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Fusible links

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fvalarm(at)rapidnet.net
Guest

Posted: Tue Dec 02, 2014 9:45 am Post subject: Fusible links

I can't find the detail in the book.  When making a fusible link, the inner

"fuse" wire is 22 AWG in this case.  Is it necessary to strip the insulation

off?  



Thanks



Bevan

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Dec 02, 2014 11:42 am Post subject: Fusible links

At 11:44 2014-12-02, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "B Tomm" <fvalarm(at)rapidnet.net>



 



 I can't find the detail in the book.  When making a fusible link, the inner

 "fuse" wire is 22 AWG in this case.  Is it necessary to strip the insulation

 off?  

 	


   I presume you're asking about the insulation on the

   22AWG wire? No, in fact, you ADD insulation over it



   See  http://tinyurl.com/msx5ofe



   Where are you considering the use of a fusible link?

   I crafted that comic-book waaayyy back when we were

   wrestling with the notion of extending the BUS in a 

   fuse block up to a one-terminal-BUS at the input side

   of the alternator field breaker. A breaker upstream

   of a crow-bar ov protection module.



   I think we also dabbled with the use of fusible links

   on the meter-leads to a shunt. As a general rule, the

   fusible link is attractive only when a fuse holder

   is a little 'messy' . . . The TC fleet has used two

   fuses in clips to protect ammeter wires for decades.



 [img]cid:.0[/img]



   The last time I was able to walk down the A36

   production line (about 10 years ago) the clipped-in

   fuses for various 'minor' tasks were quite visible.



   The need to extend the bus to accommodate the only

   circuit breaker in the airplane was a special case.



   Like Figure Z-13/20, and to some extend Z-19, I've

   regretted having published the ideas. While useful

   and appropriate to the special cases, they've 

   morphed into other forms that may or may not

   have been through PCQDR (preliminary, critical

   and qualification design review).



   Can or should we talk about it?



 

   Bob . . .

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fvalarm(at)rapidnet.net
Guest

Posted: Tue Dec 02, 2014 1:55 pm Post subject: Fusible links

Thanks Bob,

  

 I had done it on mine a couple years back, but the  other day I was helping a hangar neighbour make some improvements.  He has  a rear mounted battery on a BD4 (engine in front).  He has one electronic  ignition which was powered by an 18 awg wire connected on the firewall at  the input power terminal at the starter solenoid.  This fat wire was only  powered when the master solenoid (located in back next to the battery) was  active.  Not ideal for electrically dependant ignition.  There was a  spare 18 awg wire already running all the way back to the battery and the owner  wanted to use that.  I suggested that we fuse it but that fuse would have  to activate  "slower" than the breaker on the panel.  I therefore  suggested a fusible link and that is where I crossed the line.  Since it  was such a good idea, and I had suggested it, it was suggested that I do  it     Not a problem since I had materials left over.   Just couldn't remember if the 22awg wire (now hidden under the silicone  impregnated sleeve)  on my RV7 had been stripped or not.  My thinking  initially was that it must have been stripped because we really don't want any  combustible material "inside" the fuse if possible. It didn't strip well, so I  re-did it without stripping as you have confirmed.  Thank  you.

  

 Bevan



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert  L. Nuckolls, III

Sent: Tuesday, December 02, 2014 11:41  AM

To: aeroelectric-list(at)matronics.com

Subject: Re:  Fusible links

 

At 11:44 2014-12-02, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message    posted by: "B Tomm" <fvalarm(at)rapidnet.net>



I can't find    the detail in the book.  When making a fusible link, the inner

"fuse"    wire is 22 AWG in this case.  Is it necessary to strip the    insulation

off?  

	


  I presume you're asking  about the insulation on the

  22AWG wire? No, in fact, you ADD  insulation over it



  See http://tinyurl.com/msx5ofe



  Where are you  considering the use of a fusible link?

  I crafted that comic-book  waaayyy back when we were

  wrestling with the notion of extending the  BUS in a 

  fuse block up to a one-terminal-BUS at the input  side

  of the alternator field breaker. A breaker upstream

  of  a crow-bar ov protection module.



  I think we also dabbled with the  use of fusible links

  on the meter-leads to a shunt. As a general rule,  the

  fusible link is attractive only when a fuse holder

  is a  little 'messy' . . . The TC fleet has used two

  fuses in clips to  protect ammeter wires for decades.



[img]cid:776342221(at)02122014-0CF9[/img]



  The last  time I was able to walk down the A36

  production line (about 10 years  ago) the clipped-in

  fuses for various 'minor' tasks were quite  visible.



  The need to extend the bus to accommodate the  only

  circuit breaker in the airplane was a special case.



   Like Figure Z-13/20, and to some extend Z-19, I've

  regretted having  published the ideas. While useful

  and appropriate to the special  cases, they've 

  morphed into other forms that may or may not

   have been through PCQDR (preliminary, critical

  and qualification  design review).



  Can or should we talk about it?



 

  Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Dec 03, 2014 8:27 am Post subject: Fusible links

At 15:53 2014-12-02, you wrote:

Thanks Bob,



I had done it on mine a couple years back, but the other day I was 

helping a hangar neighbour make some improvements.  He has a rear 

mounted battery on a BD4 (engine in front).  He has one electronic 

ignition which was powered by an 18 awg wire connected on the 

firewall at the input power terminal at the starter solenoid.  This 

fat wire was only powered when the master solenoid (located in back 

next to the battery) was active.  Not ideal for electrically 

dependant ignition.  There was a spare 18 awg wire already running 

all the way back to the battery and the owner wanted to use that.  I 

suggested that we fuse it but that fuse would have to 

activate  "slower" than the breaker on the panel.  I therefore 

suggested a fusible link and that is where I crossed the line.  Since 

it was such a good idea, and I had suggested it, it was suggested 

that I do it     Not a problem since I had materials left 

over.  Just couldn't remember if the 22awg wire (now hidden under the 

silicone impregnated sleeve)  on my RV7 had been stripped or not.  My 

thinking initially was that it must have been stripped because we 

really don't want any combustible material "inside" the fuse if 

possible. It didn't strip well, so I re-did it without stripping as 

you have confirmed.  Thank you.



    Okay, this is a situation similar

    to the "bus extension" to panel mounted

    breaker for a crowbar ov protection

    system.



    Keep in mind that circuit protection is

    to keep the smoke in wires. Further, the

    'rule of thumb' for always hot wires from

    a battery bus is to protect at 5A or less

    Given that fuses are MUCH faster than

    breakers . . . 7A fuse is a comfortable

    alternative to the 5A breaker.



    This is a convention driven by concerns

    for crash safety. Limit the energy available

    on an always-hot wire for the purposes of

    reducing risk of post crash fire. I don't

    believe for a minute that anyone did any

    tests combined with statistical analysis

    to come up with that 5A number . . . but

    intuitively, one finds comfort in protecting

    an always-hot wire at the lowest practical

    value.



    I suspect that the electronic ignition runs

    on MUCH less than 5A. What size is the panel

    mounted breaker?  If it were my airplane,

    I'd drive the ignition supply wire from the

    battery through a 7A fuse and eliminate the

    panel mounted breaker.



    If that breaker EVER trips, then  there's

    something seriously wrong with either

    the ignition system or the power pathway

    feeding it . . . the notion of resetting it

    is does not stand on favorable probabilities

    for recovery-by-reset. A 7A fuse, 5A breaker,

    or fusible link in the tail does not alter

    the probabilities . . .

   Bob . . .

ceengland7(at)gmail.com
Guest

Posted: Wed Dec 03, 2014 9:17 am Post subject: Fusible links

On 12/3/2014 10:26 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>





 At 15:53 2014-12-02, you wrote:

 Thanks Bob,



 I had done it on mine a couple years back, but the other day I was 

 helping a hangar neighbour make some improvements.  He has a rear 

 mounted battery on a BD4 (engine in front).  He has one electronic 

 ignition which was powered by an 18 awg wire connected on the firewall 

 at the input power terminal at the starter solenoid. This fat wire was 

 only powered when the master solenoid (located in back next to the 

 battery) was active.  Not ideal for electrically dependant ignition.  

 There was a spare 18 awg wire already running all the way back to the 

 battery and the owner wanted to use that.  I suggested that we fuse it 

 but that fuse would have to activate  "slower" than the breaker on the 

 panel.  I therefore suggested a fusible link and that is where I 

 crossed the line.  Since it was such a good idea, and I had suggested 

 it, it was suggested that I do it     Not a problem since I had 

 materials left over.  Just couldn't remember if the 22awg wire (now 

 hidden under the silicone impregnated sleeve)  on my RV7 had been 

 stripped or not.  My thinking initially was that it must have been 

 stripped because we really don't want any combustible material 

 "inside" the fuse if possible. It didn't strip well, so I re-did it 

 without stripping as you have confirmed.  Thank you.



    Okay, this is a situation similar

    to the "bus extension" to panel mounted

    breaker for a crowbar ov protection

    system.



    Keep in mind that circuit protection is

    to keep the smoke in wires. Further, the

    'rule of thumb' for always hot wires from

    a battery bus is to protect at 5A or less

    Given that fuses are MUCH faster than

    breakers . . . 7A fuse is a comfortable

    alternative to the 5A breaker.



    This is a convention driven by concerns

    for crash safety. Limit the energy available

    on an always-hot wire for the purposes of

    reducing risk of post crash fire. I don't

    believe for a minute that anyone did any

    tests combined with statistical analysis

    to come up with that 5A number . . . but

    intuitively, one finds comfort in protecting

    an always-hot wire at the lowest practical

    value.



    I suspect that the electronic ignition runs

    on MUCH less than 5A. What size is the panel

    mounted breaker?  If it were my airplane,

    I'd drive the ignition supply wire from the

    battery through a 7A fuse and eliminate the

    panel mounted breaker.



    If that breaker EVER trips, then  there's

    something seriously wrong with either

    the ignition system or the power pathway

    feeding it . . . the notion of resetting it

    is does not stand on favorable probabilities

    for recovery-by-reset. A 7A fuse, 5A breaker,

    or fusible link in the tail does not alter

    the probabilities . . .

   Bob . . .

Probably a safe assumption for 'traditional' a/c engines with stock fuel 
	


delivery, but different for 'alternative' (automotive-based) engines and 

increasingly, a/c engines, more current is required. Most 

automotive-based engines use high pressure fuel injection which must be 

included in current calculations. There's now a growing wave of 

automotive style injection on a/c engines, as well. High pressure 

gerotor or roller-vane fuel pumps typically draw 6-10 amps continuous. 

Even the little turbine style pumps (which must be installed inside the 

fuel tank; the input must be kept flooded) typically draw 3-4 amps. So 

total current demand to keep an 'electronic' engine running usually 

exceeds 10 amps; often as high as 15.



So what's the solution? Dedicated fuse bus at the battery to distribute 

power to the various engine control components?



Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Dec 03, 2014 11:20 am Post subject: Fusible links

Probably a safe assumption for 'traditional' a/c engines with stock 

fuel delivery, but different for 'alternative' (automotive-based) 

engines and increasingly, a/c engines, more current is required. Most 

automotive-based engines use high pressure fuel injection which must 

be included in current calculations. There's now a growing wave of 

automotive style injection on a/c engines, as well. High pressure 

gerotor or roller-vane fuel pumps typically draw 6-10 amps 

continuous. Even the little turbine style pumps (which must be 

installed inside the fuel tank; the input must be kept flooded) 

typically draw 3-4 amps. So total current demand to keep an 

'electronic' engine running usually exceeds 10 amps; often as high as 15.



So what's the solution? Dedicated fuse bus at the battery to 

distribute power to the various engine control components?



    He was talking about an ignition system. Energy

    to light the fires is quite nominal. Not aware of

    any ignition that requires more than 3A. Lightspeed's

    flame throwing CD ignition runs 2.6A at 2700 rpm on

    a 6 cyl engine.



    Fuel delivery is another matter and, as you've noted,

    can be all over the map. TBI systems run on a few amps

    while some 40+ psi rail fed injector systems can be

    MUCH higher.



    I'd treat this like the heavy duty e-bus feeder

    illustrated in Z-32 . . . except the e-bus alt feed

    switch becomes a fuel system control switch. The

    relay could be a solid state device or one of the

    sealed electro-mechanical critters.



    This comports nicely with the TC aircraft philosophy

    for achieving a Max-Cold state of all wires when

    crew operated switches are placed to OFF.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Dec 03, 2014 2:15 pm Post subject: Fusible links

At 14:08 2014-12-03, you wrote:

 	  Quote: 	
		    Not aware of

     any ignition that requires more than 3A. Lightspeed's

     flame throwing CD ignition runs 2.6A at 2700 rpm on

     a 6 cyl engine.

If you are using a PSRU (propeller speed reduction unit) on a 6 

cylinder engine you will have a higher engine RPM, perhaps in the 

range of 4 - 5 k rpm.  This higher speed will translate to a higher 

current flow to the electronic CD ignition.  An MSD 6A automotive CD 

ignition module is specified at 1A / 1K RPM, which translates to 

perhaps 5A worst case.


	


   Hmmmm . . . that's too bad. There's no good reason

   for ignition systems to draw that much current.



   I've talked with the guys at EmagAir about this

   several times. A take-away from those conversations

   says that it's most important to get an adequate spark

   delivered right on time. Magnetos have proven their

   ability to deliver adequate sparks while running . . .

   and they're certainly not flame throwers. Certainly

   hard to fiddle with the timing . . . and you need

   some kind of monkey motion like impulse couplers or

   shower-of-sparks to effect nice starts . . . but

   there's hundreds of thousands flying with few

   critical issues.



   Being able to advance the spark at low manifold

   pressures gets you some benefit . . .but the spark

   doesn't need to be any hotter . . . in fact, worst

   case sparking requirements are at max cylinder pressure

   which probably means a boosted engine at max retard

   timing.



   The legacy Kettering coil, condenser, points system

   delivers about 30-40 mJ per spark. For a 6-cyl engine

   running 2400 rpm, 40 rev/sec, 3 sparks per rev, energy

   at the plugs comes to about 120 mJ per rev or 4800

   mJ per second. Assume a really lousy system efficiency

   of say 50% and we need to draw 9.6 watts from the

   ship's bus or about 700 mA.



   Now, deliver that energy even while cold and with

   a soggy battery . . . and be able to advance the

   timing at low manifold pressures, and you've got

   a perfectly adequate ignition system.



   So be curious and skeptical when someone says

   their 'flame throwing ignition system' is going

   to do great things for your airplane. If you're

   flying a racer, maybe. If you've got a nice

   point-a to point-b transportation machine that

   carries battery energy to implement Plan-B, perhaps

   all that flame at the spark plugs suggests a

   need to re-think the planning.



   Elegant solutions benefit from good stewardship

   of energy. It starts with the airfoils and

   extends down to batteries and fuel aboard.

   Bob . . .

fvalarm(at)rapidnet.net
Guest

Posted: Wed Dec 03, 2014 2:56 pm Post subject: Fusible links

Thanks Bob,



The literature that came with the LightSpeed says the breaker should be 7.5

amp.  (IO-540)  You still recommend a 5 amp breaker (since he really wants

some form of disconnect on the panel) and a (??? Value fuse, fusible link,

breaker)at the rear for the feed from the battery.



Perhaps I should suggest a 5 or 7.5 amp slow blo fuse at the battery, and a

simple switch on the panel in place of the breaker if he must have a

disconnect.



Bevan 



--

lyleapgmc

Joined: 19 Feb 2014
Posts: 57

Posted: Wed Dec 03, 2014 7:10 pm Post subject: Fusible links

Hi,

I've been involved in electronics for some 30 years.  I know what a 

fusible link is in an automobile.  They do come in a variety of designs, 

some very much like a fuse as we know them.

I have always questioned the value of a fusible link such as is used in 

automobiles.  They are a length of wire, usually 4 wire gauges smaller 

than the wire they are protecting.  They are most often a hassle to 

replace.  Why would not a common fuse perform the same function and be 

much more easily replaced?

Inquiring minds want to know,

Lyle

On 12/3/2014 4:14 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckolls.bob(at)aeroelectric.com>

 At 14:08 2014-12-03, you wrote:

>  Not aware of

>     any ignition that requires more than 3A. Lightspeed's

>     flame throwing CD ignition runs 2.6A at 2700 rpm on

>     a 6 cyl engine.

> If you are using a PSRU (propeller speed reduction unit) on a 6 

> cylinder engine you will have a higher engine RPM, perhaps in the 

> range of 4 - 5 k rpm.  This higher speed will translate to a higher 

> current flow to the electronic CD ignition.  An MSD 6A automotive CD 

> ignition module is specified at 1A / 1K RPM, which translates to 

> perhaps 5A worst case.

-- 

Lyle

Sent from my Gateway E4610D desktop

fvalarm(at)rapidnet.net
Guest

Posted: Wed Dec 03, 2014 8:53 pm Post subject: Fusible links

The advantages of the fusible link in this case is:



Must be slower acting than the breaker.  I blew quite a few fuses until I

found that I needed a fuse of about double the value to ensure the breaker

trips first.  This would suggest a 15 amp fuse which is larger than desired.

Robust (although a fuse in an inline holder is equally suitable in this

regard.)

There's no place to mount a breaker near the battery where it is easily

accessible and yet not in the way for battery access through the small panel

where it is located.

Cost and availability.  We're trying to get this airplane back in the air so

it can go home.  They can make more permanent changes there.



Bevan



--

fvalarm(at)rapidnet.net
Guest

Posted: Thu Dec 04, 2014 9:15 pm Post subject: Fusible links

Bob ,

  

 Was that photo of the fuses/wiring in the engine  compartment?

  

 Bevan



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert  L. Nuckolls, III

Sent: Tuesday, December 02, 2014 11:41  AM

To: aeroelectric-list(at)matronics.com

Subject: Re:  Fusible links

 

At 11:44 2014-12-02, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message    posted by: "B Tomm" <fvalarm(at)rapidnet.net>



I can't find    the detail in the book.  When making a fusible link, the inner

"fuse"    wire is 22 AWG in this case.  Is it necessary to strip the    insulation

off?  

	


  I presume you're asking  about the insulation on the

  22AWG wire? No, in fact, you ADD  insulation over it



  See http://tinyurl.com/msx5ofe



  Where are you  considering the use of a fusible link?

  I crafted that comic-book  waaayyy back when we were

  wrestling with the notion of extending the  BUS in a 

  fuse block up to a one-terminal-BUS at the input  side

  of the alternator field breaker. A breaker upstream

  of  a crow-bar ov protection module.



  I think we also dabbled with the  use of fusible links

  on the meter-leads to a shunt. As a general rule,  the

  fusible link is attractive only when a fuse holder

  is a  little 'messy' . . . The TC fleet has used two

  fuses in clips to  protect ammeter wires for decades.



[img]cid:307341305(at)05122014-0D5B[/img]



  The last  time I was able to walk down the A36

  production line (about 10 years  ago) the clipped-in

  fuses for various 'minor' tasks were quite  visible.



  The need to extend the bus to accommodate the  only

  circuit breaker in the airplane was a special case.



   Like Figure Z-13/20, and to some extend Z-19, I've

  regretted having  published the ideas. While useful

  and appropriate to the special  cases, they've 

  morphed into other forms that may or may not

   have been through PCQDR (preliminary, critical

  and qualification  design review).



  Can or should we talk about it?



 

  Bob . . .

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