I'm putting together the perfect 9A in my head and need some advice. I want an IFR glass panel which would free up the vacuum pump position. Should I install a back up alternator in this spot in case the main failed or would I be better off with a second battery. I'm thinking of double electronic ignition which would need a second battery but one EI and one magneto is also an option. Thanks for your input.
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back up alternator or extra battery
- Thread starter VaNewbie
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Can you post a picture of the second battery location??? Thanks.
Ralph Inkster
Well Known Member
I installed a second battery on the opposite side of the firewall recess, but I have a fixed pitch so didn't have to worry about a prop gov cable.
The second battery was a industrial type used for security systems in buildings, not huge CCA as it would never be used to start the engine. The same size as a PC680 & the best part, it was about 1/3 the cost of an Odessey.
The second battery was a industrial type used for security systems in buildings, not huge CCA as it would never be used to start the engine. The same size as a PC680 & the best part, it was about 1/3 the cost of an Odessey.
MacCool
Well Known Member
Can't take credit...the mounting bracket was installed by the builder. He'd had a second battery in that tray but the second owner took it out for weight. I re-installed.
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FireMedic_2009
Well Known Member
Backup alternator
It’s more money but a backup alternator is a much better option. If your main alternator goes out then you are stranded somewhere for at least a day. With a backup alternator you can easily fly to a bigger airport or continue to get back home
It’s more money but a backup alternator is a much better option. If your main alternator goes out then you are stranded somewhere for at least a day. With a backup alternator you can easily fly to a bigger airport or continue to get back home
Roy Thoma
Well Known Member
Dual alternator, single battery
I have two alternators and a single battery. If/When I build again I'll do the same. IFR capable plane with two PMAG's. The second alternator probably has a higher initial cost than a second battery AND it has ZERO scheduled ongoing costs. The second alternator can power my plane indefinitely with everything other than seat heaters and pitot heat on, while a second battery would have a limited time/range even with reduced loads.
Regards
I have two alternators and a single battery. If/When I build again I'll do the same. IFR capable plane with two PMAG's. The second alternator probably has a higher initial cost than a second battery AND it has ZERO scheduled ongoing costs. The second alternator can power my plane indefinitely with everything other than seat heaters and pitot heat on, while a second battery would have a limited time/range even with reduced loads.
Regards
A battery is just storage - an alternator is production.
My 9A is dependent on power for both engine and nav, I opted for one large battery (ETX900) and dual alternators. I put the B&C 410H on the vacuum pad, it can handle all in-flight full-IFR loads and I only need to pull from the battery for exterior lights on the approach at night.
My 9A is dependent on power for both engine and nav, I opted for one large battery (ETX900) and dual alternators. I put the B&C 410H on the vacuum pad, it can handle all in-flight full-IFR loads and I only need to pull from the battery for exterior lights on the approach at night.
Carl Froehlich
Well Known Member
Attached photo is how one RV-14A builder added a second 680 battery to the firewall.
The most likely electrical failure we need to manage is loss of alternator. A backup alternator mitigates this risk. It does not mitigate the less probable but more severe power failure risks. In other words having an extra alternator does not help if you have a failure that prevents power from getting to the panel. I have a standby alternator for one reason, to get me home if the primary fails.
I also suggest that you consider the planes mission. Backup batteries are fine built do they support full IFR flight for 2-3 hours? Full IFR as in EFIS, comm, XPDR, etc.
I suggest that a shift of thought from backup batteries to backup electrical power modes opens doors to more redundant designs. Two batteries provide more reduncancy than a single battery and two alternators.
Carl
Two PC-625 batteries, no “backup batteries”.
The most likely electrical failure we need to manage is loss of alternator. A backup alternator mitigates this risk. It does not mitigate the less probable but more severe power failure risks. In other words having an extra alternator does not help if you have a failure that prevents power from getting to the panel. I have a standby alternator for one reason, to get me home if the primary fails.
I also suggest that you consider the planes mission. Backup batteries are fine built do they support full IFR flight for 2-3 hours? Full IFR as in EFIS, comm, XPDR, etc.
I suggest that a shift of thought from backup batteries to backup electrical power modes opens doors to more redundant designs. Two batteries provide more reduncancy than a single battery and two alternators.
Carl
Two PC-625 batteries, no “backup batteries”.
Precisely.
Single alternator and dual batteries, if you lose the alternator you are still looking at shortening your trip and landing somewhere to get it fixed. With dual alternators, you continue mission and get it fixed at the next opportunity.
Remember our fuel requirements for IFR - primary plus a missed, distance to alternate, plus 45 minutes. If you carry that much fuel then you need to carry that much battery also - fuel in the tank doesn't do you much good in the soup with a dark panel. A second alternator eliminates that constraint.
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Back up Generator
at 2.6 lbs the Monkworkz Generator is lighter than any worthwhile backup battery, won't need replacing on a regular interval and with 30 amps its enough power to run almost everything in most experimental planes.
It kicks in automatically when the bus voltage drops below 13.7 V, plays nice with other power sources, is completely self exciting/doesn't need phantom current
More info here:
https://monkworkz.com/resourses/
at 2.6 lbs the Monkworkz Generator is lighter than any worthwhile backup battery, won't need replacing on a regular interval and with 30 amps its enough power to run almost everything in most experimental planes.
It kicks in automatically when the bus voltage drops below 13.7 V, plays nice with other power sources, is completely self exciting/doesn't need phantom current
More info here:
https://monkworkz.com/resourses/
Toobuilder
Well Known Member
I have the Monkworks unit as a backup and it works as advertised. Essentially zero effort. Also has enough grunt to power my entire ship and EFI system by itself.
larrynew
Well Known Member
I'm also using the Monkworkz backup and it's been flawless. I run it ON all the time and it kicks in automatically if the main alternator goes offline. I get an annunciation on my G3X screen when the backup is supplying power. I use about 22amps with everything on and the Monkworkz generator puts out 30amps.
For those with G3X Touch systems, I integrated it as recommended by Bill but I used Active HIGH. Active LOW did not work for me as it kept the annunciation on all the time whether the generator was on or off.
From Bill: "pins 40-43 on J244, they are called* DISCRETE IN* 1-4" connected to pin 5 on the output side of the generator. (EDIT) The new versions of the generator (20.x on your circuit board inside one of the two windows where the cooling air comes out) use pin 2. From Bill: You should be using pin 2 for annunciation, that pin only has two states: grounded or open. The Garmin should interpret that pin on a discreet input set up as " active low “.
For those with G3X Touch systems, I integrated it as recommended by Bill but I used Active HIGH. Active LOW did not work for me as it kept the annunciation on all the time whether the generator was on or off.
From Bill: "pins 40-43 on J244, they are called* DISCRETE IN* 1-4" connected to pin 5 on the output side of the generator. (EDIT) The new versions of the generator (20.x on your circuit board inside one of the two windows where the cooling air comes out) use pin 2. From Bill: You should be using pin 2 for annunciation, that pin only has two states: grounded or open. The Garmin should interpret that pin on a discreet input set up as " active low “.
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BillL
Well Known Member
Absolutely!!!
My TCW backup battery (small one) weighs the same as the Monkworkz, so I installed the generator as the backup.
My TCW backup battery (small one) weighs the same as the Monkworkz, so I installed the generator as the backup.
dmattmul
Well Known Member
I’m electrically dependent ignition and panel. When deciding between battery and backup alt it came down verifying to the health of my backup battery, what and how am I going to be certain I can count on that backup battery. I knew I was too cheap to replace a couple year old battery that was still good…..
How often are you going to load check the backup battery, and how often are you replacing that backup battery? Complacency rules when everything has been working great and then something goes wrong, will your backup battery have 30 min run time?
In almost 10 years of flying my main alt has failed once a long way from home, my SD8 got me back to Kansas from the East Coast. My Backup alt has also failed but my main alt was working fine. Both times I had an alternator keeping things charged and a battery as a 3rd backup. If both Alternators quit I have my battery to rely on which I view as an emergency situation, hard to verify capacity in the moment………..
-How new and what condition is the battery in?
-Real life load check on battery at beginning of life and end of life?
How often are you going to load check the backup battery, and how often are you replacing that backup battery? Complacency rules when everything has been working great and then something goes wrong, will your backup battery have 30 min run time?
In almost 10 years of flying my main alt has failed once a long way from home, my SD8 got me back to Kansas from the East Coast. My Backup alt has also failed but my main alt was working fine. Both times I had an alternator keeping things charged and a battery as a 3rd backup. If both Alternators quit I have my battery to rely on which I view as an emergency situation, hard to verify capacity in the moment………..
-How new and what condition is the battery in?
-Real life load check on battery at beginning of life and end of life?
I flew a Challenger and it has this really cool sling out ram air generator, some of you must fly a Boing or Airbus, dont they have a RAT? That would be kind of cool and easy I think. Seeing all these gear driven alternate alternators and all I can picture is my friends gear driven generator breaking apart in his engine and destroying it. I like belt drive after hearing him tell me that story..
Also I am curious about this electronic ignition do those take a lot of power or are they something that doesn't take very many amps?
Also I am curious about this electronic ignition do those take a lot of power or are they something that doesn't take very many amps?
MacCool
Well Known Member
Can't speak to other EI systems, but Pmags generate their own power and are self-sustaining if the engine is running above about 900 RPM.
FireMedic_2009
Well Known Member
I totally agree. How often will you actually do a load test on your batteries? It’s kind of a pain. How easy is it to check your backup alternator? Pretty easy and you can do it every flt as a test. And as mentioned, he had his main alternator fail and was able to fly back home. Can’t do that with a 2nd battery. If your main alt is a 3-wire it’s easy to keep the main alt off during start to check the the backup Alt. If a 1-wire Alt, then you’ll need to use an alt contactor to disconnect the B-lead which you should have incase you have a runaway voltage even though a rare event
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Nuckolls Z-101 - Dual Alternator, Single Battery
For many of the reasons already mentioned in this thread (no need to maintain/test 2nd battery, alternator produces electrons for EI & EFIS boxes as long as there's fuel, etc.), Bob Nuckolls came up with the Z-101 architecture ~3-4 years ago.
https://vansairforce.net/community/showpost.php?p=1423014&postcount=29
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z101B.pdf
I retrofitted this into my RV-7A and would absolutely do this for again any electrically-dependent EAB. The only backup battery in my plane is the one on the G5 backup flight display. Since the backup alternator removes the need for the TCW backup battery many people use, I replaced it with the TCW Intelligent Power Stabilizer to handle any voltage sag during cranking.
For many of the reasons already mentioned in this thread (no need to maintain/test 2nd battery, alternator produces electrons for EI & EFIS boxes as long as there's fuel, etc.), Bob Nuckolls came up with the Z-101 architecture ~3-4 years ago.
https://vansairforce.net/community/showpost.php?p=1423014&postcount=29
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z101B.pdf
I retrofitted this into my RV-7A and would absolutely do this for again any electrically-dependent EAB. The only backup battery in my plane is the one on the G5 backup flight display. Since the backup alternator removes the need for the TCW backup battery many people use, I replaced it with the TCW Intelligent Power Stabilizer to handle any voltage sag during cranking.
Toobuilder
Well Known Member
My L-39 also had a RAT for standby electrical power - the complexity involved is inappropriate for something as small and light as an RV.
Curious about your buddy's gear driven generator "breaking apart in his engine" when most units are driven off the spline driven vacuum pump pad and are completely external to the engine. A generator mounted on the vacuum pump pad could theoretically grind itself into dust without affecting the core engine.
In general, EI's are extremely low draw devices. I have measured a SDS CPI unit at 1.69 amps (6 cylinder, 2700 RPM). Does not take much of a battery to extend ignition supply past fuel supply.
rocketman1988
Well Known Member
Unless you are running electronic fuel injection, too. Then you better plan aroun 10 amps…
Toobuilder
Well Known Member
I must have missed the part in Ruready's post where he was discussing EFI, but to be clear, its not the EFI system, but the electric pumps that pull the power. Run a mechanical pump and even EFI becomes an electrical non - issue from a power consumption standpoint.
It was an old c210 with a Continental maybe a 470? cant rember, maybe it was a starter not a generator, I have always had lycomings and never heard of starters and gens or alts that were gear driven, it was either a gen or starter and was gear driven on the back of the engine and it broke up and ingested into the engine and destroyed it.
So not a fan of anything gear driven after hearing that.. but maybe I dont need to be after you saying certain gd items cant get into the engine like that.
Was curious about what you actually need to make it back home without an alternater after reading alot of posts here say it cant be done with a back up battery, thats why I asked about loads of the EI, my EFIS takes .5 amps and any AGM battery at an auto parts store is at least 15 to 30 amp/hour.. that could run my EFIS for a lot longer than a trip home from the islands. Hand prop and get home. Nothing wrong with standby alts, just saying if I was stuck without one I would not be stranded, get a battery from autozone for a hundred bucks, wire it in and get on your way, stop every hour and get a new battery if you need more than 10amps to keep you going. Dont be stuck. Heck, put a fluke on the new batteries to make sure they have a full charge, buy 3 of them wire them together and you should be over 60amp/hour. that shoud be over 5 hours flying on min power
So not a fan of anything gear driven after hearing that.. but maybe I dont need to be after you saying certain gd items cant get into the engine like that.
Was curious about what you actually need to make it back home without an alternater after reading alot of posts here say it cant be done with a back up battery, thats why I asked about loads of the EI, my EFIS takes .5 amps and any AGM battery at an auto parts store is at least 15 to 30 amp/hour.. that could run my EFIS for a lot longer than a trip home from the islands. Hand prop and get home. Nothing wrong with standby alts, just saying if I was stuck without one I would not be stranded, get a battery from autozone for a hundred bucks, wire it in and get on your way, stop every hour and get a new battery if you need more than 10amps to keep you going. Dont be stuck. Heck, put a fluke on the new batteries to make sure they have a full charge, buy 3 of them wire them together and you should be over 60amp/hour. that shoud be over 5 hours flying on min power
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Toobuilder
Well Known Member
Its not that a back up battery "can't" get you back home, rather, its the fact that a battery is finite resource and a alternator/generator is not (well, its dependant on fuel supply). There are a wide range of equipment configurations and mission requirements out there - some airplanes use no electrical at all (like my Taylorcraft), and some are power hungry with full EFI/EI and glass in the panel (like my Rocket). Even if I shed all nonessential items in flight, my Rocket still requires a hefty battery solution if I want to match my fuel supply - in this case, the second generator more than pays its weight onto the airplane. Other airplanes - not so much.
Carl Froehlich
Well Known Member
For those flying IFR and/or with electrically dependent engine and settle on single battery with dual alternators I recommend you carefully verify your backup power modes work as you think they will. The simple (but not definitive) test is hop in the plane, set up cruise and then turn off your master switch. What happens? If you end up sitting on backup batteries how much flying time do you have with a full IFR panel?
I have never found any single battery setup that does not have (practicable) single point failure risks.
Carl
I have never found any single battery setup that does not have (practicable) single point failure risks.
Carl
