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airlincoln(at)sbcglobal.n
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 Posted: Wed Sep 09, 2009 11:45 am Post subject: ANL current limiters in Z13-8 |
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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?
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.
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.
Thanks.
Lincoln Keill
RV-7A fuselage
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longg(at)pjm.com
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| Posted: Wed Sep 09, 2009 12:22 pm Post subject: ANL current limiters in Z13-8 |
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Lincoln,
You may have read Bob’s dribs and drabs on how ANL’s (search list for lots on this item) are of the slow-blow variety and will accommodate n percentage of higher current just prior to blasting off the firewall. You should need no more than 80% of your total draw. E.G. – a 40A ANL may not blow until it loads up 50+ amps
Cost is not the issue, they are mostly the same. If you can get one with a slightly lower rating (35) and your total draw is 40, you’d be good to fly and have a margin of safety.
I think most rigs today with modern equipment have far less draw than most believe. Putting a meter on is the only sure fire way to tell what your day to day requirements are. I’ve got all kinds of EFIS IFR junk, but none of them draw much more than 3 amps when they are really sweating.
I’ve also got a 80 amp (bargain basement item) alternator that helps keep the nose down, but unless I install central air-conditioning, I’ll never use the capacity. I’ve got a 30 A ANL in front of the load.
Glenn
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Wednesday, September 09, 2009 3:44 PM
To: aeroelectric-list(at)matronics.com
Subject: ANL current limiters in Z13-8
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?
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.
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.
Thanks.
Lincoln Keill
RV-7A fuselage
Do Not Archive
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longg(at)pjm.com
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| Posted: Wed Sep 09, 2009 12:22 pm Post subject: ANL current limiters in Z13-8 |
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Lincoln,
Sorry, yes #3 applies to the ANL. Having that big circuit breaker on the panel is great if you need an alternate heat source in the cab, but not very good design when we have these great ANL fuses. I’ve no experience on #2 as I just went by Bob’s drawing.
Glenn
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Lincoln Keill
Sent: Wednesday, September 09, 2009 3:44 PM
To: aeroelectric-list(at)matronics.com
Subject: ANL current limiters in Z13-8
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?
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.
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.
Thanks.
Lincoln Keill
RV-7A fuselage
Do Not Archive
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0123456789
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mprather(at)spro.net
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| Posted: Wed Sep 09, 2009 1:08 pm Post subject: ANL current limiters in Z13-8 |
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I've also got a 80 amp (bargain basement item) alternator that helps
keep the nose down, but unless I install central air-conditioning, I'll
never use the capacity. I've got a 30 A ANL in front of the load.
Glenn
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Glenn,
Does your battery charging current go through this ANL? If so, on a cold
morning after a hard start, I believe your alternator might produce its
rated output (restoring the battery) for some amount of time (many
seconds), unrelated to bus loads. Seems like the ANL might be opened as a
result.
Regards,
Matt-
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Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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| Posted: Wed Sep 09, 2009 5:56 pm Post subject: ANL current limiters in Z13-8 |
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Matt;
Don't forget that ANL fuses will carry considerably more than twice their
rated current almost indefinitely, certainly for many minutes. It's unlikely
that starting, even on those difficult cold mornings will drain the battery
enough that the alternator would work hard and long enough to "blow" the
ANL. The time constant graph for a 35 amp ANL shown in the attached link is
vertical at 90 amps meaning that it will hold indefinitely at that current
flow or any lesser value. It's unlikely that an 80 amp alternator would be
putting out over 100 amps for an extended period, and that's what it would
take to open the ANL. Under ideal conditions the 80 Amp alternator might
make it to 90 Amps, but not a lot more.
http://www.aeroelectric.com/articles/anl/anlvsjjs.html
Bob McC
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Bob McC
Falco #908
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nuckolls.bob(at)aeroelect
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| Posted: Thu Sep 10, 2009 7:29 pm Post subject: ANL current limiters in Z13-8 |
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At 02:43 PM 9/9/2009, you wrote:
| Quote: | 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.
| Quote: | 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 . . .
| Quote: | 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 . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
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