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Questions for Bob after talking to B&C...

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 29, 2013 4:13 pm Post subject: Questions for Bob after talking to B&C...

At 04:08 PM 4/29/2013, you wrote:

 	  Quote: 	
		  



Bob,



B&C recommended I ask you these questions because they did not know 

the answer for them. As you may know, they have a document called 

the 504-500 linked here http://www.bandc.biz/pdfs/504-500_REV_G.pdf. 

This document shows wiring of the S704-1 when using the PMR1C-14 

regulator for the SD-8. Anyway, the wiring on the newest revision of 

Z-13/8 (R) conflicts with their wiring diagram on a couple of 

points, can you please help me understand which one I should use? 

Here are specifically my questions that remained unanswered after 

talking to them:



1. On Z-13/8 (R) you have a jumper going between the positive side 

of the coil and the common pin. On their 505-500 they have nothing. 

On your older Z-13/8 (Q) you had a diode. What is the reason for 

this and which one should I follow?



2. On Z-13/8 (R) you have wired the common on the relay with a 30A 

inline fuse. On their 504-500 they used a 10A breaker. Both are 

wired using a 14AWG wire. What is the reason for such a large fuse? 

Should I really use 30A on this?


	


    Either one works fine. The fuse was selected for

    robustness . . . sorta like a mini current limiter.

    Actually, if you'd like for your SD-8 to be self

    exciting, you can wire it per



http://tinyurl.com/cdnqdf9



    In that drawing I show s fusible link but a 20

    to 30 amp inline fuse would be fine too.

   Bob . . .

idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Mon Apr 29, 2013 6:23 pm Post subject: Re: Questions for Bob after talking to B&C...

Bob,



Thanks for the response, but what about my question #1? should I do the diode between the common and coil or just a standard jumper? I also notice on the Z25L pdf that you linked to you have a diode between the N.O. pin and the Coil as well. What are these for and which method should I use?



Thanks,

Matt

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 30, 2013 7:08 am Post subject: Questions for Bob after talking to B&C...

At 09:23 PM 4/29/2013, you wrote:

 	  Quote: 	
		  



Bob,



Thanks for the response, but what about my question #1? should I do 

the diode between the common and coil or just a standard jumper? I 

also notice on the Z25L pdf that you linked to you have a diode 

between the N.O. pin and the Coil as well. What are these for and 

which method should I use?


	


   I'm not trying to be obtuse. Your question seems

   to offer the notion that there are errors of function

   between the various drawings cited. They all function

   as advertised with respect to the installation and

   operation of an SD-8 alternator. Yes, there are

   variations on a theme which are insignificant to

   the function.



   If you want me to pick one for you, then go with

   the wiring shown in Z-13/8.



   Bob . . .

idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Tue Apr 30, 2013 9:35 am Post subject: Re: Questions for Bob after talking to B&C...

I was not trying to imply that one was incorrect, I just do not understand the purpose of the diode in that application and whether it is necessary or not. B&C support was unable to tell me what it was there for either and directed me to ask you.



- Matt



 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 09:23 PM 4/29/2013, you wrote:

 	  Quote: 	
		  



Bob,



Thanks for the response, but what about my question #1? should I do 

the diode between the common and coil or just a standard jumper? I 

also notice on the Z25L pdf that you linked to you have a diode 

between the N.O. pin and the Coil as well. What are these for and 

which method should I use?



	


   I'm not trying to be obtuse. Your question seems

   to offer the notion that there are errors of function

   between the various drawings cited. They all function

   as advertised with respect to the installation and

   operation of an SD-8 alternator. Yes, there are

   variations on a theme which are insignificant to

   the function.



   If you want me to pick one for you, then go with

   the wiring shown in Z-13/8.



   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Tue Apr 30, 2013 4:42 pm Post subject: Re: Questions for Bob after talking to B&C...

Matt,

Bob's and B&C's drawings do not conflict.  They are different.  There are many different ways to wire an aircraft.  I suggest that you use one of Bob's drawings because his are for the whole electrical system, not just a part of it.

Z-13/8 Rev Q has two diodes connected to the dynamo relay.  These diodes potentially provide power to the relay from two sources: 1. The main power bus.  2. The dynamo.  The diodes isolate the two sources from each other until the relay is energized

Z-13/8 Rev R does not have diodes. 

 You asked which drawing to use.  I suggest Z-13/8 Rev R with a minor change:  Move the jumper from the common terminal of the dynamo relay to the normally open terminal.  The reason is that there could be a failure mode when there is no power available at the main power bus to operate the dynamo relay.  There will always be power available from the dynamo.  And if there isn't, then there is no reason to turn the dynamo relay on.  Perhaps Bob will comment on this suggestion.

 	  Quote: 	
		  1. Am I correct that the S704-1 relay used for the backup alternator is wired to the regulator with the N.O. lead? 	


Yes

 	  Quote: 	
		  2. Can I use the N.C. lead for an "Aux Alt Offline" light? I assume this will be powered when the switch is off (or breaker tripped) right? 	


Yes and Yes.  But why have a light?  It will always be on.  Lights should warn of an unusual situation.

 	  Quote: 	
		  3. If I use an S704-1 relay for the E-Bus feed switch I would wire the Battery bus to the N.O. as well correct? 	


Yes

The two parallel lines below the relay coil represent the metal core of the relay.  When the coil is energized, the core becomes a magnet and pulls the movable contact towards the core and towards the normally open contact.  So the contact closest to the core is N.O.

 	  Quote: 	
		  4. Lastly, if I want to add a light for when the E-Bus feed switch is closed where would I do that? it looks like when the switch is open the N.C. is powered from the Main bus and the N.O. powered from the battery bus, so I do not see where I would tap in a light that is only powered when the switch is closed. Should I just wire the light at the switch to accomplish this instead of at the relay (using Pin 1 on the switch?).

	


  I think that a light will be useful to warn you if the E-Bus switch has been left on after shutdown.  You do not want the battery to run down.  You are correct that there will be power on both the N.O. and COM relay terminals.  A light can not be connected there.  And a light can not be connected to terminal 1 of the switch because it will be in series with the relay coil.  In that case, the light could illuminate dimly with the switch off.  Or the relay might not shut off with the switch.  Of course the light will not illuminate with the switch on because the light will then have ground connected to both of its terminals.  Use a DPST or a DPDT switch for the E-Bus relay.  One half of the switch will operate the relay and the other half will operate the light.

Joe

_________________
Joe Gores

idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Tue Apr 30, 2013 7:43 pm Post subject: Re: Questions for Bob after talking to B&C...

 	  user9253 wrote: 	
		  Matt,

Bob's and B&C's drawings do not conflict.  They are different.  There are many different ways to wire an aircraft.  I suggest that you use one of Bob's drawings because his are for the whole electrical system, not just a part of it.

Z-13/8 Rev Q has two diodes connected to the dynamo relay.  These diodes potentially provide power to the relay from two sources: 1. The main power bus.  2. The dynamo.  The diodes isolate the two sources from each other until the relay is energized

Z-13/8 Rev R does not have diodes. 

 You asked which drawing to use.  I suggest Z-13/8 Rev R with a minor change:  Move the jumper from the common terminal of the dynamo relay to the normally open terminal.  The reason is that there could be a failure mode when there is no power available at the main power bus to operate the dynamo relay.  There will always be power available from the dynamo.  And if there isn't, then there is no reason to turn the dynamo relay on.  Perhaps Bob will comment on this suggestion.

 	  Quote: 	
		  1. Am I correct that the S704-1 relay used for the backup alternator is wired to the regulator with the N.O. lead? 	


Yes

 	  Quote: 	
		  2. Can I use the N.C. lead for an "Aux Alt Offline" light? I assume this will be powered when the switch is off (or breaker tripped) right? 	


Yes and Yes.  But why have a light?  It will always be on.  Lights should warn of an unusual situation.

 	  Quote: 	
		  3. If I use an S704-1 relay for the E-Bus feed switch I would wire the Battery bus to the N.O. as well correct? 	


Yes

The two parallel lines below the relay coil represent the metal core of the relay.  When the coil is energized, the core becomes a magnet and pulls the movable contact towards the core and towards the normally open contact.  So the contact closest to the core is N.O.

 	  Quote: 	
		  4. Lastly, if I want to add a light for when the E-Bus feed switch is closed where would I do that? it looks like when the switch is open the N.C. is powered from the Main bus and the N.O. powered from the battery bus, so I do not see where I would tap in a light that is only powered when the switch is closed. Should I just wire the light at the switch to accomplish this instead of at the relay (using Pin 1 on the switch?).

	


  I think that a light will be useful to warn you if the E-Bus switch has been left on after shutdown.  You do not want the battery to run down.  You are correct that there will be power on both the N.O. and COM relay terminals.  A light can not be connected there.  And a light can not be connected to terminal 1 of the switch because it will be in series with the relay coil.  In that case, the light could illuminate dimly with the switch off.  Or the relay might not shut off with the switch.  Of course the light will not illuminate with the switch on because the light will then have ground connected to both of its terminals.  Use a DPST or a DPDT switch for the E-Bus relay.  One half of the switch will operate the relay and the other half will operate the light.

Joe 	




Thanks Joe, What happens if the Aux alternator is turned on while under normal operations and both alternators are feeding the electrical system at one time?



As for the ebus feed light, what about putting the anode of the LED on the N.O. contact of the relay (coming from the battery bus) and the cathode on the side of the coil where the switch is connected?



Thanks,

Matt

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Wed May 01, 2013 5:29 am Post subject: Re: Questions for Bob after talking to B&C...

Matt,

 	  Quote: 	
		  Thanks Joe, What happens if the Aux alternator is turned on while under normal operations and both alternators are feeding the electrical system at one time? 	


I do not think that anything will blow up.  But the voltage might not be steady.  Bob can answer better than I can.

 	  Quote: 	
		  As for the ebus feed light, what about putting the anode of the LED on the N.O. contact of the relay (coming from the battery bus) and the cathode on the side of the coil where the switch is connected? 	


 In other words, connect the diode in parallel with the relay coil.  The Diode needs a series resistor to limit current.  It is good wiring practice to be able to shut off all battery loads as close to the battery as possible.  Thus the master contactor and E-bus relay should both be located near the battery.  If a wire is connected to the battery side of the E-Bus relay and run into the cockpit, that wire will always be hot with no way to shut it off.  In the event of an imminent  forced off-airport landing, the pilot needs to shut off all electrical sources to prevent sparks that could ignite gasoline.  Same thing in case of smoke in the cockpit.  Using a double pole switch will eliminate that long hot wire run.  And the switch will be located for easy connection to a light.

  Another option is to connect an un-switched light to the E-Bus.  It will warn if either the master switch or E-Bus switch is left on.

Or the pilot could just look at his electronic devices to be sure they are off before she exits the aircraft.  Then no light is needed.

  I think that having an avionics master is a bad idea.  It is a single point of failure.  I routinely leave all of my radios and EFIS on, even when cranking the engine.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 01, 2013 6:43 am Post subject: Questions for Bob after talking to B&C...

At 12:35 PM 4/30/2013, you wrote:

 	  Quote: 	
		  



I was not trying to imply that one was incorrect, I just do not 

understand the purpose of the diode in that application and whether 

it is necessary or not. B&C support was unable to tell me what it 

was there for either and directed me to ask you.


	


   Understand. The general rule of thumb is that inductive

   loads (especially coils of relays and contactors) be

   transient suppressed with some technology that satisfies

   design goals.



   Here's a data dump on the background for selection and

   incorporation of inductive load transient mitigation:

http://tinyurl.com/ccuvhaf

http://tinyurl.com/c6zodmx

http://tinyurl.com/cxlx35m

http://tinyurl.com/c2c38ce



    In some instances, drawings that I produce may NOT

    include a transient suppressor. This is the case when

    the electronics that drive the relay have field collapse

    transient suppression built in . . . or when incorporation

    of the feature adds no value. In the case where a crowbar

    ovm is wired across an alternator control relay, components

    within the ovm take care of the problem; no additional

    suppression is needed.



    My train of thought was getting de-railed by references to

    N.O. or N.C. contacts on relays; vagaries of design that

    did not impact the physics. Forgive me if I came off

    unnecessarily terse . . . our trains of thought were

    running on different tracks! Hope the narrative above

   helps.



   Bob . . .

idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Wed May 01, 2013 6:50 am Post subject: Re: Questions for Bob after talking to B&C...

 	  user9253 wrote: 	
		  Matt,

 	  Quote: 	
		  Thanks Joe, What happens if the Aux alternator is turned on while under normal operations and both alternators are feeding the electrical system at one time? 	


I do not think that anything will blow up.  But the voltage might not be steady.  Bob can answer better than I can.

 	  Quote: 	
		  As for the ebus feed light, what about putting the anode of the LED on the N.O. contact of the relay (coming from the battery bus) and the cathode on the side of the coil where the switch is connected? 	


 In other words, connect the diode in parallel with the relay coil.  The Diode needs a series resistor to limit current.  It is good wiring practice to be able to shut off all battery loads as close to the battery as possible.  Thus the master contactor and E-bus relay should both be located near the battery.  If a wire is connected to the battery side of the E-Bus relay and run into the cockpit, that wire will always be hot with no way to shut it off.  In the event of an imminent  forced off-airport landing, the pilot needs to shut off all electrical sources to prevent sparks that could ignite gasoline.  Same thing in case of smoke in the cockpit.  Using a double pole switch will eliminate that long hot wire run.  And the switch will be located for easy connection to a light.

  Another option is to connect an un-switched light to the E-Bus.  It will warn if either the master switch or E-Bus switch is left on.

Or the pilot could just look at his electronic devices to be sure they are off before she exits the aircraft.  Then no light is needed.

  I think that having an avionics master is a bad idea.  It is a single point of failure.  I routinely leave all of my radios and EFIS on, even when cranking the engine.

Joe 	




Joe, are you saying that the E-Bus relay should be located on the Engine side of the Firewall? I thought it was on the cockpit side for heat protection.



- Matt

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Wed May 01, 2013 7:37 am Post subject: Re: Questions for Bob after talking to B&C...

Matt,

 	  Quote: 	
		   are you saying that the E-Bus relay should be located on the Engine side of the Firewall? 	


Yes

 	  Quote: 	
		  I thought it was on the cockpit side for heat protection. 	


Theoretically speaking, a relay will last longer in a cool environment.  Practically speaking, the life of a relay will not be significantly shortened if located in the engine compartment.  Automobiles have relays located in the engine compartment.  It must get pretty hot under the hood in the summer when stuck in a traffic jam.  The master contactor is a big relay usually located inside of the cowl.  Relays can be used for different reasons like circuit isolation or to handle loads that are too big for a small switch.  In the case of an E-bus relay, I believe the purpose is remote control.  After all, a simple switch can carry the E-bus loads without using a relay.  Remote control using relays or contactors allows power to be shut off near the source, thus reducing the chances of smoke or fire in case of an accident.  When the engine quits over hostile terrain and the pilot is busy looking for a survival crash site, will she remember to shut off the master and E-Bus?  

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 01, 2013 8:21 am Post subject: Questions for Bob after talking to B&C...

At 08:29 AM 5/1/2013, you wrote:




Matt,



 > Thanks Joe, What happens if the Aux alternator is turned on while 

under normal operations and both alternators are feeding the 

electrical system at one time?



I do not think that anything will blow up.  But the voltage might not 

be steady.  Bob can answer better than I can.



     Running two alternators at the same time never

     offers a potential for hazard. The alternator with

     the higher regulation set point will attempt to shoulder

     all system loads. In Z-12, the second, smaller alternator

     is constantly connected to the bus and is normally switched

     ON. Design goals for this configuration call for the smaller

     alternator regulator to be set at 13.6 volts while the main

     alternator is set for 14.6.



     This means that the standby alternator is not capable of

     charging the battery. Further, the standby regulator

     senses a 'too high' bus voltage while the main alternator

     is running. This causes the standby system to simply relax.

     Standby alternator field voltage goes to zero.



     If the main alternator quits, bus voltage sags. The SB

     regulator wakes up and brings the SB alternator on line.

     The SB regulator doesn't have a low voltage warning system.

     Instead, the light monitors field voltage. If the voltage

     comes up, the valid assumption is that the alternator is now

     loaded due to a perceived drop in bus voltage. An added feature

     measures load on the alternator and flashes the light if loads

     exceed the alternator's rated current.



     The SD-8 doesn't have that much sophistication. If it is

     paralleled with a second alternator, it will STILL attempt

     to pick up all system loads if its regulator is set higher

     than its companion alternator. If loads exceed SD-8 output,

     the bus voltage sags and the companion alternator will come

     on line and pick up the difference while allowing the SD-8

     to run 'full bore'.



     If the main alternator voltage is set higher, the SD-8

     will shut down and remain unloaded unless and until the

     main alternator fails or is shut off. At that time, continued

     flight with the SD-8 calls for reducing system loads to

     some value at or below the SD-8 output of 8-10 amps.



     But in either instance, there is no immediate hazard to

     electrical system operation with paralleled alternators

     of equal or different sizes.

   Bob . . .

idleup

Joined: 06 Aug 2011
Posts: 19

Posted: Wed May 01, 2013 10:03 am Post subject: Re: Questions for Bob after talking to B&C...

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 08:29 AM 5/1/2013, you wrote:

Matt,



 > Thanks Joe, What happens if the Aux alternator is turned on while 

under normal operations and both alternators are feeding the 

electrical system at one time?



I do not think that anything will blow up.  But the voltage might not 

be steady.  Bob can answer better than I can.



     Running two alternators at the same time never

     offers a potential for hazard. The alternator with

     the higher regulation set point will attempt to shoulder

     all system loads. In Z-12, the second, smaller alternator

     is constantly connected to the bus and is normally switched

     ON. Design goals for this configuration call for the smaller

     alternator regulator to be set at 13.6 volts while the main

     alternator is set for 14.6.



     This means that the standby alternator is not capable of

     charging the battery. Further, the standby regulator

     senses a 'too high' bus voltage while the main alternator

     is running. This causes the standby system to simply relax.

     Standby alternator field voltage goes to zero.



     If the main alternator quits, bus voltage sags. The SB

     regulator wakes up and brings the SB alternator on line.

     The SB regulator doesn't have a low voltage warning system.

     Instead, the light monitors field voltage. If the voltage

     comes up, the valid assumption is that the alternator is now

     loaded due to a perceived drop in bus voltage. An added feature

     measures load on the alternator and flashes the light if loads

     exceed the alternator's rated current.



     The SD-8 doesn't have that much sophistication. If it is

     paralleled with a second alternator, it will STILL attempt

     to pick up all system loads if its regulator is set higher

     than its companion alternator. If loads exceed SD-8 output,

     the bus voltage sags and the companion alternator will come

     on line and pick up the difference while allowing the SD-8

     to run 'full bore'.



     If the main alternator voltage is set higher, the SD-8

     will shut down and remain unloaded unless and until the

     main alternator fails or is shut off. At that time, continued

     flight with the SD-8 calls for reducing system loads to

     some value at or below the SD-8 output of 8-10 amps.



     But in either instance, there is no immediate hazard to

     electrical system operation with paralleled alternators

     of equal or different sizes.

   Bob . . . 	




Bob, thanks for the very detailed explanation of how the two alternators will respond to one other when in operation at the same time.



- Matt

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 01, 2013 10:43 am Post subject: Questions for Bob after talking to B&C...

 	  Quote: 	
		  In the case of an E-bus relay, I believe the purpose is remote 

control.  After all, a simple switch can carry the E-bus loads 

without using a relay.  Remote control using relays or contactors 

allows power to be shut off near the source, thus reducing the 

chances of smoke or fire in case of an accident.


	


   Correct. The e-bus alternate feed relay is

   actually a mini-contactor for a two layer

   electrical system. Layer 1 is a battery and

   SD-8 alternator driving a small bus (e-bus).

   Closing a big battery contactor to add a second layer

   consisting of larger alternator and bus that

   runs items not necessary for en route endurance

   operations.



 	  Quote: 	
		     When the engine quits over hostile terrain and the pilot is busy 

 looking for a survival crash site, will she remember to shut off 

 the master and E-Bus?


	


    Exactly. The function of the alternate feed

    relay is to facilitate actions that get the

    electrical system down to max-dark. This is

    why the wires on the hot side of the alternate

    feed relay are marked with the (*) calling for

    'short as practical'.



    Environmental temperatures for off-the-shelf

    automotive relays are not a major concern. Everything

    used under the hood of a car is entirely suited

    for use under the cowl of an airplane.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 01, 2013 10:52 am Post subject: Questions for Bob after talking to B&C...

 	  Quote: 	
		  

Bob, thanks for the very detailed explanation of how the two 

alternators will respond to one other when in operation at the same time.



- Matt


	


   It occurs to me that the narration I offered was

   true of two alternators like a L60/SD-20 pair

   or perhaps an L60/SD-8 pair. If the two alternators

   are of similar or equal size -AND- depending on

   regulator dynamics, it's possible that the two

   systems will launch into a sort of volley-ball

   behavior where they toss system loads back and

   forth at each other.



   About 30 years ago I proposed a PARALLELING

   regulator design for the Cessna 303 Crusader's

   dual alternators. That was the first time I

   witnessed this effect. Again, no particular

   hazard is created but the behavior can be

   annoying to spectacular.

   Bob . . .

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