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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sat Jan 02, 2010 9:13 am Post subject: Questions about circuit protection

1/2/2010



Hello Matthew Schumacher, You wrote: "I think I will just get fuse blocks 

per your recommendation for the reasons you mention, but also because 

problems with a fuse can be remedied in the air quickly and easily."



If you are thinking of replacing fuses in the air to trouble shoot and solve 

an electrical problem please think again. There are several disadvantages. 

Some are:



1) Your airplane's Operating Limitations (part of its airworthiness 

certificate) will require you to equip the aircraft in accordance with 14 

CFR 91.205 if you fly at night or IFR.



Paragraph 91.205 (c) (6) says: "One spare set of fuses, or three spare fuses 

of each kind required, that are accessible to the pilot in flight."



This means that, by regulation, if you design your airplane so that you have 

access to those fuse blocks in flight then you must also have available to 

you all those spare fuses while in flight. Do you want to create that burden 

/ nuisance / danger?



2) Trouble shooting an electrical system in flight by fumbling around to 

locate and then insert the appropriate fuse is not a good idea, particularly 

at night or IFR when you should be concentrating on flying the airplane.



So fuse blocks are a good idea, but where you locate them has some 

operational and safety implications. Please read some more of Bob Nuckolls' 

philosophy regarding electrical problems / failures in flight.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



=========================================================



Time: 07:42:35 PM PST US

From: Matthew Schumacher <schu(at)schu.net>

Subject: Re: AeroElectric-List: Questions about circuit protection.

First, thank you very much for looking at my stuff Bob.  I greatly

appreciate it and have donated to keep this list going...



..................................... big skip 

.....................................



I know that fuses/breakers/fuselinks protect the wiring, what I was

missing was the part about problems with one component spreading to

others instead of being isolated.  I think I will just get fuse blocks

per your recommendation for the reasons you mention, but also because

problems with a fuse can be remedied in the air quickly and easily.



Thanks again,

schu

speedy11(at)aol.com
Guest

Posted: Sat Jan 02, 2010 9:25 am Post subject: Questions about circuit protection

Often times we get admonishments on this forum to not do something and our  questions are never answered.  While the admonishment is fine (and  welcomed) when coming from someone so educated in electricity as Bob,  getting the questions answered is the desire.

 Yes, you can bundle some of the lighting on a single breaker - realizing  that the breaker and wires need to be sized accordingly for the load.   Bob's advice is to consider using fuses.  You can have a fuse for each  light for a fraction of the cost in weight and money as the breaker.   Personally, I chose breakers for my airplane.

 Personally I would not use a single breaker for the E-bus and omit breakers  for individual devices on the bus.  Again you would have to size the  breaker for the entire load and wiring would have to match.  In my opinion,  not a logical approach.  Bob's argument for fuses should again be  considered.

 As far as fuselinks, I don't understand them either.  I haven't  studied them because I had no application for them.

 Regards,

 Stan Sutterfield

 Do not archive

  	  Quote: 	
		     Can I group up some of the lighting on a

single    breaker?  Also, what about using a breaker for the entire e-bus

then    omitting the breakers for the devices on the ebus?  The lines will

be    real short and it eliminates the single point of failure (breaker.)

Also,    what about fuselinks?  I understand them to be like a fuse that

blows    extremely slowly, but I'm not fully understanding when and where

to use    them. 	


 

  

  [quote][b]

schu(at)schu.net
Guest

Posted: Sat Jan 02, 2010 11:09 am Post subject: Questions about circuit protection

bakerocb(at)cox.net wrote:

 	  Quote: 	
		   If you are thinking of replacing fuses in the air to trouble shoot and

 solve an electrical problem please think again. There are several

 disadvantages. Some are:

 

 1) Your airplane's Operating Limitations (part of its airworthiness

 certificate) will require you to equip the aircraft in accordance with

 14 CFR 91.205 if you fly at night or IFR.

 

 Paragraph 91.205 (c) (6) says: "One spare set of fuses, or three spare

 fuses of each kind required, that are accessible to the pilot in flight."

 

 This means that, by regulation, if you design your airplane so that you

 have access to those fuse blocks in flight then you must also have

 available to you all those spare fuses while in flight. Do you want to

 create that burden / nuisance / danger?


	




Hold on, back the truck up.  Are you saying that if I put the fuses

under the panel where they aren't accessible then my airplane will still

meet 14 CFR 91.205 (c) and that I won't need to carry spares?



I would read "that are accessible to the pilot in flight" to mean that

the fuse panel is accessible to the pilot, not the fusees since who

cares if you can get to the fuses if you can't get to the panel.



schu

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 02, 2010 10:38 pm Post subject: Questions about circuit protection

 	  Quote: 	
		  

Hold on, back the truck up.  Are you saying that if I put the fuses

under the panel where they aren't accessible then my airplane will still

meet 14 CFR 91.205 (c) and that I won't need to carry spares?



I would read "that are accessible to the pilot in flight" to mean that

the fuse panel is accessible to the pilot, not the fusees since who

cares if you can get to the fuses if you can't get to the panel.


	


    First, 14 CFR 91.205 doesn't apply to an amateur built

    airplane. That's not to imply that the FARS don't have

    some things to be considered . . . but you have no

    obligation to consult these documents that apply to

    type certificated aircraft only. Further, 91.205 isn't

    the ONLY milestone at which your project is essentially

    "un-certifiable".



    But assume you adopt failure tolerance as a

    design goal. For every piece of equipment

    "critical" for the manner in which you plan to use

    the airplane, then that piece of equipment needs to

    be backed up with a plan-B. There are 100 times

    more failures in a piece of electronics that DOES

    NOT blow a fuse than there are failures that DO

    blow a fuse. If that piece of equipment is deemed

    critical, then having spare fuses for the circuit

    that supports that system is whistling in the dark.



    So assuming you have a back up for every POTENTIALLY

    critical system, then if follows that there are NO

    critical systems. Hence, whether or not you can reach

    breakers or fuses for any system is immaterial.



    Bob . . .

bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sun Jan 03, 2010 8:32 am Post subject: Questions about circuit protection

1/3/2009



Hello Again Matthew Schumacher, You wrote:



1) "Are you saying that if I put the fuses under the panel where they aren't 

accessible then my airplane will still meet 14 CFR 91.205 (c) and that I 

won't need to carry spares?"



Yes. That is exactly what the regulation is saying. If the pilot does not 

have access, while in flight,  to the location of fuses installed in the 

aircraft's electrical system then there is no 91.205 regulatory requirment 

to carry any spare fuses.



 2) "I would read "that are accessible to the pilot in flight" to mean that 

the fuse panel is accessible to the pilot,......."



That is correct.



3) "..........not the fusees since who cares if you can get to the fuses if 

you can't get to the panel."



Again correct. Your reasoning, and the reasoning of the regulation, is that 

if you cannot get access to the location of the fuses installed in the 

electrical system while in flight then there is no reason for the pilot to 

carry, and have access to, spare fuses while in flight.



Now the wise pilot would carry some spare fuses, as well as some other spare 

items or tools (which can be discussed at length), so that he may perform 

some limited trouble shooting / repair work if needed on the ground at some 

away from home location in order to get back to home base or some other 

location where he might be able to effect a more permanent repair.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



PS: If one is designing and manufacturing a 14 CFR Part 23 type certificated 

aircraft the regulations / requirements for fuse location in the aircraft's 

electrical system are found in

Part 23.1357 (d) which says:



"If the ability to reset a circuit breaker or replace a fuse is essential to 

safety in flight, that circuit breaker or fuse must be so located and 

identified that it can be readily reset or replaced in flight."



But experimental amateur built aircraft are not required, per se, to comply 

with 14 CFR Part 23.



If we build our experimental amateur built aircraft's electrical system in 

accordance with the philosophy that things can fail and that we have a plan 

B back up that will allow graceful degradation and continued safe flight to 

an acceptable landing site then no fuse in our electrical system would be 

"essential to safety in flight".

====================================================



Time: 11:09:21 AM PST US

From: Matthew Schumacher <schu(at)schu.net>

Subject: Re: AeroElectric-List: Questions about circuit protection

bakerocb(at)cox.net wrote:

 	  Quote: 	
		   If you are thinking of replacing fuses in the air to trouble shoot and

 solve an electrical problem please think again. There are several

 disadvantages. Some are:



 1) Your airplane's Operating Limitations (part of its airworthiness

 certificate) will require you to equip the aircraft in accordance with

 14 CFR 91.205 if you fly at night or IFR.



 Paragraph 91.205 (c) (6) says: "One spare set of fuses, or three spare

 fuses of each kind required, that are accessible to the pilot in flight."



 This means that, by regulation, if you design your airplane so that you

 have access to those fuse blocks in flight then you must also have

 available to you all those spare fuses while in flight. Do you want to

 create that burden / nuisance / danger?


	




Hold on, back the truck up.  Are you saying that if I put the fuses

under the panel where they aren't accessible then my airplane will still

meet 14 CFR 91.205 (c) and that I won't need to carry spares?



I would read "that are accessible to the pilot in flight" to mean that

the fuse panel is accessible to the pilot, not the fusees since who

cares if you can get to the fuses if you can't get to the panel.



schu

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Jan 04, 2010 8:47 am Post subject: Re: Questions about circuit protection

Schu,



No switch is shown for the Hobbs meter.  I assume that an oil pressure switch will be connected in series with it.



The diode across the E-Bus relay is backwards.



The spike protection diode is missing from the dynamo relay coil.  The arrow should point towards positive.



No over-voltage protection is shown for the main alternator.  Over-voltage protection will do more towards safeguarding avionics than an avionics master switch.



Since there are only two devices connected to the avionics bus, an avionics bus is not needed.  Just connect those two devices to the switch without having a bus.  Better yet, use two switches.  If one of the devices starts smoking, you can shut it off and continue to use the other.  Wire the E-Bus diode directly to the main power bus without a switch.  An avionics master switch makes it convenient to shut off all of the avionics at once.  But when it fails, so will everything connected to it.  In addition, individual downstream switches will not get exercised, leading to corrosion and eventual failure of seldom used switches.



Fuses offer better protection than circuit breakers.  And fuses are less expensive.  Yes, more than one load can be connected to a fuse or circuit breaker.  But if one of the loads shorts out, it will blow the fuse and remove power from the other loads.  It is better to install a larger fuse block so that each load can have its own fuse.  Regulations for type certificated aircraft require that critical fuses be replaceable in flight.  However, it is better not to have any critical equipment.  Backup equipment makes critical devices non-critical.  Fuses should be replaced on the ground, not in the air.



I like your schematic.  What program do you use to draw it and to convert it a pdf?



Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 04, 2010 9:51 am Post subject: Questions about circuit protection

 	  Quote: 	
		  Wire the E-Bus diode directly to the main power bus without a 

switch.  An avionics master switch makes it convenient to shut off 

all of the avionics at once.  But when it fails, so will everything 

connected to it.  In addition, individual downstream switches will 

not get exercised, leading to corrosion and eventual failure of 

seldom used switches.


	


   True with one minor exception. Assuming one adds an "avionics master switch"

   in series with the normal feed path diode, it's still backed up by the

   alternate feed path switch. So its addition doesn't offer an increased

   risk for loss of the bus. Both the AV master and E-bus Alt Feed switches

   will get operated once per flight cycle as a part of pre-flight . . .

   so corrosion from dis-use is not a concern either.



   Otherwise . . . well stated sir.



   Bob . . .

schu(at)schu.net
Guest

Posted: Mon Jan 04, 2010 11:28 am Post subject: Questions about circuit protection

user9253 wrote:

 	  Quote: 	
		   

 

 Schu,

 

 No switch is shown for the Hobbs meter.  I assume that an oil pressure switch will be connected in series with it.

 

 The diode across the E-Bus relay is backwards.

 

 The spike protection diode is missing from the dynamo relay coil.  The arrow should point towards positive.

 

 No over-voltage protection is shown for the main alternator.  Over-voltage protection will do more towards safeguarding avionics than an avionics master switch.

 

 Since there are only two devices connected to the avionics bus, an avionics bus is not needed.  Just connect those two devices to the switch without having a bus.  Better yet, use two switches.  If one of the devices starts smoking, you can shut it off and continue to use the other.  Wire the E-Bus diode directly to the main power bus without a switch.  An avionics master switch makes it convenient to shut off all of the avionics at once.  But when it fails, so will everything connected to it.  In addition, individual downstream switches will not get exercised, leading to corrosion and eventual failure of seldom used switches.

 

 Fuses offer better protection than circuit breakers.  And fuses are less expensive.  Yes, more than one load can be connected to a fuse or circuit breaker.  But if one of the loads shorts out, it will blow the fuse and remove power from the other loads.  It is better to install a larger fuse block so that each load can have its own fuse.  Regulations for type certificated aircraft require that critical fuses be replaceable in flight.  However, it is better not to have any critical equipment.  Backup equipment makes critical devices non-critical.  Fuses should be replaced on the ground, not in the air.

 

 I like your schematic.  What program do you use to draw it and to convert it a pdf?

 

 Joe

 




	


Joe,



Thanks for your helpful comments.



I would like to get an oil pressure switch for the hobbs (and for an

idiot light) but I don't know where to source that.  I looked around at

Aircraft Spruce but didn't find anything.  Do you know where I can find

this?



Thanks for finding the diode issues.  I'll correct them in the drawing.



There is over voltage protection internal to the main alternator since

it is a plane power unit.



The schematic was written in visio with the aeroelectric stencil set:



http://www.lucubration.com/open-source-projects/aeroelectric-visio-symbols.html



Converting to pdf is a little bit more involved but not bad (right

Tim?).  Simply install any postscript compatible printer (I like the

apple color laser PS models), then tell windows that the port used is

"save as file."  When you print to that printer then it will prompt you

for a file name, call the file drawing.ps or whatever, then use a

postscript to pdf converter to make the pdf.  A free online one is

http://ps2pdf.com .  The advantage to doing it this way is postscript is

a vector based image not raster.  This means that it isn't a 'picture'

as much as a set of points what the printer fills in (not unlike a cad

file.)  This is why the file size is so small and why you can zoom in as

close as you want and the edges are still sharp.  The pdf viewer can

re-render the image at any ratio.



Clear as mud?



schu

schu(at)schu.net
Guest

Posted: Mon Jan 04, 2010 11:59 am Post subject: Questions about circuit protection

user9253 wrote:

 	  Quote: 	
		   The spike protection diode is missing from the dynamo relay coil.  The arrow should point towards positive.


	


Joe,



I looked at the dynamo relay coil but it is wired exactly as shown in

Z-25 and Z-13/8.



Bob, I would be very grateful if you could explain what the two diodes

are for on the self exciting SD-8 drawing since since they are wired

differently than the other relays.



Thanks,

schu

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Jan 04, 2010 12:02 pm Post subject: Re: Questions about circuit protection

Schu,

Thanks for the info about using Visio.

As for an oil pressure switch, your engine needs an oil pressure port and the switch threads would have to match.  I do not know where to buy it.

There was a recent discussion on AeroElectric about Hobbs meters.  Read what others said:

http://forums.matronics.com/viewtopic.php?t=66204&highlight=hobbs

Joe

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Jan 04, 2010 12:25 pm Post subject: Re: Questions about circuit protection

 	  Quote: 	
		  I looked at the dynamo relay coil but it is wired exactly as shown in

Z-25 and Z-13/8. 	


Schu,

It looks like I was wrong about the diode missing from your dynamo relay coil.  The over-voltage protection probably shorts out any spike and thus the diode is not needed.

As for the two diodes, they isolate the two power sources from each other.  The dynamo is one source and the other source is a combination of the battery and main alternator.

Joe

_________________
Joe Gores

tim2542(at)sbcglobal.net
Guest

Posted: Mon Jan 04, 2010 12:55 pm Post subject: Questions about circuit protection

Matt wont your EFIS track your hours for you? Maybe you don't need a Hobbs

at all. I know the GRT stuff does this, I believe it tracks engine and

flight time separately and automatically. I bet your AFS does as well.

Tim



--

schu(at)schu.net
Guest

Posted: Mon Jan 04, 2010 3:55 pm Post subject: Questions about circuit protection

Tim Andres wrote:

 	  Quote: 	
		   

 

 Matt wont your EFIS track your hours for you? Maybe you don't need a Hobbs

 at all. I know the GRT stuff does this, I believe it tracks engine and

 flight time separately and automatically. I bet your AFS does as well.

 Tim


	


It does, but I want something more reliable than the EFIS, and it also

serves as total time which is nice, but your right, I can go without it.



schu

trigo(at)mail.telepac.pt
Guest

Posted: Mon Jan 04, 2010 6:07 pm Post subject: Questions about circuit protection

Whenever this “fuses versus circuit breakers” discussion comes afloat, I always wonder why TC aircraft always used circuit breakers…  

   

Carlos  

   

   

[quote] --

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 04, 2010 8:25 pm Post subject: Questions about circuit protection

At 01:56 PM 1/4/2010, you wrote:

 	  Quote: 	
		  



user9253 wrote:

 > The spike protection diode is missing from the dynamo relay 

 coil.  The arrow should point towards positive.



Joe,



I looked at the dynamo relay coil but it is wired exactly as shown in

Z-25 and Z-13/8.



Bob, I would be very grateful if you could explain what the two diodes

are for on the self exciting SD-8 drawing since since they are wired

differently than the other relays.


	


   Those are "steering" diodes that make power available

   from either the battery or a spinning alternator to

   get the relay to energize.



   The relay doesn't need an coil suppression diode

   with an OV module installed.



   Bob . . .

bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Tue Jan 05, 2010 5:38 am Post subject: Questions about circuit protection

1/3/2010 -- 1/5/2010



Hello Bob Nuckolls, May I "Make your day by showing you where you are

wrong?"



You wrote (see your posting copied below):



"First, 14 CFR 91.205 doesn't apply to an amateur built airplane."



and



"....... but you have no obligation to consult these documents that apply to

type certificated aircraft only."



Those statements are not correct. Each experimental amateur built aircraft

will be issued an initial airworthiness certificate in accordance with FAA

Order 8130.2F (or the current version of that order). That airworthiness

certificate will include a number of Operating Limitations, written in

accordance with that order, that apply to that specific aircraft.



Per FAA Order 8130.2F the Operating Limitations will state: "After

completion of Phase I flight testing, unless appropriately equipped for

night and/or instrument flight in accordance with 91.205, this aircraft is

to be operated under VFR, day only."



That sentence means that if one is operating his aircraft at night or in

instrument conditions it must be equipped in accordance with 91.205. The

attached document will provide additional details on this subject.



'OC' Says: "The best investment we can make is the effort to gather and

understand knowledge."



===========================================================

Time: 10:38:19 PM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

Subject: Re: Questions about circuit protection



 	  Quote: 	
		  Hold on, back the truck up.  Are you saying that if I put the fuses

under the panel where they aren't accessible then my airplane will still

meet 14 CFR 91.205 (c) and that I won't need to carry spares?



I would read "that are accessible to the pilot in flight" to mean that

the fuse panel is accessible to the pilot, not the fusees since who

cares if you can get to the fuses if you can't get to the panel.


	


    First, 14 CFR 91.205 doesn't apply to an amateur built

    airplane. That's not to imply that the FARS don't have

    some things to be considered . . . but you have no

    obligation to consult these documents that apply to

    type certificated aircraft only. Further, 91.205 isn't

    the ONLY milestone at which your project is essentially

    "un-certifiable".



    But assume you adopt failure tolerance as a

    design goal. For every piece of equipment

    "critical" for the manner in which you plan to use

    the airplane, then that piece of equipment needs to

    be backed up with a plan-B. There are 100 times

    more failures in a piece of electronics that DOES

    NOT blow a fuse than there are failures that DO

    blow a fuse. If that piece of equipment is deemed

    critical, then having spare fuses for the circuit

    that supports that system is whistling in the dark.



    So assuming you have a back up for every POTENTIALLY

    critical system, then if follows that there are NO

    critical systems. Hence, whether or not you can reach

    breakers or fuses for any system is immaterial.



    Bob . . .

ABEA_Minimum_Inst_Requirements_9.doc

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 05, 2010 7:04 am Post subject: Questions about circuit protection

At 06:52 PM 1/4/2010, you wrote:

  	  Quote: 	
		   Whenever this “fuses versus circuit breakers” discussion comes afloat, I always wonder why TC aircraft always used circuit breakers…

  

 Carlos 	


   They didn't. The first airplanes to get electrical

   systems at Cessna used fuses. They were cartridge

   fuse holders with caps that could easily be dropped

   on the floor and be difficult to find. When miniature,

   low cost breakers came along, they offered a means

   by which operational and environmental concerns

   for the use of glass cartridge fuses could be

   addressed.



   It wasn't until the blade fuse came along that

   environmental issues were resolved for re-considering

   fuses in airplanes. It wasn't until we address the

   ideas of failure tolerant system design that the

   operational issues were resolved.



   If the TC aircraft guys were so disposed, they

   could do exactly what we're doing right now. But

   regulatory inertia makes this unlikely to happen.



   Bob . . .    [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 05, 2010 9:04 am Post subject: Questions about circuit protection

At 07:15 AM 1/5/2010, you wrote:



 	  Quote: 	
		  1/3/2010 -- 1/5/2010



Hello Bob Nuckolls, May I "Make your day by showing you where you are

wrong?"



You wrote (see your posting copied below):



"First, 14 CFR 91.205 doesn't apply to an amateur built airplane."


	


    Thanks for posting the review of instrumentation

    requirements! With your permission, I'll post it

    to aeroelectric.com and index it in the reference

    documents section.



        Bob . . .

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