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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Wed May 02, 2007 10:28 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob,  

   

I have been guilty of asking a lot of questions before reading your files and thanks to Gilles, Ken and yourself for the advice and patience.  

Your files are a gold mine of good engineering design.  

My project is for conversion of a Quickie Q-200 with Jab 3300 single phase PM alternator and a regulator like the SD-8 setup to make a safe dual independent power supply ready for an EFI conversion.  

The original Quickie circuit has no relays and protection is by fuses to each connection and the DPST master switch which isolates battery from alternator from bus.  

Z-25 covers everything I think I need except for the dual independent source for the ebus.  

For this I have copied a practice I have seen here in Oz which I understand is approved by CASA as a dual independent power supply by taking the centre tap from two diodes back to back and I have shown the setup at the bottom of Z-25 following. I have also included an over current module “A” which I had from another installation. (Gilles has pointed out that either the fusible link or the OCM is redundant).  

The ebus feed that I have shown here is I think similar to what you have done in Z-19 note 24.  

I want to keep the thing as simple as possible and have left the SPDT master switch but would use a relay if you advise.  

I would welcome your advice on the merits of fusible links vs CB which reset or can be reset, and whether you think the OCM is worth keeping, or if you see something wrong with the diagram.  

Thanks  

Peter.   

   

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klehman(at)albedo.net
Guest

Posted: Thu May 03, 2007 4:19 am Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Peter



Much as I hate attachments (slow dial up connection), I took a quick 

look and I really think you are kidding yourself about this.



Look at all the things that can fail your alternator and it's wiring. I 

suspect that a modern sealed battery is an order of magnitude more 

reliable for its first couple of years of life. Even in the unlikely 

event that the battery did fail, it is unlikely to do so in a manner 

that will bring down your system. I suspect that your proposal adds no 

reliability to your electrical supply. A separate small battery would be 

there if it were my system and I was concerned about supply reliability. 

Yes I'd keep a fuselink, C/B, or fuse near the battery so that a short 

in the alternator or all that wiring doesn't draw a lot of current out 

of the battery.



Now for the sake of discussion... If you really want to do this - what 

about considering a separate alternator feed right from the alternator 

that would include a second rectifier/regulator operating with or 

without a separate battery  Separate wiring and no excess connections 

such as loadmeters.



The last time I bought a battery, there was a well dressed guy trying to 

talk the price down a bit on a flooded cell motorcycle battery. When I 

asked for a small AGM battery by part number, the salesman said "so nice 

to have a customer that understands value". Both batteries were 

interchangeble but mine was over twice the money and should last many 

times longer than the cheap one.



Ken



Peter Harris wrote:



 	  Quote: 	
		   Bob,



 I have been guilty of asking a lot of questions before reading your 

 files and thanks to Gilles, Ken and yourself for the advice and patience.



 Your files are a gold mine of good engineering design.



 My project is for conversion of a Quickie Q-200 with Jab 3300 single 

 phase PM alternator and a regulator like the SD-8 setup to make a safe 

 dual independent power supply ready for an EFI conversion.



 The original Quickie circuit has no relays and protection is by fuses 

 to each connection and the DPST master switch which isolates battery 

 from alternator from bus.



 Z-25 covers everything I think I need except for the dual independent 

 source for the ebus.



 For this I have copied a practice I have seen here in Oz which I 

 understand is approved by CASA as a dual independent power supply by 

 taking the centre tap from two diodes back to back and I have shown 

 the setup at the bottom of Z-25 following. I have also included an 

 over current module “A” which I had from another installation. (Gilles 

 has pointed out that either the fusible link or the OCM is redundant).



 The ebus feed that I have shown here is I think similar to what you 

 have done in Z-19 note 24.



 I want to keep the thing as simple as possible and have left the SPDT 

 master switch but would use a relay if you advise.



 I would welcome your advice on the merits of fusible links vs CB which 

 reset or can be reset, and whether you think the OCM is worth keeping, 

 or if you see something wrong with the diagram.



 Thanks



 Peter.

nuckollsr(at)cox.net
Guest

Posted: Thu May 03, 2007 4:16 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

At 04:24 PM 5/3/2007 +1000, you wrote:



 	  Quote: 	
		  Bob,



I have been guilty of asking a lot of questions before reading your files 

and thanks to Gilles, Ken and yourself for the advice and patience.


	


    No problem. Let's see if we can speed up the process

    of getting the nuts separated from the shells.

 	  Quote: 	
		  Your files are a gold mine of good engineering design.


	


    I thank you for the kind words . . .

 	  Quote: 	
		  My project is for conversion of a Quickie Q-200 with Jab 3300 single phase 

PM alternator and a regulator like the SD-8 setup to make a safe dual 

independent power supply ready for an EFI conversion.



The original Quickie circuit has no relays and protection is by fuses to 

each connection and the DPST master switch which isolates battery from 

alternator from bus.



Z-25 covers everything I think I need except for the dual independent 

source for the ebus.



For this I have copied a practice I have seen here in Oz which I 

understand is approved by CASA as a dual independent power supply by 

taking the centre tap from two diodes back to back and I have shown the 

setup at the bottom of Z-25 following. I have also included an over 

current module A which I had from another installation. (Gilles has 

pointed out that either the fusible link or the OCM is redundant).


	


    Hmmm . . . when folks "who know more about building airplanes than we do"

    get into the loop . . . well. Let's not go there.

 	  Quote: 	
		  The ebus feed that I have shown here is I think similar to what you have 

done in Z-19 note 24.



I want to keep the thing as simple as possible and have left the SPDT 

master switch but would use a relay if you advise.



I would welcome your advice on the merits of fusible links vs CB which 

reset or can be reset, and whether you think the OCM is worth keeping, or 

if you see something wrong with the diagram.


	


   How do you plan to use this airplane. Are you intending to

   file for flight into IMC? Are you planning a vacuum system or

   all electric? What plans do you have for electronic and/or attitude

   displays?



   Do you plan a wing leveler? GPS or magnetically aided . . . or both?



   Do you plan to fly at night? What equipment items did you plan to

   power from the e-bus?



   Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Thu May 03, 2007 4:54 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob,

The aircraft will be used only for VFR day. It is equipped with a compass

and a GPS for nav and the usual engine instruments all of which are fused

off the main bus. For ignition it has a single electronic ignition module

and a single magneto. I also have a Ray Allen T2-7A servo for aileron reflex

which is non essential. 

No wing leveler or other electricals. No pneumatics .

For monitoring the electrical system I have a dual voltmeter/ampmeter also

an alternator no charge warning light. I have ordered the OVM crowbar module

and have the parts to do the self excitation as in Z-25. The jab regulator

looks like it is in the same family as the PMR 1-14.

 	  Quote: 	
		  From the ebus I plan to supply an EFI system including an ECU, Fuel pump and

two injectors as well as the EI module. Total load is expected to be less 
	


than 8A. I would use LED s to indicate each of the dual sources active and

would operate with both sources normally active.

Thanks Bob

Peter

--

nuckollsr(at)cox.net
Guest

Posted: Fri May 04, 2007 4:18 am Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

At 10:51 AM 5/4/2007 +1000, you wrote:




<peterjfharris(at)bigpond.com>



Bob,

The aircraft will be used only for VFR day. It is equipped with a compass

and a GPS for nav and the usual engine instruments all of which are fused

off the main bus. For ignition it has a single electronic ignition module

and a single magneto. I also have a Ray Allen T2-7A servo for aileron reflex

which is non essential.



No wing leveler or other electricals. No pneumatics .



For monitoring the electrical system I have a dual voltmeter/ampmeter also

an alternator no charge warning light. I have ordered the OVM crowbar module

and have the parts to do the self excitation as in Z-25. The jab regulator

looks like it is in the same family as the PMR 1-14.



 >From the ebus I plan to supply an EFI system including an ECU, Fuel pump and

two injectors as well as the EI module. Total load is expected to be less

than 8A. I would use LED s to indicate each of the dual sources active and

would operate with both sources normally active.



   Hmmm . . . that's a lot of snort to keep the engine

   running.  Okay, over the terrain you expect to fly, what's

   the general availability of alternate landing sites? How

   much ENDURANCE do you expect to plan for?  Servicing an

   8A engine requirement for 3+ hours doesn't seem like a

   really useful philosophy. It would make you carry around

   a LOT of lead having a low-probability of ever being

   needed. Also, I'm skeptical of the 8A figure. Do you

   know anyone flying this engine from whom you might get

   some real, operating measurements?



   Bob . . .

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Fri May 04, 2007 1:15 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob,

The EFI including pump, ECU and injectors together with his main bus radio

and instruments is using 4A according to advice from the guy who engineered

this simple single body TBI system. (I don't have a figure for the separate

ebus draw for the EFI so you would need to discount for radio and

instruments)I could also run the electronic ignition module and ignition

coil for additional ebus current I guessed 4A but it would probably be less.

I am using a Bosch HE coil.

Alternative landing sites are up to 1hr apart. The endurance is 41/2HRS.

Thanks

Peter  



--

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Fri May 04, 2007 5:57 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob,

Just to clarify I do not propose to use Z-19 , only the two diodes dual feed

as shown in Z-19 and note 24. What I have in mind is to use Z-25 just as I

have shown it in my post ie Z-25 plus the double diode feed from Z-19

Peter



--

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Sun May 06, 2007 1:40 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Ken,

The idea of a second regulator feed I like better than a second battery, a

very good idea I think. The PM alternator itself is likely to be very

reliable long term.

What protection would you use for the second feed? Is this a case for a

transorb and a CB which can be reset on the panel?

I am already using the diodes as shown switched NC with a green LED to show

each side active. Now Z-25 solves the problem of running the alternator

without the battery.

Peter



--

nuckollsr(at)cox.net
Guest

Posted: Sun May 06, 2007 9:03 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

At 07:13 AM 5/5/2007 +1000, you wrote:



 	  Quote: 	
		  

<peterjfharris(at)bigpond.com>



Bob,

The EFI including pump, ECU and injectors together with his main bus radio

and instruments is using 4A according to advice from the guy who engineered

this simple single body TBI system. (I don't have a figure for the separate

ebus draw for the EFI so you would need to discount for radio and

instruments)I could also run the electronic ignition module and ignition

coil for additional ebus current I guessed 4A but it would probably be less.

I am using a Bosch HE coil.

Alternative landing sites are up to 1hr apart. The endurance is 41/2HRS.

Thanks

Peter


	


    So how much batter-only endurance are you designing for? What

    plans are you making for preventative maintenance to make

    sure that design goals slip for lack of due diligence in

    maintenance?



    Assuming you're considering a battery capacity on the order

    of the popular 3 x 6 x 7 inch form-factor, a 4A load on a

    new battery will give you just over two hours of operation

    assuming that nothing in your system gives up above 10.5

    volts. See:



http://www.aeroelectric.com/Pictures/Curves/17AH_Capcity_vs_Load.gif



    Here we see that a 17 ah battery will carry 4A for about 3 hours.



http://www.aeroelectric.com/Pictures/Curves/28AH_12V_Capacity_vs_Load.gif



    To go out for duration of fuel aboard, you'll need to upsize to

    the 28 ah critter for an increase to something on the order of

    360 minutes or 6 hours.



    It's my recommendation that you consider z21 posted at:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z21A.pdf



    Stuff needed to keep the engine running should run from

    the battery bus and be switched by their own power switches

    SEPARATE from DC power management for the rest of the airplane.

    You don't need the diodes. A battery does not fail in a manner

    that takes the rest of the system down. Tying the alternator

    directly to the battery al-la Z13/8 lets you load-shed the

    main bus plus contactor and run only battery bus + ebus loads.

    Even the e-bus can be shed if desired.



    I presume you're planning on carrying flight-bag backups

    for the panel mounted hardware like



http://www.aeroelectric.com/Pictures/Misc/Failure_Tolerance.pdf



    This architecture meets the design goals of dual supplies

    for keeping the engine lit up.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Sun May 06, 2007 9:06 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

At 11:46 AM 5/5/2007 +1000, you wrote:



 	  Quote: 	
		  

<peterjfharris(at)bigpond.com>



Bob,

Just to clarify I do not propose to use Z-19 , only the two diodes dual feed

as shown in Z-19 and note 24. What I have in mind is to use Z-25 just as I

have shown it in my post ie Z-25 plus the double diode feed from Z-19

Peter


	


   Never thought you were proposing Z-19. That effort was produced

   for other builders. You don't need the diodes. See my earlier

   post on this topic and the new figure Z-21

   Bob . . .

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Sun May 06, 2007 10:20 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob, thanks I see now that battery capacity design and maintenance will do

the job the simplest way.

Yes I do have a Magellan 315 and it is loaded with bush air strips as well

as regular airports.

I am not sure if I understand what the self excitation feature is

contributing, do we need it here?

Peter 



--

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Mon May 07, 2007 1:31 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob disregard my question about the self excitation feature, now I

understand how it works. (slow to catch on due to aging brain syndrome)

Thanks for your help .

Peter



--

klehman(at)albedo.net
Guest

Posted: Tue May 08, 2007 5:12 am Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

With my belt drive dynamo I feel that the regulator is not really a weak 

point in the system compared to the belt, bearings, wiring, etc.



However with a Jabiru that has I think a direct drive dynamo, would 

there be any value in having a second regulator that could be manually 

connected to the battery or the e-bus?

Regulator failures do seem to happen much more often than dynamo 

failures. Personally I'd be content with Z-21 as it is probably more 

reliable than his EFI system, but Peter seems reluctant to just rely on 

battery power for extended endurance after an alternator failure. A 

second regulator is light and wouldn't necesarilly need OV protection if 

switched in manually. However it would only cater to a regulator problem 

and wouldn't help if the dynamo quit...  



I should find note 25 for Z-21 as well.  I semi followed the discussion 

on self excitation a few months ago but it is not obvious to me how the 

two resistors and diode achieve self excitation when I look at Z-21 now.



Ken



Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



 At 07:13 AM 5/5/2007 +1000, you wrote:



> 

> <peterjfharris(at)bigpond.com>

>

> Bob,

> The EFI including pump, ECU and injectors together with his main bus 

> radio

> and instruments is using 4A according to advice from the guy who 

> engineered

> this simple single body TBI system. (I don't have a figure for the 

> separate

> ebus draw for the EFI so you would need to discount for radio and

> instruments)I could also run the electronic ignition module and ignition

> coil for additional ebus current I guessed 4A but it would probably 

> be less.

> I am using a Bosch HE coil.

> Alternative landing sites are up to 1hr apart. The endurance is 41/2HRS.

> Thanks

> Peter

    So how much batter-only endurance are you designing for? What

    plans are you making for preventative maintenance to make

    sure that design goals slip for lack of due diligence in

    maintenance?



    Assuming you're considering a battery capacity on the order

    of the popular 3 x 6 x 7 inch form-factor, a 4A load on a

    new battery will give you just over two hours of operation

    assuming that nothing in your system gives up above 10.5

    volts. See:



 http://www.aeroelectric.com/Pictures/Curves/17AH_Capcity_vs_Load.gif



    Here we see that a 17 ah battery will carry 4A for about 3 hours.



 http://www.aeroelectric.com/Pictures/Curves/28AH_12V_Capacity_vs_Load.gif



    To go out for duration of fuel aboard, you'll need to upsize to

    the 28 ah critter for an increase to something on the order of

    360 minutes or 6 hours.



    It's my recommendation that you consider z21 posted at:



 http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z21A.pdf



    Stuff needed to keep the engine running should run from

    the battery bus and be switched by their own power switches

    SEPARATE from DC power management for the rest of the airplane.

    You don't need the diodes. A battery does not fail in a manner

    that takes the rest of the system down. Tying the alternator

    directly to the battery al-la Z13/8 lets you load-shed the

    main bus plus contactor and run only battery bus + ebus loads.

    Even the e-bus can be shed if desired.



    I presume you're planning on carrying flight-bag backups

    for the panel mounted hardware like



 http://www.aeroelectric.com/Pictures/Misc/Failure_Tolerance.pdf



    This architecture meets the design goals of dual supplies

    for keeping the engine lit up.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Tue May 08, 2007 6:21 am Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

At 09:05 AM 5/8/2007 -0400, you wrote:



 	  Quote: 	
		  



With my belt drive dynamo I feel that the regulator is not really a weak 

point in the system compared to the belt, bearings, wiring, etc.


	




   Certainly things that move, flex, need lubrication, and vibrate

   are victims of certain kinds of stresses and have obvious

   limitations to service life.



   Things that don't move and need grease are not immune from

   their own stresses which can have an effect on service life

   too. Just because it's "solid state" doesn't mean that it's

   automatically more likely to outlive any other component

   of the system.



 	  Quote: 	
		  However with a Jabiru that has I think a direct drive dynamo, would there 

be any value in having a second regulator that could be manually connected 

to the battery or the e-bus?


	


   The key term here is "value". Indeed, a calculation of

   cost-of-ownership along with a probability study for

   any particular failure offers the math and statistics

   junkie an opportunity for a couple-hundred hour high.



   Adding another regulator increased parts count not only

   by doubling the number of regulators but adds a switch

   to select between them which has its own unique failure

   modes.



 	  Quote: 	
		  Regulator failures do seem to happen much more often than dynamo failures.


	


   . . . an anecdotal observation that may be true but to

   simply add-another-regulator may not be the optimal

   solution. WHY does the regulator fail? If it had a better

   heat sink, would it last longer? If it were redesigned

   slightly, would it last longer? Until one knows root cause

   of a failure, the only "remedy" is to play swap-tronics . . .

   add-a-spare, change brands, etc. It may be comforting

   from the neophyte's perspective but in fact could have

   no useful effect on probability of avoiding a sweaty

   experience while airborne.



 	  Quote: 	
		    Personally I'd be content with Z-21 as it is probably more reliable than 

 his EFI system, but Peter seems reluctant to just rely on battery power 

 for extended endurance after an alternator failure.


	


   I don't read that into his words. His question was

   to identify a methodology for crafting "dual, independent

   power supply". His original notion was that diodes were

   necessary to acquire independence . . . which is not

   the case. Moving the alternator feed from bus to battery

   side of the contactor covers the issues for a failed

   battery contactor.

 	  Quote: 	
		    A second regulator is light and wouldn't necesarilly need OV protection 

 if switched in manually. However it would only cater to a regulator 

 problem and wouldn't help if the dynamo quit...


	


   The dynamo is wire wound around a stack of laminations

   with no moving parts. If these things quit, then it's

   because a wire broke. That's an exceedingly rare event

   unworthy of worry.

 	  Quote: 	
		  I should find note 25 for Z-21 as well.  I semi followed the discussion on 

self excitation a few months ago but it is not obvious to me how the two 

resistors and diode achieve self excitation when I look at Z-21 now.


	


   It' provides a high source impedance "leakage" around

   SCR's internal to the regulator such that the rectifier/

   regulator is never completely shut down. This causes

   output from a dynamo to keep a low voltage charge on the

   output filter capacitor sufficiently elevated to keep

   the regulator's control circuits from shutting down.



   Note 25 is a general note for Appendix Z found on page

   Z-11 of



   http://aeroelectric.com/articles/Rev11/AppZ_R11J.pdf



   The foundation for this exchange rests solidly on

   the notion that a WELL MAINTAINED battery is the most

   reliable source of energy aboard the aircraft. Of course

   one strives to reduce likelihood of charging system

   failure . . . but this is ALWAYS best achieved by

   increasing service life of the existing components

   as opposed to increasing numbers of components.



   Bob . . .

echristley(at)nc.rr.com
Guest

Posted: Tue May 08, 2007 11:04 am Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

 	  Quote: 	
		  > 

 However with a Jabiru that has I think a direct drive dynamo, would 

 there be any value in having a second regulator that could be manually 

 connected to the battery or the e-bus?


	




Sometimes redundancy means two pieces of hardware dying at the same 

time.  I installed two hard drives in a RAID configuration on my 

computer for the sake of redundancy.  I found a good deal on 7200RPM IBM 

drives, so I bought a couple.  Ran great for years.  Fast and reliable.  

Then both drives crapped out (technical term) within hours of one 

another.  I lost nearly everything.  I noticed the problems with one 

drive, and the other died before I could finish a backup.  The serial 

numbers were within about 4 units of one another.  They lived in the 

same environment, and fed off the same power supply.

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Tue May 08, 2007 1:50 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Bob the true practical value of Z-21 is still sinking in and I have been

researching batteries. The experienced advice that I am getting down here is

not for Odyssey incidentally because of variable quality and that ties in

with a recent post. Sometimes I think that we get suspect product down here

because we are a long way from the big market. I have been shown an

HGL35-12. I was definitely interested in Ken's original suggestion to

consider dual regulators because I had never seen the idea before. I had a

regulator failure years ago and with the unprotected Quickie circuit and a

Revmaster PM installation with no warning on a 900 NM trip. The battery was

almost boiling when I arrived after the second leg of the trip. Scary. No

concern for that issue with any of your circuits but it is still in my mind

that the regulator is the weakest link in the power supply and may be a

candidate for a properly designed duplication?

Peter



--

nuckollsr(at)cox.net
Guest

Posted: Tue May 08, 2007 6:11 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

At 07:47 AM 5/9/2007 +1000, you wrote:



 	  Quote: 	
		  

<peterjfharris(at)bigpond.com>



Bob the true practical value of Z-21 is still sinking in and I have been

researching batteries. The experienced advice that I am getting down here is

not for Odyssey incidentally because of variable quality and that ties in

with a recent post. Sometimes I think that we get suspect product down here

because we are a long way from the big market. I have been shown an

HGL35-12. I was definitely interested in Ken's original suggestion to

consider dual regulators because I had never seen the idea before. I had a

regulator failure years ago and with the unprotected Quickie circuit and a

Revmaster PM installation with no warning on a 900 NM trip. The battery was

almost boiling when I arrived after the second leg of the trip. Scary. No

concern for that issue with any of your circuits but it is still in my mind

that the regulator is the weakest link in the power supply and may be a

candidate for a properly designed duplication?


	


    The "no sweat" electrical system is one that can tolerate any

    single failure. You experienced what appears to be a runaway

    that ran unabated. This produced a second failure which, if

    allowed to run longer, might have smoked lots of stuff.



    One can stack redundancy on top of redundancy but in every

    case you first need to do drill:



    How can this part fail?



    Is it preflight detectable? If so, is it on my

    preflight check list to look?



    How will I know that it failed while in flight?



    If failure occurs in flight, is it useful for

    comfortable termination of flight?



    If so, what's the plan-b for replacing its

    usefulness?



    Finally, the most effective failure mitigation

    plans include a preventative maintenance program

    that tracks time in service and/or present

    degradation of performance so that a replacement

    is made long before failure.



    A "Plan-B" for a failed part is best crafted from

    completely different parts and architecture. For

    example, hand-helds in the flight bag are totally

    independent of panel mounted hardware and (assuming

    batteries have been maintained) can be counted

    on to function when needed.



    So, if you've done the homework and preventative

    maintenance that insures sweat-free termination

    of flight in spite of a failed regulator then

    adding a second, switched regulator is not the

    minimum parts count nor totally independent scenario

    for plan-b.



    For example, the Cessna Skymaster and Beech Barons

    had single regulators driving both alternators in

    parallel. Someone thought that "twin engine reliability"

    could be maintained by providing a second regulator that

    could be switched in to replace a failed main regulator.

    But suppose a short on the field circuit takes out

    one regulator. Switching in the standby regulator

    produces TWO failed regulators.



    If it were my airplane, Z-21 would be the way to

    go. If the engine were fitted with dual ECFI systems

    like the Subaru conversions featured in Z-19, then

    a second battery provides total separation of power

    sources for dual engine electronics. Given that your

    engine is fitted with a single system, then there

    ARE single points of failure that are not going to

    go away no matter how many power sources you carry.

    Hence, I'd be more interested in believing that the

    ECFI had the reliability of propeller bolts than with

    stacking on more power sources.

    Bob . . .

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Tue May 08, 2007 8:32 pm Post subject: BASIC DUAL INDEPENDENT POWER SUPPLY

Thanks Bob I am going down that path. And you make a good point about the

reliability of the ECU.

Peter

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