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First Engine Start Problem
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dan(at)azshowersolutions.
Guest

Posted: Fri Dec 30, 2011 3:05 pm Post subject: First Engine Start Problem

I would like to thank all who responded to the issue at hand. I learned many things here, most importantly, how my electrical system is designed to work along with how I need to work. In the world of reading schematics and interpreting how they are to be used...I am STILL learning. My assumptions believing the E-switch was to be on sifted back to when I was flying the rented 172 and of course, there IS a switch that needed to be on for the radios, intercom, Etc... So much for the ASSuming.

 I was quite surprised when I found my diode in backwards as I am usually quite anal when building circuits, yet, I am now actually glad it happened in this manner as I would have been utilizing my system incorrectly. Thank you Joe for bringing up the  possibility of the reversed diode...Spot On Sir.

And Thanks again to Bob N. for pointing my brain cell (the one that is still working) to the possible overloading as well as taking a better look at what my Plan_B needs to look like. I will most likely move any lights over to the Main, but more importantly take a close look at how much time a given instrument (as well as combined gizmos) should take me. I will most likely leave my D-100, GPS and the radio where they sit. knowing I can turn one or two off to get my butt to the safety line will always be there. 

I Wish everyone a Happy New Year!

Dan



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

To: aeroelectric-list(at)matronics.com

Sent: Fri, December 30, 2011 9:26:38 AM

Subject: Re: Re: First Engine Start Problem



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



At 08:33 PM 12/29/2011, you wrote:

 	  Quote: 	
		   Just got back from the airport and found the following:

 1.I took the ammeter reading across the Alternate switch (with the Master switch off). I was reading at 5.2 A with everything on and that was without keying the mic for transmission. I assume that would bump it up even more (didn't get a chance to try that).


	


  Okay, how does 5.2A fit into your Plan-B?



[quote] 2. The Diode between the two buses WAS backwards. I changed it and now my panel lights up when the Master switch is on. Would this have had any bearing on why my fuseable link burned or do you think I need to move some things to the Main bus? The components I have on the E-bus are as follows:

 Dynon D100, Garmin   

  	  Quote: 	
		  [b]

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user9253

Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan

Posted: Fri Dec 30, 2011 4:48 pm Post subject: Re: First Engine Start Problem

 	  Quote: 	
		  The guys that were working with me asked me why that link was there...I did not have a good answer for them. . . .So...I am now reluctant to put another fuseable link in place . . . 	


Without a fusible link and in the event of a short circuit or heavy overload, the full length of  the circuit wire could become red hot or even white hot.  Think of a fusible link as a robust, slow blowing, fuse.  Having a fusible link will ensure that heat and smoke from a circuit fault will occur at a known safe location rather than at a random location in the wire harness.

  The diode might have been conducting more current than it was designed to carry.  A simple test will confirm that it is still blocking reverse current.  With the master switch off and the E-Bus switch on, the main bus should not be energized and anything connected to it should not be powered.

Joe

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_________________
Joe Gores

dan(at)azshowersolutions.
Guest

Posted: Fri Dec 30, 2011 5:21 pm Post subject: First Engine Start Problem

Now that I know why and how the fuseable link burned, I will be replacing it. I have already called my buddies and gave them the answer I was (at the time) unsure about. Joe, I'm glad you addressed the integrity of the diode. It re-affirmed my thoughts as well and I have already decided to replace it (cheap insurance). 

Thanks again for the assistance.

Dan



From: user9253 <fran4sew(at)banyanol.com>

To: aeroelectric-list(at)matronics.com

Sent: Fri, December 30, 2011 5:48:09 PM

Subject: Re: First Engine Start Problem



 --> AeroElectric-List message posted by: "user9253" <fran4sew(at)banyanol.com (fran4sew(at)banyanol.com)>

 	  Quote: 	
		   The guys that were working with me asked me why that link was there...I did not have a good answer for them. . . .So...I am now reluctant to put another fuseable link in place . . .


	


Without a fusible link and in the event of a short circuit or heavy overload, the full length of  the circuit wire could become red hot or even white hot.  Think of a fusible link as a robust, slow blowing, fuse.  Having a fusible link will ensure that heat and smoke from a circuit fault will occur at a known safe location rather than at a random location in the wire harness.

  The diode might have been conducting more current than it was designed to carry.  A simple test will confirm that it is still blocking reverse current.  With the master switch off   

 [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Dec 30, 2011 7:17 pm Post subject: First Engine Start Problem

At 06:48 PM 12/30/2011, you wrote:


 > The guys that were working with me asked me why that link was 

there...I did not have a good answer for them. . . .So...I > am now 

reluctant to put another fuseable link in place . . .



Without a fusible link and in the event of a short circuit or heavy 

overload, the full length of  the circuit wire could become red hot 

or even white hot.  Think of a fusible link as a robust, slow 

blowing, fuse.  Having a fusible link will ensure that heat and smoke 

from a circuit fault will occur at a known safe location rather than 

at a random location in the wire harness.



    Which is the function of all protective devices for wire.

    Fuses are very fast comparted to circuit breakers.

    Circuit breakers are very fast compared to 'current limiters'

    which are manufactured versions of fusible links. See:



http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf



    Note that an ANL35 will carry 80 amps indefinitely at

    room temperature. Say what???? A 35 amp fuse needs to

    be operated at no more than 75% of rating to avoid long

    term weakening of the fusible element. The difference in

    these two devices is their application. A line fault where

    a fuse is wired upstream of a breaker will probably open a

    fuse several times the size of the breaker. Current limiters

    (and fusible links) are used upstream of both fuses and

    breakers in cars and airplanes. They have VERY long time

    constants compared to the downstream devices . . . yet they

    provide the same 'weak link in chain' that guarantees a

    predictable failure. The provide an orderly failure

    location for a faulted feeder that is robust enough not to

    compromise the performance of downstream protection.



    This is exactly what YOUR fusible link did. Had it not been

    installed, you would have probably overheated if not smoked

    the protected wire . . . possibly damaging other wires in

    the bundle.



    If you wanted to put a 20A, in-line fuse holder in its

    place, that would be fine too as long as you don't have

    BREAKERS downstream.



    I'm working an accident case right now that involved

    poor choice and placement of fuses and breakers combined

    with an architecture that offered several single points

    of failure for all ignition to the engine . . . not good.



    We'll discuss it in detail once the dust settles on

    the legal tug-of-war.



    The lesson here is that the 'rating' of a fuse, breaker,

    limiter, or link is only roughly tied to performance.

    Until you trade of TIME to OPERATE values, you don't know

    the whole story.



The diode might have been conducting more current than it was 

designed to carry.  A simple test will confirm that it is still 

blocking reverse current.  With the master switch off and the E-Bus 

switch on, the main bus should not be energized and anything 

connected to it should not be powered.



    Replacing it is a good idea. It's easier to simply

    install a new one than it is to test the old one for

    changes in performance due to the fault condition.



    Bob . . .

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dan(at)azshowersolutions.
Guest

Posted: Sat Dec 31, 2011 6:45 am Post subject: First Engine Start Problem

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

 To: aeroelectric-list(at)matronics.com 

 Sent: Friday, December 30, 2011 8:14 PM

 Subject: Re: AeroElectric-List: Re: First Engine Start Problem

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

 This is exactly what YOUR fusible link did. Had it not been

  installed, you would have probably overheated if not smoked

  the protected wire . . . possibly damaging other wires in

  the bundle. 

Which is something that concerns me due to my knee jerk reaction of sticking an 18 Ga wire in and starting my engine 3 times that day. The total time I ran the engine between the three starts was about 10 min.  My thinking that the running of the engine may not have been so bad but the starts  put strain on the circuit with that diode reversed. I will certainly inspect that complete circuit looking for any sign of where the wire got too hot.  I also have a concern for the wires up stream of the main bus going to the switch. The 5A circuit breaker did not fail, but I will check that fuse link as well. Is there anything else I might be missing that needs a look?

Thanks again,

Dan

=======================-=     * AeroElectric www.hnbsp;                    = "http://www.matronics.com/Navigator?AeroElectric-List" target="_blank">htnbsp;                 -Matt Dralle,tribution" =======

 [b]

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jason(at)jasonbeaver.com
Guest

Posted: Fri Jan 06, 2012 12:30 am Post subject: First Engine Start Problem

On Dec 30, 2011, at 7:14 PM, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		     If you wanted to put a 20A, in-line fuse holder in its

   place, that would be fine too as long as you don't have

   BREAKERS downstream.


	


Bob, can you explain what is bad about having circuit breakers downstream of fuses?  I wired my Lightspeed Plasma II ignition through a fuse on the battery bus to the breaker on the panel because I didn't want such a long, always-hot wire from the battery directly to the panel.  Should I rewire this?



thanks,



jason

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retasker(at)optonline.net
Guest

Posted: Fri Jan 06, 2012 10:03 am Post subject: First Engine Start Problem

If the current ratings are similar, the fuse will always blow first, so the breaker serves no purpose.  If the fuse 

current rating is some significant multiple of the breaker rating that might work - which might be okay to protect 

against shorts in the wire up to the breaker - but what is the point.

Dick Tasker

Jason Beaver wrote:

 	  Quote: 	

 On Dec 30, 2011, at 7:14 PM, Robert L. Nuckolls, III wrote:

>    If you wanted to put a 20A, in-line fuse holder in its

>    place, that would be fine too as long as you don't have

>    BREAKERS downstream.

 Bob, can you explain what is bad about having circuit breakers downstream of fuses?  I wired my Lightspeed Plasma II ignition through a fuse on the battery bus to the breaker on the panel because I didn't want such a long, always-hot wire from the battery directly to the panel.  Should I rewire this?

 thanks,

 jason

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 06, 2012 6:55 pm Post subject: First Engine Start Problem

At 02:16 AM 1/6/2012, you wrote:




On Dec 30, 2011, at 7:14 PM, Robert L. Nuckolls, III wrote:



 >   If you wanted to put a 20A, in-line fuse holder in its

 >   place, that would be fine too as long as you don't have

 >   BREAKERS downstream.



Bob, can you explain what is bad about having circuit breakers 

downstream of fuses?  I wired my Lightspeed Plasma II ignition 

through a fuse on the battery bus to the breaker on the panel because 

I didn't want such a long, always-hot wire from the battery directly 

to the panel.  Should I rewire this?



    Probably. Put the one and only protective device

    (5A breaker or fuse) at the battery bus with no further

    devices downstream.



    If THAT protection opens, it is because the ignition

    system is hurt bad . . . and you'll need to rely on the

    second, totally independent system to bring your flight

    to an orderly conclusion.



    To have a 'breaker' downstream of a fuse turns the

    breaker into a switch. Breakers are so much slower than

    a fuse that a 5A fuse upstream of the 5A breaker will

    always open first. In fact, a 10A fuse upstream of a

    5A breaker will still open before the 5A breaker.



    The "fuse" symbol often found upstream of breakers in

    aircraft power distribution diagrams is a CURRENT LIMITER,

    a robust, special kind of fuse with fusing dynamics

    that are very unlike their little plastic, plug-in

    cousins. For example:



http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf



    Note that a '35 Amp' ANL will carry 80 amps about

    indefinitely which is a 200% overload. The ANL and close

    cousins are suited for protecting fat-wire feeders to

    busses downstream that might mount circuit breakers.



   Here we see:



http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ATC_Specs.pdf



    that a 200% overload on a 5A ATC plastic fuse is expected

    to open it in something on the order of 300 milliseconds.

    In the last data sheet we see:



http://aeroelectric.com/Mfgr_Data/Breakers/Eaton/Eaton_4200.pdf



    that a Series 4200 miniature breaker under 200% overload

    can take from 2 to 20 seconds to open and still be "in spec".



    As a matter of simple design goals, a single

    feeder needs only one protective device located as near

    to the power source (bus) as practical. Any device upstream

    of a breaker needs to be robust enough to stay closed during

    operation of the downstream device. Finally, all robust fuses

    and indeed any protective device over 5A is discouraged for

    use on always hot feeders. This design rule is cited in the

    FARS and generally refers to circuit breakers. We know that

    a 5A breaker will open a 10A fuse . . . so it follows that

    one COULD consider 10A ATC fuses on battery bus feeders without

    presenting potential fault energy worst than a 5A breaker.

   Bob . . .

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