---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 05/05/14: 13 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:01 AM - Intercom to Radio Wiring (Ron Walker) 2. 04:54 AM - Re: Intercom to Radio Wiring (Jared Yates) 3. 06:42 AM - Re: Re: How do I prevent starter engaged LED from failing? (Robert L. Nuckolls, III) 4. 06:49 AM - Re: Intercom to Radio Wiring (Robert L. Nuckolls, III) 5. 07:18 AM - Re: Intercom to Radio Wiring (Tim Andres) 6. 08:39 AM - Re: Intercom to Radio Wiring (Sprocket) 7. 08:41 AM - Re: Alternative battery technologies . . . (B Tomm) 8. 08:41 AM - Re: Alternative battery technologies . . . (B Tomm) 9. 12:26 PM - Re: Intercom to Radio Wiring (Robert L. Nuckolls, III) 10. 12:34 PM - Re: Alternative battery technologies . . . (Robert L. Nuckolls, III) 11. 03:52 PM - Re: How do I prevent starter engaged LED from failing? (eschlanser) 12. 05:21 PM - Re: trim indicator buffer (D L Josephson) 13. 06:35 PM - Re: Re: How do I prevent starter engaged LED from failing? (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 04:01:21 AM PST US Subject: AeroElectric-List: Intercom to Radio Wiring From: Ron Walker This is a question regarding technique rather than specific equipment. I'm about to start my third try to wire my 4 place intercom to my radio. My goal is to get all the wires at the connector to actually look semi-decent and not the fat-collection-of-rats-nest bundle that has resulted from my first two attempts. It CAN be done, I've seen it. I just don't know any of the secrets ... wondering what they are ? Is there a technique or process/pattern to this ? With all the wires coming in - 3 from each headset connection, 2 additional pair for ptt, power and then the connections to the radio - there's gotta be something I'm missing because I've seen it done nicely ... I checked the aeroconnections site and used a couple of the tricks there, but they really didn't get me very far. Any advice other than hiring the task out ? Thanks --Ron ________________________________ Message 2 _____________________________________ Time: 04:54:26 AM PST US Subject: Re: AeroElectric-List: Intercom to Radio Wiring From: Jared Yates Hi Ron, I ran into the same problem. This was my solution to combining the left audio, right audio, and ground signals for the right front and rear passengers: http://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg I brought all of the incoming wires into a regular machined-pin 25-pin d-sub connector. Then I used an opposite-sex solder d-sub to make the one shown in the picture. I soldered a little piece of wire across the appropriate pins. I think in the final configuration I stripped a 5/8" or so long piece off of the end of a longer wire, soldered the stripped part across the cups, and then connected the other end of that wire to the intercom input. This would be an option if you run out of pins. I didn't take a picture of the final configuration, but I think I did run short of pins on at least one of them. When it was done I potted the whole thing to keep it from shorting. As for the ptt and the rest, my intercom might have been a little bit different. I had an input pin for each front seat occupant, so that when the right front keys, only his mic goes to the radio, etc. Mine were also only single wires- one end went to the intercom, then the other end went to local ground after passing through the switch. Another problem was turning big shields into wires that I could crimp into machined pins. I used crimped on terminals of various types. If I had a large size change, I might crimp a yellow "handshake" connector on the big clump of shields, and then crimp a red one onto a single 22-gauge piece of wire that went to the machined pin. Sometimes I would bring two large clumps of shields into each end of a yellow splice, then stick a 22-gauge wire in one of the ends along with the shields. I'll not imply that the above is necessarily the best way- my mission wasn't to win any awards, but just to have a reliable mode of transportation- but so far it is all working just fine. In the end, I wouldn't say it's a rat's nest (though some might), but perhaps more of a bird's nest. On Mon, May 5, 2014 at 6:59 AM, Ron Walker wrote: > > This is a question regarding technique rather than specific equipment. > > I'm about to start my third try to wire my 4 place intercom to my radio. > My goal is to get all the wires at the connector to actually look > semi-decent and not the fat-collection-of-rats-nest bundle that has > resulted from my first two attempts. It CAN be done, I've seen it. I > just don't know any of the secrets ... wondering what they are ? > > Is there a technique or process/pattern to this ? With all the wires > coming in - 3 from each headset connection, 2 additional pair for ptt, > power and then the connections to the radio - there's gotta be something > I'm missing because I've seen it done nicely ... > > I checked the aeroconnections site and used a couple of the tricks > there, but they really didn't get me very far. > > Any advice other than hiring the task out ? > > Thanks > > --Ron > > ________________________________ Message 3 _____________________________________ Time: 06:42:06 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: How do I prevent starter engaged LED from failing? At 12:07 AM 5/5/2014, you wrote: >I have had an LED indicate "Gear in transit" for 10 years with no >protection.... > >Best... > Thanks Bob . . .I'm not surprised. Folks who don't work up to their eyeballs in TC aviation have some difficult grasping the significance of the hat-dances we do to get a part holy-watered. The control of emitted stresses and demonstrating immunity to external stresses under DO160/MilSTD704 is a kind of 99+ percentile hedge against conditions known to manifest in at least some situations. There's an alternator regulator on Bonanzas and Barons that NEVER saw the lights of a DO160 test lab. It was added to the airplane's TC WWWAAaaayy back when . . . before Part 23 aviation got so tightly wrapped up in mandated hat-dancing. If the airframe manufacturer accomplished enough testing on the airplane to demonstrate 99+ percent 'suitability to task' then the addition was allowed. This particular design has a vulnerability to certain noises from brush bounce in alternators that causes the OV protection to trip. Further, there's a 1= percent probability that new alternators of this vintage will exhibit the noise. Ever so often, on at least 3 occasions I was involved in over the last 30 years, that 1 percent minus stress comes together with a 1 percent minus vulnerability and you get a rash of airplanes that can't be delivered because the alternator(s) keep tripping off line under certain conditions. The obvious fix is to put a fully qualified, regulator on. But with production volumes so low, nobody is very excited about launching in to a new design program . . . even when I have the design already done! So, a suitable 'band-aid' not unlike those things we've resorted to for over a century has erected a reasonable wall of separation between the waring factions and all is now serene in the universe. What does this have to do with adding protection to the LED indicators attached directly to a bus-driven source? Simply this: The probability that any given led is going to get toasted by one of the stresses predicted by DO160/MilSTD704 is very low. But as experienced practitioners of the design arts, probability does not figure into robustness of a design. DO160/MilSTD704 is not a probability game, it's a robustness game. As a matter of design goals, I recommend the diode as depicted in the drawings. But as Bob (and no doubt many others) has observed . . . Gee, been doing this for years without the protection and I've had no problems. The lesson-learned here has nothing to do with holding the LED-toasting dragons at bay and leaving the pilot unaware of a stuck contactor . . . it's about ROBUST design that chooses to ignore low probability events and design for worst case. Here's where your failure mode effects analysis tools come into play. Suppose the LED DOES get toasted. How long will it take you to discover that fact and what is the probability that LED failure will be co-incident with an LED-toasting dragon? If your checklist for engine cranking includes something like: STARTER - Engage. Observe STARTER ENGAGED light is illuminated. When engine starts STARTER - Disengage. Observe START ENGAGED light is dark. . . . and you're covered with the same blanket that has enveloped many other 'unprotected' installations. DO160/MilSTD704 robustness is but one of many tools we can apply to reduction of risk. Knowledge and understanding is the most powerful of those tools. Bob . . . ________________________________ Message 4 _____________________________________ Time: 06:49:03 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Intercom to Radio Wiring At 06:51 AM 5/5/2014, you wrote: >Hi Ron, I ran into the same problem. =C2 This was >my solution to combining the left audio, right >audio, and ground signals for the right front and rear passengers: > >htt p://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg Looks like a good lick to me . . . One of my pet peeves concerning the design of many appliances is the dearth of pin-outs necessary for graceful termination of wires in a common installation. Many times it's not a big deal to the next larger size d-sub connector on the product to assist the installer in termination of multiple wires to grounds or paralleled loads. Mr. Yates' solution is a rational and robust solution to your installation problem . . . perhaps a bit more 'bulk' than soldering them into heat-shrink covered lumps . . . but certainly more elegant in appearance and maintainability. Bob . . . ________________________________ Message 5 _____________________________________ Time: 07:18:14 AM PST US Subject: Re: AeroElectric-List: Intercom to Radio Wiring From: Tim Andres If your using Bob's technique to terminate the shields, make the pig tails long enough so they are just outside the hood of the D-sub. The short length of un-shielded wire should not cause any problem. You can also daisy chain all the grounds into the minimum required number before it enters the hood. Otherwise there may be too much bulk to get the hood on. Tim > On May 5, 2014, at 3:59 AM, Ron Walker wrote: > > > This is a question regarding technique rather than specific equipment. > > I'm about to start my third try to wire my 4 place intercom to my radio. > My goal is to get all the wires at the connector to actually look > semi-decent and not the fat-collection-of-rats-nest bundle that has > resulted from my first two attempts. It CAN be done, I've seen it. I > just don't know any of the secrets ... wondering what they are ? > > Is there a technique or process/pattern to this ? With all the wires > coming in - 3 from each headset connection, 2 additional pair for ptt, > power and then the connections to the radio - there's gotta be something > I'm missing because I've seen it done nicely ... > > I checked the aeroconnections site and used a couple of the tricks > there, but they really didn't get me very far. > > Any advice other than hiring the task out ? > > Thanks > > --Ron > > > > > > ________________________________ Message 6 _____________________________________ Time: 08:39:08 AM PST US From: Sprocket Subject: Re: AeroElectric-List: Intercom to Radio Wiring I totally agree. One of the benefits of packaging the audio products that I have developed in d-sub backshells is that there are a lot more pins availa ble for grounds. In fact, I usually reserve a whole row of pins for ground, whether they are needed or not. This simplifies installation and saves time and money. The availability of a whole class of through-hole components that have a max imum height sized to fit in these packages makes even small volume designs f easible without having to resort to surface mount devices. Cheers, Vern Little Vx Aviation ========================== ========================== Sent from my iThing. It is responsible for all gramma and typo terrors. > On May 5, 2014, at 6:46 AM, "Robert L. Nuckolls, III" wrote: > > At 06:51 AM 5/5/2014, you wrote: >> Hi Ron, I ran into the same problem. =C3=82 This was my solution to combi ning the left audio, right audio, and ground signals for the right front and rear passengers: >> >> http://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg > > Looks like a good lick to me . . . > > One of my pet peeves concerning the design of many > appliances is the dearth of pin-outs necessary > for graceful termination of wires in a common > installation. > > Many times it's not a big deal to the next > larger size d-sub connector on the product to > assist the installer in termination of multiple > wires to grounds or paralleled loads. > > Mr. Yates' solution is a rational and robust > solution to your installation problem . . . > perhaps a bit more 'bulk' than soldering > them into heat-shrink covered lumps . . . but > certainly more elegant in appearance and > maintainability. > > > Bob . . . > > > 3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3 D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3 D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3 D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3 D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > ________________________________ Message 7 _____________________________________ Time: 08:41:45 AM PST US From: "B Tomm" Subject: RE: AeroElectric-List: Alternative battery technologies . . . _____ From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Sunday, May 04, 2014 9:16 AM Subject: AeroElectric-List: Alternative battery technologies . . . The battery-buzz these days is focused on lithium . . . and for good reason. They ARE lighter yet retain many of the desirable qualities of a lead=acid battery for engine cranking. Another rising-star wannabe is a product by FireFly Energy . . . an svrla battery that features a carbon foam plate material with a advertised gee-whiz feature of offering a lower weight replacement for the legacy lead grids. This is not a 'new' idea . . . I think the patents have already been renewed once . . . but only recently have potential consumers of this technology been able to put their hands on real product. http://tinyurl.com/kfzsj5p This is a group 31 battery (read BIG) that weighed in at 73.6 pounds and presented and open circuit voltage of 13.09V at ~20C right out of the box. A 600A load drops voltage to 9.30V. Therefor (13.1 - 9.30)/600 = 0.00633 Ohms internal resistance. Okay, how about available capacity under various loads? Emacs! When discharged at 5A, it took 20+ hours to take it down to 10.0V. So one could say that the capacity of this battery at 20-hour rate is over 100aH. Not bad for a 75# battery. At higher rates, we see that the capacity drops off pretty much like all other batteries . . . the 50A discharge delivered only 80Ah . . . one might extrapolate from this data that the battery's one-hour rate (as an aircraft battery would clock in at about 65Ah. Again, not bad for a 12V, 75# battery. >From the data taken, we can estimate that a 24V cousin of the same active materials would be slightly more than the 75# due to addition of extra cell walls. The internal resistance would go up by a factor of 4. Twice as many half-sized cells in series. A 4x increase in internal resistance would have a profound effect on delivered capacity at the higher rates. In other words, when sliced up and reassembled as a 24V battery, this device would not be able to deliver 1/2 the one-hour rate deduced above . . . it's more likely to be down to something like 20Ah or so. I'm going to see if I can model the 24v version and do some predicted plots. >From the aircraft perspective, the 24v version would be unable to start a turbine engine. While the capacity is there at moderate discharge rates . . . internal resistance kills its cranking abilities. The plots above include some charging performance data on a Schumacher XC75W picked up new at a Walmart store a few weeks ago. http://tinyurl.com/k7fatrm On the outside of the box it says 3A charger/maintainer, 5A charger, 20A charger and 75A engine cranking output. Okay, the first recharge cycle of the 100Ah "AGM" battery under test produced the recharge curve in black. It topped off at about 15.7 volts and had the battery 'wheezing' from the vent valves. The second recharge in the "GEL" mode produced the curve in blue which topped off at 14.8 volts. MUCH better. The third recharge in the "STD" mode produced the curve in red which again topped off at 15.7 volts and squeezed a few more molecules of disassociated hydrogen and oxygen from the cell vents. Clearly, this charger is not programmed for the advertised service. Either I have a bad charger or Schumacher has stubbed their toe. This is like finding a Fluke voltmeter that's only good to 2% or so . . . I am told that Schumacher's engineering staff is willing to talk. I'll be looking for a contact in that venue to discuss my findings on this particular Schumahcer product. In the mean time, know that the 20A rate appears to be a modulated 'peak' rate. Time to stuff 100Ah plus back into this battery at the 20A setting on the charger took 8+ hours. Not a big deal. It was reasonably expeditious and didn't abuse the battery in the GEL mode . . . other modes are yet to be explained/understood. So what about these 'new' technologies? Mixed bag. Clearly the carbon foam battery plate is not ready for prime-time in aviation. Service in anything but moderate rate discharge in RV's, boats, etc would be disappointing at anything over .3C rates. Pretty sure I'm not ready to poke out $375 for one of these things. Tho I AM glad my client was willing . . . The charger was disappointing on two fronts. It's clearly NOT a 20A fast charger. It's also unsuited to the tasks advertised for maintenance of AGM/Flooded batteries. MUCH too abusive. A learned professor once opined "Numbers not accompanied by degrees of uncertainty are meaningless" (Walter Lewin). Another pretty sharp cookie was known to have said, " . . . when you cannot measure [a thing], when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind . . ."(Lord Kelvin). This is a good illustration of the difficulties encountered by the CONSUMING community when factions of the SUPPLIER community get into rock-throwing contests (Recall the tiff that Odyssey got into with one of the battery maintainer guys? I forget which). It would have been good and responsible for both parties to publish the numbers instead of throwing rocks with consumers caught in the middle. Now that I have the numbers . . . I can go back to the folks who have claimed certain kinds of performance based on those numbers for clarification . . . Watch this space. Bob . . . ________________________________ Message 8 _____________________________________ Time: 08:41:53 AM PST US From: "B Tomm" Subject: RE: AeroElectric-List: Alternative battery technologies . . . Excellent study and report Bob. Thanks for sharing. Bevan _____ From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Sunday, May 04, 2014 9:16 AM Subject: AeroElectric-List: Alternative battery technologies . . . The battery-buzz these days is focused on lithium . . . and for good reason. They ARE lighter yet retain many of the desirable qualities of a lead=acid battery for engine cranking. Another rising-star wannabe is a product by FireFly Energy . . . an svrla battery that features a carbon foam plate material with a advertised gee-whiz feature of offering a lower weight replacement for the legacy lead grids. This is not a 'new' idea . . . I think the patents have already been renewed once . . . but only recently have potential consumers of this technology been able to put their hands on real product. http://tinyurl.com/kfzsj5p This is a group 31 battery (read BIG) that weighed in at 73.6 pounds and presented and open circuit voltage of 13.09V at ~20C right out of the box. A 600A load drops voltage to 9.30V. Therefor (13.1 - 9.30)/600 = 0.00633 Ohms internal resistance. Okay, how about available capacity under various loads? Emacs! When discharged at 5A, it took 20+ hours to take it down to 10.0V. So one could say that the capacity of this battery at 20-hour rate is over 100aH. Not bad for a 75# battery. At higher rates, we see that the capacity drops off pretty much like all other batteries . . . the 50A discharge delivered only 80Ah . . . one might extrapolate from this data that the battery's one-hour rate (as an aircraft battery would clock in at about 65Ah. Again, not bad for a 12V, 75# battery. >From the data taken, we can estimate that a 24V cousin of the same active materials would be slightly more than the 75# due to addition of extra cell walls. The internal resistance would go up by a factor of 4. Twice as many half-sized cells in series. A 4x increase in internal resistance would have a profound effect on delivered capacity at the higher rates. In other words, when sliced up and reassembled as a 24V battery, this device would not be able to deliver 1/2 the one-hour rate deduced above . . . it's more likely to be down to something like 20Ah or so. I'm going to see if I can model the 24v version and do some predicted plots. >From the aircraft perspective, the 24v version would be unable to start a turbine engine. While the capacity is there at moderate discharge rates . . . internal resistance kills its cranking abilities. The plots above include some charging performance data on a Schumacher XC75W picked up new at a Walmart store a few weeks ago. http://tinyurl.com/k7fatrm On the outside of the box it says 3A charger/maintainer, 5A charger, 20A charger and 75A engine cranking output. Okay, the first recharge cycle of the 100Ah "AGM" battery under test produced the recharge curve in black. It topped off at about 15.7 volts and had the battery 'wheezing' from the vent valves. The second recharge in the "GEL" mode produced the curve in blue which topped off at 14.8 volts. MUCH better. The third recharge in the "STD" mode produced the curve in red which again topped off at 15.7 volts and squeezed a few more molecules of disassociated hydrogen and oxygen from the cell vents. Clearly, this charger is not programmed for the advertised service. Either I have a bad charger or Schumacher has stubbed their toe. This is like finding a Fluke voltmeter that's only good to 2% or so . . . I am told that Schumacher's engineering staff is willing to talk. I'll be looking for a contact in that venue to discuss my findings on this particular Schumahcer product. In the mean time, know that the 20A rate appears to be a modulated 'peak' rate. Time to stuff 100Ah plus back into this battery at the 20A setting on the charger took 8+ hours. Not a big deal. It was reasonably expeditious and didn't abuse the battery in the GEL mode . . . other modes are yet to be explained/understood. So what about these 'new' technologies? Mixed bag. Clearly the carbon foam battery plate is not ready for prime-time in aviation. Service in anything but moderate rate discharge in RV's, boats, etc would be disappointing at anything over .3C rates. Pretty sure I'm not ready to poke out $375 for one of these things. Tho I AM glad my client was willing . . . The charger was disappointing on two fronts. It's clearly NOT a 20A fast charger. It's also unsuited to the tasks advertised for maintenance of AGM/Flooded batteries. MUCH too abusive. A learned professor once opined "Numbers not accompanied by degrees of uncertainty are meaningless" (Walter Lewin). Another pretty sharp cookie was known to have said, " . . . when you cannot measure [a thing], when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind . . ."(Lord Kelvin). This is a good illustration of the difficulties encountered by the CONSUMING community when factions of the SUPPLIER community get into rock-throwing contests (Recall the tiff that Odyssey got into with one of the battery maintainer guys? I forget which). It would have been good and responsible for both parties to publish the numbers instead of throwing rocks with consumers caught in the middle. Now that I have the numbers . . . I can go back to the folks who have claimed certain kinds of performance based on those numbers for clarification . . . Watch this space. Bob . . . ________________________________ Message 9 _____________________________________ Time: 12:26:18 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Intercom to Radio Wiring At 10:38 AM 5/5/2014, you wrote: >I totally agree. One of the benefits of packaging the audio >products that I have developed in d-sub backshells is that there are >a lot more pins available for grounds. In fact, I usually reserve a >whole row of pins for ground, whether they are needed or not. > >This simplifies installation and saves time and money. > >The availability of a whole class of through-hole components that >have a maximum height sized to fit in these packages makes even >small volume designs feasible without having to resort to surface >mount devices. Isn't this business fun? Bob . . . ________________________________ Message 10 ____________________________________ Time: 12:34:06 PM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Alternative battery technologies . . . At 10:41 AM 5/5/2014, you wrote: >Excellent study and report Bob. Thanks for sharing. > >Bevan You're welcome. The next phase of the study will involve disassembly of the battery. We want to see if our 'predictors' based on experience and deduction about this technology were correct. About 8 years ago we spent a little money getting to know the designers a little better. Funny thing about that physics-stuff . . . you cannot shuffle the numbers and simple- ideas at the convenience of marketing department. Attempts to ignore -or- shuffle can be embarrassing, expensive and sometimes dangerous. Bob . . . ________________________________ Message 11 ____________________________________ Time: 03:52:06 PM PST US Subject: AeroElectric-List: Re: How do I prevent starter engaged LED from failing? From: "eschlanser" Joe and Bob, I thought that an LED was a type of diode. It seems like one should not have to stick a second diode on the circuit when using an LED. For your review, here is an attachment of my solution. My engine/starter is in a state of storage so the LED based circuit cannot be tested yet. I chickened out and replaced the diode with a mini bulb. Seemed like the simplest way in my case. Thank you, Eric Schlanser Read this topic online here: http://forums.matronics.com/viewtopic.php?p=422865#422865 Attachments: http://forums.matronics.com//files/starter_warn_light_circuit3_451.pdf ________________________________ Message 12 ____________________________________ Time: 05:21:19 PM PST US From: D L Josephson Subject: AeroElectric-List: Re: trim indicator buffer > Well considered critical review from kindred herders > of electrons is solicited and welcome. I would add another 0.1 from pin 3 to ground, to keep noisy trim pots from making the reading jumpy, and maybe another one between pins 2 and 6 to slow down the op amp. ________________________________ Message 13 ____________________________________ Time: 06:35:47 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: How do I prevent starter engaged LED from failing? At 05:48 PM 5/5/2014, you wrote: > >Joe and Bob, > >I thought that an LED was a type of diode. It seems like one should >not have to stick a second diode on the circuit when using an LED. It IS a diode. It has ratings and limits like any other diode. When caused to conduct current in a forward direction, it exhibits a voltage drop quite a bit higher than power steering or detection diodes . . . and it emits light while doing it. Apply voltage in the reverse direction and you not only get no light . . . you may punch out the magic stuff between the terminals that emits the light. Here's an exemplar set of plots on a bright, white LED. http://tinyurl.com/q4f25xe Emacs! For a diode rated at 30 mA, one selects a resistor that produces no more than 30 mA at maximum expected system voltage (call it 15v). In the curve above we see that voltage drop is 3.4V at 30 mA. (15-3.4)/.030 = 386 ohms. So the resistor to choose is no smaller than this calculated value to stay below the diode's rated maximum operating current. Emacs! Reverse voltage is another mater. Note that around 18volts, the current takes a sharp spike toward very high . . . read damaged junction. Now, the SOURCE of a reverse voltage in our applications MUST be reactive. I.e., inductive response to rapid drop in applied current . . . like a contactor opening up. The inductive culprit is not necessarily a DEVICE . . . even long wires between the battery and the victim device can offer the inductive storage need to offer a reverse voltage spike. It WILL be short, it may not have much energy in it . . . but it quite likely to exceed 18 volts. Hence, legacy design goals include the addition of a diode across the LED wired to conduct in case such a led-killing dragon should come along. Not saying it WILL . . . in fact, many builders are flying 'unprotected' leds with no regrets. There are Bonanzas with low probability of an antagonist jumping up to irritate a less-than- robust regulator . . . rare but not zero. > > >For your review, here is an attachment of my solution. My >engine/starter is in a state of storage so the LED based circuit >cannot be tested yet. I chickened out and replaced the diode with a >mini bulb. Seemed like the simplest way in my case. Can you articulate the source of your 'fear?' I thought that the explanations and experiences shared here on the List would have assuaged your concerns. By all means, use the LED without protection . . . and simply watch it for failure. It's a no-risk event easily spotted throughout its lifetime on the airplane. I'm concerned that you were offered 'too much' information . . . that's always a risk in this data exchange venue . . . it was never intended to be a 'cook book . . . do this and trust me'. But the fact that you 'chickened out' and regressed to a legacy technology suggests that the List did not serve you well. Don't hesitate to bring perceptions of poor service to my attention or anyone else's . . . this List is all about reducing risk through knowledge and understanding . . . not about anointing any one process or technology. 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.