do have a slight mystery, though, that I would sure appreciate your thoughts on. We've had the primary alternator's (100 A) field circuit fuse blow (fuse not CB) while deploying the landing gear, on two occasions - once two months ago and once this morning. Here's some background info. We have a fuse tray that pulls out of the panel holding blade type fuses that light up when they've blown -- saved a bunch of real estate on the panel. The landing gear are powered by an electric motor driven hydraulic pump that can pull almost 80 A at times. On the first occasion the field fuse blew I'd eventually attributed it to being because one of our two PC680 batteries (in series for 28 VDC) was heat damaged from sitting down stream of the oil cooler and was not holding a charge well and maybe not compensating for the big current draw from the hydraulic pump motor as well as it should. The battery issue was corrected (replaced) a couple months ago and all has been well until this morning when the field fuse blew again on landing gear extension. On both occasions the fuse blew on landing gear extension which seems to be the least loaded gear operation since the weight of the gear and their gas spring struts want to deploy the gear anyway - the pump can barely keep up. But, we do have a modification to our landing gear system where the inboard gear doors close after gear go down and the pump typically cycles very quickly several time while it's closing the inboard doors. For more background, we splurged on expensive hermetically sealed contactors rated for 100 A continuous for switching the hydraulic pump motor -- Tyco Kilovac EV100 relays with built in voltage suppression diodes. I know you're the architect of the amazing crow bar over voltage protection featured in our L3RC-28 linear alternator regulator from B & C Specialties. In talking with TJ at B&C today, he said if the regulator sees over 32 VDC for more than 5 milliseconds that the crow bar over voltage will short the field circuit to trip the CB or fuse. We're both wondering if using a 5A fuse vs. a 5A CB could make a difference.? Anyway, what do you think about this? It has only happened twice. Could the field current to drive a 100A alternator under a high load exceed the 5A fuse limit? Should we try a 7A fuse? Is this likely from an over-voltage condition and if so what's causing it? Could it be that the regulator isn't dropping the field strength fast enough after the landing gear/hydraulic motor stops running and causing an over voltage spike that's tripping the crow bar over voltage circuit? Thanks in advance for your help! Valin Thorn StarHawk Lancair Legacy -- N321TF Sedona, Arizona ------------------------------------------------------------------------------------- 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.