---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 09/24/06: 17 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:39 AM - Re: Mogas versus 100LL (N395V) 2. 05:57 AM - Re: Mogas versus 100LL (Gary Casey) 3. 06:14 AM - Re: Avionics bus (Gary Casey) 4. 08:26 AM - Re: strobe wiring (Tim Juhl) 5. 09:25 AM - Re: strange electrical failure in flight (Vern Little) 6. 01:54 PM - Re: Mogas versus 100LL (Robert L. Nuckolls, III) 7. 02:02 PM - Re: Z13/8 & Z32 Relays (was Eeeeek! Another fear and question) (Robert L. Nuckolls, III) 8. 03:18 PM - Wiring codes and contactor strapping (Robert L. Nuckolls, III) 9. 04:09 PM - Re: Wiring codes and contactor strapping (Cleone Markwell) 10. 04:20 PM - Best wiring techniques to use? () 11. 04:30 PM - Re: Re: Mogas versus 100LL (PSILeD@aol.com) 12. 04:37 PM - Re: Wiring codes and contactor strapping (Larry Rosen) 13. 05:00 PM - Re: Mogas versus 100LL (Jim Baker) 14. 05:53 PM - Re: Mogas versus 100LL () 15. 07:08 PM - Re: Re: Avionics bus (Robert L. Nuckolls, III) 16. 07:48 PM - Re: Eeeeek! Another fear and question. (Kingsley Hurst) 17. 09:33 PM - Avionics ground block (Jekyll) ________________________________ Message 1 _____________________________________ Time: 05:39:58 AM PST US Subject: AeroElectric-List: Re: Mogas versus 100LL From: "N395V" --> AeroElectric-List message posted by: "N395V" It is my understanding that spending too much time in an FBO listening to old farts spout OWTs will fry your brain and cause you to post fuel related blather and weird misinformation on the aeroelectric forum. DO NOT ARCHIVE -------- Milt N395V F1 Rocket Read this topic online here: http://forums.matronics.com/viewtopic.php?p=63547#63547 ________________________________ Message 2 _____________________________________ Time: 05:57:57 AM PST US From: Gary Casey Subject: AeroElectric-List: Re: Mogas versus 100LL Yes, this probably should go over to the engine list, but one more short comment (can't help myself): Cetane rating is essentially the inverse of the Octane rating - a fuel with a high Cetane rating will spontaneously ignite very easily, and that is what you want for a diesel engine. Cetane and Octane ratings, as far as I know, are never used at the same time. It's not a different phenomena that is being rated - the scale is just reversed. Also, someone mentioned the "cutting torch" effect of running lean - this indeed was the conventional thought in the automotive world back when I "grew up" in it. the idea was that you always have to run rich of stoichiometric (even richer that peak EGT) or the left over oxygen in the exhaust would oxidize (burn) the exhaust valve. Yesterday's equivalent of an urban legend, as George Braly has so often pointed out. The valve and valve seats just aren't that hot. Gary Casey > > I believe you are referring to something called the Cetane rating > Ron. The only place I've ever heard this term used is in > association with > DIESEL engines. Since the fuel is injected directly into the highly > heated and compressed air in the diesel's cylinders, it must burn at a > certain rate so as not to spontaneously combust and cause > detonation.... ________________________________ Message 3 _____________________________________ Time: 06:14:40 AM PST US From: Gary Casey Subject: AeroElectric-List: Re: Avionics bus --> AeroElectric-List message posted by: Gary Casey I had my panel "professionally" wired and the result was slightly different than I had specified - probably just as much my fault as theirs as I didn't supervise as closely as I should have. The panel has a Chelton Primary Flight Display (PFD) which includes a (VFR) GPS as well as a conventional radio stack, including both nav/coms, transponder, GPS and autopilot, powered by a separate "avionics" bus. It has 1 battery and 1 alternator. I had asked for an E-bus so that one of the com radios would be powered by the main bus and only essential radios off the E-bus. I ended up wiring it so that the PFD is powered from the battery through the main contactor and the "avionics bus" is also powered directly from the battery through a fusible link and an automotive DIN relay. Works just fine and the backup in case the main bus goes away is no problem as all avionics and vacuum-powered gyros would still be functional. If the avionics bus goes away I lose both coms, but still have GPS navigation capability. I could carry a hand-held com (I lost mine - anyone seen it....?). Right now my thought is just to leave it the way it is. Any comments? Gary Casey ________________________________ Message 4 _____________________________________ Time: 08:26:05 AM PST US Subject: AeroElectric-List: Re: strobe wiring From: "Tim Juhl" --> AeroElectric-List message posted by: "Tim Juhl" Thanks for your observations. In other aircraft that I have owned where the power pack was mounted near the strobe I have also experienced interference that I could hear in the headphones. In most cases I just learned to live with it. I think in my case I will simply isolate the strobe wire from everything else as much as possible. Better to be safe than sorry. Thanks! Tim Juhl -------- DO NOT ARCHIVE ______________ CFII Champ L16A flying Zodiac XL - Working on Flaps and Ailerons Read this topic online here: http://forums.matronics.com/viewtopic.php?p=63577#63577 ________________________________ Message 5 _____________________________________ Time: 09:25:38 AM PST US From: Vern Little Subject: Re: AeroElectric-List: strange electrical failure in flight --> AeroElectric-List message posted by: Vern Little This comment reminds me of a problem that I had with an externally regulated alternator. If the voltage drop between the battery and the regulator is too high (or there is too much resistance in the circuit), the alternator output will be too high, and it will be load dependent-- the more devices you turn on, the higher the alternator voltage. I had a faulty master switch that caused overvoltages due to this effect (loose rivets on the terminals). Once the switch was replaced, the alternator voltage stablized. Exacerbating this problem can be a loose alternator belt, which will cause oscillations in the output voltage. When the belt slips, the regulator tries to force the alternator output higher... then the belt grabs and it takes a moment for the regulator to turn the output back down. The resulting spike can trip overvoltage circuits. This will be more noticable at low engine RPMs. As a note: I had an overvoltage 'event' due to the faulty master while I was flying over the mountains. I switched the master switch OFF, and continued to fly: My Dynon EFIS has an internal battery, my Garmin GPS has an internal battery, my RMI engine monitor runs off an external backup battery, and I have a hand-held nav/com. I do not have an electronic ignition. This is a good example of a redundant design. In none of my overvoltage cases did my B&C OVM-14 trip-- the overvoltage was not enough to do so. Instead, my Monroy ATD-300 gave me a voice warning 'Check Voltage'. Clever little device. Vern Little > > The big increase in voltage with load could be due to high resistance in the > regulator sense circuit. The more load you add, the higher the current in > the alternator field coil. If the sense circuit is also the field coil > supply, any resistance in the circuit will cause a voltage drop and the > regulator will increase the voltage to make up for the sensed drop in > voltage. So, if you add lots of load, you could be getting voltage spikes > over 16v which would trip an overvoltage protector which you probably also > have. Check to see if your alternator field circuit breaker tripped. > > I had to reduce the resistance in my field circuit to .02 ohms by removing > the fuse and wiring it directly to the buss through a fuse link before I > could get reliable operation from my system. > > Dave Reel - RV8A > > ________________________________ Message 6 _____________________________________ Time: 01:54:34 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Mogas versus 100LL --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 07:22 AM 9/22/2006 -0400, you wrote: >--> AeroElectric-List message posted by: FLYaDIVE@aol.com > >HERE WE GO AGAIN! > >Ron: > >STOP talking to those "locals at the airport". They don't know what they are >talking about and you are propagating a HUGE misconception. It's been an interesting thread . . . but never did see any words that were trading off the features of Mogas vs. 100LL . . . I WAS interested because I don't understand how or why they would be compared to each other. Mogas is intended for engines that originally ran on 80 octane avgas. I know folks that have been using 90+ Mogas in their airplanes for decades before EAA got the "Mogas STC gleam" in their eye. We sold 91+ mogas at 1K1 and about half the fleet anchored there uses the less expensive fuel. I'll suggest that the Mogas experiment has been quite successful. As for 100LL . . . every year at OSH they've been telling us that the stuff was "going away soon" . . . that started up 15 or more years ago. During on of my earliest trips to OSH I met an retired GM engine-guru who was building a Longez powered with an O-235. He still had "pull" at GM and was running his engine in a test cell to experiment with some alternatives to 100LL. He observed that lower octane mogas would run fine in any engine when peak pressures before and during combustion were limited . . . like when operating at low manifold pressures. He hypothesized that the only time he NEEDED high manifold pressures was during takeoff and early climb phase. High altitude cruise would not allow him to take advantage of the octane rating of 100LL because the spark from mags was too late and full-throttle manifold pressure was too low. He also hypothesized that the ability of electronics for controlling a two-fluids (air/gasoline) system could be easily adapted to controlling a three-fluids system (air/gasoline/water+alcohol). His goal was to see if practical techniques could be crafted to allow burning lower octane fuels in non- turbocharged)100 octane engines. He reasoned that when 100LL finally bit the dust, there might be a way to avoid junking 100,000 or so airplanes that needed that fuel. The last time we talked, he was thinking he'd need to carry about 10 gallons of water-alcohol to supplement the standard Longez fuel load. I've lost track of him . . . it would be interesting to see what he ultimately discovered. Here are a few interesting links that speak to the need for matching burn characteristics of the fuel to the engine. http://en.wikipedia.org/wiki/Detonation_internal_combustion_engine http://www.technologyreview.com/read_article.aspx?id=16727&ch=energy Bob . . . ________________________________ Message 7 _____________________________________ Time: 02:02:19 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Z13/8 & Z32 Relays (was Eeeeek! Another fear and question) --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 10:57 PM 9/23/2006 -0400, you wrote: >--> AeroElectric-List message posted by: Larry Rosen > >Would a solid-state relay, like the power link Jr. > provide a more reliable, >lower current draw solution to the S-704-1 relays shown on Z13/8 and >Z32? What are the disadvantages to this type of relay other than cost? Define "reliable". If you mean longer service life, yeah, probably. Current draw on an S-704 is about 100 mA. If your scrambling for that small of a savings, perhaps you need to re-evaluate your e-bus loads vs. battery sizing. No disadvantage at all other than cost. But in the failure tolerant system, "reliability" of any single parts is moot. >Other than "tradition" what is the rational for wanting a contact in a >always hot feed of more than a few amps? The rationale for both battery contactors being located right at the battery is to minimize length of always-hot wire in the airplane when the master switch is OFF. The reasoning is that post-crash fires are much less likely if the battery's ability to burn wires is minimized. Hence, small always hot feeders (dome lights, clock, hobbs meter, etc) have been blessed in small aircraft because they can be protected at the battery with 5A or less breaker/fuse. If one subscribes to this notion (many do not . . . there's a bunch of airplanes flying with 10 and 15 amp e-bus alternate feed paths that do not use the relay), then some sort of mini-contactor is called for. Bob . . . ________________________________ Message 8 _____________________________________ Time: 03:18:00 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Wiring codes and contactor strapping --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" >Looking at Figure Z-19; The 4AWG wire from the Main Battery Contactor >to the Engine Battery Contactor has a break with a small box in it. >What does this represent? This is the circuit I have decided to use >on re-wiring my 601 HD, now with a Corvair engine. I built the >plane from 1998 to 2001 and then flew it for 284 hours. My first >attempt at wiring up the DC circuit was a failure mainly because of >using too small wiring on the heavy current lines and then I bought your >book and have gathered most of the new parts and expect to strip out >the old wiring this next week and start over. Thanks! See list of notes and codes in lower right corner of drawing. The symbol used suggests you can replace this wire with a strip of brass sheet to jumper between closely spaced contactors. See pictures in this directory: http://www.aeroelectric.com/Pictures/Wiring_Technique/Contactor_Interconnect Bob . . . --------------------------------------------------------- < What is so wonderful about scientific truth...is that > < the authority which determines whether there can be > < debate or not does not reside in some fraternity of > < scientists; nor is it divine. The authority rests > < with experiment. > < --Lawrence M. Krauss > --------------------------------------------------------- ________________________________ Message 9 _____________________________________ Time: 04:09:12 PM PST US From: Cleone Markwell Subject: Re: AeroElectric-List: Wiring codes and contactor strapping --> AeroElectric-List message posted by: Cleone Markwell At 05:15 PM 9/24/2006, you wrote: >--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" > > > >>Looking at Figure Z-19; The 4AWG wire from the Main Battery Contactor >>to the Engine Battery Contactor has a break with a small box in it. >>What does this represent? This is the circuit I have decided to use >>on re-wiring my 601 HD, now with a Corvair engine. I built the >>plane from 1998 to 2001 and then flew it for 284 hours. My first >>attempt at wiring up the DC circuit was a failure mainly because of >>using too small wiring on the heavy current lines and then I bought your >>book and have gathered most of the new parts and expect to strip out >>the old wiring this next week and start over. Thanks! > > > See list of notes and codes in lower right corner of drawing. > The symbol used suggests you can replace this wire with > a strip of brass sheet to jumper between closely spaced > contactors. See pictures in this directory: > >http://www.aeroelectric.com/Pictures/Wiring_Technique/Contactor_Interconnect > > > Bob . . . > > > --------------------------------------------------------- > < What is so wonderful about scientific truth...is that > > < the authority which determines whether there can be > > < debate or not does not reside in some fraternity of > > < scientists; nor is it divine. The authority rests > > < with experiment. > > < --Lawrence M. Krauss > > --------------------------------------------------------- > > ________________________________ Message 10 ____________________________________ Time: 04:20:35 PM PST US Subject: AeroElectric-List: Best wiring techniques to use? From: --> AeroElectric-List message posted by: Need a bit of help to determine best wiring techniques to use. This is for a Europa XS/Rotax 914 and B+C SD20S/LR3C, start point for schematic was Z13/8. Battery is 10 feet behind motor, Flaming River mechanical battery cut off switch 3 feet ahead of battery aft side of passenger headrest. http://www.flamingriver.com/index.cfm?ptype=article&article_id=22 1) I am looking to use #4 MIL-W-22759/16 Tefzel wire for battery and ground. There will be approx a 3 foot run of unprotected wire to the battery cut off switch. Is there any extra protection that would be prudent to incorporate? Some sort of robust sleeve on 1 wire, or a fusible link? Or just not worry about it (not run too close near anything that conducts)? I have the heavy duty Rotax starter, supposedly draws less amps than old style, old style starter draw was I think 60 amps, not sure what momentary is. 2) I need to somehow get power and ground to 2 fuel pumps, wingtip Strobe/Position LEDs and pitch servo. The headrest is approx 6 feet closer to the battery (14 foot round trip) compared to the firewall mounted ground and main bus. If I put a mini power and ground bus in or near the headrest, would I be negating the concept of single point ground? Would stealing power from the NO side of the battery cut off likely cause any noise or other problems? Or just make extra runs from firewall? 3) Would it be advisable to series the battery cut off with the negative or positive? Reason? I don't have any science to back this up, but I read that when making model electric aeroplane battery packs, if you need to make one lead longer than the other, make the negative longer than the positive, it can help with black wire disease (what I have always done)?? Overall scheme, plenty more time will be spent with battery cutoff opened. 4) I will need to somehow break into the #4 battery wire not going to the battery cut off switch. Instead of cutting the wire and putting on a lug on each side, and screwing them back together along with an additional #10 wire ring, could I carefully strip, lets say an inch of insulation off the #4, and strip 3" off the #10, then strip back the #10 to 1" except for 2 strands, then wrap the 2 strands over the 1" of #4 and 1" of #10 and solder/heat shrink? I would use the adhesive lined heat shrink. 5) What is good practice to follow, the number of lugs I can stack on the NO side of the battery cutoff switch stud? 6) I forget the exact diameter of the NO side of the battery cutoff switch stud, lets say it is 5/16". If lets say I wanted to stack a #4 and a #10,is it acceptable to stack a ring terminal that has a smaller footprint on top of one with a larger footprint? Or in this instance because loss of this connection can cause loss of main and e-bus, use the same size lug, make a brass insert and crimp/solder in the smaller wire? 7) The Flaming River switch has copper threaded studs, came with a brass nut and brass lock-washer. Would it be advisable to use a Phosphor bronze star washer instead of the brass lock-washer? Ron Parigoris ________________________________ Message 11 ____________________________________ Time: 04:30:56 PM PST US From: PSILeD@aol.com Subject: Re: AeroElectric-List: Re: Mogas versus 100LL Back in the 1950's my Dad and I raced outboards with Mercury motors. We ran alcohol fuel and nitro methane as an additive. They did indeed melt the top of the piston if they were run too lean. Been there, done that. Never heard of it in a 4 stroke engine though. Paul DO NOT ARCHIVE ________________________________ Message 12 ____________________________________ Time: 04:37:55 PM PST US From: Larry Rosen Subject: Re: AeroElectric-List: Wiring codes and contactor strapping --> AeroElectric-List message posted by: Larry Rosen You can also see some nice looking ones here for Lancair Legacy power grids Larry Cleone Markwell wrote: > --> AeroElectric-List message posted by: Cleone Markwell > > At 05:15 PM 9/24/2006, you wrote: >> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" >> >> >> >>> Looking at Figure Z-19; The 4AWG wire from the Main Battery Contactor >>> to the Engine Battery Contactor has a break with a small box in it. >>> What does this represent? This is the circuit I have decided to use >>> on re-wiring my 601 HD, now with a Corvair engine. I built the >>> plane from 1998 to 2001 and then flew it for 284 hours. My first >>> attempt at wiring up the DC circuit was a failure mainly because of >>> using too small wiring on the heavy current lines and then I bought >>> your >>> book and have gathered most of the new parts and expect to strip out >>> the old wiring this next week and start over. Thanks! >> >> >> See list of notes and codes in lower right corner of drawing. >> The symbol used suggests you can replace this wire with >> a strip of brass sheet to jumper between closely spaced >> contactors. See pictures in this directory: >> >> http://www.aeroelectric.com/Pictures/Wiring_Technique/Contactor_Interconnect >> >> >> >> >> Bob . . . >> >> >> --------------------------------------------------------- >> < What is so wonderful about scientific truth...is that > >> < the authority which determines whether there can be > >> < debate or not does not reside in some fraternity of > >> < scientists; nor is it divine. The authority rests > >> < with experiment. > >> < --Lawrence M. Krauss > >> --------------------------------------------------------- >> >> >> >> > > ________________________________ Message 13 ____________________________________ Time: 05:00:06 PM PST US From: "Jim Baker" Subject: Re: AeroElectric-List: Mogas versus 100LL X-mailer: Pegasus Mail for Windows (4.41) --> AeroElectric-List message posted by: "Jim Baker" > He still had "pull" at GM and > was running his engine in a test cell to experiment with > some alternatives to 100LL. Snip > there might be a way to > avoid junking 100,000 or so airplanes that needed > that fuel. May I direct you attention to the following site..... http://www.gami.com/prism.html I've seen the system run ( I'm about 30 miles due west of ADA, OK ) on a TSIO540 which was switched from 100LL under high load to MOGAS without a tick or falter. We are constrained in so many ways by the set timing of our magnetos. I can imagine the intractability of our modern automotive engines if they were similarly constrained. You ought to see the PRISM developmental sparkplugs....the ign harness terminal is offset to one side and the other side has a connection for a fiber optic pressure transducer. Quite the set- up. Told one of the guys they'd make money just selling the accessory plug socket for the wrench. Jim Baker 580.788.2779 Elmore City, OK ________________________________ Message 14 ____________________________________ Time: 05:53:03 PM PST US Subject: Re: AeroElectric-List: Mogas versus 100LL From: --> AeroElectric-List message posted by: All this talk about cause and effect of detonation. I am going to make an attempt to "Not go there" by the use of a orderly flow of electrons. My Rotax 914 turbo has a ARM1 fuel Ratio Meter installed. http://www.splitsec.com/ Click Products Click Air/fuel Ratio Meters ARM1 It is driven by a O2 sensor screwed into a stainless steel bung welded just downstream of the turbo. When you are creating a good percentage of motors potential BTUs, you want mixture rich of 14.7 The TCU besides controlling the wastegate, controls a solenoid that enrich-ens the mixture when boosting over 108% power. If the solenoid is not working perfect, there is a leak in the intake, one or both of the carbs are not doing their job it can net a mixture a bit too lean. I am anticipating the ARM to be a nice tool, along with a CHT on each side of motor, and EGT on each side of motor. I will taint the mixture just a tad rich, main jets and jet needles, and lean just a bit to my liking. I am going to lean by introducing a controlled leak between carb float bowl and intake manifold downstream of the carbs. In addition if I see things running too lean (when not leaning) because of the distinct possibility of motorcycle type causes (carb snot, plugged jet, leaking manifold, leaking critical hoses to fuel pressure regulator of float bowl) I am incorporating an emergency rich button that will allow me to activate the enrichment solenoid, reduce power and hopeful get things in order and "Not go there" (detonation), instead of getting to your destination probably OK, but having caused damage to your motor. I will use primary MoGas, but the O2 sensor gives plenty of warning when and if lead is degrading its range. I expect use in a 100% 100LL environment, my dart throw is min of 75 hours, probably longer if using TCP or alternative. O2 sensors will quickly loose their ability to very fast sense 14.7 which would be detrimental if it was controlling mixture, but a second or 2 lag for monitor is not a problem. As long as range on power up is had, should be good to go. I know some have said that you can only expect from a O2 sensor 14.7 and anything else is only window dressing, but after talking to Split second, they spent a reasonable amount of time mapping the EG01 sensor, and say their monitor will show lean and rich of 14.7. Anyway glance ARM1, if too much left, do something. Will let you know how it all works out. Ron Parigoris ________________________________ Message 15 ____________________________________ Time: 07:08:42 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Avionics bus --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 06:13 AM 9/24/2006 -0700, you wrote: >--> AeroElectric-List message posted by: Gary Casey > >I had my panel "professionally" wired and the result was slightly >different than I had specified - probably just as much my fault as >theirs as I didn't supervise as closely as I should have. The panel >has a Chelton Primary Flight Display (PFD) which includes a (VFR) GPS >as well as a conventional radio stack, including both nav/coms, >transponder, GPS and autopilot, powered by a separate "avionics" >bus. It has 1 battery and 1 alternator. I had asked for an E-bus so >that one of the com radios would be powered by the main bus and only >essential radios off the E-bus. I ended up wiring it so that the PFD >is powered from the battery through the main contactor and the >"avionics bus" is also powered directly from the battery through a >fusible link and an automotive DIN relay. Works just fine and the >backup in case the main bus goes away is no problem as all avionics >and vacuum-powered gyros would still be functional. If the avionics >bus goes away I lose both coms, but still have GPS navigation >capability. I could carry a hand-held com (I lost mine - anyone seen >it....?). Right now my thought is just to leave it the way it is. >Any comments? Hard to say . . . it's all dependent on how strongly you're oriented to achieving your design goals. Keep in mind that the main bus doesn't "go away" . . . it simply becomes too much stuff to operate for extended periods of time battery only. The simplest thing to do is run it as-built and treat it like a TC aircraft . . . carry hand-held backups. I'd be careful about and "band aids" in an attempt to dual feed the avionics bus. You should have a diode in series with your avionics master so that you don't back-feed the main bus from a battery fed avionics bus. Also, fusible links are not crash-safety oriented devices. Use a real fuse. Bob . . . --------------------------------------------------------- < What is so wonderful about scientific truth...is that > < the authority which determines whether there can be > < debate or not does not reside in some fraternity of > < scientists; nor is it divine. The authority rests > < with experiment. > < --Lawrence M. Krauss > --------------------------------------------------------- ________________________________ Message 16 ____________________________________ Time: 07:48:17 PM PST US From: "Kingsley Hurst" Subject: RE: AeroElectric-List: Eeeeek! Another fear and question. --> AeroElectric-List message posted by: "Kingsley Hurst" Bob, You said : > I was able to design the system so that the relay > was closed and bounce free before current flowed in the > contacts. Further, I was able to shut off all current flow > electronically before the relay contacts were opened. You have me with my thinking cap on now ! If the current didn't flow before the contacts were closed and was shut off before the contacts opened, what was the purpose in having a relay ? It seems you had complete control over the current flow without the relay !! Just wondering ?? Regards Kingsley in Oz. ________________________________ Message 17 ____________________________________ Time: 09:33:47 PM PST US Subject: AeroElectric-List: Avionics ground block From: "Jekyll" --> AeroElectric-List message posted by: "Jekyll" I'm planning a ground block for panel components using a fast-on tab ground (purchased from SteinAir) soldered to brass bar stock. I plan to ground all avionics to this and then run a common ground wire to the main F/W mounted ground block. My question is thus: do I need to insulate the ground block from the aluminum frame or will the wires carry the ground better than the airframe, thus carrying the common ground to the main block? Jekyll, RV-7A Read this topic online here: http://forums.matronics.com/viewtopic.php?p=63701#63701