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1. 08:29 PM - Re: ANL current limiters in Z13-8 (Robert L. Nuckolls, III)
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Subject: | Re: ANL current limiters in Z13-8 |
At 02:43 PM 9/9/2009, you wrote:
>Spent an hour or so trying to visualize where everything is going to
>mount on the firewall while studying Z-13/8 and came upon Note 10
>regarding current limiters. I understand that these are replacing
>the In-Line Fuses referred to in Chapter 10 of AEC but had these questions:
>
>1. With a 40A alternator, do I use a 40A ANL current limiter?
Yes, or even a 30 - 35 amp device. These are "current limiters",
not fuses. They are EXCEEDINGLY robust and VERY slow. Thus they
are used not for the protection of feeders to individual accessories
like fuses/breakers. They are intended to separate a hard fadeult in
a robust feeder (like the alternator b-lead) where shorted diodes
in the alternator would offer battery fed fault currents on
the order of many hundreds of amps.
Cars don't use them and to the best of my knowledge, the
risks have been low(?). But one wonders sometimes as to
the root cause of some car-fires that start under the hood.
In any case, if you co the mini-ANL route, they're small,
light and no big deal to install.
http://www.knukonceptz.com/productMaster.cfm?category=Mini-ANL%20Fuse
You can make your own mounting block with a chunk of phenolic,
delrin, etc and some 10-32 hardware.
As you can see here . . .
http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf
the "current limiter" is quite robust.
>2. Any reason the 4 AWG wire (and ANL current limiter) from the
>alternator B lead can't go to the "downstream" side of the battery
>contactor instead of the "upstream" side of the starter
>contactor? They both seem to be electrically equivalent
>particularly since the wire between them is so short.
The current limiter is a hedge against failed
alternator diodes. You can put the devise at either
end of the b-lead feeder . . .
I draw it at the starter contactor end becuase it's
more difficult to mount it on the back of the alternator.
Of course you can put it in the middle . . .
>3. The following is found under Note 10. in AEC: "Alternator
>noises in the system are reduced by not mounting the alternator
>breaker on the panel in the traditional fashion...consider
>installing the breaker as close as possible to the starter
>contactor" -- Is this referring to the ANL current limiter
>described above or the circuit breaker for the alternator field? If
>the latter, I'm confused and hope someone can provide some more explanation.
This is referring to the legacy practice of brining
alternator b-leads into the cockpit to tie to a 60A
or so breaker on the panel. There's no practical, or
safety related reason for doing this . . . we quit doing
it at Beech years ago.
There are reasons to keep it forward of the firewall
to reduce the level of magnetic interference to compass
and/or coupled to adjacent instrumentation or avionics
wires.
Bob . . .
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( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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