---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 11/17/09: 19 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:07 AM - Re: Please review my electrical system (Deviation of Z-13) (John Morgensen) 2. 06:16 AM - Re: Fuel pump control (Joe) 3. 06:53 AM - Re: Please review my electrical system (Deviation of Z-13) (John Morgensen) 4. 07:05 AM - Re: Please review my electrical system (Deviation of Z-13) (Joe) 5. 08:25 AM - Re: Fuel pump control (Jeff Page) 6. 10:29 AM - EFIS backup battery switch wiring (messydeer) 7. 10:49 AM - Re: EFIS backup battery switch wiring (messydeer) 8. 11:50 AM - Re: EFIS backup battery switch wiring (edleg) 9. 12:16 PM - Re: Please review my electrical system (Deviation of Z-13) (user9253) 10. 12:25 PM - Re: Re: EFIS backup battery switch wiring () 11. 12:26 PM - Re: Please review my electrical system (Deviation of Z-13) (Robert L. Nuckolls, III) 12. 12:58 PM - Re: EFIS backup battery switch wiring (messydeer) 13. 03:55 PM - Re: EFIS backup battery switch wiring (Robert L. Nuckolls, III) 14. 04:29 PM - Re: EFIS backup battery switch wiring (messydeer) 15. 07:12 PM - Re: EFIS backup battery switch wiring (edleg) 16. 07:37 PM - Re: EFIS backup battery switch wiring (messydeer) 17. 08:09 PM - Re: Re: EFIS backup battery switch wiring (Richard E. Tasker) 18. 08:49 PM - Re: Re: EFIS backup battery switch wiring (Kevin Horton) 19. 10:36 PM - Re: Re: EFIS backup battery switch wiring (Jay Hyde) ________________________________ Message 1 _____________________________________ Time: 06:07:37 AM PST US From: John Morgensen Subject: Re: AeroElectric-List: Please review my electrical system (Deviation of Z-13) ________________________________ Message 2 _____________________________________ Time: 06:16:02 AM PST US From: "Joe" Subject: Re: AeroElectric-List: Fuel pump control The RV-12 has a mechanical fuel pump on the engine and an electrical fuel pump near the fuel tank. The electric fuel pump runs continuously whenever the master switch is on. There is no discrete switch for the electric fuel pump. The pre-flight check is to turn on the master switch and observe the fuel pressure to be sure the electric pump is working. Then start the engine and watch for an increase in fuel pressure to be sure that the mechanical fuel pump is also working. Yes, it wastes electricity and wears out the electric fuel pump. On the other hand, most automotive fuel pumps last the life of the vehicle. Airplanes are used a lot less then cars. I would not expect the electric fuel pump in the RV-12 to wear out soon. The big advantage of wiring the electric fuel pump to run continuously is that it helps to prevent mismanagement of the fuel system, a major cause of accidents. The RV-12 fuel system does not have a fuel selector valve because there is only one fuel tank. There is no mixture control. The only thing for the pilot to mismanage is the emergency fuel shut-off valve handle that is located on the floor. The handle must be pulled up to shut off. The simpler the system is, the less chance for malfunction or error. Joe ________________________________ Message 3 _____________________________________ Time: 06:53:42 AM PST US From: John Morgensen Subject: Re: AeroElectric-List: Please review my electrical system (Deviation of Z-13) I investigated this earlier and this is what I found: 1. No harm is done with both alternators online. The theory that there is a problem stems from twin engine systems with elaborate schemes to deal with 2 alternators. I am using Z-13/8 and there are only 3 switches: Main: (off)- (battery contactor)-(battery+main alternator) Aux feed: (off)-(on) Aux Alt: (off)-(on) The endurance bus can be powered by: Battery only Battery + Main Alternator Battery + Aux Alternator Aux Alternator only The Aux Feed provides a path that does not include the battery contactor. Hope this helps, John Morgensen Grumman AA1B 150hp - For Sale RV4 - Flying RV9A - wiring Matthew Schumacher wrote: > List, > > I've been working on the wiring diagram for my airplane (electric panel, > IFR, plane power internally regulated main alt and a SD-8 backup). So > I've been reading though Bob's book and am familiar with the Z-13 wiring > diagram, however there are a two things about it that I don't like: > > 1. It is possible to turn on both alternators at once. It is my > understanding that you don't want to have both alternators online at > once and I don't want the pilot to be able to cause damage by not using > the correct switches. > > 2. Alternate feed switches. Feed switches seem cumbersome since it > requires the pilot to know something about the electrical system. > > I think I have a new wiring diagram that addresses these things, but I > want to run it past this list and perhaps Bob so that others can help me > find the problems. > > Here is how it works: > > The avionics bus is treated like the endurance bus since the avionics > are the only things I care about if my alternator fails (I have mags and > a mechanical fuel pump.) When the master switch is on, the battery > pulls the battery contactor which brings the main alternator and battery > into the system. Should something happen to the main alternator the > battery will continue to power the system unless I switch the ALT switch > to AUX. When the alternator switch is on AUX it takes out the main alt > and powers up the SD-8 wired up with the self exciting hack. This will > allow my aux alternator to power the avionics bus (when the Avionics > master is on AUX) but will keep my master contactor and battery separate > from the rest of the system. In the event that I want to charge my main > battery I can turn the master switch off which will then allow me to > charge my battery should I desire to try and bring the main alternator > back after a dead battery. > > In order to clear up any confusion here are the basic switches, > settings, and mode of operation: > > Master: on, Alt: main, Avionics: main; Normal operation running on the > main alternator and battery. > > Master on, Alt: Aux, Avionics: Main; Aux alternator is online and master > alternator is offline, battery is powering everything. > > Master on, Alt: Aux, Avionics: Aux; Aux alternator is powering avionics, > main alternator is offline, and battery is powering everything except > avionics. > > Master off, Alt: Main, Avionics: main; Nothing is powered up. > > Master off, Alt: aux, Avionics: main; Avionics are off, Aux alternator > is online and is charging the battery. > > Master Off, Alt: aux, Avoinics: aux; Avionics are on aux alternator, aux > alternator is online and is charging the battery. > > Perhaps it would be more intuitive if I name the switches like this: > > Battery: On | Off (Aux Charge) > Alternator : MAIN | AUX > Avionics: MAIN | OFF | AUX > > This setup reduces the panel down to 3 switches and gives the operator > good control over the system, allows for the battery to be isolated or > charged from the aux alternator, and gives a way for non critical > devices to run off the battery. > > If this doesn't look sane to you please post some feedback. Any help I > can get is greatly appreciated. > > Thanks, > schu > > ________________________________ Message 4 _____________________________________ Time: 07:05:44 AM PST US From: "Joe" Subject: Re: AeroElectric-List: Please review my electrical system (Deviation of Z-13) Schu, It is easier for me to visualize a circuit by looking at an electrical schematic rather than reading about it. If I understand correctly, you intend to have one switch control two alternators. It seems like a single point of failure. What happens when the switch fails? Switches probably fail about as often as alternators. It is my understanding that it will not hurt to have two alternators on line at once. Power will be drawn from the one with the highest voltage. Bob will correct me if I am wrong. Having one switch for the avionics is also a single failure point. In Z-13/8, inadvertently turning on both the master switch and the E-Bus Alternate feed switch will not hurt anything. The Endurance Bus will draw from the highest voltage source. After engine shut down, it is important to remember to shut off both the master switch and the E-Bus Alternate Feed switch. Keeping the electrical controls simple is a worthwhile goal. Having options in case of a failure is another worthwhile goal. Aircraft design is a matter of compromises. It is hard to improve on Bob's designs. They have been scrutinized by many and have evolved over the years. Joe ________________________________ Message 5 _____________________________________ Time: 08:25:45 AM PST US From: "Jeff Page" Subject: AeroElectric-List: Re: Fuel pump control Thanks for everyone's replys. The following is exactly the trick I was hoping for ! Jeff Page Dream Aircraft Tundra #10 > From: Steve Ruse > Subject: Re: AeroElectric-List: Fuel pump control >> > It is pretty simple to do this if you use a fuel pump and relay coil > that require the same voltage. Use a pressure sensor to control the > relay. Connect the relay output to the fuel pump AND to the relay > coil (input). That way when the fuel pump comes on (due to a low > pressure signal), the relay locks itself on, regardless of the state > of the pressure sensor. To turn the pump off, you would have a > momentary switch in the circuit that would break the connection to the > relay coil. This used to be called a "seal-in" circuit for industrial > controls. > > Steve Ruse ________________________________ Message 6 _____________________________________ Time: 10:29:27 AM PST US Subject: AeroElectric-List: EFIS backup battery switch wiring From: "messydeer" Hello :-) I have an MGL Enigma EFIS and will put in a backup battery. In regular operation, both the main and backup battery are to be wired to the EFIS. The Enigma automatically switches to backup when it senses a main battery low voltage. I was thinking of maybe some wiring of a 2-10 that would do the following: Down position: main buss to EFIS. Middle position: backup battery to EFIS (for backup battery check) Up position: both batteries to EFIS. Or maybe just a two position switch, one position would be for both batteries, the other just to the backup. The backup check position could be a momentary on, I suppose, that just takes the main battery offline. Hold it in this position and see if the EFIS still works, then release. -------- Dan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273305#273305 ________________________________ Message 7 _____________________________________ Time: 10:49:14 AM PST US Subject: AeroElectric-List: Re: EFIS backup battery switch wiring From: "messydeer" Well, I got one possibility figured out using a 2-10. Figure attached. -------- Dan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273310#273310 Attachments: http://forums.matronics.com//files/enigma_efis_backup_switch_wiring_with_2_10_162.pdf ________________________________ Message 8 _____________________________________ Time: 11:50:53 AM PST US Subject: AeroElectric-List: Re: EFIS backup battery switch wiring From: "edleg" With one switch you are putting all your eggs (and faith) in a single point of failure. What use is having emergency backup power if you can not use it if the only switch is broken? Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273314#273314 ________________________________ Message 9 _____________________________________ Time: 12:16:35 PM PST US Subject: AeroElectric-List: Re: Please review my electrical system (Deviation of Z-13) From: "user9253" Oops my mistake, there was no schematic in the daily digest that is emailed to me. Now I see it on the online forum. Most aircraft have the battery contactor and starter contactor wired in series so that the starter can be shut off in case it welds shut. There is no way to disconnect the main alternator from the battery. Moving the alternator wire to the other side of the battery contactor will fix both issues. Will the avionics momentarily lose power when the avionics master switch is operated? Do the master switch and alternator switch have a center off position? There needs to be a way to kill power in case of smoke in the cockpit. Most pilots are familiar with switches being off when in the down position. Switches that accomplish your goals are available that are off when down. The 22mfd capacitor should be 22,000mfd. There is a hot wire from the battery to master switch terminal 5. If it starts smoking inside of the cockpit, there is no way to shut it off. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273318#273318 ________________________________ Message 10 ____________________________________ Time: 12:25:20 PM PST US From: Subject: Re: AeroElectric-List: Re: EFIS backup battery switch wiring Dan, Turn the master on, turn the EFIS on . Turn the master off. If EFIS remains on the systemn works. Don VS RV7 flying ---- messydeer wrote: > > Well, I got one possibility figured out using a 2-10. Figure attached. > > -------- > Dan > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=273310#273310 > > > > > Attachments: > > http://forums.matronics.com//files/enigma_efis_backup_switch_wiring_with_2_10_162.pdf > > > > > > > ________________________________ Message 11 ____________________________________ Time: 12:26:03 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Please review my electrical system (Deviation of Z-13) At 08:52 AM 11/17/2009, you wrote: > >I investigated this earlier and this is what I found: > >1. No harm is done with both alternators online. The theory that >there is a problem stems from twin engine systems with elaborate >schemes to deal with 2 alternators. Correct . . . and the "problem" was that light twins fitted with alternators were plagued with inability to make two alternators PARALLEL . . . i.e. share total loads. I've developed several approaches to alternator paralleling. Quite frankly, if you have TWO alternators capable of carrying most if not all of total system loads, then Z-14 and NO paralleling is the better way to go. But the system is not placed at risk by having two alternators on at the same time. Unless they are calibrated to within millivolts of each other, the device with the higher set-point "hogs" the load until it reaches its output limit. The bus voltage then sags until the alternator with the lower setpoint picks up the difference. Bob . . . --------------------------------------- ( It's MATRONICS FUND RAISER MONTH! ) ( Do your part to keep this marvelous ) ( tool sharp and available to all our ) ( brothers in the OBAM aviation ) ( community. ) --------------------------------------- ________________________________ Message 12 ____________________________________ Time: 12:58:16 PM PST US Subject: AeroElectric-List: Re: EFIS backup battery switch wiring From: "messydeer" Turns out I had the wiring to the EFIS wrong. There are separate terminals for the backup and main power inputs, so I've redrawn it. It looks like if I forgot to turn off the EFIS switch, my backup battery would run dead. But I suppose I otta notice that my screen is still powered up. I would think that would be pretty obvious. -------- Dan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273325#273325 Attachments: http://forums.matronics.com//files/enigma_efis_backup_switch_wiring_with_2_10_150.pdf ________________________________ Message 13 ____________________________________ Time: 03:55:53 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: EFIS backup battery switch wiring >I have an MGL Enigma EFIS and will put in a backup battery. In >regular operation, both the main and backup battery are to be wired >to the EFIS. The Enigma automatically switches to backup when it >senses a main battery low voltage. > >I was thinking of maybe some wiring of a 2-10 that would do the >following . . . What does the manufacturer of the EFIS system recommend? Bob . . . --------------------------------------- ( It's MATRONICS FUND RAISER MONTH! ) ( Do your part to keep this marvelous ) ( tool sharp and available to all our ) ( brothers in the OBAM aviation ) ( community. ) --------------------------------------- ________________________________ Message 14 ____________________________________ Time: 04:29:46 PM PST US Subject: AeroElectric-List: Re: EFIS backup battery switch wiring From: "messydeer" Thanks, Bob. >From the manual: "...One power switch for the main incoming 12 or 24 V feed (switch in positive supply lead), another for the backup battery. In flight, both switches would be on allowing the charging of the backup battery. Preflight check would involve switching main power on, then battery power on. Check of battery power would involve switching main power off and verifying that Enigma continues to operate. Voltage on the backup battery should be measured by means of the backup voltage readouts which can be placed on any display..." Imaged referred to attached. -------- Dan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273357#273357 Attachments: http://forums.matronics.com//files/mgl_enigma_odyssey_installation_198.bmp ________________________________ Message 15 ____________________________________ Time: 07:12:57 PM PST US Subject: AeroElectric-List: Re: EFIS backup battery switch wiring From: "edleg" In simple terms... if the backup battery is not on its own switch it won't charge. Two switches is simple. Trying to find a special switch to do all things at once leaves you with a non-common fix if it fails away from your home airport..... Two switches lets you troubleshoot power problems, and lets the EFIS be powered fully during a voltage drop, like during an engine start. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273386#273386 ________________________________ Message 16 ____________________________________ Time: 07:37:38 PM PST US Subject: AeroElectric-List: Re: EFIS backup battery switch wiring From: "messydeer" Thanks, E., for bringing up the issue of single point of failure. Hadn't thought about that, which makes me ask some questions about DPDT vs SPST switches. Looking at the schematic of a DPDT switch it looks like there are two circuits, an upper and a lower. Their terminals are separate but contained in the same housing. They also use the same lever and the mechanism the lever connects to that makes and brakes the contacts. If the only way a switch failed was through these shared components, then a DPDT would have the same reliability as a SPST, so there would be a single point of failure. And if DPDT's never failed at these shared components, then having one DPDT would be just as reliable as having two SPST's, and there wouldn't be a single point of failure. I'm sure the truth lies somewhere between these two extremes. If it turns out that a DPDT has 90% of the reliabilty as two SPST's, I might stick with just one DPDT. If it has only 20% of the reliabilty of two SPST's, I might consider going with two switches. -------- Dan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=273392#273392 ________________________________ Message 17 ____________________________________ Time: 08:09:50 PM PST US From: "Richard E. Tasker" Subject: Re: AeroElectric-List: Re: EFIS backup battery switch wiring The issue is not so much about what the relative reliability is. The issue is that if the DPDT switch fails you may not be able to connect to either source of electrons. If one of the SPST switches fails, you always have the other one. Dick Tasker messydeer wrote: > > Thanks, E., for bringing up the issue of single point of failure. Hadn't thought about that, which makes me ask some questions about DPDT vs SPST switches. > > Looking at the schematic of a DPDT switch it looks like there are two circuits, an upper and a lower. Their terminals are separate but contained in the same housing. They also use the same lever and the mechanism the lever connects to that makes and brakes the contacts. > > If the only way a switch failed was through these shared components, then a DPDT would have the same reliability as a SPST, so there would be a single point of failure. > > And if DPDT's never failed at these shared components, then having one DPDT would be just as reliable as having two SPST's, and there wouldn't be a single point of failure. > > I'm sure the truth lies somewhere between these two extremes. If it turns out that a DPDT has 90% of the reliabilty as two SPST's, I might stick with just one DPDT. If it has only 20% of the reliabilty of two SPST's, I might consider going with two switches. > > -------- > Dan > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=273392#273392 > > > ________________________________ Message 18 ____________________________________ Time: 08:49:16 PM PST US From: Kevin Horton Subject: Re: AeroElectric-List: Re: EFIS backup battery switch wiring What are the consequences of failure of both poles in that switch, given how you will operate the aircraft (day/night and VFR/IFR) and the backups you have installed? If you are certain that you will be able to safely get the aircraft on the ground with an acceptable workload, then the potential single point failure is acceptable. Kevin Horton Sent from my iPod On 2009-11-17, at 10:36 PM, "messydeer" wrote: > > > > Thanks, E., for bringing up the issue of single point of failure. > Hadn't thought about that, which makes me ask some questions about > DPDT vs SPST switches. > > Looking at the schematic of a DPDT switch it looks like there are > two circuits, an upper and a lower. Their terminals are separate but > contained in the same housing. They also use the same lever and the > mechanism the lever connects to that makes and brakes the contacts. > > If the only way a switch failed was through these shared components, > then a DPDT would have the same reliability as a SPST, so there > would be a single point of failure. > > And if DPDT's never failed at these shared components, then having > one DPDT would be just as reliable as having two SPST's, and there > wouldn't be a single point of failure. > > I'm sure the truth lies somewhere between these two extremes. If it > turns out that a DPDT has 90% of the reliabilty as two SPST's, I > might stick with just one DPDT. If it has only 20% of the reliabilty > of two SPST's, I might consider going with two switches. > > -------- > Dan > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=273392#273392 > > ________________________________ Message 19 ____________________________________ Time: 10:36:16 PM PST US From: "Jay Hyde" Subject: RE: AeroElectric-List: Re: EFIS backup battery switch wiring There is one quite important thing to note, no matter how one wires the switches (I used two DPST switches in the Sling - one for the power to the Enigmas and one to the backup batteries)- that is that the backups will not charge unless the voltage to them is sufficiently high. Obvious of course, but where this becomes a problem is if you have a diode between your main bus and the e-bus. You get a 0.7v drop across it and then there are some voltage drops inside the Enigma and the backup batt gets a voltage of between 12.5 -13v. To solve this we now run the aircraft with the e-bus alt feed permanently on, which boosts the e-bus voltage back up sufficiently to charge the backup battery. Jay -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Kevin Horton Sent: 18 November 2009 06:43 AM Subject: Re: AeroElectric-List: Re: EFIS backup battery switch wiring What are the consequences of failure of both poles in that switch, given how you will operate the aircraft (day/night and VFR/IFR) and the backups you have installed? If you are certain that you will be able to safely get the aircraft on the ground with an acceptable workload, then the potential single point failure is acceptable. Kevin Horton Sent from my iPod On 2009-11-17, at 10:36 PM, "messydeer" wrote: > > > > Thanks, E., for bringing up the issue of single point of failure. > Hadn't thought about that, which makes me ask some questions about > DPDT vs SPST switches. > > Looking at the schematic of a DPDT switch it looks like there are > two circuits, an upper and a lower. Their terminals are separate but > contained in the same housing. They also use the same lever and the > mechanism the lever connects to that makes and brakes the contacts. > > If the only way a switch failed was through these shared components, > then a DPDT would have the same reliability as a SPST, so there > would be a single point of failure. > > And if DPDT's never failed at these shared components, then having > one DPDT would be just as reliable as having two SPST's, and there > wouldn't be a single point of failure. > > I'm sure the truth lies somewhere between these two extremes. If it > turns out that a DPDT has 90% of the reliabilty as two SPST's, I > might stick with just one DPDT. If it has only 20% of the reliabilty > of two SPST's, I might consider going with two switches. > > -------- > Dan > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=273392#273392 > > ------------------------------------------------------------------------------------- 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.