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bicyclop(at)pacbell.net
Guest

Posted: Thu Jan 26, 2012 3:44 pm Post subject: Fuses instead of breakers

I'll try and find it. I know that Klaus is adamant       about having a breaker and not a fuse.

       

       Ed

     

     On 1/25/2012 9:56 AM, Robert L. Nuckolls, III wrote:     [quote]       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]

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 26, 2012 5:02 pm Post subject: Fuses instead of breakers

At 02:43 PM 1/26/2012, you wrote:

 --> AeroElectric-List message posted by: Jeff Page <jpx(at)qenesis.com>



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



 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.



    Oh absolutely. The fact that such a level was

    given without an accompanying I(squared)T time

    constant goes to suggest the arbitrary nature

    of the value. As we've discussed here before,

    seeing a 5A number on a protective device

    is a small bit of knowledge about how the

    device performs. I'd have to go arm-wrestle with

    dragons to get a 10A fuse attached to a battery

    bus in a TC aircraft . . . but you and I know

    that a 10A ATC fuse is faster than a miniature

    5A breaker and is  . . . therefore  . . . a

    rational crash safety substitute for always-hot

    feeders.



    What controls the pump motor . . . a contactor?



 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.



    Agreed. Those relays are not specifically

    crafted for motor control service. Having

    a crew-operated means by which a runaway

    can be controlled seems prudent.



 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.



    There are no doubt many hundreds if not

    thousands of these flying. To the best of my

    knowledge, they are not "special" devices

    deserving of extra-ordinary attention.



    Discussions not withstanding, the published

    current draw values for LSE products say that

    the greatest current draw for a 6-cylinder

    system is 2.1A at 13.8 volts.



 [img]cid:.0[/img]



    Given that the device features a switchmode power

    supply with  a wide range of operating voltages,

    we know that this is a constant-power mode of

    operation. So 2.1 x 13.8 sez the critter needs

    right at 30 watts for operation at MAX RPM. One

    can expect the current to climb as voltage goes

    down . . . so if you're operating battery only

    and the battery is down on that 11-volt-slide-

    to-darkness, the ignition system current will

    have risen to something around 2.7 amps.



    Likewise, operating current on a 29 volt bus

    will be down around 1.0 amps. The 4-Cylinder

    systems are still more frugal in their demands

    on the electrical system.



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

 something new and useful every week !



    Thanks for getting involved and asking. It's

    through EXCHANGES of observation and events that

    I learn useful things too. Folks have often

    asked why the 'Connection is up to Revision 12

    in "just 23 years of publication". I tell

    them that my education came from a collaboration

    with colleagues who spoke engineereze. And we

    hammered on a different class of airplane. When I

    sat down to do the first chapters of the

   'Connection, I realized that I could not answer

    questions without knowing what the questions

    are. Further, they needed to be written in

    OBAMeze.



    It's the collective participation of all

    the builders on the List/emails/telephone/

    seminars that drive what goes into the

    next revision. It's truly a work in progress

    that would not have happened without this

    join venture arena.



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 26, 2012 5:21 pm Post subject: Fuses instead of breakers

 	  Quote: 	
		  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.


	


   I would agree that when the installed system is

   at risk for an event triggered by conditions

   of installation and/or manufacturing mod levels

   then the system is indeed still 'experimental'.



   Now that the 'student installer' has graduated

   from the lab to the working environment, I'll

   suggest that the risk for substitution is

   microscopically low.



   This is something that we must always keep in

   mind. Instructions and ratings are important.

   When in doubt, go measure it. It's entirely

   possible that the builder who experienced this

   event might not have survived to give us his

   particular dark-n-stormy-night narrative.

   We wouldn't be having this discussion about that

   particular event . . . indeed we wouldn't even

   know the details.



   But the fact is that he DID experience a trip in

   a critical system power feeder which prompted further

   investigation and he shared his discovery with

   the rest of us. That information goes to making

   us MORE confident, not less.



   I recall a discussion here on the list a some

   time back where wires in the wreckage were found

   pulled out of the terminal crimps. Hmmm . . .

   we'll never know if this failure-to-follow the

   instructions precipitated the event . . . but

   the overt evidence of failure in craftsmanship

   does raise valid questions.



   So if one chooses to explore departures from

   published instructions, any such departure needs

   to be considered carefully. It's not difficult,

   just rigorous. Get on the List and let's talk

   about it. Bundle all the concerns together and

   develop a plan to morph an experiment into a

   recipe for success.



   But if you don't want to be an explorer or

   crafter of new recipes, that's fine too. The

   vast majority of our brothers building OBAM

   aircraft are not explorers and the last thing

   they want to do is experiment. This venue for

   acquiring a personally owned aircraft recognizes

   that too. Most never frequent this List and

   don't need to . . . their relationship with

   their airplane's electrical system is no

   different than the average spam can driver

   in a 172 . . . and that's okay.

   Bob . . .

Tundra10

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

Posted: Fri Jan 27, 2012 11:51 am Post subject: Fuses instead of breakers

 	  Quote: 	
		    >......Are there any other reasons why a pullable circuit breaker  

 would be  >preferred for this situation ?

 There are two seperate potential issues here.  First, is there an  

 alternate source

 of hydraulic pressure?  If you have a practical hand pump available, then

 the nuisance trip issue is just that.  If the electric pump is your  

 only practical

 source of hydraulic power, then things are a little different.  I  

 could envision

 a scenario where the motor for the hydraulic pump has degraded such that

 the current draw trips the circuit protection, leaving you with a  

 gear up landing,

 or potentially worse, a partial gear landing.  Personally, I would prefer

 resettable circuit protection in that scenario.


	


There is a manual hand pump, so no emergency is created.



 	  Quote: 	
		   "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. "


	


Hmmm.  If it immediately resumed functioning after resetting the  

breaker, perhaps

the ignition never failed, but the heat (and probably higher currents  

operating at

high temperatures) caused the breaker to nuisance trip.



 	  Quote: 	
		   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.

          There are no doubt many hundreds if not

          thousands of these flying. To the best of my

          knowledge, they are not "special" devices

<          deserving of extra-ordinary attention.
	




They just get extra attention since pilots are more concerned with their

ignition failing than say their nav lights going out 



 	  Quote: 	
		   The relays are Bosch 12V/20A  0 332 209 137

          Those relays are not specifically

          crafted for motor control service. Having

          a crew-operated means by which a runaway

          can be controlled seems prudent.


	


A pullable breaker would stop current flow caused by a stuck relay,

and the manual pump could be used to operate the gear, so there is

no significant flight risk.

Those relays do look undersized to me.

Better relays might reduce long term maintenance however.  Or perhaps

just carry a spare along might be the most practical approach.  I think

the latter ?



Jeff Page

Dream Aircraft Tundra #10

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 27, 2012 12:43 pm Post subject: Fuses instead of breakers

There is a manual hand pump, so no emergency is created.



     Then a robust fuse solution goes toward a cleaner

     panel and possibly a cleaner plan B. When THIS

     happens, do THAT . . . every time.



 >"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.

 > . . .<snip>

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

 >and provided service throughout the remainder of that flight."



Hmmm.  If it immediately resumed functioning after resetting the

breaker, perhaps the ignition never failed, but the heat (and probably

higher currents operating at high temperatures) caused the breaker

to nuisance trip.



     The keyword here is "nuisance". I've had to cut the

     TC guys some slack for being somewhat submissive to

     nuisance trips . . . to strive for the elegant solution

     can sometimes be very time consuming and expensive.

     One is well advised to trade off cost/benefit ratios.



     In the OBAM aircraft world, we're not only able, we are

     encouraged to refine any system's configuration in way

     that increases the displacement between it's experimental

     roots and an enduring recipe for success.



     But when one gets a 'nuisance trip' with current protection

     that is nearly 2.5 times the published draw numbers . . .

     there are reasons to seek answers to some serious questions.

     There is a clash of postulates which beg resolution.



They just get extra attention since pilots are more concerned with their

ignition failing than say their nav lights going out 



     ABSOLUTELY! Which is why I've recommended that electrically

     dependent engine accessories drive from always hot battery

     bus with totally independent power paths. If two ignition

     systems require power and two batteries are available, then

     split the systems between the batteries.



     But when a 2A device trips a 5A breaker . . . well . . .



A pullable breaker would stop current flow caused by a stuck relay,

and the manual pump could be used to operate the gear, so there is

no significant flight risk.



     Great.



Those relays do look undersized to me.



Better relays might reduce long term maintenance however.  Or perhaps

just carry a spare along might be the most practical approach.  I think

the latter ?



     I thought we were talking about a much larger

     hydraulic system. The amount of snort needed to

     operate the gear in floats is much smaller than

     that used on a GlasAir or Lancair. I think these

     relays will be fine and since you have a backup

     hand pump, your risks are quite low.

   Bob . . .

jbr79r(at)yahoo.com
Guest

Posted: Fri Jan 27, 2012 3:37 pm Post subject: Fuses instead of breakers

Hi Bob

I built a cold air induction for my glasair and will have an alternate filtered air when on the ground.  I take off with 10 deg of flaps.  Could there be a way to sequence this alternate air door with the flaps?  When the flaps come up the the door opens to allow ram air and when the flaps come down it closes the ram air.  Am I getting to complicated?

Jim



 

James Robinson Glasair lll  N79R Spanish Fork UT  U77



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

 To: aeroelectric-list(at)matronics.com 

 Sent: Friday, January 27, 2012 1:40 PM

 Subject: Re: Re: Fuses instead of breakers

  

 

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



There is a manual hand pump, so no emergency is created.



    Then a robust fuse solution goes toward a cleaner

    panel and possibly a cleaner plan B. When THIS

    happens, do THAT . . . every time.



 	  Quote: 	
		  "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.

 . . .<snip>

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

and provided service throughout the remainder of that flight."


	


Hmmm.  If it immediately resumed functioning after resetting the

breaker, perhaps the ignition  never failed, but the heat (and probably

higher currents operating at high temperatures) caused the breaker

to nuisance trip.



    The keyword here is "nuisance". I've had to cut the

    TC guys some slack for being somewhat submissive to

    nuisance trips . . . to strive for the elegant solution

    can sometimes be very time consuming and expensive.

    One is well advised to trade off cost/benefit ratios.



    In the OBAM aircraft world, we're not only able, we are

    encouraged to refine any system's configuration in way

    that increases the displacement between it's experimental

    roots and an enduring recipe for success.



    But when one gets a 'nuisance trip' with current protection

    that is nearly 2.5 times the published draw numbers . . .

    there are reasons to  seek answers to some serious questions.

    There is a clash of postulates which beg resolution.



They just get extra attention since pilots are more concerned with their

ignition failing than say their nav lights going out 



    ABSOLUTELY! Which is why I've recommended that electrically

    dependent engine accessories drive from always hot battery

    bus with totally independent power paths. If two ignition

    systems require power and two batteries are available, then

    split the systems between the batteries.



    But when a 2A device trips a 5A breaker . . . well . . .



A pullable breaker would stop current flow caused by a stuck relay,

and the manual pump could be used to operate the gear, so there is

no significant flight risk.



    Great.



Those relays do look undersized to me.



Better relays  might reduce long term maintenance however.  Or perhaps

just carry a spare along might be the most practical approach.  I think

the latter ?



    I thought we were talking about a much larger

    hydraulic system. The amount of snort needed to

    operate the gear in floats is much smaller than

    that used on a GlasAir or Lancair. I think these

    relays will be fine and since you have a backup

    hand pump, your risks

mrspudandcompany(at)veriz
Guest

Posted: Fri Jan 27, 2012 4:56 pm Post subject: Fuses instead of breakers

Hi Bob

		I built a cold air induction for my glasair and will have an

alternate filtered air when on the ground.  I take off with 10 deg of flaps.

Could there be a way to sequence this alternate air door with the flaps?

When the flaps come up the the door opens to allow ram air and when the

flaps come down it closes the ram air.  Am I getting to complicated?

		Jim



				Is your alternate air door electrically

operated?  If so, you can use a switch, activated by the flaps, to open the

door when flaps are up, and close as soon as flaps are cycled down.



				Roger

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jbr79r(at)yahoo.com
Guest

Posted: Fri Jan 27, 2012 6:47 pm Post subject: Fuses instead of breakers

Thanks Roger

It was going to be a simple cable operation, but I thought I would explore other alternatives before making a final decision.

Jim

 

James Robinson Glasair lll  N79R Spanish Fork UT  U77



        From: ROGER &  JEAN CURTIS <mrspudandcompany(at)verizon.net>

 To: aeroelectric-list(at)matronics.com 

 Sent: Friday, January 27, 2012 5:53 PM

 Subject: RE: AeroElectric-List: Re: Fuses instead of breakers

  

 

 

        Hi Bob

        I built a cold air induction for my glasair and will have an

alternate filtered air when on the ground.  I take off with 10 deg of flaps.

Could there be a way to sequence this alternate air door with the flaps?

When the flaps come up the the door opens to allow ram air and when the

flaps come down it closes the ram air.  Am I getting to complicated?

        Jim



                Is your alternate air door electrically

operated?  If so, you can use a switch, activated by the flaps, to open the

door when flaps are up, and close as soon as flaps are cycled down.



                Roger

msausen

Joined: 25 Oct 2007
Posts: 559
Location: Appleton, WI USA

Posted: Sat Jan 28, 2012 5:53 am Post subject: Fuses instead of breakers

Back when this came up a couple years ago, and Bob C and I discussed possible solutions to this, I did some testing with a 10amp breaker and a 7.5 amp breaker switch.  Klaus calls out for power to always be hot from the battery which is not something I am fond of so I figured a switch breaker would be a better choice than two breakers and a switch.  In running these two devices in series with the approx length of wire needed, I was able to repeatedly get the breaker switch to "blow" without tripping the 10amp. I know this is a bit of a given but I wanted to see it for myself.



  I have a dual LSE3 config and I'm now considering simplifying this by having one off of my vp200 and the other direct to the battery with just a 7.5 amp fuse or breaker.  This way if there is a nuisance trip, I can reset via the vp200 and run off a single lse if needed until I land.  Of course that still does leave a potential failure mode should both trip and the vp200 connected one not come back online.



Michael 



On Jan 26, 2012, at 2:21 PM, "bcondrey" <bob.condrey(at)baesystems.com> wrote:



 	  Quote: 	
		   

 

 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

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=364895#364895

bcondrey

Joined: 03 Apr 2006
Posts: 580

Posted: Sat Jan 28, 2012 7:36 am Post subject: Re: Fuses instead of breakers

In the spirit of trying to move the ball forward I'll suggest that fusible links to protect the battery feeders are probably the best way to go in a cost/weight/reliability trade.  They provide protection of the feeder wires, have a slow time constant so a panel CB will trip first, are inexpensive and lightweight.  A larger CB would does the job also but with more weight and cost.



If you've only got a single LSE then maybe no issue since you'll always have a mag to fall back on.  If you're running a pair of them however, you need to fully understand failure modes and mitigate the risks.  This thread started with the question of whether a fuse would be an adequate substitute for a CB in this application.  Given what I believe to be true about the ignitions, the answer is a qualified NO.  Qualified because it's only a REAL issue if you don't have a mag to fall back on.  Installing as recommended by the manufacturer using a panel mounted CB gives you a solid install.  Just make sure you don't do something that compromises that by putting a fuse upstream or substituting a fuse for the panel CB.  If you want to protect the feeder use a slightly larger CB or fusible link.  You can do a very simple experiment as Michael did to validate the fuse issue (when upstream of a CB).  



Bob C

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 28, 2012 7:53 am Post subject: Fuses instead of breakers

At 07:49 AM 1/28/2012, you wrote:


Sausen)" <rvbuilder(at)sausen.net>



   Back when this came up a couple years ago, and Bob C and I 

discussed possible solutions to this, I did some testing with a 10amp 

breaker and a 7.5 amp breaker switch.  Klaus calls out for power to 

always be hot from the battery which is not something I am fond of so 

I figured a switch breaker would be a better choice than two breakers 

and a switch.  In running these two devices in series with the approx 

length of wire needed, I was able to repeatedly get the breaker 

switch to "blow" without tripping the 10amp. I know this is a bit of 

a given but I wanted to see it for myself.



   It's not always a 'given'. Thermally operated feeder protection

   have what is called and I(squared)*T constant. Meaning that if

   you plot trip times versus fault current, you find that doubling

   the fault current produces a trip in 1/4th the time.



   Combine this knowledge with the manufacturer's specs for I(squared)*T

   for any given device and you can deduce the probability that one

   device will trip before the other. But understand too that thermally

   activated circuit protection are not "calibrated devices". Look at

   the response curves for an exemplar miniature breaker . . .



http://www.aeroelectric.com/Pictures/Curves/Exemplar_Circuit-Breaker_Trip_Response.pdf



   For any given fault current combined with ambient temperature

   the trip times can vary widely. On top of that variation you

   can add "preheat" influences and manufacturing tolerances.

   Bottom line is that one should be very cautious about putting

   two protective devices in series with any notions about one

   tripping before the other.



   Your power company has done these studies. As you travel

   up the energy-chain from a hair dryer plugged into the

   wall to the alternator that provides watt-seconds to dry

   your hair, each protective device upstream of any

   other protective device is many times more robust.



   You don't want the protective device in hair dryer

   being over stressed but the whole neighborhood goes

   dark instead.



   Let's talk design goals:



   (1) It's a GOOD thing to be able to cut all power to

   every other accessory in the airplane and NOT have

   the engine stop. Solution - electronic ignitions

   and fuel pumps should power from an always hot

   battery bus.



   (2) It's a GOOD thing to have always hot wires in

   the airplane limited in their ability to produce

   fault currents likely to ignite post crash fires.

   Solution - protect such feeders at the battery bus

   with I(squared)*T constants that reduce such risk

   to acceptable levels. Question - what's an acceptable

   level?  Answer - Don't know from first hand knowledge.

   However, folks-who-claim-to-know-more-about-airplanes-

   than-we-do have declared that 5A circuit protection

   is the golden number.



   Exceptions - They did not specify an I(squared)*T

   constant for that protection.



   What's the prudent system integrator to do? Well,

   for starters we can deduce that the exemplar 5A

   breaker common to GA, AT, and Military aircraft

   is "blessed" so we are on reasonably sound foundation

   using that performance for a baseline. What's good

   for 100,000 airplanes is good for my RV.



   Okay, it's easily demonstrated that a miniature 5A

   breaker in series with a 10A ATC fuse will not

   open before the fuse does. But what are the risks

   for raising the always hot feeder protection to

   say 15 or 20A ATC fuse? Who knows? It's a certainty

   that some agency would love to have a $million$ budget

   to research an answer and then write rules about

   it.



   So what's a reasonable approach for standing off

   the worries amongst those in our numbers who do

   worry about it a lot?



   I suggest that it is quite simple:



   But a bigger fuse in at the battery bus. I don't

   care if you go to 20A. 20A wire too? No. We already

   KNOW that a 20A steady state current will not burn

   a 22AWG wire.



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



   So wire with 20AWG or even 18AWG. Remember, we're

   talking about crash safety. What is the likelihood

   that your 20A/18AWG, always-hot feeder will be

   placed in a potential position for setting you

   on fire? Very low. Further, keep in mind that an

   always hot wire in a wreck may not get hard-faulted

   in a way that would open even the 5A breaker. A

   soft-fault on a 12 volt battery feeder protected

   at 5A is VERY capable of starting fires. So that

   5A number goes more to setting rules and stopping

   arguments than it does to any scientific hedge

   against conflagration.



   The rational solution:



   (1) I suggest that agonizing over fuse sizes

   is a waste of intellectual and emotional

   capital. Make the fuse BIG in comparison to system

   DEMAND. Make the wire mechanically robust which

   makes it QUITE capable of meeting system demands

   but not necessarily capable of meeting AC43-13

   temperature rise recommendations - you're never going

   to load the wire that hard. This is a special

   case that does not fit the legacy design goals

   for wire/breaker/fuse sizing.



   (2) Don't get wrapped around the axle of crash safety.

   That problem has been painted with a VERY broad

   brush. Better that you crash for reasons

   beyond your control than because ignition or fuel

   pump supply feeders protection were too light

   and the engine quit.



I have a dual LSE3 config and I'm now considering simplifying this by 

having one off of my vp200 and the other direct to the battery with 

just a 7.5 amp fuse or breaker.  This way if there is a nuisance 

trip, I can reset via the vp200 and run off a single lse if needed 

until I land.  Of course that still does leave a potential failure 

mode should both trip and the vp200 connected one not come back online.



   It's my considered recommendation that the LSE

   system not depend on ANY other features in your

   power distribution beyond a fuse at the battery

   bus (not a breaker . . . we want it to be FAST)

   and a switch on the panel. You want to be able

   to shut the MASTER off without having the engine

   quit. Same thing for your fuel pumps if you have

   them.



   Remove the term NUISANCE TRIP from the lexicon

   of talking about your airplane's electrical systems.

   The only circuits that EVER nuisance trip are those

   not properly crafted to design goals . . . like

   those stated above.



   ANY time you hear a hangar-tale or ramp-rumor

   about somebody's system tripping but the day was

   saved by pushing a breaker back in, then thank

   your stars for the fact that you participate

   on the AeroElectric-List and folks have helped

   you design for robustness. YOUR airplane is not

   going to suffer nuisance trips. If it EVER does,

   you'll find out why and make appropriate changes

   to see that it never happens again. Then you'll

   share that event with the rest of us on the List

   just in case you've discovered some new condition

   that others need to be aware of.



   Further, if we do find that an LSE product is

   fitted with any sort of CROWBAR ov protection

   (which I doubt) then I think it is prudent

   to ask that your devices be delivered with that

   feature disabled. There is no good reason to

   build such a feature into any accessory. Even

   LSE says it's mandatory that your SHIP'S SYSTEM

   be fitted with ov protection.



   Finally, if the foregoing does not give you sufficient

   confidence based upon understanding the potential effects

   of departing from the manufacturer's recipe for

   success, then please follow the manufacture's

   recommendations TO THE LETTER. Keeping the engine

   running should be the LEAST of your worries.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 28, 2012 8:05 am Post subject: Fuses instead of breakers

At 09:36 AM 1/28/2012, you wrote:


<bob.condrey(at)baesystems.com>



In the spirit of trying to move the ball forward I'll suggest that 

fusible links to protect the battery feeders are probably the best 

way to go in a cost/weight/reliability trade. They provide protection 

of the feeder wires, have a slow time constant so a panel CB will 

trip first, are inexpensive and lightweight.  A larger CB would does 

the job also but with more weight and cost.



   Except that they are overly robust and do not even

   come close to addressing concerns for crash safety.

   A 20A ATC fuse is an excellent middle ground that

   offers approximately 10X operational robustness

   factor and still reacts quickly to crash induced

   hard faults.



   There is no good reason to "double up" with breakers

   on the panel. Fuses/breaker/limiters/links are to protect

   wires. Only ONE is needed between the ignition system's

   power source and the electronics. So the up-sized fuse

   makes the most sense.



If you've only got a single LSE then maybe no issue since you'll 

always have a mag to fall back on.  If you're running a pair of them 

however, you need to fully understand failure modes and mitigate the risks.



   That's what the List is all about . . .



This thread started with the question of whether a fuse would be an 

adequate substitute for a CB in this application.  Given what I 

believe to be true about the ignitions, the answer is a qualified 

NO.  Qualified because it's only a REAL issue if you don't have a mag 

to fall back on.



   Are you offered a dual failure hypothesis?



Installing as recommended by the manufacturer using a panel mounted 

CB gives you a solid install.



   Operationally correct but no consideration

   for crash-safety.



Just make sure you don't do something that compromises that by 

putting a fuse upstream or substituting a fuse for the panel CB.  If 

you want to protect the feeder use a slightly larger CB or fusible 

link.  You can do a very simple experiment as Michael did to validate 

the fuse issue (when upstream of a CB).



   Don't over-simply such experiments. The devil is

   in the details. Better you have ONE protective

   device crafted for robustness while not seriously

   disregarding crash safety.

   Bob . . .

Tundra10

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

Posted: Sat Jan 28, 2012 10:27 am Post subject: Fuses instead of breakers

 	  Quote: 	
		         I thought we were talking about a much larger

       hydraulic system. The amount of snort needed to

       operate the gear in floats is much smaller than

       that used on a GlasAir or Lancair. I think these

       relays will be fine and since you have a backup

       hand pump, your risks are quite low.


	


So perhaps 10AWG wire is not required ?



The installation instructions show 12AWG with a 25A pullable breaker.   

Many builders are happily flying with this installation.



The hydralic pump motor is a Parker-Oildyne series 108 12VDC permanent  

magnet motor code AE 0.327".

The pressure switches are 500psi.  I assume this means that there will  

be brief spikes above

this pressure at the motor when it first starts up, but after the  

fluid is moving, it must be less than 500psi.



Based on the small graph, the current at 500psi is 17A to produce a  

flow of 51 cubic inches per minute, but I have no method to estimate  

the inrush current as the motor starts up.  The graph stops at 2000psi  

at 48A continuous (but not for long according to the intermittent use  

temperature graph).  The successful use of small relays would indicate  

the inrush current is not significant ?



I don't know how to estimate the inrush current, nor the amount of  

voltage sag that would negatively impact the motor at startup.

So I can't calculate any possible advantages of heavier wire 



Jeff Page

Dream Aircraft Tundra #10

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 28, 2012 12:12 pm Post subject: Fuses instead of breakers

So perhaps 10AWG wire is not required ?



 The installation instructions show 12AWG with a 25A pullable breaker.   

 Many builders are happily flying with this installation.



    Well, let's run the numbers and see . . .



 The hydralic pump motor is a Parker-Oildyne series 108 12VDC permanent  

 magnet motor code AE 0.327".



    AHA! REAL stick-to-your-grey-matter data. It's amazing

    what you can discover if given a few numbers.  In this case:



 [img]cid:.0[/img]



    Okay. The critical numbers here are the cubic inch displacement

    per revolution (0.0321). The current at any two flow points which

    gives you the slope of the line in PSI/AMP. The point where

    pressure goes to zero but flow is max. This point establishes

    the internal energy dissipation in motor and pump. We could

    develop all the torque and CEMF constants for the motor

    in numbers . . . but the questions yield nicely to a

    pencil and straight-edge solution too.



    I've extended the curves to the point where flow goes to

    zero (stall) and current goes to zero (which provides

    the anchor point for zero load RPM of the motor. But to

    get to THE question of the moment, I deduce that stall

    current for this motor is on the order of 70 amps. This

    current is EQUAL to that demanded of a 3200 PSI condition

    which can never be achieved because of the relief valves.



 The pressure switches are 500psi.  I assume this means that there will  

 be brief spikes above this pressure at the motor when it first starts

 up, but after the fluid is moving, it must be less than 500psi.



    Actually no. Pressure induced motor current is dominant only

    after the motor is stable at some speed. During start up, the

    flows can be no greater than what the system back pressure

    allows and is probably quite low. Motor current is high because

    the armature is accelerating to a stable operating point. If

    pressure reliefs are set for 500 psi then the maximum operating

    current for the motor will be 17A and probably achieved only

    when all cylinders reach their limits causing flow resistance

    to spike. Only then would we expect the pressure to climb

    rapidly for the moon . . . and were it NOT for relief valves,

    the current would approach stall or a hose will blow off.



    Now, if you started the motor up to FURTHER extend/retract

    the gear against hard stops, you get the same 70A inrush

    which would fall only to 17A and stay there as the relief valves

    cracked. System pressure would never exceed 500 PSI.   



 Based on the small graph, the current at 500psi is 17A to produce a  

 flow of 51 cubic inches per minute, but I have no method to estimate  

 the inrush current as the motor starts up.  The graph stops at 2000psi  

 at 48A continuous (but not for long according to the intermittent use  

 temperature graph).



    Now you know how to do it.



 The successful use of small relays would indicate the inrush

 current is not significant ?



    No, it's always significant.



    Keep in mind that system wiring can have a profound

    effect on inrush currents. 70A at 12v implies a motor

    resistance of 12/70 or 0.17 ohms. 10AWG wire is one

    millohm per foot. So adding say 10' of 10AWG in the total

    loop resistance takes your motor + wire up to 180

    milliohms for a new inrush of 12/.180 or 66 amps. Of

    course, this doesn't account for any sag in electrical

    system voltage during inrush. 12AWG wire is 1.6 milliohms

    per foot so inrush comes down some more.



    Since the running current cannot exceed 17A due to

    action of relief valves, you COULD consider a 14AWG

    or even 16AWG feeder for the purpose of limiting

    inrush . . . assuming that becomes a design goal.



    This would have no effect on available system pressure

    because that is set by relief valves. It WOULD reduce

    available flow at that pressure because motor voltage

    hence RPM is slightly reduced. Wired per the instructions,

    it seems that your inrush will be on the order of 50-65

    amps which is no big deal on a 30A relay.



 I don't know how to estimate the inrush current, nor the amount of  

 voltage sag that would negatively impact the motor at startup.

 So I can't calculate any possible advantages of heavier wire 



    The 'advantages' if any are murky. The system you're installing

    has a successful track record with components specified

    by the manufacturer. I can see no compelling reason

    to alter that recipe.



 

   Bob . . .

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Tundra10

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

Posted: Sun Jan 29, 2012 8:52 am Post subject: Fuses instead of breakers

Bob,



Thank you ever so much for your analysis, and your time that you  

obviously took to teach it.  I was looking at that graph, thinking it  

appeared they were providing lots of information, yet it seemed  

insufficient.



Now that you have taught me how easy it is to extend the lines, I am  

disappointed I didn't think of that myself, but now I can use that  

technique to great benefit in the future.



Also very important, is that I can wire my aircraft, _knowing_ that  

the installation is the best possible compromise of all the factors,  

rather than blindly following the installation instructions of a  

company who's expertise is building floats, rather than electrical  

design.



In this case, your analysis confirms their installation instructions  

are excellent, providing confidence that they offer a solid product.



Thanks !!



Jeff Page

Dream Aircraft Tundra #10

natsuto
Guest

Posted: Tue Feb 14, 2012 6:03 pm Post subject: Re: Fuses instead of breakers

I promptly pull the hangar and wired directly to the battery Klaus's instructions. I've always wanted, he wrote: There is a reason. Has been working ever since.

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Feb 15, 2012 6:35 am Post subject: Fuses instead of breakers

At 08:03 PM 2/14/2012, you wrote:

 	  Quote: 	
		  



I promptly pull the hangar and wired directly to the battery Klaus's 

instructions. I've always wanted, he wrote: There is a reason. Has 

been working ever since.


	


    When one is unsure of elegant alternatives

    to common sense design goals, it is good to follow

    the manufacturer's instructions.



    At the same time, the manufacturer's instructions

    my be only one of several recipes for success.

    This is how the "experimental" airplane becomes

    a teaching tool where new recipes can be considered

    and proven. Just as the student in the chemistry

    lab is learning by 'experiment' the teacher knows the

    outcome of every lesson. For the teacher, the lab

    is a tool to share recipes and the behavior of

    their ingredients . . . anything but an experiment.

    For the student, the experience morphs an experiment

    into useful knowledge and skills. The next time that

    recipe is repeated, the outcome is predictable.



    At the same time, the teacher is ever mindful of

    individual willingness to expand on their experimental

    experiences. The explorer is well advised to temper

    their quest for discovery with any admonition the

    teacher may offer like, "Don't do that! You'll set

    the lab on fire . . . or put your eye out!"



    The word experimental is synonymous with explore

    and discovery. But just as the automotive industry

    is discovering that the lithium battery may not

    yet be ready for prime time (perhaps influenced

    by institutional pressure to 'hurry up and save

    the planet'?) they have learned a lot and are still

    in the discovery phase.



    In experimental aviation we have a rich

    library of historical successes (and failures)

    to study. The trick is to shun any form of

    pressure, be it institutional or from the hangar

    mate next door. In experimental aviation we need

    not "launch any new recipe into the sky before it's

    time."

   Bob . . .

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