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Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Tue Jan 24, 2012 11:23 am Post subject: Fuses instead of breakers

I really like the idea of using fuses rather than breakers.  The ATC  

style fuses look like a excellent product.



However, I cannot find any "slo-blow" versions.  Do they exist ? How  

do I decide on the size of the fuse when manufacturers of products  

recommend a breaker or slow-blo fuse ?



For example, the Lightspeed ignition instructions suggest a 5A breaker  

with an 18AWG wire.  So a 7.5A or 10A fuse could easily be used with  

that wire.



An ATC fuse typically blows at 125% of rating within a second, much  

faster than a breaker.  How do I know what the peak current is on  

various devices to know that there will not be a nuisance trip (a  

really bad thing for electronic ignitions) with a fast blow fuse ?



Jeff Page

Dream Aircraft Tundra #10

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 24, 2012 1:30 pm Post subject: Fuses instead of breakers

At 01:16 PM 1/24/2012, you wrote:




I really like the idea of using fuses rather than breakers.  The ATC

style fuses look like a excellent product.



   They are . . .



However, I cannot find any "slo-blow" versions.  Do they exist ? How

do I decide on the size of the fuse when manufacturers of products

recommend a breaker or slow-blo fuse ?



    Excellent question. It's not always clear to me why

    any given installation instruction calls for a "slow-blow"

    fuse. WAAaayyy back when, one could purchase fuses for a

    given current rating that offered different time constants.



    In automobiles I've found that many fuses are way 'oversized'

    to the task while still appropriate to protection of the

    wire. I don't think there are any fuses in my mini-van under

    10A and most are over 10A.



For example, the Lightspeed ignition instructions suggest a 5A breaker

with an 18AWG wire.  So a 7.5A or 10A fuse could easily be used with

that wire.



    The Lightspeed ignition draws about 2.8A max (full increase

    RPM and highest operating temperature) so a 5A fuse is

    quite adequate to the load. Heavier wire is sometimes called

    out just for mechanical robustness even when the current levels

    are low. I think I heard one ol' greybeard at Beech speak

    to a policy of "no wires under 20AWG in the engine compartment."

    Magneto's were wired with 18AWG shielded even tho much smaller

    wire would have provided proper electrical function.



An ATC fuse typically blows at 125% of rating within a second, much

faster than a breaker.  How do I know what the peak current is on

various devices to know that there will not be a nuisance trip (a

really bad thing for electronic ignitions) with a fast blow fuse ?



    There was a rule of thumb years ago for always-hot battery

    feeders not to be protected at levels above 5A. But that

    rule of thumb got codified later:

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

Sec. 23.1361 Master switch arrangement.



(a) There must be a master switch arrangement to allow ready disconnection

of each electric power source from power distribution systems, except as

provided in paragraph (b) of this section. The point of disconnection must be

adjacent to the sources controlled by the switch arrangement. If separate

switches are incorporated into the master switch arrangement, a means must be

provided for the switch arrangement to be operated by one hand with a single

movement.



(b) Load circuits may be connected so that they remain energized when the

master switch is open, if the circuits are isolated, or physically shielded,

to prevent their igniting flammable fluids or vapors that might be liberated

by the leakage or rupture of any flammable fluid system; and



         (1) The circuits are required for continued operation of the 

engine; or



         (2) The circuits are protected by circuit protective devices 

with a rating

         of five amperes or less adjacent to the electric power source.



         (3) In addition, two or more circuits installed in accordance with the

         requirements of paragraph (b)(2) of this section must not be 

used to supply a

         load of more than five amperes.



(c) The master switch or its controls must be so installed that the switch

is easily discernible and accessible to a crewmember.

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

     Now interestingly enough . . . one can do an experiment where

     a 5A breaker and a 10A ATC fuse are connected in series. Dead fault

     the circuit on a 12v battery and the fuse always blows before the

     breaker trips. From this I would deduce that a 5A breaker of the battery

     bus which is compliant with the FAR cited above can be replaced by a

     10A fuse in the same location and still be satisfy the design goal.

     The 10A fuse is faster than a 5A breaker and dumps less energy into

     the fault than a the breaker.



     High inrush devices are generally limited to motors and incandescent

     lamps. For those circuits, fatter fuses and commensurate increases in

     wire size are not without reasonable justification.



     Input to the Lightspeed ignition has, at most, a filter capacitor

     preceding the switchmode power supply. A 5A fuse is fine. But given

     the fatter-wire recommendations for installation, then a 7.5 or

     10A  FUSE PROTECTED feeder can be brought from the battery bus

     without insulting design goals for crash safety cited in 23.1361(b)(2)

     above.



     For all other systems (not critical to keeping the engine running!)

     the experiment is low risk. If you get nuisance trips, upsize the

     fuse. You need not necessarily upsize the wire too. Keep in mind that

     20A through a 22AWG wire will not burn the wire. See:



http://aeroelectric.com/Pictures/Wire/22AWG_20A.pdf



     While your concerns are noteworthy, they can be addressed with

     a very broad brush applying common sense. If I were building

     an airplane today, I'd protect the electronic ignition battery

     feeders at 10A and wire with 20AWG wire that still fits in

     the smaller pins for fire wall penetration and/or interface to

     the electronics. This offers a mechanically and electrically

     robust feeder to the ignition that does not argue with crash

     safety design goals.



   Bob . . .

fvalarm(at)rapidnet.net
Guest

Posted: Tue Jan 24, 2012 1:44 pm Post subject: Fuses instead of breakers

I used a lot of fuses (4 fuse blocks) and about a dozen breakers (for things

that I need/want control of in flight or during maintenance.  I like to have

each on it's own circuit.  I don't know of any Slo-blo fuses, but there may

be.  It may be that you would simply use a higher value fuse.  Something

that protects the wire against hard faults.



I was going to use Lightspeed but changed my mind to P-mags partially for

this reason, they are self powered once flying, therefore do not depend on

ship's power for normal operation.



Bevan 



--

mauledriver(at)nc.rr.com
Guest

Posted: Tue Jan 24, 2012 8:38 pm Post subject: Fuses instead of breakers

You could use a breaker for this particular circuit.  I haven't thought about electronic ignitions specifically but I too like fuses over breakers.  But convinced myself to use 4 breakers anyway, 2 for the 2 voltage regulators, 1 for the AP, and one for the flaps.  Not sure I would have used all 4 now that I've flown it a bit but it made sense to me at the time.  So I still have 2 dozen fuses...



Just a thought.



 Bil

Sent from my iPad



On Jan 24, 2012, at 2:16 PM, Jeff Page <jpx(at)qenesis.com> wrote:



 	  Quote: 	
		   

 

 I really like the idea of using fuses rather than breakers.  The ATC style fuses look like a excellent product.

 

 However, I cannot find any "slo-blow" versions.  Do they exist ? How do I decide on the size of the fuse when manufacturers of products recommend a breaker or slow-blo fuse ?

 

 For example, the Lightspeed ignition instructions suggest a 5A breaker with an 18AWG wire.  So a 7.5A or 10A fuse could easily be used with that wire.

 

 An ATC fuse typically blows at 125% of rating within a second, much faster than a breaker.  How do I know what the peak current is on various devices to know that there will not be a nuisance trip (a really bad thing for electronic ignitions) with a fast blow fuse ?

 

 Jeff Page

 Dream Aircraft Tundra #10

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 25, 2012 8:53 am Post subject: Fuses instead of breakers

At 10:33 PM 1/24/2012, you wrote:




You could use a breaker for this particular circuit.  I haven't 

thought about electronic ignitions specifically but I too like fuses 

over breakers.  But convinced myself to use 4 breakers anyway, 2 for 

the 2 voltage regulators, 1 for the AP, and one for the flaps.  Not 

sure I would have used all 4 now that I've flown it a bit but it made 

sense to me at the time.  So I still have 2 dozen fuses...



     As long as your wiring is adequately protected then

     what you've installed is not "wrong" . . . just different.

     If the voltage regulators are fitted with crowbar

     ov protection, then panel mounted breakers are

     indicated. If you believe that the AP and flaps

     have failure modes for which you desire a crew

     driven mitigation, then in-reach breakers are also

     indicated. Some folks may find justification for

     debating the rationale for your design but the

     bottom line is this. What you've done does not

     increase risk. It MIGHT drive some small risk to

     a yet smaller value. But everybody hopes that you'll

     fly this airplane throughout it's useful lifetime

     never having encountered an urge to touch any of

     those breakers in flight.

   Bob . . .

Dennis Johnson

Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.

Posted: Wed Jan 25, 2012 9:08 am Post subject: Fuses instead of breakers

Hi Jeff,

  

 Regarding what size fuse to use, I have a Lightspeed electronic ignition  with a 5 amp fuse.  In about 500 hours of flying, I've blown the fuse  once.  Don't know why it blew, and the engine kept running on the  magneto.  On the ground, I replaced the fuse and it's been fine  since.  Next time I have convenient access to the battery bus, I might put  a 7.5 amp fuse instead.

  

 Dennis  

   [quote][b]

bicyclop(at)pacbell.net
Guest

Posted: Wed Jan 25, 2012 9:27 am Post subject: Fuses instead of breakers

Just one more thing to think about if you are doing       this with a Lightspeed ignition. From what I've read, there is       some sort of crowbar inside the ignition module to protect it from       an overvoltage event. If a fuse is fitted and the crowbar kicks       it, you'll not be able to reset it as easily as with a breaker -       if you can reach the fuse at all. I've heard of at least one case       where an airplane was brought down because it was wired       differently than the installation instructions in that regard.

       

       Ed Holyoke

     

     On 1/25/2012 8:48 AM, Robert L. Nuckolls, III wrote:     [quote]--> AeroElectric-List message posted by: "Robert L.       Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> (nuckolls.bob(at)aeroelectric.com)       

       

       At 10:33 PM 1/24/2012, you wrote:       

       --> AeroElectric-List message posted by: Bill Watson       <mauledriver(at)nc.rr.com> (mauledriver(at)nc.rr.com)       

       

       You could use a breaker for this particular circuit.  I haven't       thought about electronic ignitions specifically but I too like       fuses over breakers.  But convinced myself to use 4 breakers       anyway, 2 for the 2 voltage regulators, 1 for the AP, and one for       the flaps.  Not sure I would have used all 4 now that I've flown       it a bit but it made sense to me at the time.  So I still have 2       dozen fuses...       

       

           As long as your wiring is adequately protected then       

           what you've installed is not "wrong" . . . just different.       

           If the voltage regulators are fitted with crowbar       

           ov protection, then panel mounted breakers are       

           indicated. If you believe that the AP and flaps       

           have failure modes for which you desire a crew       

           driven mitigation, then in-reach breakers are also       

           indicated. Some folks may find justification for       

           debating the rationale for your design but the       

           bottom line is this. What you've done does not       

           increase risk. It MIGHT drive some small risk to       

           a yet smaller value. But everybody hopes that you'll       

           fly this airplane throughout it's useful lifetime       

           never having encountered an urge to touch any of       

           those breakers in flight.       

       

       

         Bob . . . 

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

     [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 25, 2012 9:48 am Post subject: Fuses instead of breakers

 	  Quote: 	
		  Next time I have convenient access to the battery bus, I might put a 

7.5 amp fuse instead.


	


    Good idea.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 25, 2012 10:00 am Post subject: Fuses instead of breakers

At 11:24 AM 1/25/2012, you wrote:

 Just one more thing to think about if you are doing this with a Lightspeed ignition. From what I've read, there is some sort of crowbar inside the ignition module to protect it from an overvoltage event. If a fuse is fitted and the crowbar kicks it, you'll not be able to reset it as easily as with a breaker - if you can reach the fuse at all. I've heard of at least one case where an airplane was brought down because it was wired differently than the installation instructions in that regard.



    Can you elaborate on what you've read and give us sources?

    I'm unaware of any crowbar ov protection built into the

    LSE system. Is this called out in any of their published

    literature?  I found this on the Lightspeed site:

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

 Electrical System Requirements 



 All Plasma CDI systems can be used with 12 or 24 volt electrical systems.  Input voltages above 35 volts or reversed polarity can cause system damage. 



 For this reason it is mandatory that all aircraft using Plasma CD Ignitions are equipped with over-voltage protection in their alternator charging system(s).  Over-voltage protection is a requirement for certified aircraft.  Power connection must be directly to the battery terminals to avoid voltage spikes and electrical noise.  Aluminum should never be used as an electrical conductor for the Plasma CDI.  Use only the supplied aircraft quality stranded wire. 



 Minimum supply voltage for starting is 6.5 Volts. 



 Minimum operating voltage is 5.5 Volts.

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

    This statement argues against any built-in ov

    protection. At the same time, the very wide operating

    voltage for the system guarantees that a properly

    designed 14v system will NEVER offer a threat to

    the LSE system.



    I am presently participating in an analysis of

    cause and effect for simultaneous failure of

    dual LSE systems. Root cause for that event

    was a failure to craft a failure tolerant 

    architecture . . . a design goal which is foundation

    for all efforts here on the AeroElectric-List.



    It's a certainty that no builder who participates

    here on the List will suffer such an event.



 

   Bob . . .    [quote][b]

Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Wed Jan 25, 2012 2:29 pm Post subject: Fuses instead of breakers

I appreciate everyone's comments regarding sizing fuses.



The reference to the FARs regarding battery bus circuits was useful.   

My design doesn't exceed those specifications.  Fortunately, with an  

amateur-built aircraft, no bureaucrat can claim that a 5A circuit  

protective device would be the size of both the fuse and the circuit  

breaker.

So a 10A fuse will probably work reliably with a Lightspeed ignition.  Thanks.



How about another example ?  The popular approach is to use a pullable  

breaker for the hydralic pump for the amphibious landing gear.  If I  

use a switch and a fuse, what size fuse ?  I appreciate that I can  

always install a bigger fuse if nuisance pops occur, but it seems more  

professional to do the initial design with a good idea that the  

correct fuse was chosen in the first place 



So, does this logic work ?

The pressure switch deactivates the pump at 500psi, but there will  

likely be short term pressure spikes above that.  So, pick 1000psi.

The current versus pressure chart for the motor, shows 3A at 500psi  

and 5A at 1000psi, as well as 23A at 3000psi, which is probably almost  

stalling the motor.  So assume a typical current of 3A and spikes of  

less than a half second to 10A.

Since a 10A fuse should blow after 1 second with 12.5A, that should be  

sufficient to avoid a nuisance pop ?



During that half second, I want full power to the motor, so I will use  

10A for the gauge versus wire length calculation.  To drop 5% power  

through wire resistance, that gives me 18' for 16AWG wire.  I should  

be able to get to the pump and back in less than 18', so 16AWG should  

be sufficient.

A 30 degree rise for 16AWG wire requires 19A, so I could safely upsize  

to a 15A or 20A fuse.



With your experience, should I start with a 10A or 15A fuse and expect  

it not to nuisance trip ?



Are there any other reasons why a pullable circuit breaker would be  

preferred for this situation ?



Jeff Page

Dream Aircraft Tundra #10

bcondrey

Joined: 03 Apr 2006
Posts: 580

Posted: Wed Jan 25, 2012 6:34 pm Post subject: Re: Fuses instead of breakers

I'll second the earlier comment on LSE ignitions having a crowbar setup.  I had initially installed fuses to power a dual Plasma III setup.  During a discussion with Klaus he quickly took exception to this and told me verbally that they DID have a crowbar setup (but I did not get into a discussion with him about the triggering criteria).  Since it's a pretty long wire run in an RV-10 from the standard battery location to where the ignition boxes are located, he recommended having 7.5 amp CBs on the panel and if I felt the need to protect the feeders (he didn't) from the batteries to use 10 amp CBs back there, guaranteeing that the 7.5s would be what tripped during whatever event trips the crowbar.



His very clear preference is to simply run the shielded, #18 (I think) wire all the way back and direct connect to the battery.  I couldn't in good conscience live with a pair of always hot, unprotected wires for a run of that long and replaced the fuses near the batteries with 10 amp CBs and put 7.5 amp CBs on the panel as he recommended.



Above conversation took place with him about 3-4 years ago but I remember it very clearly.



Bob C.

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 25, 2012 6:52 pm Post subject: Fuses instead of breakers

At 04:27 PM 1/25/2012, you wrote:




I appreciate everyone's comments regarding sizing fuses.



The reference to the FARs regarding battery bus circuits was useful.

My design doesn't exceed those specifications.  Fortunately, with an

amateur-built aircraft, no bureaucrat can claim that a 5A circuit

protective device would be the size of both the fuse and the circuit

breaker.



    Who said anything about regulations? Just because it's

    in a holy-watered book doesn't mean it's not a

    valuable ingredient in a recipe for success.



So a 10A fuse will probably work reliably with a Lightspeed ignition.  Thanks.



    Absolutely.



How about another example ?  The popular approach is to use a pullable

breaker for the hydraulic pump for the amphibious landing gear.  If I

use a switch and a fuse, what size fuse ?



    BIG and beefy . . . in fact for things like hydraulic pump

    motors you would consider ANL style current limiters. That's

    what we used on the Beech products.



I appreciate that I can

always install a bigger fuse if nuisance pops occur, but it seems more

professional to do the initial design with a good idea that the

correct fuse was chosen in the first place 



    Absolutely!!!!! Which is why we have the List. There are

    fuses, then there are Fuses and then FUSES. Circuit breakers

    come in many flavors of operating speed too. The differences

    can be significant in crafting a trip-free system. Recall

    years back we discussed the fact that there are tens of

    thousands of TC aircraft flying with an alternator b-lead

    breaker designed to nuisance trip?  60A circuit breakers

    on 60A alternators. An alternator that will put out MORE

    than 60A under some conditions.



So, does this logic work ?

The pressure switch deactivates the pump at 500psi, but there will

likely be short term pressure spikes above that.  So, pick 1000psi.

The current versus pressure chart for the motor, shows 3A at 500psi

and 5A at 1000psi, as well as 23A at 3000psi, which is probably almost

stalling the motor.  So assume a typical current of 3A and spikes of

less than a half second to 10A.



Since a 10A fuse should blow after 1 second with 12.5A, that should be

sufficient to avoid a nuisance pop ?



    Don't agonize over it. You're wanting to protect what size wire?

    Scratch that. Wire with 10 AWG and use an ANL35 or equal. 10AWG

    is plenty heavy and will reduce voltage drop in the system. It's

    the 10x inrush current of what is probably a PM motor that drives

    the selection of protection . . .

During that half second, I want full power to the motor, so I will use

10A for the gauge versus wire length calculation.  To drop 5% power

through wire resistance, that gives me 18' for 16AWG wire.  I should

be able to get to the pump and back in less than 18', so 16AWG should

be sufficient.



    I'd go with the 10AWG. If 23A and 5000 PSI is a data point, then

    its doubtful that the motor is anywhere near stall. I'll bet inrush

    is 2 to 3 times that amount.



A 30 degree rise for 16AWG wire requires 19A, so I could safely upsize

to a 15A or 20A fuse.



With your experience, should I start with a 10A or 15A fuse and expect

it not to nuisance trip ?



Are there any other reasons why a pullable circuit breaker would be

preferred for this situation ?



    What controls the pump motor . . . a contactor?

    Is it tailored for intermittent duty, hi-inrush

    service like a starter-contactor? Sticking of this

    device might pose an in-flight concern. However,

    if you have a dual path e-bus, you can kill the

    main bus and shut down a runaway pump motor while

    retaining the electro-whizzies needed for comfortable

    completion of flight.



    Your question goes to exactly the kind of exercise

    every electrical system benefits . . . failure mode

    effects analysis, "What if . . . and how do I deal

    with it as a maintenance event as opposed to an

    emergency?" If an FMEA calls for a second disconnect

    such as a pullable breaker, then by all means.



    Worrying about poorly considered failures tends to

    stack redundancy on top of redundancy. It drives up

    parts count, cost of ownership and adds to system

    complexity. Complexity makes the pilot's job more

    difficult and risky. Well considered FMEA tends

    to produce the elegant solution: Just enough hardware

    with minimum risk and simpler to operate.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 25, 2012 6:55 pm Post subject: Fuses instead of breakers

 	  Quote: 	
		  During a discussion with Klaus he quickly took exception to

this and told me verbally that they DID have a crowbar setup

(but I did not get into a discussion with him about the

triggering criteria).


	


    Hmmmm . . . I'll be seeing Klaus in the not too distant

    future. I'll inquire.

   Bob . . .

loboflyer(at)gmail.com
Guest

Posted: Wed Jan 25, 2012 7:51 pm Post subject: Fuses instead of breakers

Bob, please do.  In the meantime, for those of us just getting to wiring, would this be reasonable, or overkill?



Battery Bus Input terminal (not fused) ---> Fusible Link ---> Panel Breaker ---> Switch ---> LSE box?

 

I'm not sure how ground would best get there since Klaus calls out shielded wire and it might be a little bit of a run to the FW ground or battery ground. 



Thoughts?  (Or am I overthinking this?)



  -Jeff-

 



On Wed, Jan 25, 2012 at 7:52 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

[quote] --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

 

 

 

 	  Quote: 	
		   During a discussion with Klaus he quickly took exception to

 this and told me verbally that they DID have a crowbar setup

 (but I did not get into a discussion with him about the

 triggering criteria).

 	
 



    Hmmmm . . . I'll be seeing Klaus in the not too distant

    future. I'll inquire.

 

 

   Bob . . . 

[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 25, 2012 8:31 pm Post subject: Fuses instead of breakers

At 09:47 PM 1/25/2012, you wrote:

Bob, please do.  In the meantime, for those of us just getting to 

wiring, would this be reasonable, or overkill?



Battery Bus Input terminal (not fused) ---> Fusible Link ---> Panel 

Breaker ---> Switch ---> LSE box?



   At the moment, I see no reason to treat the LSE

   ignition system any differently than any similar

   system offered to the TC aircraft world.



   If based on what I know now, I'd go 10A fuse at

   the battery bus driving a 20AWG non-shielded wire

   to an ON/OFF switch on the panel and then to the

   ignition system.



I'm not sure how ground would best get there since Klaus calls out 

shielded wire and it might be a little bit of a run to the FW ground 

or battery ground.



   Shielded wire for this application is completely

   unwarranted. There is no potential antagonist/

   victim scenario which would capacitively couple

   into our out of the LSE product. Grounding of the

   LSE ignition module should be no more complex

   than to take a 20AWG wire to the firewall ground

   bus.



Thoughts?  (Or am I overthinking this?)



   I don't think so. Klaus worries about some things

   that are either insignificant or non existent. "Noise"

   on the bus is NOT mitigated by connecting to the

   battery. I think I explain this in the battery

   chapter of the book. Batteries are simply not

   filters of any small excursions of bus voltage

   at any frequency.



   This is precisely why DO-160 and Mil-STD-704

   tell the TC aircraft designer to EXPECT certain

   kinds of noise on the ship's DC bus. See:



http://www.aeroelectric.com/Pictures/Curves/MSTD704_28V_Noise.jpg



   That flat top in the plot between 1 and 5 Khz

   is 1 volt RMS or about 3 volts peak to peak

   on a 28 volt system. Cut those numbers in half

   on a 14 volt system. The amplitude for expected

   noise falls off on either side . . . but the

   point is, NOTHING . . . especially the battery

   will mitigate this noise. Hence the admonition,

   "It's there son, learn to live with it."



   Indeed we who have run the gauntlet on qualification

   for TC aircraft have learned to live with it . . .

   in face, it's such a benign stress that "dealing

   with it" is not even much of a technically intellectual

   exercise.



   It makes no sense to build crowbar ov protection

   into a product when it's so easy to build passive

   shutdown protection. I did this little fast-disconnect

   switch to qualify an automotive seat warmer onto

   a 28v aircraft.



http://aeroelectric.com/Pictures/Schematics/80v_Surge_Protection.jpg



   this circuit simply 'disconnects' the vulnerable

   device from the bus during the transient and reconnects

   when the event is over.



   But more important is the fact that in a 14 volt

   airplane, the maximum alternator-runaway event is

   limited to 20 volts . . . which is well inside the

   LSE's NORMAL operating voltage.



   Finally, you could treat a robust feeder from

   battery to ignition system just like a fat feeder

   to the e-bus. It might look something like this:



http://aeroelectric.com/Pictures/Schematics/Battery_Feed_for_Ignition.pdf



   This satisfies the design goals for crash safety

   by having a pilot operated disconnect at the battery.

   The relay only draws about 100 mA so it's not a big

   budget energy consumer for battery only operations.

   Modern relays are quite reliable . . . and this one

   gets pre-flight tested.



   Point is there's a lot of ways to skin cats-of-

   legitimate-worry. The task is to separate real worries

   from bogus worries.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 26, 2012 4:47 am Post subject: Fuses instead of breakers

At 09:47 PM 1/25/2012, you wrote:

Bob, please do.  In the meantime, for those of us just getting to 

wiring, would this be reasonable, or overkill?



   P.S. to previous post.



   I too would like to see an ignition system power from

   the battery bus. NOT for reasons of noise but for

   reasons of risk mitigation. When I have smoke in the

   cockpit, I'd like to KILL the entire electrical system

   without causing the engine to stop. This is why I've

   advocated that ANY electrically dependent engine get

   power directly from battery busses. This philosophy

   is illustrated in the Z-figures.



   Bob . . .

Paul Valovich

Joined: 11 Jan 2006
Posts: 75

Posted: Thu Jan 26, 2012 7:01 am Post subject: Fuses instead of breakers

I built my RV-8A referencing Z13/8: forward mounted battery, one LSI, one mag. Three fuze blocks in fwd baggage compartment inaccessible in flight. Three panel mounted CBs – Alt Field, Aux Alt Field and LSI.  

   

I do not feel that a fuze-blowing event for most circuits would benefit from restable CBs – something caused the initial overvoltage and chances that the fix is a reset CB are very slim. Design redundant systems, include internal avionics batteries where it makes sense, execute proper failure procedures, land as soon as practicable – or as soon as possible – and sort it out on the ground.  

   

For the normal and backup alternators – and LSI – I felt that there was benefit from a reset capability. Nuisance trips, one time spikes, intermittent short, etc. I just might need the few minutes (perhaps) between trigger events to land.  

   

140 hours of trouble-free electrons so far.  

Paul Valovich  

N192NM  

      [quote][b]

bcondrey

Joined: 03 Apr 2006
Posts: 580

Posted: Thu Jan 26, 2012 12:01 pm Post subject: Re: Fuses instead of breakers

FWIW, this subject has been discussed before on the AeroElectric list.  Use the search function for the words "Klaus" and "crowbar" and you'll find a couple threads from early 2009.  Turns out that it's not just over-voltage events that will cause them to crowbar but apparently over-temp.  This was posted on Feb 1, 2009:



"I have had to do one inflight reset on the Plasma III on one system 

once. The reset was successful and power was restored to the unit. I 

removed the unit and sent it back to Klaus for inspection. The fault 

was determined to be an overheat situation. That unit was located in 

an area without any real ventilation and without an form of cooling 

while operation in Arizona during the summer. the compartment temp 

was estimated to have exceeded 200 deg. F. The unit was modified to 

the latest version (lower heat output components and a ventilation 

port. The aircraft was modified to provide air circulation in that 

compartment. After 300+ hours on that unit no faults noted. The 

point, when the unit faulted it tripped the CB and was then reset and 

provided service throughout the remainder of that flight. "



Without getting into the discussion of whether the design should or shouldn't be modified, my purpose on posting (now and back in early 2009) is simply to make those with dual LSE ignition setups aware that fuses can't be arbitrarily substituted for CBs in this case.



Bob C

Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Thu Jan 26, 2012 12:46 pm Post subject: Fuses instead of breakers

At 04:27 PM 1/25/2012, you wrote:



 	  Quote: 	
		   The reference to the FARs regarding battery bus circuits was useful.

 My design doesn't exceed those specifications.  Fortunately, with an

 amateur-built aircraft, no bureaucrat can claim that a 5A circuit

 protective device would be the size of both the fuse and the circuit

 breaker.

     Who said anything about regulations? Just because it's

     in a holy-watered book doesn't mean it's not a

     valuable ingredient in a recipe for success.


	


I merely meant that a 5A fuse and a 5A breaker behave differently, but since

the protection type is not specified, the rule could be interpreted as  

a maximum

of a 5A fuse.



 	  Quote: 	
		   Are there any other reasons why a pullable circuit breaker would be

 preferred for this situation ?

     What controls the pump motor . . . a contactor?

     Is it tailored for intermittent duty, hi-inrush

     service like a starter-contactor? Sticking of this

     device might pose an in-flight concern. However,

     if you have a dual path e-bus, you can kill the

     main bus and shut down a runaway pump motor while

     retaining the electro-whizzies needed for comfortable

     completion of flight.


	


The float manufacturer (Montana) supplies the pump and control circuitry

already mounted.  The relays are Bosch 12V/20A  0 332 209 137

The diagram shows a 25A pullable breaker feeding the relays.  A 1A fuse

protects the relay control wiring.  So a pullable breaker would be a  

convenient

way to deal with a stuck relay or a defective pressure switch.  That  

is perhaps

what I should do.



I will be interested in the results of your discussions with Klaus  

about powering the Lightspeed ignition.  I know two people who are  

about to install these.



Thanks again for all the great advice.  Even while lurking, I learn  

something new

and useful every week !



Jeff Page

Dream Aircraft Tundra #10

longg(at)pjm.com
Guest

Posted: Thu Jan 26, 2012 12:57 pm Post subject: Fuses instead of breakers

I tried the "fuse" test once. The test was to install the P-III with a fuse and see if I could guess where I might be when it fails. Mine failed on the run-up pad. I promptly pulled up to the hangar and wired it directly to the battery per Klaus's instructions. I always figured he wrote them for a reason. Been working ever since. I mounted mine upside down on the bottom of the avionics panel where they get plenty of fresh air.



Best Wishes,

Glenn



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