---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 11/18/14: 7 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:24 AM - Re: Flyback Diodes (Bill Watson) 2. 07:36 AM - Re: Fire-Sale Phase V (Hariharan Gopalan) 3. 07:57 AM - Re: Fire-Sale Phase V (Justin Jones) 4. 08:24 AM - Re: Fire-Sale Phase V (Robert L. Nuckolls, III) 5. 11:23 AM - Re: Flyback Diodes (Robert L. Nuckolls, III) 6. 11:48 AM - Re: Re: Wiring schematic question (Peter Pengilly) 7. 12:33 PM - Re: Wiring schematic question (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 06:24:05 AM PST US From: Bill Watson Subject: Re: AeroElectric-List: Flyback Diodes So, the diode we find jumpered between the coil contacts on let's say, our starter relay, prevents a high voltage shooting back thru our starter switch and arcing the contacts when we let go of the starter key/switch? Or does it prevent a power surge from hitting the entire electrical system? Bill "waking up brain cells in disuse since early adolescence" Watson (nice video, thanks!) On 11/17/2014 12:07 PM, Eric Page wrote: > The following video was just posted by a fellow on YouTube who I > follow. It does a very nice job of illustrating the purpose and > effect of using flyback or catch diodes on inductive loads like relay > coils. > > Since the topic has arisen here a number of times, I thought this > might be of interest. > > http://www.youtube.com/watch?v=c6I7Ycbv8B8 > > Eric > ________________________________ Message 2 _____________________________________ Time: 07:36:04 AM PST US Subject: Re: AeroElectric-List: Fire-Sale Phase V From: Hariharan Gopalan Please invoice rdu.hari@gmail.com Thanks Hari On Mon, Nov 17, 2014 at 10:18 PM, Charlie England wrote: > ceengland7@gmail.com> > > On 11/17/2014 8:37 PM, Robert L. Nuckolls, III wrote: > >> nuckolls.bob@aeroelectric.com> >> >> >> Excellent! Please invoice to mcsophie@gmail.com (different from my >>> aeroelectric subscription). >>> >>> Thanks, >>> >>> Charlie >>> >> >> Done. >> >> >> Bob . . . >> > And done. > > Thanks, > > Charlie > > ________________________________ Message 3 _____________________________________ Time: 07:57:22 AM PST US From: Justin Jones Subject: Re: AeroElectric-List: Fire-Sale Phase V Bob, I would like one of them if you have any left. Thanks Justin jmjones2000@mindspring.com > On Nov 17, 2014, at 3:30 PM, Robert L. Nuckolls, III wrote: > > > I have two, legacy crowbar overvoltage modules > left from inventory. $20 each post-paid to US > addresses. > > > Bob . . . > > > > ________________________________ Message 4 _____________________________________ Time: 08:24:32 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Fire-Sale Phase V At 09:33 2014-11-18, you wrote: >Please invoice rdu.hari@gmail.com > >Thanks >Hari already sold Bob . . . ________________________________ Message 5 _____________________________________ Time: 11:23:56 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Flyback Diodes At 08:19 2014-11-18, you wrote: So, the diode we find jumpered between the coil contacts on let's say, our starter relay, prevents a high voltage shooting back thru our starter switch and arcing the contacts when we let go of the starter key/switch? Yes . . . Or does it prevent a power surge from hitting the entire electrical system? Not at all. Contactor/relay coil flyback, catch or suppression diodes have been part-and-parcel of the system designer's toolbox for quite a few years. While I was a tech writer at Cessna (65-69), our chief scientist, Gordon Wood, Phd, purchased this nifty peak-reading voltmeter (Hewlett-Packard I think) and did some battery and starter contactor behavior studies in the labs. "My gawd Mabel . . . did you see the size of that spike?!?!?! Gee whiz . . . over 400 volts . . . that sounds dangerous." This was exactly the time when Aircraft Radio Corporation, recently purchased by Cessna, was producing Cessna branded 300, 500 and ultimately 400 Series radios and autopilots. When the radios began to show up with transistorized audio/modulator and dc/dc converters for vacuum tube high voltage, we began to experience a rash of un-explained failures in the transistors of newly installed radios. We were building 10,000 airplanes a year back then . . . needless to say, even a few percent failure rate in radios was a SIGNIFICANT impact to corporate bottom line. The quest was on . . . if not to understand what was really happening . . . then at least to stop the failures. About that same time, Cessna hired Wichita University to craft a course on "The Industrial use of Transistors," which was well attended by about 20 folks from both Cessna plants and your's truly. The instructor was extremely well versed in the topic being that he was both a college prof and a sought after consultant. Not a great teacher . . . but Jerry Wedel I learned how to 'pick his brain' in useful ways by the questions we asked. We sat on opposite sides of the class and stroked him to our great advantage. Back then, the power transistors of choice were germanium, mostly PNP devices with max operating voltages on the order of 30 volts. Hmmmm . . . Mean while, back at the airplane farm, Gordon was poking around the electrical systems of our airplanes in search of clues. It was quickly discovered that adding the diode across the contactor coil completely eliminated the gawd-awful spike. Whew! Slew that dragon. But that still didn't fix the radio failures. About then, flight test pilots discovered that if the radios were OFF during engine start, the did not suffer the failures. You know what came next. The avionics master switch was born. Simultaneously, a new line of thought was launched into the aviation consciousness . . . and a new phrase was oft repeated on avionics benches across the world, "Damn, I think a spike got it." It took about two decades before anyone really began to sift the simple-ideas for properties of materials and management of energy (it's called engineering) and figure out what was really going on. Turns out that transistor failures in the radios were not suffering the effects of high voltage spikes . . . but second breakdown effects in relatively fragile transistors due to LOW voltage effects, i.e. brownout during cranking. Batteries back then were pretty sorry things by today's standards. Our 'airplane patch' east of the plant would have hundreds of new airplanes parked out there awaiting ferry pilots. The batteries were NEVER attended to in a manner consistent with their physics . . . hence, more that a few airplanes needed to be propped, jumped and/or battery charged . . . but only AFTER the pilot had attempted to start the airplane perhaps with one or more radios turned ON. It was also not well understood that those spectacular contactor coil spikes never went anywhere . . . at least not out onto the ship's electrical system. 99% of energy stored on the contactor's inductance was dissipated in the air-gap of the spreading switch contacts as the battery master was turned OFF or the starter switch was released. The diodes across the coil were a good thing, it saved wear and tear on switches . . . but had no significance on the life span of a radio or any other appliance. In still later years, there was some earnest debate about OTHER effects of adding diodes across relay or contactor coils. Simple measurements demonstrated that adding the diode caused there to be a DELAY in relay/ contactor drop-out . . . the diode cause coil current to be sustained for some milliseconds after the switch opened as energy stored in the coil was dissipated in circuit resistance. Hmmm . . . if the contactior's release is delayed/slowed, does that also translate into a slower contact spreading velocity which in turn aggravates the arcing? Intuitively it seems likely . . . indeed, many articles have been written, some by folks working for big-name companies that thoroughly described the diode induced drop-out DELAY . . . and then extrapolated that good information into an erroneous assumption that influences on drop-out delay were equally applicable to contact spreading velocity . . . without making a single measurement. On page 4 of this document http://tinyurl.com/n296nl6 there are 'scope displays that demonstrate approx 5x increase in dropout delay for having added a plain-vanilla diode across a relay coil. At the same time, the contact spreading times are very similar demonstrating no significant difference in the arc signature. Bill "waking up brain cells in disuse since early adolescence" Watson (nice video, thanks!) The youtube tutorial was nicely done and confirms the value of adding SOME form of coil spike suppression . . . but to extrapolate the demonstration's significance for other features of relay performance is fraught with opportunity for error. Bob . . . ________________________________ Message 6 _____________________________________ Time: 11:48:52 AM PST US From: Peter Pengilly Subject: Re: AeroElectric-List: Re: Wiring schematic question If you have no master relay or starter relay then the thick wire from the battery to the starter will be hot at all times - there are a few accident scenarios where you could wish you hadn't done that, but its a judgement over risk and reward! I have a similar set up on my One Design, except that I used a starter relay, and also brought out the wire that controls the NL solenoid to a switch on the panel to provide an emergency off should the start relay weld itself together (used the suggestion in the Sky-Tec documentation). Yes that is a few additional ounces, but you already have a starter and a battery so the penalty is not that large. If you are worried about ounces then swap out your mags for P-mags? Peter On 18/11/2014 06:31, Ryan wrote: > Thanks Bob. > > That all makes good sense after reading through it. > > Much appreciated. > > Ryan > > ------------------------------------------------------------------------ > Date: Tue, 18 Nov 2014 00:00:09 -0600 > To: aeroelectric-list@matronics.com > From: nuckolls.bob@aeroelectric.com > Subject: AeroElectric-List: Re: Wiring schematic question > > At 03:41 2014-11-17, you wrote: > Hi Bob, > > I have been in email discussion with Greg Jones at B&C about a few > things on my Pitts Special and he suggested you would be best to speak > with about the Aerobatic Aircraft wiring schematic on their website, > it was made mention that you drew it up. > Drawing number 420-506 > > http://www.bandc.biz/pdfs/420-506_Indexed_Diagram_with_BOM.pdf > http://www.bandc.biz/pdfs/420-506_REVB.pdf > > I had a couple of > questions, hopefully you can assist a little. > > Looking at the mag switch portion of the diagram. Should it not be > drawn that the impulse magneto is the OFF-START/ON? > If the OFF-START/ON switch (Right Mag) is used and the start button > engaged the starter would not power unless the Left Mag were also on. > Am I missing something here? > > *Those drawings were sorta copied from my originals * > * but with errors. See > > * > *http://tinyurl.com/lsqz36k > > * > * Here you see two options for toggle switch control * > * of magnetos . . . one option uses push button to energize * > * starter, the other uses the left mag switch to energize * > * the starter. BOTH versions lock the starter out if * > * the non-impulse coupled magneto is not OFF. > > * > > Might I also ask what the function of the momentary side of the mag > switch is for - (ON)-OFF-ON? > > * Same as left side. It was selected to be mechanically * > * identical to the left mag switch so that BOTH switches * > * are MAG-ON with the switch in the middle . . . it's a * > * carry over from the arguments I've received from human * > * factors guys . . . NORMAL ON and OFF positions for both * > * mags should look the same. > > > * > > I am running an SD-8 dynamo and my intention is to have no master > solenoid (as shown in the schematic) and also not use a starter > solenoid, I am using the Skytec NL starter and they have an option of > wiring the starter using the internal solenoid of the starter. Do you > foresee any problem here? > > *If they use a two-stage solenoid for pinion gear * > * extension . . . > > * > *http://tinyurl.com/nx6xavk > > * > * then there are extra-ordinary stresses on the * > * switch that actually controls the starter solenoid. * > * Your choice. I recommend either an external contactor * > * or at least a buffer-relay to control starter * > * solenoid. > > * > > My biggest concern was having the starter engage and not be able to > shut it off. I see the B&C starter has an Emergency Starter Off how > does this disable their system as the way I see it, if the solenoid > contacts welded themselves closed, the starter is still feed power. > > * Emergency starter off? Don't know what this is * > * other than to simply turn the battery master switch * > * off. > > * > > I contacted Skytec and they said, due to the way their starter is made > this can't happen so a starter 'kill' isn't required. If power is > removed from the start solenoid the starter 'will' disengage, I guess > the only real danger in this situation is a stuck start switch but > turning off the master would solve that I guess. > > * I haven't a clue as to what they're talking about. * > * In every Z-figure and every TC aircraft, the battery * > * master relay is the back-up for a stuck-starter-contactor. > > * > > Bob . . . > * > > ========== > _blank">www.aeroelectric.com > " target="_blank">www.buildersbooks.com > ="_blank">www.homebuilthelp.com > ="_blank">www.mypilotstore.com > ank">www.mrrace.com > ="_blank">http://www.matronics.com/contribution > ========== > -List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List > ========== > http://forums.matronics.com > ========== > > * > * > > > * ________________________________ Message 7 _____________________________________ Time: 12:33:23 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: Wiring schematic question At 03:41 2014-11-17, you wrote: Hi Bob, I have been in email discussion with Greg Jones at B&C about a few things on my Pitts Special and he suggested you would be best to speak with about the Aerobatic Aircraft wiring schematic on their website, it was made mention that you drew it up. Drawing number 420-506 http://www.bandc.biz/pdfs/420-506_Indexed_Diagram_with_BOM.pdf http://www.bandc.biz/pdfs/420-506_REVB.pdf I had a couple of questions, hopefully you can assist a little. My apologies, I didn't 'scope out the rest of the diagram. No, that general architecture was not suggested by me but the diagram does have some features borrowed from the z-figures of that era. For one thing, the MOV's as transient suppressors was NOT a good idea. We abandoned that recommendation in the AeroElectic Connection . . . oh . . .I forget. But a long time ago. With an SD-8, one is indeed strapped for 'surplus energy' so elimination of the battery contactor is a useful thing from the energy management perspective. Do you KNOW what your ship's running loads are? How big is your battery? What kind of strobe system . . . and current draw? As long as your battery is in good condition and fully charged at engine start, the probability of a contactor sticking is very low. It's the tentative closures when a soggy battery is trying to grunt the starter that gets you a stuck contactor. At the same time, the modern intermittent duty starter contactors are much more resistant to sticking under all conditions . . . again assuming that you 'drive 'em hard' . . . 20AWG wire to the 5A coil is a good idea. As far as compliance with legacy notions of seeking 'Max Cold' conditions in the wiring with all switches OFF, you COULD use a battery master relay that did not carry starter current while locating the external starter contactor adjacent to the battery too. However, your risks are low using the diagram as published. The only changes I would recommend are using diodes across the contactor coils . . . and the starter contactor that B*C sells already has one installed. Ditch the MOVs. Does this cover 'the rest of the story?' Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.