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BATTERY FUSE

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user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Sat Mar 04, 2017 8:21 am Post subject: BATTERY FUSE

A friend of mine is building a plane with an 8 cylinder automotive engine.  I noticed that he had installed a 100 amp ANL fuse in series with the battery cable.  The fuse is located 6 inches from the battery and all battery current will go through that fuse including starter current.  I asked my friend if that 100 amp ANL will handle the starter current.  His response was, "It's a 35 amp battery."  I told him that a 100 amp ANL might not handle starting current.  He said that if it doesn't, he will replace it with a 150 amp.

  I think that the fuse will need to be bigger, like 200 amp or more.  Actually I do not think that there should be a fuse in series with the battery cable at all.  It is one more thing to fail and it adds resistance to the battery cranking circuit.  How can I convince my friend that fuse is not necessary or even desired?  If he will not change his mind, what size ANL fuse should he use?

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Joe Gores

yellowduckduo(at)gmail.co
Guest

Posted: Sat Mar 04, 2017 10:21 am Post subject: BATTERY FUSE

Tell him to crank it for 20 seconds and check the temperature of the ANL??

If he was serious about "It's a 35 amp battery", the larger implications 

are scary for someone trying to run an automotive engine!



A few guys put the blinders on by putting all their dollars and faith in 

a particular vendor who may not be giving the best advice, they may be 

unreceptive to any other ideas.  Some guys just have to learn the hard 

way but assure him that an ANL in the ground circuit is not standard 

practice.  And don't put yourself in the position where a friend or 

lawyer will claim you oversaw the project.



Does his second engine ground path provide a current path to the 

alternator? That reduces the chance that he will notice if the ANL pops 

during a successful engine start though. He does have a second heavy 

grounding strap/wire on his electric dependent engine??



FWIW with a crude meter I used to see well over 100 amps cranking sixes 

and eights although it pulses heavily at each compression stroke.  DC 

(no typo) clamp on meters can be had for under $20. these days on ebay 

but they are not very useful for pulsating loads like a starter. The 100 

ANL will probably work ...for awhile.  And hopefully he'll be on the 

ground when it goes bad.  I've also seen some 4 cylinder engines that 

turn over faster and draw more current than the slower cranking larger 

engines.



Ken



On 04/03/2017 11:21 AM, user9253 wrote:

 	  Quote: 	
		   



 A friend of mine is building a plane with an 8 cylinder automotive engine.  I noticed that he had installed a 100 amp ANL fuse in series with the battery cable.  The fuse is located 6 inches from the battery and all battery current will go through that fuse including starter current.  I asked my friend if that 100 amp ANL will handle the starter current.  His response was, "It's a 35 amp battery."  I told him that a 100 amp ANL might not handle starting current.  He said that if it doesn't, he will replace it with a 150 amp.

    I think that the fuse will need to be bigger, like 200 amp or more.  Actually I do not think that there should be a fuse in series with the battery cable at all.  It is one more thing to fail and it adds resistance to the battery cranking circuit.  How can I convince my friend that fuse is not necessary or even desired?  If he will not change his mind, what size ANL fuse should he use?



 --------

 Joe Gores





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 http://forums.matronics.com/viewtopic.php?p=466858#466858

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user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Sat Mar 04, 2017 11:00 am Post subject: Re: BATTERY FUSE

I should have been more specific about the battery cable. He put the ANL in the positive cable, not the ground cable.

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Joe Gores

Kellym

Joined: 10 Jan 2006
Posts: 1706
Location: Sun Lakes AZ

Posted: Sat Mar 04, 2017 12:23 pm Post subject: BATTERY FUSE

The battery cable doesn't need protection. If it shorts, it will be a 

very short term welding cable. As I'm sure you are trying to persuade, 

the ANL should go in the alternator power output cable, and be sized 

appropriate to the alternator capacity. Battery size is mostly irrelevant.

The battery/starter cables only need to carry big current during 

cranking, and fusing that circuit makes zero sense. If they fail during 

cranking, it will be on the ground, and not a hazard to pilot or pax.



On 3/4/2017 12:00 PM, user9253 wrote:

 	  Quote: 	
		   



 I should have been more specific about the battery cable.  He put the ANL in the positive cable, not the ground cable.



 --------

 Joe Gores





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=466862#466862

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Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Sun Mar 05, 2017 8:34 am Post subject: Re: BATTERY FUSE

One thing that wasn't mentioned in the other responses...



I'm sure you're aware -- but your friend clearly is not -- that a "35-amp battery" is in no way limited to a maximum current output of 35 amps.  That number is an expression of battery capacity: in this case 35 ampere-hours.



A battery's ability to grunt large output currents depends on its internal resistance, which will vary with chemistry, physical construction, temperature, age, and so on.  A lead-acid starting battery is typically capable of supplying hundreds of amps.



Eric



 	  user9253 wrote: 	
		  A friend of mine is building a plane with an 8 cylinder automotive engine.  I noticed that he had installed a 100 amp ANL fuse in series with the battery cable.  The fuse is located 6 inches from the battery and all battery current will go through that fuse including starter current.  I asked my friend if that 100 amp ANL will handle the starter current.  His response was, "It's a 35 amp battery."  [SNIP]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 05, 2017 1:15 pm Post subject: BATTERY FUSE

At 10:21 AM 3/4/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 A friend of mine is building a plane with an 8 cylinder automotive engine.  I noticed that he had installed a 100 amp ANL fuse in series with the battery cable.  The fuse is located 6 inches from the battery and all battery current will go through that fuse including starter current.  I asked my friend if that 100 amp ANL will handle the starter current.  His response was, "It's a 35 amp battery."  I told him that a 100 amp ANL might not handle starting current.  He said that if it doesn't, he will replace it with a 150 amp.

   I think that the fuse will need to be bigger, like 200 amp or more.  Actually I do not think that there should be a fuse in series with the battery cable at all.  It is one more thing to fail and it adds resistance to the battery cranking circuit.  How can I convince my friend that fuse is not necessary or even desired?  If he will not change his mind, what size ANL fuse should he use? 	


    Fuses are cheap, after he pops the first one,

    he'll discover that upsizing the limiter is

    indicated.



    Over a century of experience and product

    evolution it was rationally deduced that

    fat wires in light aircraft do not benefit

    from the addition of over current protection.

    Consider that hard-fault protection for

    battery excited fat-wires can exceed 1000

    amps. Okay, what's a hard fault? Get out

    your hammers, chisels and pry-bars. What

    would you do to create a connection to any

    'grounded' feature of the aircraft such

    that great amounts of current can flow . . .

    for seconds if not tens of seconds?



    Experience and experiments tell us

    that inadvertent and tentative contact

    of fat wires against anything 'grounded'

    is orders of magnitude more likely to burn

    away the conductors . . . with no observable

    damage to the fat-wire.



    I share your concerns but perhaps for not

    the same reasons.    Clearly, this gentleman

    doesn't have a very good grasp of the simple-

    ideas behind the performance and selection of

    components. It seem likely that the conversation

    you had with him about a battery fuse could

    be repeated many times over concerning other

    aspects of the build.



    Perhaps the best thing we can do for him

    is get him a copy of the 'Connection and

    see how or if it changes his levels of

    curiosity/awareness. I'll donate one to

    the cause. Send me you mailing address.



 

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Sun Mar 05, 2017 3:10 pm Post subject: Re: BATTERY FUSE

Bob and others, thanks for your input.  My friend already has a copy of your book.  Thanks for the offer.  I will quote some of the comments to my friend (and leave out others that he might take offense to).

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Joe Gores

Bill Allen

Joined: 24 Aug 2009
Posts: 42
Location: UK

Posted: Sun Mar 05, 2017 11:01 pm Post subject: BATTERY FUSE

I think that this maybe an example of how what is appropriate standard practice in one industry is not appropriate in another.  International safety standards for autos require that, in the event of an impact sufficient to trigger the airbags, certain other items are also activated, amongst which is the automatic battery disconnect. Most vehicles also have separate feeds/fusible links for the starter and consumers, with just the battery feed to the starter becoming disconnected in an impact.

Other inappropriate (to aviation) items are fault detection which place the engine management in "limp mode" which will get a car home at low speed, but cause a forced landing in an aircraft.

There are many other reasons why auto engines have a much higher risk of failure than aircraft engines, but to successfully transfer an auto engine to an aviation environment requires a much deeper understanding of the environment and operation of both than would at first appear. I hope your friend has done his homework.

Bill Allen

LongEzDiesel G-LEZE

CozyIV G-BYLZ

VariEze N2CR



On Sun, 5 Mar 2017 at 21:27, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		  At 10:21 AM 3/4/2017, you wrote:  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> A friend of mine is building a plane with an 8 cylinder automotive engine.  I noticed that he had installed a 100 amp ANL fuse in series with the battery cable.  The fuse is located 6 inches from the battery and all battery current will go through that fuse including starter current.  I asked my friend if that 100 amp ANL will handle the starter current.  His response was, "It's a 35 amp battery."  I told him that a 100 amp ANL might not handle starting current.  He said that if it doesn't, he will replace it with a 150 amp.   I think that the fuse will need to be bigger, like 200 amp or more.  Actually I do not think that there should be a fuse in series with the battery cable at all.  It is one more thing to fail and it adds resistance to the battery cranking circuit.  How can I convince my friend that fuse is not necessary or even desired?  If he will not change his mind, what size ANL fuse should he use? 	


    Fuses are cheap, after he pops the first one,    he'll discover that upsizing the limiter is    indicated.    Over a century of experience and product    evolution it was rationally deduced that    fat wires in light aircraft do not benefit    from the addition of over current protection.    Consider that hard-fault protection for    battery excited fat-wires can exceed 1000    amps. Okay, what's a hard fault? Get out    your hammers, chisels and pry-bars. What    would you do to create a connection to any    'grounded' feature of the aircraft such    that great amounts of current can flow . . .    for seconds if not tens of seconds?    Experience and experiments tell us    that inadvertent and tentative contact    of fat wires against anything 'grounded'    is orders of magnitude more likely to burn    away the conductors . . . with no observable    damage to the fat-wire.    I share your concerns but perhaps for not    the same reasons.    Clearly, this gentleman    doesn't have a very good grasp of the simple-    ideas behind the performance and selection of    components. It seem likely that the conversation    you had with him about a battery fuse could    be repeated many times over concerning other    aspects of the build.    Perhaps the best thing we can do for him    is get him a copy of the 'Connection and    see how or if it changes his levels of    curiosity/awareness. I'll donate one to    the cause. Send me you mailing address. 

   Bob . . .   

	




-- 



Bill AllenLongEz160 N99BA FD51

CZ4 G-BYLZ EGBJ

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