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Z8 scrapped . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 05, 2010 8:31 am Post subject: Z8 scrapped . . .

I've been wrestling with the design goals for

tying two alternators to their own dedicated

battery busses and then tying one or both

to a main bus.



Alternators using B&C alternator controllers

are not suited to this idea at all. They're

marginally okay if one of the alternators is

the SD-20 with an SB-1 regulator set to "relax"

the SD-20 when the main alternator is functional

(al la Z-12). But managing the input terminals

to the alternator controllers from an always

hot battery bus adds more poles to a DC

MASTER switch or adds complexity to the system

when handled with multiple switches . . . with

an attendant risk of mis-positioned switches

causing mis-behaviors.



There's also the issue of compliance with the

legacy "switches-off, max-cold" philosophy

for fat wires. The design demands either

b-lead disconnect contactors or fat diodes

on heat sinks.



The design looks better with internally regulated

alternators because they don't have the LV warning

systems and they do regulated voltage sensing

internally at the b-lead. But this demands b-lead

contactors as opposed to b-lead diodes because

the voltage drop across the diode cannot be

compensated for by sensing bus volts downstream

of the diode. So one COULD do some Z24-like

implementations of two alternators driving

dedicated batteries . . . but we still have

paralleling issues and increased pilot workload

to properly position switches.



The system was looking like we needed 5 contactors

total. 2 battery, 2 b-lead, 1 starter.



Finally, with the Z-8 dual-battery/dual-alternator

configuration, you can't have both alternators

driving the main bus at the same time . . . because

of load sharing issues. So this means that while

you can have both alternators running to support

their respective flying loads, only one can be

connected to the main bus at a time.



If one wants two, capable alternators and two

batteries, then Z-14 is still the architecture

of choice offering totally independent systems

with cross-tie capabilities.  Z-13/8 is still the

elegant choice for low-cost, light-weight,

simple-operation.



This has been a useful exercise in that it validates

the work already published and illuminated the

messiness of what was initially perceived as another

recipe for success.



My recommendations for optimizing Noah's adaptation

of an SD-20 into his project is replace the SB-1

regulator with a generic "ford" style regulator,

add a b-lead contactor to implement fat-wire

disconnection when parked. Take field power/

voltage sensing directly from the battery bus

through a fusible link then to 5A breaker, crowbar

ovm and then to contactor+regulator bus

connection. Placard the system against

simultaneous operation of both alternators.



Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 05, 2010 8:46 am Post subject: Z8 scrapped . . .

My recommendations for optimizing Noah's adaptation

of an SD-20 into his project is replace the SB-1

regulator with a generic "ford" style regulator,

add a b-lead contactor to implement fat-wire

disconnection when parked. Take field power/

voltage sensing directly from the battery bus

through a fusible link then to 5A breaker, crowbar

ovm and then to contactor+regulator bus

connection. Placard the system against

simultaneous operation of both alternators.



   ALTERNATIVELY



Consider going to Z-14. Use aux battery consistent

with experimentation to deduce smallest

satisfactory performance. Set the SB-1

up to 14.4 volts.



Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Sun Mar 07, 2010 7:27 pm Post subject: Re: Z8 scrapped . . .

 	  nuckolls.bob(at)aeroelect wrote: 	
		  

... SNIP

My recommendations for optimizing Noah's adaptation

of an SD-20 into his project is replace the SB-1

regulator with a generic "ford" style regulator,

add a b-lead contactor to implement fat-wire

disconnection when parked. Take field power/

voltage sensing directly from the battery bus

through a fusible link then to 5A breaker, crowbar

ovm and then to contactor+regulator bus

connection. Placard the system against

simultaneous operation of both alternators.



Bob . . . 	




Bob, previously I stated my desire to use a standby 30a ER alternator in place of the SD 8 in Z-13/8. I've been lurking as others, like Noah, pushed the thread. 

I have a B&C LR-3 for the main alt and intended to use another one for the standby. I have a mechanical "either, or" lockout device for the two alternator field switches. As long as the two systems are mutually exclusive, am I correct to understand that the prohibition re dual LR-3's, mentioned at the beginning of your post, no longer applys? And that the suggested mods in the quote above for Noah's system would not apply to Z-13/8 as I intend to modify it?



Thanks,

John

longg(at)pjm.com
Guest

Posted: Mon Mar 08, 2010 7:07 am Post subject: Z8 scrapped . . .

John,



I'm vaguely interested. What is it you are running that requires 30 amps

of power running as a backup? Is that air-conditioning? If you're

essential + engine bus pulls 30 amps, you've got big dependencies. This

is a backup up right, ala emergency power source?



Glenn E. Long



--

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 08, 2010 7:13 am Post subject: Z8 scrapped . . .

 	  Quote: 	
		  



Bob, previously I stated my desire to use a standby 30a ER 

alternator in place of the SD 8 in Z-13/8. I've been lurking as 

others, like Noah, pushed the thread.


	


   Understand.



 	  Quote: 	
		  

I have a B&C LR-3 for the main alt and intended to use another one 

for the standby. I have a mechanical "either, or" lockout device for 

the two alternator field switches. As long as the two systems are 

mutually exclusive, am I correct to understand that the prohibition 

re dual LR-3's, mentioned at the beginning of your post, no longer 

applys? And that the suggested mods in the quote above for Noah's 

system would not apply to Z-13/8 as I intend to modify it?


	




    Generally. Here's some data points to ponder for

    creative integration of two alternators onto a

    single bus:



    (1) You can have two alternators "always on" but

    be aware that their ability to share total loads

    is poor to nil . . . it takes special regulators

    that talk to each other and direct the choir for

    the proper mix of field excitation. Hence it is

    recommended that two alternators be used in a main/sb

    or main/aux mode where one is used to back up the

    other.



    (2) You can still operate in an always-on mode IF

    you set the regulator setpoint for the aux alternator

    about a volt lower than the main alternator. Like

    the SB-1 controller functionality illustrated in

    Z12. This provides an automatic transfer of load

    to the aux alternator if the main shuts down.



                     CAUTION



    This configuration offers a risk of NOT being

    aware of a main alternator failure. The SB-1

    regulator has circuitry that senses when the

    aux alternator becomes loaded and lights a light.

    That same light is use to annunciate alternator

    overload . . . reduce loads until the light stops

    flashing. If you don't have and SB-1, then some

    simple circuit that watches alternator field

    voltage and lights a light for anything over

    1 volt of applied excitation is called for.



    (3) You can operate in an either/or mode where

    only one alternator is switched on at a time.

    In this case, a low volts warning light prompts

    the changeover.



                     CAUTION



    I would advise against wiring the two systems

    such than turning one alternator on disables the

    other. There is no risk to hardware by having both

    alternators on at a time . . . but crafting circuits

    common to both systems adds a risk of single failure

    disabling both alternators. Keep them separate.



                     -----*****-----



    Beyond these three rules-of-thumb, I recommend striving

    for max-cold of ship's wiring when all switches are

    off. Try to limit protection for small always-hot

    wires to 5A breakered, 7A fused. Strive for minimum

    parts count. Strive  for simple switching protocols

    that limit if not eliminate any possibility that

    mis-positioning of switches can go unnoticed and

    negate your best laid plans and fondest wishes.



    All of these ideas are NOT regulations. Just because

    you do something that is not specifically illustrated

    in the Z-figures is not necessarily courting unhappy

    days in the cockpit. We build experimental airplanes

    and exploration of alternative recipes for success

    is encouraged . . . with limitations. Study, understand

    and take action by DESIGN to eliminate single points

    of system failure . . . which INCLUDES pilot understanding

    of how the system will or will not function.



    Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Mon Mar 08, 2010 11:15 am Post subject: Re: Z8 scrapped . . .

 	  longg(at)pjm.com wrote: 	
		  John,



I'm vaguely interested. What is it you are running that requires 30 amps

of power running as a backup? 



Glenn E. Long



-- 	




Hi Glenn,



I like to do arc welding while flying .



I was initially considering Z-19 but was always a little uncomfortable with the finite supply of power if alt 1 quit. So it wasn't so much that I needed 30 amps (it's a 40a unit, but pulleyed to reduce wear, so 30 a (at) max cruise rpm) as what was available at a reasonable price and weight. Ignition, fuel pump, EFI , navcom, EFIS put my electrical needs at about 12-15 amps. With just engine needs at about 10-12 amps.

The extra alternator gives me more comfort and less weight for the same cost than an extra battery.



John

flagstone(at)cox.net
Guest

Posted: Mon Mar 08, 2010 12:05 pm Post subject: Z8 scrapped . . .

Hi Bob:

  

 Excellent description.  I have a follow-up  questions to #2:

 [quote]       (2) You can still operate in an always-on mode    IF

    you set the regulator setpoint for the aux    alternator

    about a volt lower than the main alternator.    Like

    the SB-1 controller functionality illustrated    in

    Z12. This provides an automatic transfer of    load

    to the aux alternator if the main shuts    down.



                        CAUTION



    This configuration offers a risk of NOT    being

    aware of a main alternator failure. The    SB-1

    regulator has circuitry that senses when    the

    aux alternator becomes loaded and lights a    light.

    That same light is use to annunciate    alternator

    overload . . . reduce loads until the light    stops

    flashing. If you don't have and SB-1, then    some

    simple circuit that watches alternator    field

    voltage and lights a light for anything    over

    1 volt of applied excitation is called    for.

    

   Wouldn't the aux come on whenever the system    loads exceed the main alternator's capability and the system voltage    drops below the set point of the aux regulator, not just when the main    alternator fails? So set  up in that configuration, wouldn't  the two    LR-3's  work just like the LR-3/SB-1 combination except for the    annunciation function?  Then, wouldn't you be able to tell which    alternators are on and how hard each is working by the load meters?  In    that situation, does it really matter if they don't share the    loads?

    

    

   Thanks

    

   Mark

[b]

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Mon Mar 08, 2010 12:13 pm Post subject: Re: Z8 scrapped . . .

 	  nuckolls.bob(at)aeroelect wrote: 	
		   	  Quote: 	
		  

	




    Generally. Here's some data points to ponder for

    creative integration of two alternators onto a

    single bus:

....SNIP....



    Bob . . . 	




Give a man a fish and he eats for a day.

Teach a man to fish and he eats for a lifetime.



I am now a fisherman.



Thanks Bob.

John

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 08, 2010 1:17 pm Post subject: Z8 scrapped . . .

 	  Quote: 	
		   



   

  Wouldn't the aux come on whenever the system loads exceed the main alternator's capability and the system voltage drops below the set point of the aux regulator, not just when the main alternator fails? So set  up in that configuration, wouldn't  the two LR-3's  work just like the LR-3/SB-1 combination except for the annunciation function?  Then, wouldn't you be able to tell which alternators are on and how hard each is working by the load meters?  In that situation, does it really matter if they don't share the loads?

   	
 

     Very perceptive. You're correct. The caveat is to make SURE

     the alternator with the higher setpoint is adequately cooled.



     There have been any number of advisors calling for de-rating

     an alternator's load or adjusting pulleys to slow it down . . .

     with some notion of increasing service life for forestalling

     early failure due to "working too hard".



     Every alternator is capable of running for rated service

     life (usually thousands of hours) at FULL rated output.

     If the OBAM aircraft community is guilty of an important

     function of well considered design is that we generally

     haven't got a clue as to how well we cool . . . or don't

     cool some temperature sensitive components.



     There are thousands of 60A or larger alternators flying

     very  successfully on OBAM aircraft with very low failure

     rates due to overheating. But this probably has more to

     do with accidental de-rating. Few airplanes need more than

     20A of snort for 90 plus percent of their missions.



     Many of those builders thinks he can install some power

     hungry electro-whizzy because he believes he's got lots

     of headroom in the as-installed alternator.



     When we certify a new alternator, rules of the game

     call for an extended climb at Vy with the alternator loaded

     to full rated output. We plot the temperature rise curve

     in order to extrapolate the asymptote (temperature rise

     ceiling). We then correct for hot day conditions. Anticipated

     worst case for temperatures on diode heatsinks and stator

     windings cannot exceed manufacturer's ratings.



     So before you launch off to deliberately allow one

     alternator to operate continuously in a current limited

     condition (usually a few percent higher than nameplate

     rating), be prepared to determine that the alternator

     is not running with one foot in a bucket and the other

     in a fire.



     Back in the heyday of light twins with generators,

     turning on all electro-whizzies demanded that BOTH

     power sources carried their "share" of the load.

     This is really easy to do with carbon pile regulators.

     A simple equalizer winding added to the regulator's

     magnetics would allow the two regulators to compare

     notes and shift loads between generators for balancing.



  http://aeroelectric.com/Pictures/Schematics/Parallel_Aircraft_Generators.jpg 



     Sharing was important then because service life (brush

     wear) was affected by system loads. Alternators do

     not suffer such problems . . . but they're more difficult

     to parallel too.



     Designing a system that expects one of two alternators

     to operate in a current limited mode is not an automatic

     recipe for failure . . . but you need to do your

     homework.



     

     Bob . . .     [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 08, 2010 1:29 pm Post subject: Z8 scrapped . . .

 	  Quote: 	
		  



I was initially considering Z-19 but was always a little 

uncomfortable with the finite supply of power if alt 1 quit. So it 

wasn't so much that I needed 30 amps (it's a 40a unit, but pulleyed 

to reduce wear, so 30 a (at) max cruise rpm) as what was available at a 

reasonable price and weight.


	


    Service life is not enhanced by slowing it down.

    Performance in the original automotive application

    counted on thousands of hours under condtions far

    worse than on your airplane. If you'd really like

    to get 40A from it, change the pulley ratio. It

    will run cooler by turning faster for the same

    load.

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 08, 2010 1:29 pm Post subject: Z8 scrapped . . .

 	  Quote: 	
		  

Give a man a fish and he eats for a day.

Teach a man to fish and he eats for a lifetime.



I am now a fisherman.



Thanks Bob.


	


    Thank YOU for helping spread the value of

    what this List has to share.



    Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Mon Mar 08, 2010 5:45 pm Post subject: Re: Z8 scrapped . . .

 	  nuckolls.bob(at)aeroelect wrote: 	
		   	  Quote: 	
		  



 (it's a 40a unit, but pulleyed 

to reduce wear, so 30 a (at) max cruise rpm)



	


    Service life is not enhanced by slowing it down.

    Performance in the original automotive application

    counted on thousands of hours under condtions far

    worse than on your airplane. If you'd really like

    to get 40A from it, change the pulley ratio. It

    will run cooler by turning faster for the same

    load.

        Bob . . .

    

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




AHA! Point taken.



J



DO NOT ARCHIVE

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