Today's Message Index:
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1. 08:37 AM - Re: BATTERY FUSE (Eric Page)
2. 12:54 PM - Eye protection required (Art Zemon)
3. 01:15 PM - Re: BATTERY FUSE (Robert L. Nuckolls, III)
4. 03:16 PM - Re: BATTERY FUSE (user9253)
5. 11:01 PM - Re: BATTERY FUSE (Bill Allen)
Message 1
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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]
>
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=466889#466889
Message 2
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Subject: | Eye protection required |
This slip of paper came with my transponder antenna. Today I have learned
that I need eye protection to read AC43.13-2A =F0=9F=98=8E
-- Art Z.
Sent from my phone. Please excuse brevity and bizarre typos.
Message 3
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Subject: | Re: BATTERY FUSE |
At 10:21 AM 3/4/2017, you 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." 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 . . .
Message 4
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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).
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=466902#466902
Message 5
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Subject: | Re: 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@aeroelectric.com> wrote:
> At 10:21 AM 3/4/2017, you 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." 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 Allen
LongEz160 N99BA FD51
CZ4 G-BYLZ EGBJ
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