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Z14 Failure Modes and the Cross-Tie

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Adam(at)ValidationPartner
Guest

Posted: Sat Jan 07, 2006 2:34 pm Post subject: Z14 Failure Modes and the Cross-Tie



I'm laying out the electrical system for my all-glass, all-electric,

FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

go, using two full-size alternators. It would be very attractive to have the

ability to power both the A and B buses and recharge both batteries from a

single alternator when needed. However, I'm having trouble imagining a

failure mode where the cross-tie could be used in flight.

If the Bus A alternator's field breaker trips in flight (for example), would

it be safe to engage the cross-tie? You don't know what caused the failure,

and tying the A and B buses together could knock out the B bus.

If you get a low voltage warning on bus A, do you pull the corresponding

field breaker and engage the cross-tie? Again, if something is shorting out

the bus (such as shorted windings on the alternator), you are in danger of

overloading bus B.

Any thoughts?

Adam Molny

Legacy #151

klehman(at)albedo.net
Guest

Posted: Sat Jan 07, 2006 5:58 pm Post subject: Z14 Failure Modes and the Cross-Tie



Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

I'm laying out the electrical system for my all-glass, all-electric,

FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

go, using two full-size alternators. It would be very attractive to have the

ability to power both the A and B buses and recharge both batteries from a

single alternator when needed. However, I'm having trouble imagining a

failure mode where the cross-tie could be used in flight.

If the Bus A alternator's field breaker trips in flight (for example), would

it be safe to engage the cross-tie? You don't know what caused the failure,

and tying the A and B buses together could knock out the B bus.

If you get a low voltage warning on bus A, do you pull the corresponding

field breaker and engage the cross-tie? Again, if something is shorting out

the bus (such as shorted windings on the alternator), you are in danger of

overloading bus B.

Any thoughts?

Adam Molny

Legacy #151

klehman(at)albedo.net
Guest

Posted: Sat Jan 07, 2006 7:43 pm Post subject: Z14 Failure Modes and the Cross-Tie



Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

I'm laying out the electrical system for my all-glass, all-electric,

FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

go, using two full-size alternators. It would be very attractive to have the

ability to power both the A and B buses and recharge both batteries from a

single alternator when needed. However, I'm having trouble imagining a

failure mode where the cross-tie could be used in flight.

If the Bus A alternator's field breaker trips in flight (for example), would

it be safe to engage the cross-tie? You don't know what caused the failure,

and tying the A and B buses together could knock out the B bus.

If you get a low voltage warning on bus A, do you pull the corresponding

field breaker and engage the cross-tie? Again, if something is shorting out

the bus (such as shorted windings on the alternator), you are in danger of

overloading bus B.

Any thoughts?

Adam Molny

Legacy #151

klehman(at)albedo.net
Guest

Posted: Sun Jan 08, 2006 1:25 pm Post subject: Z14 Failure Modes and the Cross-Tie

Hi Adam I figure the most likely reason to close the crossfeed is when one alternator simply stops producing power or has been shutdown by the OV protection. Bus voltage will be nominal battery voltage in such a case. With a contactor on the output of an IR regulator even the stator and diodes are out of the circuit when I shut down an alternator or the OVP activates but I'd expect the alternator fuse/breaker/ANL to already be open anyway in that case. I agree that it might be unwise to close the crossfeed if immediately after the low voltage warning you observe that the voltage is below normal battery voltage but then again you have the option if you need the equipment and think maybe you've got a open circuited or disconnected battery (or open master contactor) that has allowed a subsequent OV excursion and alternator shutdown. Plan A would be to leave it alone til on the ground if I don't need it. Any smoke or sparks would definately keep my finger away from the crossfeed. There really isn't much of a "bus" on a small airplane with fuse blocks which makes it very difficult to imagine a shorted bus. Z-14 also gives the option of conducting a single alternator recovery flight home or to a maintanance facility. Ken Adam Molny wrote: I'm laying out the electrical system for my all-glass, all-electric, FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to go, using two full-size alternators. It would be very attractive to have the ability to power both the A and B buses and recharge both batteries from a single alternator when needed. However, I'm having trouble imagining a failure mode where the cross-tie could be used in flight. If the Bus A alternator's field breaker trips in flight (for example), would it be safe to engage the cross-tie? You don't know what caused the failure, and tying the A and B buses together could knock out the B bus. If you get a low voltage warning on bus A, do you pull the corresponding field breaker and engage the cross-tie? Again, if something is shorting out the bus (such as shorted windings on the alternator), you are in danger of overloading bus B. Any thoughts? Adam Molny Legacy #151

AdmID:83E83C29680237C6A7B9D0D346BF94A9
AdmID:699E6044ECE49308DB21D9330AB77D81

klehman(at)albedo.net
Guest

Posted: Sun Jan 08, 2006 2:05 pm Post subject: Z14 Failure Modes and the Cross-Tie

Hi Adam I figure the most likely reason to close the crossfeed is when one alternator simply stops producing power or has been shutdown by the OV protection. Bus voltage will be nominal battery voltage in such a case. With a contactor on the output of an IR regulator even the stator and diodes are out of the circuit when I shut down an alternator or the OVP activates but I'd expect the alternator fuse/breaker/ANL to already be open anyway in that case. I agree that it might be unwise to close the crossfeed if immediately after the low voltage warning you observe that the voltage is below normal battery voltage but then again you have the option if you need the equipment and think maybe you've got a open circuited or disconnected battery (or open master contactor) that has allowed a subsequent OV excursion and alternator shutdown. Plan A would be to leave it alone til on the ground if I don't need it. Any smoke or sparks would definately keep my finger away from the crossfeed. There really isn't much of a "bus" on a small airplane with fuse blocks which makes it very difficult to imagine a shorted bus. Z-14 also gives the option of conducting a single alternator recovery flight home or to a maintanance facility. Ken Adam Molny wrote: I'm laying out the electrical system for my all-glass, all-electric, FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to go, using two full-size alternators. It would be very attractive to have the ability to power both the A and B buses and recharge both batteries from a single alternator when needed. However, I'm having trouble imagining a failure mode where the cross-tie could be used in flight. If the Bus A alternator's field breaker trips in flight (for example), would it be safe to engage the cross-tie? You don't know what caused the failure, and tying the A and B buses together could knock out the B bus. If you get a low voltage warning on bus A, do you pull the corresponding field breaker and engage the cross-tie? Again, if something is shorting out the bus (such as shorted windings on the alternator), you are in danger of overloading bus B. Any thoughts? Adam Molny Legacy #151

AdmID:83E83C29680237C6A7B9D0D346BF94A9
AdmID:699E6044ECE49308DB21D9330AB77D81
AdmID:F24EE12554874507101161E0190BA573

nuckollsr(at)cox.net
Guest

Posted: Sun Jan 08, 2006 5:23 pm Post subject: Z14 Failure Modes and the Cross-Tie

99+ percent of alternator failures is to simply stop

producing for whatever reason . . . including ov trip.

A major fraction of what's left will be cause for manual

shutown . . . voltage unstable? Whatever. It is very unlikely

that any alternator failure will take out the b-lead protection.

It's axiomatic that many problems get worse when the pilot

starts messing with things in some attempt to "get all the

goodies back up and running."

The advantage of a fully dual system is that you spread

your backup systems around. One on main bus, one on aux

bus. The best thing to do when something goes T.U. on one

bus is to simply shut that one down. Go into an endurance

mode until comfortable arrival is assured. Battery on the

cold bus is held in reserve. Battery on working bus is

being supported by normal alternator operations.

When and if anything on the 'cold' bus becomes useful

or necessary in the final phase of flight. Close battery

contactor first and watch for normal battery-only

bus levels. Close crossfeed contactor second while observing both

bus voltages now show normal operational levels. Then

finish the flight.

If any voltages appear out of whack after operation of

a switch, re-open the switch immediately and finish the

flight on one bus . . . but don't do this experiment until

you have the airport in sight.

I think it's useful to think of the various system options

as tools for comfortable termination of flight by insuring

availability of minimum equipment . . . the exercises that

pilots go through to perform in-flight diagnostics and/or

get some suite of equipment up running doesn't

necessarily improve outcome is certainly a distraction

and perhaps hazardous.

Only the more complex aircraft can justify Z-14. While

complexity brings capability and convenience, it also

brings workload. If you're vfr in the clear, then perhaps

a total failure is no big deal. When you are depending on at

least the most useful of things to be working then you're

probably IFR and busy with pilot-things to do. The last

thing you want to do is troubleshoot especially when there

is risk of making a situation worse.

Bob . . .

 	  Quote: 	
		  Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

<Adam(at)ValidationPartners.com>

>

>I'm laying out the electrical system for my all-glass, all-electric,

>FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

>go, using two full-size alternators. It would be very attractive to have the

>ability to power both the A and B buses and recharge both batteries from a

>single alternator when needed. However, I'm having trouble imagining a

>failure mode where the cross-tie could be used in flight.

>

>If the Bus A alternator's field breaker trips in flight (for example), would

>it be safe to engage the cross-tie? You don't know what caused the failure,

>and tying the A and B buses together could knock out the B bus.

>

>If you get a low voltage warning on bus A, do you pull the corresponding

>field breaker and engage the cross-tie? Again, if something is shorting out

>the bus (such as shorted windings on the alternator), you are in danger of

>overloading bus B.

>

>Any thoughts?

>

>Adam Molny

>Legacy #151

>

--

-- incoming mail is certified Virus Free.

Bob . . .

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

< Throughout history, poverty is the normal condition >

< of man. Advances which permit this norm to be >

< exceeded -- here and there, now and then -- are the >

< work of an extremely small minority, frequently >

< despised, often condemned, and almost always opposed >

< by all right-thinking people. Whenever this tiny >

< minority is kept from creating, or (as sometimes >

< happens) is driven out of a society, the people >

< then slip back into abject poverty. >

< >

< This is known as "bad luck". >

< -Lazarus Long- >

<------------------------------------------------------>

http://www.aeroelectric.com

nuckollsr(at)cox.net
Guest

Posted: Mon Jan 09, 2006 8:19 am Post subject: Z14 Failure Modes and the Cross-Tie

99+ percent of alternator failures is to simply stop

producing for whatever reason . . . including ov trip.

A major fraction of what's left will be cause for manual

shutown . . . voltage unstable? Whatever. It is very unlikely

that any alternator failure will take out the b-lead protection.

It's axiomatic that many problems get worse when the pilot

starts messing with things in some attempt to "get all the

goodies back up and running."

The advantage of a fully dual system is that you spread

your backup systems around. One on main bus, one on aux

bus. The best thing to do when something goes T.U. on one

bus is to simply shut that one down. Go into an endurance

mode until comfortable arrival is assured. Battery on the

cold bus is held in reserve. Battery on working bus is

being supported by normal alternator operations.

When and if anything on the 'cold' bus becomes useful

or necessary in the final phase of flight. Close battery

contactor first and watch for normal battery-only

bus levels. Close crossfeed contactor second while observing both

bus voltages now show normal operational levels. Then

finish the flight.

If any voltages appear out of whack after operation of

a switch, re-open the switch immediately and finish the

flight on one bus . . . but don't do this experiment until

you have the airport in sight.

I think it's useful to think of the various system options

as tools for comfortable termination of flight by insuring

availability of minimum equipment . . . the exercises that

pilots go through to perform in-flight diagnostics and/or

get some suite of equipment up running doesn't

necessarily improve outcome is certainly a distraction

and perhaps hazardous.

Only the more complex aircraft can justify Z-14. While

complexity brings capability and convenience, it also

brings workload. If you're vfr in the clear, then perhaps

a total failure is no big deal. When you are depending on at

least the most useful of things to be working then you're

probably IFR and busy with pilot-things to do. The last

thing you want to do is troubleshoot especially when there

is risk of making a situation worse.

Bob . . .

 	  Quote: 	
		  Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

<Adam(at)ValidationPartners.com>

>

>I'm laying out the electrical system for my all-glass, all-electric,

>FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

>go, using two full-size alternators. It would be very attractive to have the

>ability to power both the A and B buses and recharge both batteries from a

>single alternator when needed. However, I'm having trouble imagining a

>failure mode where the cross-tie could be used in flight.

>

>If the Bus A alternator's field breaker trips in flight (for example), would

>it be safe to engage the cross-tie? You don't know what caused the failure,

>and tying the A and B buses together could knock out the B bus.

>

>If you get a low voltage warning on bus A, do you pull the corresponding

>field breaker and engage the cross-tie? Again, if something is shorting out

>the bus (such as shorted windings on the alternator), you are in danger of

>overloading bus B.

>

>Any thoughts?

>

>Adam Molny

>Legacy #151

>

--

-- incoming mail is certified Virus Free.

Bob . . .

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

< Throughout history, poverty is the normal condition >

< of man. Advances which permit this norm to be >

< exceeded -- here and there, now and then -- are the >

< work of an extremely small minority, frequently >

< despised, often condemned, and almost always opposed >

< by all right-thinking people. Whenever this tiny >

< minority is kept from creating, or (as sometimes >

< happens) is driven out of a society, the people >

< then slip back into abject poverty. >

< >

< This is known as "bad luck". >

< -Lazarus Long- >

<------------------------------------------------------>

http://www.aeroelectric.com

AdmID:506495D6A0BE8036E3BA3D8C6EA71624

klehman(at)albedo.net
Guest

Posted: Mon Jan 09, 2006 8:19 am Post subject: Z14 Failure Modes and the Cross-Tie

Hi Adam I figure the most likely reason to close the crossfeed is when one alternator simply stops producing power or has been shutdown by the OV protection. Bus voltage will be nominal battery voltage in such a case. With a contactor on the output of an IR regulator even the stator and diodes are out of the circuit when I shut down an alternator or the OVP activates but I'd expect the alternator fuse/breaker/ANL to already be open anyway in that case. I agree that it might be unwise to close the crossfeed if immediately after the low voltage warning you observe that the voltage is below normal battery voltage but then again you have the option if you need the equipment and think maybe you've got a open circuited or disconnected battery (or open master contactor) that has allowed a subsequent OV excursion and alternator shutdown. Plan A would be to leave it alone til on the ground if I don't need it. Any smoke or sparks would definately keep my finger away from the crossfeed. There really isn't much of a "bus" on a small airplane with fuse blocks which makes it very difficult to imagine a shorted bus. Z-14 also gives the option of conducting a single alternator recovery flight home or to a maintanance facility. Ken Adam Molny wrote: I'm laying out the electrical system for my all-glass, all-electric, FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to go, using two full-size alternators. It would be very attractive to have the ability to power both the A and B buses and recharge both batteries from a single alternator when needed. However, I'm having trouble imagining a failure mode where the cross-tie could be used in flight. If the Bus A alternator's field breaker trips in flight (for example), would it be safe to engage the cross-tie? You don't know what caused the failure, and tying the A and B buses together could knock out the B bus. If you get a low voltage warning on bus A, do you pull the corresponding field breaker and engage the cross-tie? Again, if something is shorting out the bus (such as shorted windings on the alternator), you are in danger of overloading bus B. Any thoughts? Adam Molny Legacy #151

AdmID:83E83C29680237C6A7B9D0D346BF94A9
AdmID:699E6044ECE49308DB21D9330AB77D81
AdmID:F24EE12554874507101161E0190BA573
AdmID:834804A500D89DCA3DDB10F5EDBDD50D

klehman(at)albedo.net
Guest

Posted: Mon Jan 09, 2006 9:30 am Post subject: Z14 Failure Modes and the Cross-Tie

Hi Adam I figure the most likely reason to close the crossfeed is when one alternator simply stops producing power or has been shutdown by the OV protection. Bus voltage will be nominal battery voltage in such a case. With a contactor on the output of an IR regulator even the stator and diodes are out of the circuit when I shut down an alternator or the OVP activates but I'd expect the alternator fuse/breaker/ANL to already be open anyway in that case. I agree that it might be unwise to close the crossfeed if immediately after the low voltage warning you observe that the voltage is below normal battery voltage but then again you have the option if you need the equipment and think maybe you've got a open circuited or disconnected battery (or open master contactor) that has allowed a subsequent OV excursion and alternator shutdown. Plan A would be to leave it alone til on the ground if I don't need it. Any smoke or sparks would definately keep my finger away from the crossfeed. There really isn't much of a "bus" on a small airplane with fuse blocks which makes it very difficult to imagine a shorted bus. Z-14 also gives the option of conducting a single alternator recovery flight home or to a maintanance facility. Ken Adam Molny wrote: I'm laying out the electrical system for my all-glass, all-electric, FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to go, using two full-size alternators. It would be very attractive to have the ability to power both the A and B buses and recharge both batteries from a single alternator when needed. However, I'm having trouble imagining a failure mode where the cross-tie could be used in flight. If the Bus A alternator's field breaker trips in flight (for example), would it be safe to engage the cross-tie? You don't know what caused the failure, and tying the A and B buses together could knock out the B bus. If you get a low voltage warning on bus A, do you pull the corresponding field breaker and engage the cross-tie? Again, if something is shorting out the bus (such as shorted windings on the alternator), you are in danger of overloading bus B. Any thoughts? Adam Molny Legacy #151

AdmID:83E83C29680237C6A7B9D0D346BF94A9
AdmID:699E6044ECE49308DB21D9330AB77D81
AdmID:F24EE12554874507101161E0190BA573
AdmID:834804A500D89DCA3DDB10F5EDBDD50D
AdmID:679109EACB011FD5036DE2BED2C725F9

nuckollsr(at)cox.net
Guest

Posted: Mon Jan 09, 2006 9:31 am Post subject: Z14 Failure Modes and the Cross-Tie

99+ percent of alternator failures is to simply stop

producing for whatever reason . . . including ov trip.

A major fraction of what's left will be cause for manual

shutown . . . voltage unstable? Whatever. It is very unlikely

that any alternator failure will take out the b-lead protection.

It's axiomatic that many problems get worse when the pilot

starts messing with things in some attempt to "get all the

goodies back up and running."

The advantage of a fully dual system is that you spread

your backup systems around. One on main bus, one on aux

bus. The best thing to do when something goes T.U. on one

bus is to simply shut that one down. Go into an endurance

mode until comfortable arrival is assured. Battery on the

cold bus is held in reserve. Battery on working bus is

being supported by normal alternator operations.

When and if anything on the 'cold' bus becomes useful

or necessary in the final phase of flight. Close battery

contactor first and watch for normal battery-only

bus levels. Close crossfeed contactor second while observing both

bus voltages now show normal operational levels. Then

finish the flight.

If any voltages appear out of whack after operation of

a switch, re-open the switch immediately and finish the

flight on one bus . . . but don't do this experiment until

you have the airport in sight.

I think it's useful to think of the various system options

as tools for comfortable termination of flight by insuring

availability of minimum equipment . . . the exercises that

pilots go through to perform in-flight diagnostics and/or

get some suite of equipment up running doesn't

necessarily improve outcome is certainly a distraction

and perhaps hazardous.

Only the more complex aircraft can justify Z-14. While

complexity brings capability and convenience, it also

brings workload. If you're vfr in the clear, then perhaps

a total failure is no big deal. When you are depending on at

least the most useful of things to be working then you're

probably IFR and busy with pilot-things to do. The last

thing you want to do is troubleshoot especially when there

is risk of making a situation worse.

Bob . . .

 	  Quote: 	
		  Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

<Adam(at)ValidationPartners.com>

>

>I'm laying out the electrical system for my all-glass, all-electric,

>FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

>go, using two full-size alternators. It would be very attractive to have the

>ability to power both the A and B buses and recharge both batteries from a

>single alternator when needed. However, I'm having trouble imagining a

>failure mode where the cross-tie could be used in flight.

>

>If the Bus A alternator's field breaker trips in flight (for example), would

>it be safe to engage the cross-tie? You don't know what caused the failure,

>and tying the A and B buses together could knock out the B bus.

>

>If you get a low voltage warning on bus A, do you pull the corresponding

>field breaker and engage the cross-tie? Again, if something is shorting out

>the bus (such as shorted windings on the alternator), you are in danger of

>overloading bus B.

>

>Any thoughts?

>

>Adam Molny

>Legacy #151

>

--

-- incoming mail is certified Virus Free.

Bob . . .

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

< Throughout history, poverty is the normal condition >

< of man. Advances which permit this norm to be >

< exceeded -- here and there, now and then -- are the >

< work of an extremely small minority, frequently >

< despised, often condemned, and almost always opposed >

< by all right-thinking people. Whenever this tiny >

< minority is kept from creating, or (as sometimes >

< happens) is driven out of a society, the people >

< then slip back into abject poverty. >

< >

< This is known as "bad luck". >

< -Lazarus Long- >

<------------------------------------------------------>

http://www.aeroelectric.com

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klehman(at)albedo.net
Guest

Posted: Mon Jan 09, 2006 10:18 am Post subject: Z14 Failure Modes and the Cross-Tie

Hi Adam I figure the most likely reason to close the crossfeed is when one alternator simply stops producing power or has been shutdown by the OV protection. Bus voltage will be nominal battery voltage in such a case. With a contactor on the output of an IR regulator even the stator and diodes are out of the circuit when I shut down an alternator or the OVP activates but I'd expect the alternator fuse/breaker/ANL to already be open anyway in that case. I agree that it might be unwise to close the crossfeed if immediately after the low voltage warning you observe that the voltage is below normal battery voltage but then again you have the option if you need the equipment and think maybe you've got a open circuited or disconnected battery (or open master contactor) that has allowed a subsequent OV excursion and alternator shutdown. Plan A would be to leave it alone til on the ground if I don't need it. Any smoke or sparks would definately keep my finger away from the crossfeed. There really isn't much of a "bus" on a small airplane with fuse blocks which makes it very difficult to imagine a shorted bus. Z-14 also gives the option of conducting a single alternator recovery flight home or to a maintanance facility. Ken Adam Molny wrote: I'm laying out the electrical system for my all-glass, all-electric, FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to go, using two full-size alternators. It would be very attractive to have the ability to power both the A and B buses and recharge both batteries from a single alternator when needed. However, I'm having trouble imagining a failure mode where the cross-tie could be used in flight. If the Bus A alternator's field breaker trips in flight (for example), would it be safe to engage the cross-tie? You don't know what caused the failure, and tying the A and B buses together could knock out the B bus. If you get a low voltage warning on bus A, do you pull the corresponding field breaker and engage the cross-tie? Again, if something is shorting out the bus (such as shorted windings on the alternator), you are in danger of overloading bus B. Any thoughts? Adam Molny Legacy #151

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nuckollsr(at)cox.net
Guest

Posted: Mon Jan 09, 2006 10:18 am Post subject: Z14 Failure Modes and the Cross-Tie

99+ percent of alternator failures is to simply stop

producing for whatever reason . . . including ov trip.

A major fraction of what's left will be cause for manual

shutown . . . voltage unstable? Whatever. It is very unlikely

that any alternator failure will take out the b-lead protection.

It's axiomatic that many problems get worse when the pilot

starts messing with things in some attempt to "get all the

goodies back up and running."

The advantage of a fully dual system is that you spread

your backup systems around. One on main bus, one on aux

bus. The best thing to do when something goes T.U. on one

bus is to simply shut that one down. Go into an endurance

mode until comfortable arrival is assured. Battery on the

cold bus is held in reserve. Battery on working bus is

being supported by normal alternator operations.

When and if anything on the 'cold' bus becomes useful

or necessary in the final phase of flight. Close battery

contactor first and watch for normal battery-only

bus levels. Close crossfeed contactor second while observing both

bus voltages now show normal operational levels. Then

finish the flight.

If any voltages appear out of whack after operation of

a switch, re-open the switch immediately and finish the

flight on one bus . . . but don't do this experiment until

you have the airport in sight.

I think it's useful to think of the various system options

as tools for comfortable termination of flight by insuring

availability of minimum equipment . . . the exercises that

pilots go through to perform in-flight diagnostics and/or

get some suite of equipment up running doesn't

necessarily improve outcome is certainly a distraction

and perhaps hazardous.

Only the more complex aircraft can justify Z-14. While

complexity brings capability and convenience, it also

brings workload. If you're vfr in the clear, then perhaps

a total failure is no big deal. When you are depending on at

least the most useful of things to be working then you're

probably IFR and busy with pilot-things to do. The last

thing you want to do is troubleshoot especially when there

is risk of making a situation worse.

Bob . . .

 	  Quote: 	
		  Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

<Adam(at)ValidationPartners.com>

>

>I'm laying out the electrical system for my all-glass, all-electric,

>FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

>go, using two full-size alternators. It would be very attractive to have the

>ability to power both the A and B buses and recharge both batteries from a

>single alternator when needed. However, I'm having trouble imagining a

>failure mode where the cross-tie could be used in flight.

>

>If the Bus A alternator's field breaker trips in flight (for example), would

>it be safe to engage the cross-tie? You don't know what caused the failure,

>and tying the A and B buses together could knock out the B bus.

>

>If you get a low voltage warning on bus A, do you pull the corresponding

>field breaker and engage the cross-tie? Again, if something is shorting out

>the bus (such as shorted windings on the alternator), you are in danger of

>overloading bus B.

>

>Any thoughts?

>

>Adam Molny

>Legacy #151

>

--

-- incoming mail is certified Virus Free.

Bob . . .

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

< Throughout history, poverty is the normal condition >

< of man. Advances which permit this norm to be >

< exceeded -- here and there, now and then -- are the >

< work of an extremely small minority, frequently >

< despised, often condemned, and almost always opposed >

< by all right-thinking people. Whenever this tiny >

< minority is kept from creating, or (as sometimes >

< happens) is driven out of a society, the people >

< then slip back into abject poverty. >

< >

< This is known as "bad luck". >

< -Lazarus Long- >

<------------------------------------------------------>

http://www.aeroelectric.com

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klehman(at)albedo.net
Guest

Posted: Mon Jan 09, 2006 12:00 pm Post subject: Z14 Failure Modes and the Cross-Tie

Hi Adam I figure the most likely reason to close the crossfeed is when one alternator simply stops producing power or has been shutdown by the OV protection. Bus voltage will be nominal battery voltage in such a case. With a contactor on the output of an IR regulator even the stator and diodes are out of the circuit when I shut down an alternator or the OVP activates but I'd expect the alternator fuse/breaker/ANL to already be open anyway in that case. I agree that it might be unwise to close the crossfeed if immediately after the low voltage warning you observe that the voltage is below normal battery voltage but then again you have the option if you need the equipment and think maybe you've got a open circuited or disconnected battery (or open master contactor) that has allowed a subsequent OV excursion and alternator shutdown. Plan A would be to leave it alone til on the ground if I don't need it. Any smoke or sparks would definately keep my finger away from the crossfeed. There really isn't much of a "bus" on a small airplane with fuse blocks which makes it very difficult to imagine a shorted bus. Z-14 also gives the option of conducting a single alternator recovery flight home or to a maintanance facility. Ken Adam Molny wrote: I'm laying out the electrical system for my all-glass, all-electric, FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to go, using two full-size alternators. It would be very attractive to have the ability to power both the A and B buses and recharge both batteries from a single alternator when needed. However, I'm having trouble imagining a failure mode where the cross-tie could be used in flight. If the Bus A alternator's field breaker trips in flight (for example), would it be safe to engage the cross-tie? You don't know what caused the failure, and tying the A and B buses together could knock out the B bus. If you get a low voltage warning on bus A, do you pull the corresponding field breaker and engage the cross-tie? Again, if something is shorting out the bus (such as shorted windings on the alternator), you are in danger of overloading bus B. Any thoughts? Adam Molny Legacy #151

nuckollsr(at)cox.net
Guest

Posted: Mon Jan 09, 2006 12:00 pm Post subject: Z14 Failure Modes and the Cross-Tie

99+ percent of alternator failures is to simply stop

producing for whatever reason . . . including ov trip.

A major fraction of what's left will be cause for manual

shutown . . . voltage unstable? Whatever. It is very unlikely

that any alternator failure will take out the b-lead protection.

It's axiomatic that many problems get worse when the pilot

starts messing with things in some attempt to "get all the

goodies back up and running."

The advantage of a fully dual system is that you spread

your backup systems around. One on main bus, one on aux

bus. The best thing to do when something goes T.U. on one

bus is to simply shut that one down. Go into an endurance

mode until comfortable arrival is assured. Battery on the

cold bus is held in reserve. Battery on working bus is

being supported by normal alternator operations.

When and if anything on the 'cold' bus becomes useful

or necessary in the final phase of flight. Close battery

contactor first and watch for normal battery-only

bus levels. Close crossfeed contactor second while observing both

bus voltages now show normal operational levels. Then

finish the flight.

If any voltages appear out of whack after operation of

a switch, re-open the switch immediately and finish the

flight on one bus . . . but don't do this experiment until

you have the airport in sight.

I think it's useful to think of the various system options

as tools for comfortable termination of flight by insuring

availability of minimum equipment . . . the exercises that

pilots go through to perform in-flight diagnostics and/or

get some suite of equipment up running doesn't

necessarily improve outcome is certainly a distraction

and perhaps hazardous.

Only the more complex aircraft can justify Z-14. While

complexity brings capability and convenience, it also

brings workload. If you're vfr in the clear, then perhaps

a total failure is no big deal. When you are depending on at

least the most useful of things to be working then you're

probably IFR and busy with pilot-things to do. The last

thing you want to do is troubleshoot especially when there

is risk of making a situation worse.

Bob . . .

 	  Quote: 	
		  Hi Adam

I figure the most likely reason to close the crossfeed is when one

alternator simply stops producing power or has been shutdown by the OV

protection. Bus voltage will be nominal battery voltage in such a case.

With a contactor on the output of an IR regulator even the stator and

diodes are out of the circuit when I shut down an alternator or the OVP

activates but I'd expect the alternator fuse/breaker/ANL to already be

open anyway in that case. I agree that it might be unwise to close the

crossfeed if immediately after the low voltage warning you observe that

the voltage is below normal battery voltage but then again you have the

option if you need the equipment and think maybe you've got a open

circuited or disconnected battery (or open master contactor) that has

allowed a subsequent OV excursion and alternator shutdown. Plan A would

be to leave it alone til on the ground if I don't need it. Any smoke or

sparks would definately keep my finger away from the crossfeed. There

really isn't much of a "bus" on a small airplane with fuse blocks which

makes it very difficult to imagine a shorted bus. Z-14 also gives the

option of conducting a single alternator recovery flight home or to a

maintanance facility.

Ken

Adam Molny wrote:

<Adam(at)ValidationPartners.com>

>

>I'm laying out the electrical system for my all-glass, all-electric,

>FADEC-powered Lancair Legacy. The Z-14 system seems like the natural way to

>go, using two full-size alternators. It would be very attractive to have the

>ability to power both the A and B buses and recharge both batteries from a

>single alternator when needed. However, I'm having trouble imagining a

>failure mode where the cross-tie could be used in flight.

>

>If the Bus A alternator's field breaker trips in flight (for example), would

>it be safe to engage the cross-tie? You don't know what caused the failure,

>and tying the A and B buses together could knock out the B bus.

>

>If you get a low voltage warning on bus A, do you pull the corresponding

>field breaker and engage the cross-tie? Again, if something is shorting out

>the bus (such as shorted windings on the alternator), you are in danger of

>overloading bus B.

>

>Any thoughts?

>

>Adam Molny

>Legacy #151

>

--

-- incoming mail is certified Virus Free.

Bob . . .

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

< Throughout history, poverty is the normal condition >

< of man. Advances which permit this norm to be >

< exceeded -- here and there, now and then -- are the >

< work of an extremely small minority, frequently >

< despised, often condemned, and almost always opposed >

< by all right-thinking people. Whenever this tiny >

< minority is kept from creating, or (as sometimes >

< happens) is driven out of a society, the people >

< then slip back into abject poverty. >

< >

< This is known as "bad luck". >

< -Lazarus Long- >

<------------------------------------------------------>

http://www.aeroelectric.com

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