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kenryan
Joined: 20 Oct 2009
Posts: 426
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 Posted: Sat Jun 06, 2020 5:54 am Post subject: Physical construction of Z101 engine bus & battery bus |
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Could someone please re-post the link to Z101? Thanks.
On Sat, Jun 6, 2020 at 4:43 AM David Carter <david(at)carter.net (david(at)carter.net)> wrote:
| Quote: | Bob,Â
I see that both of these busses are specified with 6" max feeds from their sources (main contactor and diode bridge). What is the recommended physical realization of these bus designs? Fuse blocks on the engine side of the firewall? Inline fuses? Are the loads intended to be fused, breakered, or a mix? Similarly, what is the suggested construction of the "fat wire tie point?"
In my case, I believe everything on the engine bus will be on the cabin side of the firewall - an AFP fuel pump & two SDS CPI-2 ignition control units. I could perhaps put a pair of 6" 12 AWG wires through the firewall at the contactor & mount a fuse block on the cabin side at that point.Â
The battery bus may be only a single connection to the aux alternator, or I may find that I need a clock feed. If it's just a single feed, the bus construction doesn't get any simpler. BTW, I just noticed there are two feeds on the battery bus labeled "aux alt".Â
Also, I note that the alt feed from the relay to the engine bus is not asterisked as a short run. I think practically it will be, but I wonder if there is a reason it's not asterisked?Â
Thanks!
---
David Carter
david(at)carter.net (david(at)carter.net)
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bcone1381
Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan
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| Posted: Sat Jun 06, 2020 6:21 am Post subject: Re: Physical construction of Z101 engine bus & battery |
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https://tinyurl.com/yavoutjh
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ceengland7(at)gmail.com
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| Posted: Sat Jun 06, 2020 7:34 am Post subject: Physical construction of Z101 engine bus & battery bus |
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On 6/6/2020 7:36 AM, David Carter wrote:
| Quote: | Bob,Â
I see that both of these busses are specified with 6" max feeds from their sources (main contactor and diode bridge). What is the recommended physical realization of these bus designs? Fuse blocks on the engine side of the firewall? Inline fuses? Are the loads intended to be fused, breakered, or a mix? Similarly, what is the suggested construction of the "fat wire tie point?"
In my case, I believe everything on the engine bus will be on the cabin side of the firewall - an AFP fuel pump & two SDS CPI-2 ignition control units. I could perhaps put a pair of 6" 12 AWG wires through the firewall at the contactor & mount a fuse block on the cabin side at that point.Â
The battery bus may be only a single connection to the aux alternator, or I may find that I need a clock feed. If it's just a single feed, the bus construction doesn't get any simpler. BTW, I just noticed there are two feeds on the battery bus labeled "aux alt".Â
Also, I note that the alt feed from the relay to the engine bus is not asterisked as a short run. I think practically it will be, but I wonder if there is a reason it's not asterisked?Â
Thanks!
---
David Carter
david(at)carter.net (david(at)carter.net)
|
I think that the two feeds to the bat bus are actually the alt output, and the feed (control) to the alt's regulator. Look at the connections to the regulator, at the bottom of the drawing.
I think that the feed from the alt feed relay to the engine bus is 'protected' by the relay.
Charlie
 Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Sun Jun 07, 2020 8:37 am Post subject: Physical construction of Z101 engine bus & battery bus |
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Bob, regarding Z101, it seems that auto conversions like the Honda based Viking and Suzuki based Aeromomentum are becoming more and more popular. These engines are electrically dependent, but they do not lend themselves to a dual alternator setup. I wonder if you would consider developing a Z101-B that utilized dual batteries rather than dual alternators?
Ken
On Sat, Jun 6, 2020 at 7:00 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 08:50 AM 6/6/2020, you wrote:
| Quote: | | Could someone please re-post the link to Z101? Thanks. |
 https://tinyurl.com/yc4r5huy
 Latest iteration on the next revision level.
 I've been sifting through the details and
 I think it's 99% 'clean'.
 I'm also working on a set of notes that
 elaborates on the evolution of concepts
 illustrated.
 I'm kinda 'distracted' with a bathroom
 remodel at the moment but you guys can
 massage this thread . . .
 Bob . . .
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david(at)carter.net
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| Posted: Sun Jun 07, 2020 8:46 am Post subject: Physical construction of Z101 engine bus & battery bus |
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Thanks for the replies. I was not aware of the 9" minimum length on fusible links. Is that somewhere in the Connection? Are crimped butt connectors adequate for connecting the fusible link to the protected wire?Â
I recently received some of this fusible link wire in both 12 & 14 gauge. Anyone have experience with it?Â
Pico 8124PT 12 Gauge Fusible Link... https://www.amazon.com/dp/B0002ZGBRE?ref=ppx_pop_mob_ap_share
PICO 8125PT 14 AWG Fusible Link Wire https://www.amazon.com/dp/B004BT6NZ2?ref=ppx_pop_mob_ap_share
Regards,Â
DavidÂ
On Sun, Jun 7, 2020 at 10:50 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 07:59 PM 6/6/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
Since bob gave permission to others to answer, here are my suggestions: |
 you never need my permission . . . this is a moderated
 forum for open discussion.
| Quote: | Mount both relays as close as practical to the battery.
Doing that meets the 6" wire length rule of thumb. |
 The 6-inch rule is a holdover from waaayyy back when
 where the FAA deemed it acceptable to 'burn a piece
 of wire that is 6-inches or less in length'. I.e.
 no fault protection required.
 One can only guess details of reasoning behind this bit
 of 1960's wisdom.
 Today we can strive to keep potentially vulnerable
 (smaller gages) of 'unprotected' wires to a minimum.
 Control installation such that probability for
 hard faults to ground are exceedingly rare.
 Use of fusible link wire where practical (here
 there is a 9-inch rule of thumb for MINIMUM
 length).
 If the wire has to go through a firewall,
 provide mechanical protection over and
 above normally fused branch wires (two
 layers of heat shrink?)
| Quote: | Since you want the engine bus located on the cabin side of the firewall, also
move the diode bridge to aft of the firewall between the main power bus and the engine bus.
Move the diode feed from the main battery contactor to main power bus. Electrically it will be the
same, just connected to the other end of the 6AWG feeder.
Since there are only 2 items connected to the battery bus, consider eliminating the battery bus.
Connect both items to the battery post using inline fuses.
Use all fuses except for the alternator feed 5 amp breaker.
Fuses cost less, weigh less, and never fail to blow when required.
Never replace fuses or reset breakers in flight, except perhaps the alternator field.
|
 Sounds like a plan . . .
 Bob . . .
|
--
---
David Carter
david(at)carter.net (david(at)carter.net)
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Sun Jun 07, 2020 2:31 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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I am not speaking to any engine manufacturers recommendation (although the Honda Viking manufacturer does recommend two batteries. I just thought I was applying logic -- if dual alternator + battery (triple power source) is desirable for electrically dependent engines, wouldn't that reasoning imply that if the second alternator is not practical, a second battery could be used as the third power source? I could ask you a similar question: Are not two independent power sources (battery and alternator) sufficient to meet the needs of the electrically dependent engine. Obviously you saw value in adding the second alternator. Why no value in adding the second battery?
On Sun, Jun 7, 2020 at 12:32 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 11:32 AM 6/7/2020, you wrote:
| Quote: | | Bob, regarding Z101, it seems that auto conversions like the Honda based Viking and Suzuki based Aeromomentum are becoming more and more popular. These engines are electrically dependent, but they do not lend themselves to a dual alternator setup. I wonder if you would consider developing a Z101-B that utilized dual batteries rather than dual alternators? |
 Is it not possible/practical to maintain one battery
 such that it is capable of supporting the engine
 in an alternator-out scenario?
 How are the duties of two batteries allocated in what
 I presume is a engine manufacturer's recommendation
 for dual batteries?
 Bob . . .
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foghorn757(at)gmail.com
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| Posted: Sun Jun 07, 2020 6:23 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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SDSEFI recommends 2 alternators and a battery. If you have a single battery and alternator they recommend an additional battery that is only connected to the ENG BUS for an emergency. The recommended procedure is to charge that battery on the 1st of the month and load test yearly.
I’m going with 2 alternators and an ETX-900 battery for my dual SDSEFI setup.
Jeff Parker757-817-4929
| Quote: | On Jun 7, 2020, at 18:37, Ken Ryan <keninalaska(at)gmail.com> wrote:
I am not speaking to any engine manufacturers recommendation (although the Honda Viking manufacturer does recommend two batteries. I just thought I was applying logic -- if dual alternator + battery (triple power source) is desirable for electrically dependent engines, wouldn't that reasoning imply that if the second alternator is not practical, a second battery could be used as the third power source? I could ask you a similar question: Are not two independent power sources (battery and alternator) sufficient to meet the needs of the electrically dependent engine. Obviously you saw value in adding the second alternator. Why no value in adding the second battery?
On Sun, Jun 7, 2020 at 12:32 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 11:32 AM 6/7/2020, you wrote:
| Quote: | | Bob, regarding Z101, it seems that auto conversions like the Honda based Viking and Suzuki based Aeromomentum are becoming more and more popular. These engines are electrically dependent, but they do not lend themselves to a dual alternator setup. I wonder if you would consider developing a Z101-B that utilized dual batteries rather than dual alternators? |
Is it not possible/practical to maintain one battery
such that it is capable of supporting the engine
in an alternator-out scenario?
How are the duties of two batteries allocated in what
I presume is a engine manufacturer's recommendation
for dual batteries?
Bob . . .
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Mon Jun 08, 2020 8:08 am Post subject: Physical construction of Z101 engine bus & battery bus |
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Bob, you said:
"If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability."
Help me understand why the following statement is not correct:
If you have TWO properly maintained alternators,
plus a battery (sized for minimum endurance requirements)
in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
Ken
On Sun, Jun 7, 2020 at 6:56 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 05:26 PM 6/7/2020, you wrote:
| Quote: | I am not speaking to any engine manufacturers recommendation (although the
Honda Viking manufacturer does recommend two batteries. I just thought
I was applying logic -- if dual alternator + battery (triple power source)
is desirable for electrically dependent engines, wouldn't that reasoning
imply that if the second alternator is not practical, a second battery
could be used as the third power source? I could ask you a similar question:
Are not two independent power sources (battery and alternator) sufficient
to meet the needs of the electrically dependent engine. Obviously you
saw value in adding the second alternator. Why no value in adding the second battery? |
 Excellent question.
 It's a problem in energy budgets combined with
 efforts to assure continued airworthiness.
 The airplane cannot do without a battery if
 you're going to have a starter. Depending on
 your planned mission profiles, you will want
 to size the battery (1) for cranking then
 (2) minimum endurance in alternator-out modes.
 This study gave impetus for the creation of
 the endurance bus . . . a fast and predictable
 way to economically tap known quantity of energy
 stored in the battery's chemistry.
 Z13/8 was a small but significant amplification
 of that idea . . . <b>the second alternator's endurance
 had no practical limits.</b> Hence, energy on the chemistry
 just might be held completely in reserve for
 descent and approach to landing.
 Z13/20 (and the aux alternator option on
 Z101) expanded the Z13/8 endurance opportunity
 by a factor of 2.5 or better.
 Okay, suppose the drive pad isn't available.
 We are still charged with identifying and the
 delivering to energy required to comfortably
 terminate a worst-case mission.
 This means that as a part of routine maintenance
 the ship's chemistry needs to be monitored for
 capability. We could certainly store that energy
 on TWO devices but to what advantage? If we're laboring
 under the notion that a battery can suddenly become
 unavailable during one tank of gas, then we have
 to assume that EITHER battery can roll over and
 die . . . okay, how would that failure be
 annunciated . . . how would remaining energy be
 managed . . . ?
 I think that's the scenario anticipated by the
 folks that crafted that battery manager with a
 full-wave rectifier that -anded- two, completely
 isolated batteries together. Assume the alternator
 has quit and some time later one battery
 craps out. How does the pilot become aware of the
 problem and what kind of energy juggling issues
 are presented when the available energy drops
 to half? This assuming he really knows that the
 two batteries were performing equally and has
 recently quantified their condition, he now
 has to come up with a new "plan C?" and perhaps
 declare an emergency.
 This scenario first assumes TWO critical failures
 during the consumption of one tank of fuel . . .
 about 3-4 hour window. Part 23 certs don't
 get concerned with dual failures at all.
 Part 25 and heavier will wade into the reliability
 quagmire with mountains of computer generated probability
 studies that get 'worked' on until somebody
 finally sprinkles the holy water and off they
 go.
 Ask Capt. Sullivan what he thinks about
 reliability studies . . .
https://www.youtube.com/watch?v=HKJ1lIh2Cgk
 So we're left to our own devices which in reality
 are not so bad.
 The short answer is: A diligently maintained
 battery is the most reliable source of energy
 on the airplane. Replacing it when ability
 to store energy drops below some benchmark
 (generally 75 to 80% of new) means that it
 always cranks the engine and will provide a
 quantified option for dealing with alternator
 failure. Two batteries just doubles your
 preventative maintenance labor. Further,
 you need to decide if plan-b can reliably
 depend on the sum total of energy in two
 batteries . . . or will they be sized to
 independently step up to the task? The
 second option calls for 2X the battery
 weight and volume; the first option complicates
 calculations and switching operations for
 carrying out a plan-b that shouldn't ever
 happen. BOTH options still demand good
 preventative maintenance.
 Just as you KNOW fuel aboard when you launch,
 you also need to know Watt-Hours aboard
 no matter how many batteries you're carrying.
 If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
 Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Mon Jun 08, 2020 9:52 am Post subject: Re: Physical construction of Z101 engine bus & battery |
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The amount of redundancy desired all depends.
Will the aircraft be flying long distances over hostile terrain or water?
Will the aircraft be flying IFR or at night?
Is the engine dependent on electrical power?
Is the pilot willing to carry extra weight to avoid repairs on long cross countries?
The important thing is to design an electrical system that does not have
unexpected failure modes and that is resistant to pilot error.
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ceengland7(at)gmail.com
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| Posted: Mon Jun 08, 2020 2:42 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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Hi Ken,
I'll take a swing at it, but would suggest that it's not quite the right question.
I get your point, but the answer 'depends'. If using electronic fuel injection, the current demands mean that a single PC680 style battery (in 'new' condition) will only buy you about 30-40 minutes of flight time after alternator failure. A 2nd PC680 only adds another 30-40 minutes. On an engine that allows two alts, either of which can keep the engine running and the panel lit, a typical alt (ex: 55A Denso) is lighter than a 2nd battery, not much more expensive (actually much cheaper than an actual Odyssey branded PC680), will keep the engine running to fuel exhaustion, and has the additional benefit of allowing a return flight (in some range-dependent situations) without the need of maintenance while on the road. Not something I would ever consider after an alt failure with only a 2nd bat for backup. Add to the mix, the fact that while a 2nd alt is pretty much an install&forget item (just a startup check each flight similar to a mag check), any battery is a constantly degrading item that requires regular capacity testing to ensure that it has enough remaining capacity to give expected duration if called upon.
Now, with carb or mech fuel injection in a VFR environment, current demands might (likely will) be low enough that a single bat & single alt back up each other. In *my* opinion, that's where Bob's statement makes sense, and where your question, as framed, doesn't need asking.
So, I think you really have to define both the mission *and the hardware* to pick an architecture.
FWIW,
Charlie
On Mon, Jun 8, 2020 at 11:15 AM Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
| Quote: | Bob, you said:
"If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability."
Help me understand why the following statement is not correct:
If you have TWO properly maintained alternators,
plus a battery (sized for minimum endurance requirements)
in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
Ken
On Sun, Jun 7, 2020 at 6:56 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 05:26 PM 6/7/2020, you wrote:
| Quote: | I am not speaking to any engine manufacturers recommendation (although the
Honda Viking manufacturer does recommend two batteries. I just thought
I was applying logic -- if dual alternator + battery (triple power source)
is desirable for electrically dependent engines, wouldn't that reasoning
imply that if the second alternator is not practical, a second battery
could be used as the third power source? I could ask you a similar question:
Are not two independent power sources (battery and alternator) sufficient
to meet the needs of the electrically dependent engine. Obviously you
saw value in adding the second alternator. Why no value in adding the second battery? |
 Excellent question.
 It's a problem in energy budgets combined with
 efforts to assure continued airworthiness.
 The airplane cannot do without a battery if
 you're going to have a starter. Depending on
 your planned mission profiles, you will want
 to size the battery (1) for cranking then
 (2) minimum endurance in alternator-out modes.
 This study gave impetus for the creation of
 the endurance bus . . . a fast and predictable
 way to economically tap known quantity of energy
 stored in the battery's chemistry.
 Z13/8 was a small but significant amplification
 of that idea . . . <b>the second alternator's endurance
 had no practical limits.</b> Hence, energy on the chemistry
 just might be held completely in reserve for
 descent and approach to landing.
 Z13/20 (and the aux alternator option on
 Z101) expanded the Z13/8 endurance opportunity
 by a factor of 2.5 or better.
 Okay, suppose the drive pad isn't available.
 We are still charged with identifying and the
 delivering to energy required to comfortably
 terminate a worst-case mission.
 This means that as a part of routine maintenance
 the ship's chemistry needs to be monitored for
 capability. We could certainly store that energy
 on TWO devices but to what advantage? If we're laboring
 under the notion that a battery can suddenly become
 unavailable during one tank of gas, then we have
 to assume that EITHER battery can roll over and
 die . . . okay, how would that failure be
 annunciated . . . how would remaining energy be
 managed . . . ?
 I think that's the scenario anticipated by the
 folks that crafted that battery manager with a
 full-wave rectifier that -anded- two, completely
 isolated batteries together. Assume the alternator
 has quit and some time later one battery
 craps out. How does the pilot become aware of the
 problem and what kind of energy juggling issues
 are presented when the available energy drops
 to half? This assuming he really knows that the
 two batteries were performing equally and has
 recently quantified their condition, he now
 has to come up with a new "plan C?" and perhaps
 declare an emergency.
 This scenario first assumes TWO critical failures
 during the consumption of one tank of fuel . . .
 about 3-4 hour window. Part 23 certs don't
 get concerned with dual failures at all.
 Part 25 and heavier will wade into the reliability
 quagmire with mountains of computer generated probability
 studies that get 'worked' on until somebody
 finally sprinkles the holy water and off they
 go.
 Ask Capt. Sullivan what he thinks about
 reliability studies . . .
https://www.youtube.com/watch?v=HKJ1lIh2Cgk
 So we're left to our own devices which in reality
 are not so bad.
 The short answer is: A diligently maintained
 battery is the most reliable source of energy
 on the airplane. Replacing it when ability
 to store energy drops below some benchmark
 (generally 75 to 80% of new) means that it
 always cranks the engine and will provide a
 quantified option for dealing with alternator
 failure. Two batteries just doubles your
 preventative maintenance labor. Further,
 you need to decide if plan-b can reliably
 depend on the sum total of energy in two
 batteries . . . or will they be sized to
 independently step up to the task? The
 second option calls for 2X the battery
 weight and volume; the first option complicates
 calculations and switching operations for
 carrying out a plan-b that shouldn't ever
 happen. BOTH options still demand good
 preventative maintenance.
 Just as you KNOW fuel aboard when you launch,
 you also need to know Watt-Hours aboard
 no matter how many batteries you're carrying.
 If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
 Bob . . .
|
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cluros(at)gmail.com
Guest
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| Posted: Mon Jun 08, 2020 3:09 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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Or I'll tackle it a different way:
What are the sudden failure rates of batteries and alternators. I've lost a couple alternators in flight, I've never heard of a good battery failing in flight.
On Mon, Jun 8, 2020, 15:49 Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:
| Quote: | Hi Ken,
I'll take a swing at it, but would suggest that it's not quite the right question.
I get your point, but the answer 'depends'. If using electronic fuel injection, the current demands mean that a single PC680 style battery (in 'new' condition) will only buy you about 30-40 minutes of flight time after alternator failure. A 2nd PC680 only adds another 30-40 minutes. On an engine that allows two alts, either of which can keep the engine running and the panel lit, a typical alt (ex: 55A Denso) is lighter than a 2nd battery, not much more expensive (actually much cheaper than an actual Odyssey branded PC680), will keep the engine running to fuel exhaustion, and has the additional benefit of allowing a return flight (in some range-dependent situations) without the need of maintenance while on the road. Not something I would ever consider after an alt failure with only a 2nd bat for backup. Add to the mix, the fact that while a 2nd alt is pretty much an install&forget item (just a startup check each flight similar to a mag check), any battery is a constantly degrading item that requires regular capacity testing to ensure that it has enough remaining capacity to give expected duration if called upon.
Now, with carb or mech fuel injection in a VFR environment, current demands might (likely will) be low enough that a single bat & single alt back up each other. In *my* opinion, that's where Bob's statement makes sense, and where your question, as framed, doesn't need asking.
So, I think you really have to define both the mission *and the hardware* to pick an architecture.
FWIW,
Charlie
On Mon, Jun 8, 2020 at 11:15 AM Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
| Quote: | Bob, you said:
"If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability."
Help me understand why the following statement is not correct:
If you have TWO properly maintained alternators,
plus a battery (sized for minimum endurance requirements)
in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
Ken
On Sun, Jun 7, 2020 at 6:56 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 05:26 PM 6/7/2020, you wrote:
| Quote: | I am not speaking to any engine manufacturers recommendation (although the
Honda Viking manufacturer does recommend two batteries. I just thought
I was applying logic -- if dual alternator + battery (triple power source)
is desirable for electrically dependent engines, wouldn't that reasoning
imply that if the second alternator is not practical, a second battery
could be used as the third power source? I could ask you a similar question:
Are not two independent power sources (battery and alternator) sufficient
to meet the needs of the electrically dependent engine. Obviously you
saw value in adding the second alternator. Why no value in adding the second battery? |
 Excellent question.
 It's a problem in energy budgets combined with
 efforts to assure continued airworthiness.
 The airplane cannot do without a battery if
 you're going to have a starter. Depending on
 your planned mission profiles, you will want
 to size the battery (1) for cranking then
 (2) minimum endurance in alternator-out modes.
 This study gave impetus for the creation of
 the endurance bus . . . a fast and predictable
 way to economically tap known quantity of energy
 stored in the battery's chemistry.
 Z13/8 was a small but significant amplification
 of that idea . . . <b>the second alternator's endurance
 had no practical limits.</b> Hence, energy on the chemistry
 just might be held completely in reserve for
 descent and approach to landing.
 Z13/20 (and the aux alternator option on
 Z101) expanded the Z13/8 endurance opportunity
 by a factor of 2.5 or better.
 Okay, suppose the drive pad isn't available.
 We are still charged with identifying and the
 delivering to energy required to comfortably
 terminate a worst-case mission.
 This means that as a part of routine maintenance
 the ship's chemistry needs to be monitored for
 capability. We could certainly store that energy
 on TWO devices but to what advantage? If we're laboring
 under the notion that a battery can suddenly become
 unavailable during one tank of gas, then we have
 to assume that EITHER battery can roll over and
 die . . . okay, how would that failure be
 annunciated . . . how would remaining energy be
 managed . . . ?
 I think that's the scenario anticipated by the
 folks that crafted that battery manager with a
 full-wave rectifier that -anded- two, completely
 isolated batteries together. Assume the alternator
 has quit and some time later one battery
 craps out. How does the pilot become aware of the
 problem and what kind of energy juggling issues
 are presented when the available energy drops
 to half? This assuming he really knows that the
 two batteries were performing equally and has
 recently quantified their condition, he now
 has to come up with a new "plan C?" and perhaps
 declare an emergency.
 This scenario first assumes TWO critical failures
 during the consumption of one tank of fuel . . .
 about 3-4 hour window. Part 23 certs don't
 get concerned with dual failures at all.
 Part 25 and heavier will wade into the reliability
 quagmire with mountains of computer generated probability
 studies that get 'worked' on until somebody
 finally sprinkles the holy water and off they
 go.
 Ask Capt. Sullivan what he thinks about
 reliability studies . . .
https://www.youtube.com/watch?v=HKJ1lIh2Cgk
 So we're left to our own devices which in reality
 are not so bad.
 The short answer is: A diligently maintained
 battery is the most reliable source of energy
 on the airplane. Replacing it when ability
 to store energy drops below some benchmark
 (generally 75 to 80% of new) means that it
 always cranks the engine and will provide a
 quantified option for dealing with alternator
 failure. Two batteries just doubles your
 preventative maintenance labor. Further,
 you need to decide if plan-b can reliably
 depend on the sum total of energy in two
 batteries . . . or will they be sized to
 independently step up to the task? The
 second option calls for 2X the battery
 weight and volume; the first option complicates
 calculations and switching operations for
 carrying out a plan-b that shouldn't ever
 happen. BOTH options still demand good
 preventative maintenance.
 Just as you KNOW fuel aboard when you launch,
 you also need to know Watt-Hours aboard
 no matter how many batteries you're carrying.
 If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
 Bob . . .
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Mon Jun 08, 2020 3:22 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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Thanks Charlie,
I am convinced that 2 alternators + 1 battery is superior to 1 alternator + 2 batteries. I am less convinced that if two alternators are not possible, a second battery adds virtually no value to the ship's overall reliability. Bob did make a pretty good argument, but it is founded on the assumption that the battery, when properly maintained, is utterly reliable. I have two problems with that assumption: 1) we know from Joe's experience that batteries can fail and 2) even with the best of intentions, maintenance (including battery maintenance) is not always perfect. To contend that having a fresh battery available at the flip of a switch adds no reliability to an electrically dependent aircraft still seems like a bit of a stretch to me.
Ken
On Mon, Jun 8, 2020 at 2:49 PM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:
| Quote: | Hi Ken,
I'll take a swing at it, but would suggest that it's not quite the right question.
I get your point, but the answer 'depends'. If using electronic fuel injection, the current demands mean that a single PC680 style battery (in 'new' condition) will only buy you about 30-40 minutes of flight time after alternator failure. A 2nd PC680 only adds another 30-40 minutes. On an engine that allows two alts, either of which can keep the engine running and the panel lit, a typical alt (ex: 55A Denso) is lighter than a 2nd battery, not much more expensive (actually much cheaper than an actual Odyssey branded PC680), will keep the engine running to fuel exhaustion, and has the additional benefit of allowing a return flight (in some range-dependent situations) without the need of maintenance while on the road. Not something I would ever consider after an alt failure with only a 2nd bat for backup. Add to the mix, the fact that while a 2nd alt is pretty much an install&forget item (just a startup check each flight similar to a mag check), any battery is a constantly degrading item that requires regular capacity testing to ensure that it has enough remaining capacity to give expected duration if called upon.
Now, with carb or mech fuel injection in a VFR environment, current demands might (likely will) be low enough that a single bat & single alt back up each other. In *my* opinion, that's where Bob's statement makes sense, and where your question, as framed, doesn't need asking.
So, I think you really have to define both the mission *and the hardware* to pick an architecture.
FWIW,
Charlie
On Mon, Jun 8, 2020 at 11:15 AM Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
| Quote: | Bob, you said:
"If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability."
Help me understand why the following statement is not correct:
If you have TWO properly maintained alternators,
plus a battery (sized for minimum endurance requirements)
in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
Ken
On Sun, Jun 7, 2020 at 6:56 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 05:26 PM 6/7/2020, you wrote:
| Quote: | I am not speaking to any engine manufacturers recommendation (although the
Honda Viking manufacturer does recommend two batteries. I just thought
I was applying logic -- if dual alternator + battery (triple power source)
is desirable for electrically dependent engines, wouldn't that reasoning
imply that if the second alternator is not practical, a second battery
could be used as the third power source? I could ask you a similar question:
Are not two independent power sources (battery and alternator) sufficient
to meet the needs of the electrically dependent engine. Obviously you
saw value in adding the second alternator. Why no value in adding the second battery? |
 Excellent question.
 It's a problem in energy budgets combined with
 efforts to assure continued airworthiness.
 The airplane cannot do without a battery if
 you're going to have a starter. Depending on
 your planned mission profiles, you will want
 to size the battery (1) for cranking then
 (2) minimum endurance in alternator-out modes.
 This study gave impetus for the creation of
 the endurance bus . . . a fast and predictable
 way to economically tap known quantity of energy
 stored in the battery's chemistry.
 Z13/8 was a small but significant amplification
 of that idea . . . <b>the second alternator's endurance
 had no practical limits.</b> Hence, energy on the chemistry
 just might be held completely in reserve for
 descent and approach to landing.
 Z13/20 (and the aux alternator option on
 Z101) expanded the Z13/8 endurance opportunity
 by a factor of 2.5 or better.
 Okay, suppose the drive pad isn't available.
 We are still charged with identifying and the
 delivering to energy required to comfortably
 terminate a worst-case mission.
 This means that as a part of routine maintenance
 the ship's chemistry needs to be monitored for
 capability. We could certainly store that energy
 on TWO devices but to what advantage? If we're laboring
 under the notion that a battery can suddenly become
 unavailable during one tank of gas, then we have
 to assume that EITHER battery can roll over and
 die . . . okay, how would that failure be
 annunciated . . . how would remaining energy be
 managed . . . ?
 I think that's the scenario anticipated by the
 folks that crafted that battery manager with a
 full-wave rectifier that -anded- two, completely
 isolated batteries together. Assume the alternator
 has quit and some time later one battery
 craps out. How does the pilot become aware of the
 problem and what kind of energy juggling issues
 are presented when the available energy drops
 to half? This assuming he really knows that the
 two batteries were performing equally and has
 recently quantified their condition, he now
 has to come up with a new "plan C?" and perhaps
 declare an emergency.
 This scenario first assumes TWO critical failures
 during the consumption of one tank of fuel . . .
 about 3-4 hour window. Part 23 certs don't
 get concerned with dual failures at all.
 Part 25 and heavier will wade into the reliability
 quagmire with mountains of computer generated probability
 studies that get 'worked' on until somebody
 finally sprinkles the holy water and off they
 go.
 Ask Capt. Sullivan what he thinks about
 reliability studies . . .
https://www.youtube.com/watch?v=HKJ1lIh2Cgk
 So we're left to our own devices which in reality
 are not so bad.
 The short answer is: A diligently maintained
 battery is the most reliable source of energy
 on the airplane. Replacing it when ability
 to store energy drops below some benchmark
 (generally 75 to 80% of new) means that it
 always cranks the engine and will provide a
 quantified option for dealing with alternator
 failure. Two batteries just doubles your
 preventative maintenance labor. Further,
 you need to decide if plan-b can reliably
 depend on the sum total of energy in two
 batteries . . . or will they be sized to
 independently step up to the task? The
 second option calls for 2X the battery
 weight and volume; the first option complicates
 calculations and switching operations for
 carrying out a plan-b that shouldn't ever
 happen. BOTH options still demand good
 preventative maintenance.
 Just as you KNOW fuel aboard when you launch,
 you also need to know Watt-Hours aboard
 no matter how many batteries you're carrying.
 If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
 Bob . . .
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ceengland7(at)gmail.com
Guest
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| Posted: Mon Jun 08, 2020 3:56 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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For me, it's not so much that a 'good battery will *fail* in flight', but that the battery's capacity is continuously degrading, whether it's used or not, and that introduces a 2nd variable in the backup plan. It's not obvious, but a tired battery may well start an engine with gusto, but if called on to supply a continuous 14A (just to the engine), it might go dead in 10-15 minutes. My personal comfort zone bends toward an alternator, if I'm going to install a backup. Again, this is driven by the relatively high current demand of the electronic injection system in my project a/c.
If I only had to support an electronic ignition (1-2 amps) and a radio, I'd be a lot more comfortable depending on the battery as backup. In fact, my current RV6 with mechanical injection and one Lightspeed has one alternator & one battery. I'm a VFR pilot and not dependent on electron delivery to keep the engine running or keep the dirty side down.
Charlie
On 6/8/2020 6:05 PM, Sebastien wrote:
| Quote: | Or I'll tackle it a different way:
What are the sudden failure rates of batteries and alternators. I've lost a couple alternators in flight, I've never heard of a good battery failing in flight.
On Mon, Jun 8, 2020, 15:49 Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:
| Quote: | Hi Ken,
I'll take a swing at it, but would suggest that it's not quite the right question.
I get your point, but the answer 'depends'. If using electronic fuel injection, the current demands mean that a single PC680 style battery (in 'new' condition) will only buy you about 30-40 minutes of flight time after alternator failure. A 2nd PC680 only adds another 30-40 minutes. On an engine that allows two alts, either of which can keep the engine running and the panel lit, a typical alt (ex: 55A Denso) is lighter than a 2nd battery, not much more expensive (actually much cheaper than an actual Odyssey branded PC680), will keep the engine running to fuel exhaustion, and has the additional benefit of allowing a return flight (in some range-dependent situations) without the need of maintenance while on the road. Not something I would ever consider after an alt failure with only a 2nd bat for backup. Add to the mix, the fact that while a 2nd alt is pretty much an install&forget item (just a startup check each flight similar to a mag check), any battery is a constantly degrading item that requires regular capacity testing to ensure that it has enough remaining capacity to give expected duration if called upon.
Now, with carb or mech fuel injection in a VFR environment, current demands might (likely will) be low enough that a single bat & single alt back up each other. In *my* opinion, that's where Bob's statement makes sense, and where your question, as framed, doesn't need asking.
So, I think you really have to define both the mission *and the hardware* to pick an architecture.
FWIW,
Charlie
On Mon, Jun 8, 2020 at 11:15 AM Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
| Quote: | Bob, you said:
"If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability."
Help me understand why the following statement is not correct:
If you have TWO properly maintained alternators,
plus a battery (sized for minimum endurance requirements)
in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
Ken
On Sun, Jun 7, 2020 at 6:56 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 05:26 PM 6/7/2020, you wrote:
| Quote: | I am not speaking to any engine manufacturers recommendation (although the
Honda Viking manufacturer does recommend two batteries. I just thought
I was applying logic -- if dual alternator + battery (triple power source)
is desirable for electrically dependent engines, wouldn't that reasoning
imply that if the second alternator is not practical, a second battery
could be used as the third power source? I could ask you a similar question:
Are not two independent power sources (battery and alternator) sufficient
to meet the needs of the electrically dependent engine. Obviously you
saw value in adding the second alternator. Why no value in adding the second battery? |
 Excellent question.
 It's a problem in energy budgets combined with
 efforts to assure continued airworthiness.
 The airplane cannot do without a battery if
 you're going to have a starter. Depending on
 your planned mission profiles, you will want
 to size the battery (1) for cranking then
 (2) minimum endurance in alternator-out modes.
 This study gave impetus for the creation of
 the endurance bus . . . a fast and predictable
 way to economically tap known quantity of energy
 stored in the battery's chemistry.
 Z13/8 was a small but significant amplification
 of that idea . . . <b>the second alternator's endurance
 had no practical limits.</b> Hence, energy on the chemistry
 just might be held completely in reserve for
 descent and approach to landing.
 Z13/20 (and the aux alternator option on
 Z101) expanded the Z13/8 endurance opportunity
 by a factor of 2.5 or better.
 Okay, suppose the drive pad isn't available.
 We are still charged with identifying and the
 delivering to energy required to comfortably
 terminate a worst-case mission.
 This means that as a part of routine maintenance
 the ship's chemistry needs to be monitored for
 capability. We could certainly store that energy
 on TWO devices but to what advantage? If we're laboring
 under the notion that a battery can suddenly become
 unavailable during one tank of gas, then we have
 to assume that EITHER battery can roll over and
 die . . . okay, how would that failure be
 annunciated . . . how would remaining energy be
 managed . . . ?
 I think that's the scenario anticipated by the
 folks that crafted that battery manager with a
 full-wave rectifier that -anded- two, completely
 isolated batteries together. Assume the alternator
 has quit and some time later one battery
 craps out. How does the pilot become aware of the
 problem and what kind of energy juggling issues
 are presented when the available energy drops
 to half? This assuming he really knows that the
 two batteries were performing equally and has
 recently quantified their condition, he now
 has to come up with a new "plan C?" and perhaps
 declare an emergency.
 This scenario first assumes TWO critical failures
 during the consumption of one tank of fuel . . .
 about 3-4 hour window. Part 23 certs don't
 get concerned with dual failures at all.
 Part 25 and heavier will wade into the reliability
 quagmire with mountains of computer generated probability
 studies that get 'worked' on until somebody
 finally sprinkles the holy water and off they
 go.
 Ask Capt. Sullivan what he thinks about
 reliability studies . . .
https://www.youtube.com/watch?v=HKJ1lIh2Cgk
 So we're left to our own devices which in reality
 are not so bad.
 The short answer is: A diligently maintained
 battery is the most reliable source of energy
 on the airplane. Replacing it when ability
 to store energy drops below some benchmark
 (generally 75 to 80% of new) means that it
 always cranks the engine and will provide a
 quantified option for dealing with alternator
 failure. Two batteries just doubles your
 preventative maintenance labor. Further,
 you need to decide if plan-b can reliably
 depend on the sum total of energy in two
 batteries . . . or will they be sized to
 independently step up to the task? The
 second option calls for 2X the battery
 weight and volume; the first option complicates
 calculations and switching operations for
 carrying out a plan-b that shouldn't ever
 happen. BOTH options still demand good
 preventative maintenance.
 Just as you KNOW fuel aboard when you launch,
 you also need to know Watt-Hours aboard
 no matter how many batteries you're carrying.
 If you have TWO properly maintained batteries,
 in all likelihood, you'll be carrying around
 $twice$ the hardware with virtually no value
 added to the ship's overall reliability.
 Bob . . .
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Mon Jun 08, 2020 4:07 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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I see definite advantage in a second battery, IN ADDITION to a battery sized and maintained to meet endurance goals. The advantage is obvious, added protection. Joe had a sudden and complete battery failure, so we know that batteries can and do fail. But more importantly, although Bob has stressed the need to know how many electrons are in the battery is as important as knowing how much fuel is in the tank, unfortunately one cannot put a dipstick in a battery and read with certainty what is in there. And as I said, even with the best of intentions, maintenance does not always get done correctly or on schedule. Add to that the fact that the battery can easily suffer abuse, simply by experiencing problems starting the engine, or leaving the master switch on; both are events that can seriously degrade a battery's capacity. To me, it is not a stretch at all to believe that even a conscientious owner might take off unknowingly with a battery whose capacity is far less than what he believes it to be. Again, it seems the hesitance to endorse two batteries is primarily based on the assumption that batteries are very reliable and completely knowable. Do we want to bet our lives on that assumption?
On Mon, Jun 8, 2020 at 3:39 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | | Quote: | If you don’t have a second alternator, you should have a small backup battery. Sizing would depend on your typical/ maximum distance between airports. Current draw of the pump, ECU, injectors and coils would be around 12 to 14 amps. A 12 amp/hour battery should give you a solid 30-40 minutes of flight time, just running the engine electrics. An 18 amp/hour one, around 1 hour. We want to be able to sustain at least 10 volts to the electrics.
We’ve found the most reliable, simple and light way to get backup battery power to the engine electrics is a single 12 to 14 gauge wire running from the backup battery, through a 30 amp ATO fuse, to a heavy duty switch, to an emergency buss where all the engine electrics can receive power. Simply charge the backup battery every 30 days and load test annually.
If you have the recommended check engine light fitted, it will warn you any time the battery voltage falls below 12.5V. You can monitor battery voltage in Gauge 3 mode. |
  A statement that is understandable and predictable.
  EVERY supplier of electrically dependent aircraft
  accessories has a vested interest in NOT having
  their product figure into the script for your
  bad day in the cockpit.
  Their "most reliable finding" focuses on
  their product . . . and while certainly
  critical for continued flight, it's not
  the only critical electro-whizzie on the
  airplane.
  All creative assemblages stand on the 3-legged
  stool of energy-management, properties-of-
  materials and refinement-of-process. It doesn't
  matter if you're cooking breakfast or building a
  space shuttle.
  I think I've suggested before that installation
  manuals for such products should call for, "Energy
  supplied by a robust, failure tolerant and competently
  maintained electrical system."
  To be sure . . . many of our brothers don't
  have strong interests or appreciation for
  elegant solutions and prefer the cookie-cutter
  approach. Nothing overtly wrong with that
  but it can generate systems with high
  costs of ownership, unnecessary weight
  and complexity. Complexity adds risk for lack of
  understanding and mis-application of features
  originally intended to keep a tense day
  in the cockpit from getting worst.
  We don't do gps receivers here . . . or engines,
  or auto-pilots. We do system integration with
  a goal of achieving the simplest, failure tolerant
  supply and distribution systems. A natural fallout
  of those endeavors is lower cost of ownership
  and weight.
  Getting back to the subject engine, what's
  the 'advantage' of carrying a second battery
  that may never be used as opposed to carrying
  one battery sized and maintained to meet
  what ever endurance goals are sought for
  the whole airplane?
 Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Mon Jun 08, 2020 4:13 pm Post subject: Re: Physical construction of Z101 engine bus & battery |
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I confirm that my PC680 failed while in flight. I sent it to Bob. He opened it
up and found a broken weld. I can not remember how old the battery was,
probably 5 years or more. That battery cranked the engine just fine on that
last flight. I did not realize the battery had failed until I reduced engine RPM
prior to landing. The alternator had been supplying power up to that point.
While battery failure is extremely rare, it can happen. If an aircraft has two
batteries, a new one can be installed every other year. Worst case is that one
battery will be 4 years old and the other one 2 years old. I am not
necessarily recommending two batteries. Having two batteries will give some
pilots peace of mind, even though heavier and more expensive.
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Joe Gores |
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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Tue Jun 09, 2020 8:30 am Post subject: Physical construction of Z101 engine bus & battery bus |
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I agree that sudden complete battery failure is extremely rare. But that is not the failure mode that is of most concern. Of most concern is that between our yearly capacity test, something happens that reduces the battery's capacity, and we don't realize it. That sort of a failure would be much more common. Two things that I can think of that might cause a reduction in capacity are a hard starting engine and inadvertently leaving the master switch on. Given that we cannot put a stick into the battery to read its actual capacity before each flight, it seems prudent to have two batteries (if battery power is the backup for an electrically dependent engine).
On Mon, Jun 8, 2020 at 4:21 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
I confirm that my PC680 failed while in flight. I sent it to Bob. He opened it
up and found a broken weld. I can not remember how old the battery was,
probably 5 years or more. That battery cranked the engine just fine on that
last flight. I did not realize the battery had failed until I reduced engine RPM
prior to landing. The alternator had been supplying power up to that point.
While battery failure is extremely rare, it can happen. If an aircraft has two
batteries, a new one can be installed every other year. Worst case is that one
battery will be 4 years old and the other one 2 years old. I am not
necessarily recommending two batteries. Having two batteries will give some
pilots peace of mind, even though heavier and more expensive.
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Joe Gores
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alec(at)alecmyers.com
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| Posted: Tue Jun 09, 2020 11:13 am Post subject: Physical construction of Z101 engine bus & battery bus |
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Joe,
Just to play devil’s advocate, if you’re prepared to replace a new battery every other year, then if you only have one battery, the worst case is that it’s 2 years old. And you’re not schlepping a 4 year old battery around with you.
Your mean battery age with two batteries would be three years; with a single battery the mean age is only one year, an improvement by a factor of 3.
\. If an aircraft has two
batteries, a new one can be installed every other year. Worst case is that one
battery will be 4 years old and the other one 2 years old. I am not
necessarily recommending two batteries. Having two batteries will give some
pilots peace of mind, even though heavier and more expensive.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496709#496709
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Tue Jun 09, 2020 1:58 pm Post subject: Re: Physical construction of Z101 engine bus & battery |
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Alec, everything you wrote is true. Keep in mind that I was not necessarily
recommending two batteries. Someone who has an electrically dependent
engine with only one alternator might want to have two batteries. If the
alternator failed a long way from an airport, would that person prefer to have
one 2-year-old battery, or . . one 2-year-old battery plus one 4-year-old
battery? Some pilots do not replace their battery until it will not crank the
engine any more. Many batteries last 5 or more years. The nice thing about
experimental aircraft is that the builder designs the electrical system the way
that they want to.
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m.whiting(at)frontier.com
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| Posted: Fri Jun 12, 2020 2:02 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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It seems to me the real question is which is more likely to fail:
1. A single battery with an age of 0 - 2 years or
2. Both batteries simultaneously where one is 0 - 2 years old and the other is 2 - 4 years old?
I am not aware of a good source of battery failure rates, but my auto experience over the course of 45 years suggests that alternative 1 has a much higher probability than alternative 2. I have almost always had at least four cars, trucks and motorcycles at any given time with battery ages between new and 8 years old. Even if I discount failures of batteries more than 4 years old (I tend to run my car batteries to failure), I have had at least two failures I can remember of with batteries less than two years old. My Current Chevy Equinox OEM battery failed 5 months after I bought the vehicle new in 2012. No charging system issues were found and the warranty replacement battery lasted 6 years. I have NEVER had two of my vehicles have battery failures at the same time or even closely spaced in time. That suggests to me that the probability of a single new battery failing is higher than the probability of simultaneous failure of two batteries: one new and one older.
I realize this isn’t exactly the same scenario since two batteries in the same vehicle could have a common failure mode such as a runaway alternator that fries them both, but it is the best I can do.
Matt
| Quote: | On Jun 12, 2020, at 4:50 PM, Alec Myers <alec(at)alecmyers.com> wrote:

Joe,
Just to play devil’s advocate, if you’re prepared to replace a new battery every other year, then if you only have one battery, the worst case is that it’s 2 years old. And you’re not schlepping a 4 year old battery around with you.
Your mean battery age with two batteries would be three years; with a single battery the mean age is only one year, an improvement by a factor of 3.
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ceengland7(at)gmail.com
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| Posted: Fri Jun 12, 2020 2:49 pm Post subject: Physical construction of Z101 engine bus & battery bus |
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I think that when doing failure analysis, you don't really pay that much attention to odds; you play 'what if'. (Actually, 'when it fails'; the assumption when doing failure analysis is that anything we can back up *will* fail). You do have to take uncontrollable stuff out of the equation; we can't carry an extra set of wings, for instance, and most of us accept the risk of a single engine, in order to be able to fly at all.
Once that's out of the way, then 'what if' starts. What if the alternator fails? It's taken off line and battery backs it up. What if the battery fails? It's taken off line and the alternator backs it up (contrary to popular internet lore). If the engine isn't electrically dependent and we're VFR with nav on our phone, we don't even care about backup at all. The what if of both failing in a single flight is considered to be so unlikely that most are willing to treat a double failure like a wing or other structural failure; we're just not going to go there.
My personal choice with a high-amps-need engine control system is to not accept the limited and continuously decreasing duration (capacity) of a standard battery, nor to accept the weight penalty of a much bigger battery or multiple batteries, in order to keep the engine running to the end of the flight. For me, that only leaves the choice of dual alternators.
FWIW,
Charlie
On Fri, Jun 12, 2020 at 5:09 PM Matthew S. Whiting <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "Matthew S. Whiting" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>
It seems to me the real question is which is more likely to fail:
1. A single battery with an age of 0 - 2 years or
2. Both batteries simultaneously where one is 0 - 2 years old and the other is 2 - 4 years old?
I am not aware of a good source of battery failure rates, but my auto experience over the course of 45 years suggests that alternative 1 has a much higher probability than alternative 2. I have almost always had at least four cars, trucks and motorcycles at any given time with battery ages between new and 8 years old. Even if I discount failures of batteries more than 4 years old (I tend to run my car batteries to failure), I have had at least two failures I can remember of with batteries less than two years old. My Current Chevy Equinox OEM battery failed 5 months after I bought the vehicle new in 2012. No charging system issues were found and the warranty replacement battery lasted 6 years. I have NEVER had two of my vehicles have battery failures at the same time or even closely spaced in time. That suggests to me that the probability of a single new battery failing is higher than the probability of simultaneous failure of two batteries: one new and one older.
I realize this isn’t exactly the same scenario since two batteries in the same vehicle could have a common failure mode such as a runaway alternator that fries them both, but it is the best I can do.
Matt
> On Jun 12, 2020, at 4:50 PM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:
>
> --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>
>
> Joe,
>
> Just to play devil’s advocate, if you’re prepared to replace a new battery every other year, then if you only have one battery, the worst case is that it’s 2 years old. And you’re not schlepping a 4 year old battery around with you.
> Your mean battery age with two batteries would be three years; with a single battery the mean age is only one year, an improvement by a factor of 3.
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