---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 02/11/05: 19 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:57 AM - Re: Re: Big H-bridge for Big Motors (Frank & Dorothy) 2. 06:00 AM - Re: Re: Big H-bridge for Big Motors (Robert L. Nuckolls, III) 3. 06:12 AM - Battery cables for aft batterys on RV-7 (Jerry Ballard) 4. 06:42 AM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Bob C.) 5. 09:02 AM - Re: Size of Fuse vs. Circuit Breaker - (Robert L. Nuckolls, III) 6. 09:13 AM - Size of Fuse vs. Circuit Breaker - Final Correction (Robert L. Nuckolls, III) 7. 10:21 AM - Re: Battery cables for aft batterys on RV-7 (Mickey Coggins) 8. 10:54 AM - Toggle switch - both master/battery and starter (Mitch Faatz) 9. 11:23 AM - Re: Big H-bridge for Big Motors (Eric M. Jones) 10. 11:32 AM - Re: Toggle switch - both master/battery and starter (Mark R Steitle) 11. 01:59 PM - Narco wiring harness- part needed (Jeff Point) 12. 03:13 PM - Re: Battery cables for aft batterys on RV-7 (Hans Teijgeler) 13. 04:31 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Bob C.) 14. 04:55 PM - Re: Size of Fuse vs. Circuit Breaker (Dennis Johnson) 15. 05:18 PM - Coax connector Garmin 196 (N27160@aol.com) 16. 05:46 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (John Schroeder) 17. 07:37 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Fiveonepw@aol.com) 18. 08:00 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (John Schroeder) 19. 09:59 PM - Re: Measurements (j1j2h3@juno.com) ________________________________ Message 1 _____________________________________ Time: 12:57:32 AM PST US From: Frank & Dorothy Subject: Re: AeroElectric-List: Re: Big H-bridge for Big Motors --> AeroElectric-List message posted by: Frank & Dorothy Robert L. Nuckolls, III wrote: >Guess it would help if I put the link in too . . . > >http://www.aeroelectric.com/Pictures/Big_H-Bridge.gif > > Hi I'm not sure what application this Big H-bridge is intended for, but I've had a bit of experience with *little* H-bridges. After burning up a few drive transistors (check out what happens if both drive transistors are enabled at once), I moved to a so-called 'smokeless' H-bridge... a simple 2-to-4 decoder IC (or circuit) prevents bad things from happening. Smart guys even used the 4th state as a brake. Frank ________________________________ Message 2 _____________________________________ Time: 06:00:19 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Big H-bridge for Big Motors --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" There was a discussion on the list concerning solid state replacement of relays with transistors for driving motors up to 7 amps or so. Yes, virtually ALL h-bridge designs are vulnerable to the condition you mentioned . . . One benefit of relays is that they can be wired so that contrary commands translate into simple, smoke-free stopping of the motor. One should take care to design switching systems that drive h-bridges to preclude simultaneous contrary commands via gates or architecture of the control switches. Either may be accomplished easily. Bob . . . At 09:38 PM 2/11/2005 +1300, you wrote: >--> AeroElectric-List message posted by: Frank & Dorothy > > >Robert L. Nuckolls, III wrote: > > >Guess it would help if I put the link in too . . . > > > >http://www.aeroelectric.com/Pictures/Big_H-Bridge.gif > > > > >Hi > >I'm not sure what application this Big H-bridge is intended for, but >I've had a bit of experience with *little* H-bridges. After burning up a >few drive transistors (check out what happens if both drive transistors >are enabled at once), I moved to a so-called 'smokeless' H-bridge... a >simple 2-to-4 decoder IC (or circuit) prevents bad things from >happening. Smart guys even used the 4th state as a brake. > >Frank ________________________________ Message 3 _____________________________________ Time: 06:12:14 AM PST US From: "Jerry Ballard" Subject: AeroElectric-List: Battery cables for aft batterys on RV-7 --> AeroElectric-List message posted by: "Jerry Ballard" I've just ordered an H-6 Subaru for an RV-7A. For CG I'll probably need to locate batteries in or aft of baggage compartment. Question1: What size wire should I run from batteries to engine compartment? Should this be a welding cable type wire? With the H-6, reducing weight is more of a concern. Question 2: I've already placed conduit to run power and/or signal wiring for AOA, Whelen strobes, and Grand Rapids EFIS from front to aft of baggage compartment. Can the battery cable be run in this conduit or should it be relocated for separation from routine power and signal wires. How much separation? Jerry ________________________________ Message 4 _____________________________________ Time: 06:42:08 AM PST US From: "Bob C. " Subject: Re: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Corrected --> AeroElectric-List message posted by: "Bob C. " Bob, I don't understand you example: "A good case in point deals with pitot tube heaters. Cold resistance is very high and warmup speeds relatively slow. Some builders have resorted to 30A fuses to protect a 14AWG wire driving a 100W heated pitot that runs under 10 amps after it warms up." If "cold resistance" is "hign" then current would be low. Why would you need to "resort to 30A fuse"? Thanks, Bob ________________________________ Message 5 _____________________________________ Time: 09:02:35 AM PST US From: "Robert L. Nuckolls, III" Corrected Subject: Re: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Corrected --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" Corrected At 08:40 AM 2/11/2005 -0600, you wrote: >--> AeroElectric-List message posted by: "Bob C. " > >Bob, > >I don't understand you example: > >"A good case in point deals with pitot tube heaters. Cold resistance >is very high and warmup speeds relatively slow. Some builders have >resorted to 30A fuses to protect a 14AWG wire driving a 100W heated >pitot that runs under 10 amps after it warms up." > >If "cold resistance" is "hign" then current would be low. Why would >you need to "resort to 30A fuse"? Good eye. Got my tongue tangled around my eyeteeth and couldn't see what I was saying. Cold resistance is LOW and inrush currents are HIGH. Further, due to slow response for temperature rise, this "inrush" current is rather extended . . . it takes about a minute for the temperature of the tube to reach final operating values in flight. The upshot is that builders have selected 14 AWG wire for low voltage drop and 30A fuses so that the relatively fast fuse is not nuisance tripped by the unique warm-up characteristics of a pitot tube that only draws about 10A in operation. Thanks for the heads-up. Bob . . . ________________________________ Message 6 _____________________________________ Time: 09:13:13 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Final Correction --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 07:23 AM 2/10/2005 -0800, you wrote: >--> AeroElectric-List message posted by: "Dennis Johnson" > > >Greetings, > >I'm finally getting to the point of beginning the detailed electrical >design stage of my Lancair Legacy. Although I'm planning to use fuses, I >noticed in AC 43.13-1B, Table 11-3, that for certain wire sizes, it calls >for a substantially larger circuit breaker rating than for a fuse. For >example, a 14 AWG wire can be protected by a 20 amp breaker or a 15 amp fuse. > >Since I'm going to be using nearly all fuses, it doesn't particularly >matter to my design, but just for educational purposes, I'm curious. I >thought that fuses generally acted faster in response to mild overloads >than breakers, but AC 43.13 seems to say the opposite. What gives? In a nutshell . . . selection of a wire size is driven by two considerations: (1) temperature rise as it affects the insulation on the wire and (2) voltage drop to be tolerated over the length of the wire run. The copper in a 22AWG wire will very happily carry 15 amps at room temperature and free air. I just hooked a 16" piece of 22759/16 to a power supply and jacked it up to 15 amps. 20 minutes later, the wire was way too hot to touch. Voltage drop was about 0.7 volts. No smells. No smoke. If this had been PVC wire instead of Tefzel, perhaps the PVC would have melted off the wire . . . no sweat, go with Teflon. The REAL answers to your questions are: (1) how will the wire to be protected be loaded? Discussion: We routinely load 4AWG FAT wires in our airplanes to 200 amps or more to crank an engine. Is this a bad deal? AC43-13 sez protect this wire at 100A breakers or 70A with fuses. Section 5 of Chapter 11 goes into lots of explanation for rating wires and takes voltage drop and temperature rise into consideration. Table 11-9 speaks to continuous current ratings for wire but consider notes at the bottom of the table where one reads that the numbers apply for 70C ambients and free air . . . higher ambient temps and burying a wire inside a bundle gives one reasons to derate a wire still further. One can tolerate what might be considered severe overloading for short times as long as voltage drop can be tolerated. I recommend 4AWG fat wiring for aircraft where battery is very close to engine. When battery and engine are on opposite ends of airplane, 2AWG is recommended. In some seaplanes, 0AWG is called for. This decision is driven by voltage drop issues during cranking. (2) what is the temperature rating of the insulation on the wire? Discussion: As long as you're not dealing with voltage drop issues, then insulation sets the current limits 105C, Tefzel limits at 150C, Teflon goes to 200C. Got some asbestos sleeving laying around? Slip that stuff over your wire and you can run it up to cherry red temperatures. Is the wire hanging out in the breeze for cooling or is it wrapped up in a bundle with lots of other wires that contribute their own heat dissipations to the equation. Note that we STILL haven't talked about fuses or circuit breakers. (3) what kind of load does the wire feed? Discussion: Are there large inrush or high momentary loads to be considered? Fuses tend to be faster than thermal breakers. Magnetic breakers are faster than most fuses. Virtually ANY form of circuit protection can be sized to adequately protect ANY wire. You won't find a considered one-size-fits-all from the charts and tables. A good case in point deals with pitot tube heaters. Cold resistance is very LOW compared to operating resistance. Further, warmup speed is relatively slow. Some builders have resorted to 30A fuses to protect a 14AWG wire driving a 100W heated pitot that runs under 10 amps after it warms up. The charts and tables will be conservative suggestions that cover most situations but understand that some systems will present special issues that drive CONSIDERED departure from suggestions. There's no substitute for knowing how the system works and selecting both wire and circuit protection based on that understanding. Bob . . . ________________________________ Message 7 _____________________________________ Time: 10:21:34 AM PST US From: Mickey Coggins Subject: Re: AeroElectric-List: Battery cables for aft batterys on RV-7 --> AeroElectric-List message posted by: Mickey Coggins Hi Jerry, To size the cable, you need to know how much current the starter will draw. No one seems to be able to tell me, but hopefully when I get my engine, I'll just test it. I've heard some pretty small numbers thrown around, since it is supposed to have a "geared starter". Also, I really don't know what kind of voltage drop the starter can handle, and still crank the engine. The engine supplier recommends AWG#6, and I hope that will work, since that's what I have installed now. If it doesn't work right, I've got a bunch of Eric's Super-2-CCA Fat Wire standing by. Mickey Jerry Ballard wrote: > --> AeroElectric-List message posted by: "Jerry Ballard" > > I've just ordered an H-6 Subaru for an RV-7A. For CG I'll probably > need to locate batteries in or aft of baggage compartment. > > Question1: What size wire should I run from batteries to engine > compartment? Should this be a welding cable type wire? With the > H-6, reducing weight is more of a concern. > > Question 2: I've already placed conduit to run power and/or signal > wiring for AOA, Whelen strobes, and Grand Rapids EFIS from front to aft > of baggage compartment. Can the battery cable be run in this conduit > or should it be relocated for separation from routine power and signal > wires. How much separation? > > Jerry -- Mickey Coggins http://www.rv8.ch/ #82007 Wiring ________________________________ Message 8 _____________________________________ Time: 10:54:01 AM PST US From: "Mitch Faatz" Subject: AeroElectric-List: Toggle switch - both master/battery and starter --> AeroElectric-List message posted by: "Mitch Faatz" With the goal of reducing my switch count, I'm wondering if it's possible to double up the Master/Battery toggle and Starter switch but not sure it's possible toggle-switch-wise. At first I thought if I could find a DPDT switch that is Off-On-(On), I could do it. I've found a red toggle switchguard that returns a toggle that is in the top position back to center (which would drop starter back to master on) and leave a toggle that is in the bottom position alone (master off stays master off). Useability sounds good, switch guard up, switch to master on, momentary full up for starter, returns to master on. With a DPDT switch I could have one pole control starter, but I'm worried about the master/battery pole. If it goes from middle position (on) to up position (momentary on for starter), will there be a brief interruption and if so will that cause a problem? Thanks in advance for any thoughts on this - Mitch Faatz RV-6A Finish Kit Auburn, CA ________________________________ Message 9 _____________________________________ Time: 11:23:45 AM PST US From: "Eric M. Jones" Subject: AeroElectric-List: Re: Big H-bridge for Big Motors --> AeroElectric-List message posted by: "Eric M. Jones" --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" >One should take care to design switching systems that drive >h-bridges to preclude simultaneous contrary commands via >gates or architecture of the control switches. Either may >be accomplished easily. >Bob . . . > AeroElectric-List message posted by: Frank & Dorothy > > >Robert L. Nuckolls, III wrote: > > >Guess it would help if I put the link in too . . . > > > >http://www.aeroelectric.com/Pictures/Big_H-Bridge.gif > >I'm not sure what application this Big H-bridge is intended for, but >I've had a bit of experience with *little* H-bridges. After burning up a >few drive transistors (check out what happens if both drive transistors >are enabled at once), I moved to a so-called 'smokeless' H-bridge... a >simple 2-to-4 decoder IC (or circuit) prevents bad things from >happening. Smart guys even used the 4th state as a brake. Having had a couple H-bridge designs shoot thru--one is advised to explore the stunningly simple and reliable intergrated circuit solutions for this design. They offer feature that you simply could not cobble together in the conventional designs---even the very clever conventional designs. For example IR3220S coupled to a pair of IRF7484Q's is 6A continuous WITHOUT a heatsink--and offers shoot-thru protection, Sleep mode, braking, torque control, self-adaptive dead time (don't ask!!!), over-temp, over-current, soft start, inrush limits, etc etc. This results in magnitudes better performance and reliability for less cost and much less size and weight. The PCB is one square inch. AN-1032 application note has everything you ever wanted to know on the subject. Not at all complicated but some SMD assembly skill is required. Regards, Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge MA 01550-2705 Phone (508) 764-2072 Email: emjones@charter.net "I only regret my economies." Reynolds Price ________________________________ Message 10 ____________________________________ Time: 11:32:48 AM PST US Subject: RE: AeroElectric-List: Toggle switch - both master/battery and starter From: "Mark R Steitle" --> AeroElectric-List message posted by: "Mark R Steitle" Mitch, That sounds like what Bob recommends in his "book", and what I purchased from B&C. It is an OFF-ON-(ON) switch. I believe it is p/n S700-2-50 (Bob can verify this). Wire it like Bob shows and it should work great. I have been looking for a switch guard that returns the switch to the center position. Can you post the source and p/n? Thanks, Mark S. -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Mitch Faatz Subject: AeroElectric-List: Toggle switch - both master/battery and starter --> AeroElectric-List message posted by: "Mitch Faatz" With the goal of reducing my switch count, I'm wondering if it's possible to double up the Master/Battery toggle and Starter switch but not sure it's possible toggle-switch-wise. At first I thought if I could find a DPDT switch that is Off-On-(On), I could do it. I've found a red toggle switchguard that returns a toggle that is in the top position back to center (which would drop starter back to master on) and leave a toggle that is in the bottom position alone (master off stays master off). Useability sounds good, switch guard up, switch to master on, momentary full up for starter, returns to master on. With a DPDT switch I could have one pole control starter, but I'm worried about the master/battery pole. If it goes from middle position (on) to up position (momentary on for starter), will there be a brief interruption and if so will that cause a problem? Thanks in advance for any thoughts on this - Mitch Faatz RV-6A Finish Kit Auburn, CA ________________________________ Message 11 ____________________________________ Time: 01:59:56 PM PST US From: Jeff Point Subject: AeroElectric-List: Narco wiring harness- part needed --> AeroElectric-List message posted by: Jeff Point Hello all, I'm in need of a radio part and I'm hoping someone has one laying around. I need Narco p/n P810, which is the D-sub connector for the wiring harness on a NAV122 VOR/ILS unit. What I really need is the sliding locking piece which attaches to the D-sub hood. If anyone has one laying around, please contact me. Thanks Jeff Point RV-6 Milwaukee WI do not archive ________________________________ Message 12 ____________________________________ Time: 03:13:04 PM PST US From: "Hans Teijgeler" Subject: Re: AeroElectric-List: Battery cables for aft batterys on RV-7 --> AeroElectric-List message posted by: "Hans Teijgeler" Mickey, For an apples-oranges comparison: I've got AWG 6 on my 17 Ah battery to run my EJ-18 starter on my EJ-25 engine and the engine cranks like mad. So far the apples. As for the oranges: my battery is on my firewall rather than in the back, which results in about 60 cm (2 ft) of cable. Hope this is of some use Cheers, Hans ----- Original Message ----- From: "Mickey Coggins" Subject: Re: AeroElectric-List: Battery cables for aft batterys on RV-7 > > The engine supplier recommends AWG#6, and I > hope that will work, since that's what I > have installed now. ________________________________ Message 13 ____________________________________ Time: 04:31:06 PM PST US From: "Bob C. " Subject: Re: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Corrected --> AeroElectric-List message posted by: "Bob C. " Bob, What's you conclusion on the pitot heater example . . . what would the appropriate wire size be 14, 16 or 18? Thanks, Bob On Fri, 11 Feb 2005 10:59:00 -0600, Robert L. Nuckolls, III wrote: > --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" Corrected > > At 08:40 AM 2/11/2005 -0600, you wrote: > > >--> AeroElectric-List message posted by: "Bob C. " > > > >Bob, > > > >I don't understand you example: > > > >"A good case in point deals with pitot tube heaters. Cold resistance > >is very high and warmup speeds relatively slow. Some builders have > >resorted to 30A fuses to protect a 14AWG wire driving a 100W heated > >pitot that runs under 10 amps after it warms up." > > > >If "cold resistance" is "hign" then current would be low. Why would > >you need to "resort to 30A fuse"? > > Good eye. Got my tongue tangled around my eyeteeth and couldn't > see what I was saying. Cold resistance is LOW and inrush currents > are HIGH. Further, due to slow response for temperature rise, this > "inrush" current is rather extended . . . it takes about a minute > for the temperature of the tube to reach final operating values > in flight. > > The upshot is that builders have selected 14 AWG wire for > low voltage drop and 30A fuses so that the relatively fast > fuse is not nuisance tripped by the unique warm-up characteristics > of a pitot tube that only draws about 10A in operation. > > Thanks for the heads-up. > > Bob . . . > > > ________________________________ Message 14 ____________________________________ Time: 04:55:24 PM PST US From: "Dennis Johnson" Subject: AeroElectric-List: RE: Size of Fuse vs. Circuit Breaker --> AeroElectric-List message posted by: "Dennis Johnson" Thanks, Matt and Bob, for responding to my question about why AC 43.13 shows different amperage ratings for fuses and circuit breakers. Matt, I'd guess you're probably right that the table was made up based on specific specs for specific fuses and breakers that were in use at that time. Thanks again, Dennis Johnson Legacy #257 Do not archive ________________________________ Message 15 ____________________________________ Time: 05:18:11 PM PST US From: N27160@aol.com Subject: AeroElectric-List: Coax connector Garmin 196 --> AeroElectric-List message posted by: N27160@aol.com I have a Garmin 196 and to keep the mounting as tight as possible, I need a coax connector for the antenna to be as compact as possible. A regular straight connector is gonna require me to drill a hole behind the 196. Any ideas for an alternative? ________________________________ Message 16 ____________________________________ Time: 05:46:39 PM PST US Subject: Re: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Corrected From: "John Schroeder" --> AeroElectric-List message posted by: "John Schroeder" We have a run of about 25' from the fuse panel to the pitot tube for an plastic airplane. That's 50' roundtrip. We used 11 amps start and ending at 7.5 to 8 for steady state. Installed 12 AWG. The pitot heat is the biggest current draw of anything in the aircraft - by a factor of about 2 to 3. Incidentally, the wire is in a conduit for about 75-80% of its length. John > > What's you conclusion on the pitot heater example . . . what would the > appropriate wire size be 14, 16 or 18? > > Thanks, > Bob > ________________________________ Message 17 ____________________________________ Time: 07:37:13 PM PST US From: Fiveonepw@aol.com Subject: Re: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Corrected --> AeroElectric-List message posted by: Fiveonepw@aol.com In a message dated 02/11/2005 7:47:16 PM Central Standard Time, jschroeder@perigee.net writes: The pitot heat is the biggest current draw of anything in the aircraft - by a factor of about 2 >> What, are ya hand-proppin' this baby?! (apologies pre-flame!) 8-) Mark do not archive ________________________________ Message 18 ____________________________________ Time: 08:00:56 PM PST US Subject: Re: AeroElectric-List: Size of Fuse vs. Circuit Breaker - Corrected From: "John Schroeder" --> AeroElectric-List message posted by: "John Schroeder" Mark - Of course, the starter draws more. But after that, can you think of any item that can draw 11 amps. If so, let me know. I always have the felling that we have forgotten something. :-)) BTW, Steve Davis said to tell you hello. We didn't get to go for barbecue this time!! Cheers, John > The pitot heat is the biggest current draw of anything in the aircraft - > by a factor of about 2 >>> > What, are ya hand-proppin' this baby?! ________________________________ Message 19 ____________________________________ Time: 09:59:16 PM PST US Subject: AeroElectric-List: Re: Measurements From: j1j2h3@juno.com --> AeroElectric-List message posted by: j1j2h3@juno.com If you're really set on accurately measuring this, you can do it with little expense, but some work in making calculations and experimenting with the set up. Analog ammeters are really millivoltmeters that are measuring the voltage drop across a resistor. The value of the resistor, referred to as a shunt, is very low and its current capacity is very high. Typically, it is just a piece of metal or wire. You can accomplish the same thing with your digital ammeter. You will have to make the shunt out of wire that is small enough to have a voltage drop that you can measure, but large enough to carry the expected maximum current and also long enough to give you a measurable resistance. Then measure its resistance and insert it in the circuit. With the circuit energized, read the voltage drop across the shunt and use the known resistance to calculated the amperage, using E = IR or I = E/R. When analog meters were used, you also had to calculate the amperage through the meter, but with digitals, this is negligible. The resistance of the shunt will also affect the final result, but can be neglected if it is very low. However, if you really wanted, you could calculate the total resistance of the circuit, again using E = IR, where E is the output voltage of your system, then recalculate the current with the shunt resistance subtracted. This will get you very, very, close, but then the resistance of the light bulb will change as the current increases with the shunt removed, so you will still have a small unknown. Jim Hasper - RV-7 Giving new meaning to the term "slow build" Franklin, TN Do not archive > > --> AeroElectric-List message posted by: "Tinne maha" > > > > > > Bob/List, > > > > I would like to measure the current used by my landing/taxi light. > The > > multi-meters I have access to only measure up to 2 amps, but I'm > sure my > > light uses more than that (on the order of 5-10 amps, I believe). > > > > Can you tell me where I can get an ammeter that measures more than > 2 amps? > > Is it inadvisable to use the ammeter I will install in my plane? > > > > Any help is appreciated. Thanks, > > Grant > >