Today's Message Index:
----------------------
1. 03:51 AM - Re: ANL current limiter location on rear battery installations (tomcostanza)
2. 07:51 AM - Re: Re: ANL current limiter location on rear battery installations (Tim Andres)
3. 02:09 PM - Re: Re: ANL current limiter location on rear battery installations (Robert L. Nuckolls, III)
4. 02:11 PM - Re: Re: LV warn light snafu? (Robert L. Nuckolls, III)
5. 04:33 PM - ANL Alternator Fuse Substitution (sam ray)
6. 05:54 PM - Re: ANL Alternator Fuse Substitution (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: ANL current limiter location on rear battery installations |
Thanks for that Bob. As often is the case, at least with me, the answer to one
question leads to more questions.
> Because fat wires in dc electrical systems are
> exceedingly hard to burn, hence there is no
> value added in attempting to protect them.
When you say "protect them", I'm not sure what you mean. Not knowing any better,
I might want to protect things near the high current path, or the battery itself,
from melting. Your thoughts?
> Hence design goals and installation that suggest extra
> attention to the insulation and support of fat wires combined
> with a crew-controlled shut-off right at the battery
> i.e. battery contactor.
Got it. But again, another question, this time about the wire supplying the main
battery buss, for example in Z-11. This is neither fused, nor does it go through
the contactor. So it isn't shut-off-able. What's the worst case if this
shorts to ground. Will the wire just burn through as if it were a fuseable
link? What if someone used a heavier wire, anticipating a more robust e-bus?
Please pardon my ignorance, and thanks so much for your patience.
--------
Clear Skies,
Tom Costanza
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=304740#304740
Message 2
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| Subject: | Re: ANL current limiter location on rear battery |
installations
Bob; this question is similar to what I was asking a few days ago but I'm n
ot =0Asure we were on the same page, probably my fault. For example the Z8
I'm using =0Adoes not show any protection device between the main bus and t
he contactor,-in =0Amy case that is a 7'~8' run from the rear mounted bat
tery to the Instrument =0Apanel where the main bus-is located.- The E b
us is protected-from both ends with =0Afuses in your drawing and I unders
tand why but do not understand why there is no =0Aprotection on the-feede
r to the main bus/fuse block=0AThanks, Tim Andres=0A=0A=0A=0A=0A___________
_____________________=0AFrom: tomcostanza <Tom@CostanzaAndAssociates.com>
=0ATo: aeroelectric-list@matronics.com=0ASent: Wed, July 14, 2010 3:50:05 A
M=0ASubject: AeroElectric-List: Re: ANL current limiter location on rear ba
stanza" =0A<Tom@CostanzaAndAssociates.com>=0A=0AThanks for that Bob.- As
often is the case, at least with me, the answer to one =0Aquestion leads to
more questions.=0A=0A=0A> Because fat wires in dc electrical systems are
=0A> exceedingly hard to burn, hence there is no =0A> value added in attemp
ting to protect them.=0A=0A=0AWhen you say "protect them", I'm not sure wha
t you mean.- Not knowing any =0Abetter, I might want to protect things ne
ar the high current path, or the =0Abattery itself, from melting.- Your t
houghts?=0A=0A=0A> Hence design goals and installation that suggest extra
=0A> attention to the insulation and support of fat wires combined =0A> wit
h a crew-controlled shut-off right at the battery =0A> i.e. battery contact
or. =0A=0A=0AGot it.- But again, another question, this time about the wi
re supplying the =0Amain battery buss, for example in Z-11.- This is neit
her fused, nor does it go =0Athrough the contactor.- So it isn't shut-off
-able.- What's the worst case if =0Athis shorts to ground.- Will the wi
re just burn through as if it were a fuseable =0Alink?- What if someone u
sed a heavier wire, anticipating a more robust e-bus?=0A=0APlease pardon my
ignorance, and thanks so much for your patience.=0A=0A--------=0AClear Ski
es,=0ATom Costanza=0A=0A=0A=0A=0ARead this topic online here:=0A=0Ahttp://f
orums.matronics.com/viewtopic.php?p=304740#304740=0A=0A=0A=0A=0A=0A=0A=0A
================
Message 3
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| Subject: | Re: ANL current limiter location on rear battery |
installations
At 05:50 AM 7/14/2010, you wrote:
<Tom@CostanzaAndAssociates.com>
Thanks for that Bob. As often is the case, at least with me, the
answer to one question leads to more questions.
BN: Because fat wires in dc electrical systems are
exceedingly hard to burn, hence there is no
value added in attempting to protect them.
When you say "protect them", I'm not sure what you mean. Not knowing
any better, I might want to protect things near the high current
path, or the battery itself, from melting. Your thoughts?
The idea of adding "protection" to any wire goes
toward risk reduction. Risk of expense for making
easily avoided repairs, risk of experiencing a
hazardous condition. When a wire is strung through
the innards of a type certificated airplane, there's
a standard waltz tune played called "Failure Mode
Effects Analysis" or FMEA for short. This exercise
considers all the potentials for increased risk and
the return on investment for adding "protection" or
risk reduction.
The fat wires in the engine cranking path and major
bus feeders were deduced to first be capable of
very high reliability. Further, when installed with
good materials and practice, they were very low risks
to the airframe even if insulation integrity was lost.
Finally, history has demonstrated that when insulation
integrity of fat wires is lost, it's likely that the
fault condition will be relatively "soft" . . . i.e.
it will arc a lot over time releasing a lot of total
energy . . . but at current levels too low to open
the traditional protective devices. Hence the part
23 rule:
------------
Sec. 23.1357 Circuit protective devices.
(a) Protective devices, such as fuses or circuit breakers, must be
installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.
------------
It was just such a fault that is believed to have
brought down Swissair Flt 111 by setting some combustible
insulation on fire after some not-designed-for-prime-time-
insulation cracked and precipitated a "soft" arcing event.
Rather than rewire thousands of airplanes with parsecs
of better wire, the Dispensers of Great Wisdom decided
that a new form of breaker was called for. Hence all
our friends at Klixon, Eaton, et. als. rushed off to
the lab to build little microprocessor based digital
signal detectors into the breakers and train them to
"listen" for soft faults.
Now, if you'd like to protect your ship's battery wire
for such events, I'm sure that somebody makes the breaker
for the job . . . but it will be big, heavy, expensive,
and probably run the lifetime of your airplane never
being called upon to trip.
> Hence design goals and installation that suggest extra
> attention to the insulation and support of fat wires combined
> with a crew-controlled shut-off right at the battery
> i.e. battery contactor.
Got it. But again, another question, this time about the wire
supplying the main battery buss, for example in Z-11. This is
neither fused, nor does it go through the contactor. So it isn't
shut-off-able. What's the worst case if this shorts to ground. Will
the wire just burn through as if it were a fuseable link? What if
someone used a heavier wire, anticipating a more robust e-bus?
Check the definition of an E-Bus. Just how "robust"
do you anticipate? See
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z32K.pdf
for recommendations concerning e-bus feeders FUSED
at greater than say 10A. In other words, if your e-bus
alternate feed path gets too big, then a crew-controlled,
mini-contactor is called for. The battery bus is another
critter. Since battery busses are located AT the battery,
their feeders are short. See that (*) on the battery
bus feeder wires? So yes, if that wire sees a fault
hard enough to smoke it, the rule 23.1357(a)(2) suggests
no hazard is presented if the wire is short because
smoke-risk is low and the event will be short lived
due to small gage of wire. At the same time, we want
that path to be very robust (low parts count and well
installed) so that reliability is high.
Please pardon my ignorance, and thanks so much for your patience.
TA: Bob; this question is similar to what I was asking a few days ago
but I'm not sure we were on the same page, probably my fault. For
example the Z8 I'm using does not show any protection device between
the main bus and the contactor, in my case that is a 7'~8' run from
the rear mounted battery to the Instrument panel where the main bus
is located. The E bus is protected from both ends with fuses in your
drawing and I understand why but do not understand why there is no
protection on the feeder to the main bus/fuse block
BN: Because that should be a "fat" wire well installed.
This same pathway falls under the FAR23 category cited
above. Legacy design goals have supported the notion
for many decades and hundreds of thousands of airplanes.
You won't find this pathway fuse or breaker protected
in any type certificated SE aircraft on a par with your
grandpa's C-170. The e-bus alternate feed wire is
longer, smaller gage and capable of being fault-powered
from either end. Further, we don't want a fault on the
alternate feed path wire to open both the alternate and
normal feed paths. Hence NO protection in the normal path
and SHORT wires there too.
Bob . . .
Message 4
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| Subject: | Re: LV warn light snafu? |
>I should have connected the alternator output leads again before
>declaring a success. I'll do that when I get out in the shop again.
Sounds like you've done a righteous job of
chasing the bugs out . . .
>And finally, assuming I've got the LV warn light problem fixed, is
>there anything I can do to test the electrical system?
Sounds like the next step is an engine-run with
the alternator delivering power.
Bob . . .
Message 5
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| Subject: | ANL Alternator Fuse Substitution |
Bob
Is it advisable to substitute a MaxiFuse for the ANL
Alternator Fuse? The MaxiFuse can be wired in-line with the
alternator wire such that it's clamped along with the
alternator 8AWG wire as it routes along the engine mount-
versus mounting the ANL fuse holder on the firewall which is
not as desirable. Is it possible to size the MaxiFuse
to provide the same level of nuisance tripping immunity, and
8AWG alternator wire protection, as the ANL fuse
would? I'm using the 40A B&C alternator.
Sam Ray
Message 6
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| Subject: | Re: ANL Alternator Fuse Substitution |
At 06:29 PM 7/14/2010, you wrote:
Bob
Is it advisable to substitute a MaxiFuse for the ANL
Alternator Fuse? The MaxiFuse can be wired in-line with the
alternator wire such that it's clamped along with the
alternator 8AWG wire as it routes along the engine mount-
versus mounting the ANL fuse holder on the firewall which is
not as desirable. Is it possible to size the MaxiFuse
to provide the same level of nuisance tripping immunity, and
8AWG alternator wire protection, as the ANL fuse
would? I'm using the 40A B&C alternator.
Absolutely. Of course, the ANL current limiters
are exceedingly robust. One NEVER nuisance trips
a current limiter. However, the lowly fuse like
the MAXI series can be sized to stay in place
on a 40A alternator. You'd want to de-rate about
25% based on the absolute max that a cold alternator
can produce. Let's call it 50A. So the MAX70
would do be optimal. But if that's hard
to find, a 60A or and 80A would be okay too
Bob . . .
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