Today's Message Index:
----------------------
1. 07:13 AM - Mounting BATT/START Relays (rvg8tor)
2. 07:49 AM - Re: Diode numbers (Robert L. Nuckolls, III)
3. 07:56 AM - Re: Re: Welding cable ()
4. 07:56 AM - Re: Re: Welding cable (Robert L. Nuckolls, III)
5. 08:23 AM - Why have a switch on ALT Field? (rvg8tor)
6. 10:55 AM - Re: Mounting BATT/START Relays (Robert L. Nuckolls, III)
7. 12:16 PM - Re: Why have a switch on ALT Field? (Robert L. Nuckolls, III)
8. 06:49 PM - Re: Why have a switch on ALT Field? (rvg8tor)
Message 1
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| Subject: | Mounting BATT/START Relays |
My battery will be just aft of the firewall so the battery relay will be mounted
on the aft side of the firewall, the start relay will be just opposite on the
forward side of the firewall. I see some who install plate nuts to mount these
relays individually, 4 nuts + 4 bolts+4 holes in the firewall. The holes
on the two relays work out so that one could just use 2 bolts and two normal nuts
(not anchor nuts) and mount the two relays through common holes in the firewall.
The only drawback I can see is that if one or the other needs to be replaced
then both you can't remove one without disturbing the other, this does not
seem like a big deal to me as they are fairly long lasting devices. Can anyone
see why my idea is a bad one? I though of heat transfer from the hot side
of the firewall, but bolts into nut plates would do that to some degree, and
all of the relays could be mounted forward of the firewall like many factory
airplanes have them.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=264914#264914
Message 2
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| Subject: | Re: Diode numbers |
At 05:29 PM 9/24/2009, you wrote:
>
>I have an electronic supply store in my town so I went out to get
>the diodes that go on the battery and start relays. I asked for the
>1N5400, after looking up in a book the guy gave me an
>NTE-5800. Near as I can tell from looking on-line they are the same
>type of diode. Is there anything quality wiser or otherwise I
>should be aware of when buying these things? They only cost .38
>each, so after ring terminals and some heat shrink I might have a
>buck into them, not bad.
Of thousands of diode part numbers on the shelves,
the vast majority of the industry's needs can be
met by perhaps a few hundred . . . maybe less.
The spike catcher diodes don't even wake up
from a sound sleep when hit by the energy from
your contactor's magnetic field collapse. I
LIKE the 5400 series devices because they're
MECHANICALLY friendly for installation. Much
smaller diodes would be electrically adequate
but these dudes (and the NTE-5800 cousins)
are most adequate to the task.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
Message 3
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| Subject: | Re: Welding cable |
Mike,
Maybe a small thing, but I would crimp "before" I'd solder. Soldering
just seals the deal.
Glenn
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
rvg8tor
Sent: Thursday, September 24, 2009 8:42 PM
Subject: AeroElectric-List: Re: Welding cable
I found my local welding shop and bought some 4 AWG. Man this stuff is
flexible, I can't believe I was trying to wrestle with the mill spec
stuff for those short runs. It is not the double insulated stuff you
showed in the picture but it seem tough. it is labeled as "Heavy Duty
Welding cable 600V -50 degrees C to 105 degrees C. I will use a crimp
on ring terminal, I have the tool from ACS for this but should I solder
the end before crimping, there are a lot of fine wires in this cable. I
will have to check the AEC Bible, I seem to remember reading something
on this subject.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=264836#264836
Message 4
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| Subject: | Re: Welding cable |
At 07:41 PM 9/24/2009, you wrote:
>
>I found my local welding shop and bought some 4 AWG. Man this stuff
>is flexible, I can't believe I was trying to wrestle with the mill
>spec stuff for those short runs.
NICE to work with . . .
> It is not the double insulated stuff you showed in the picture but
> it seem tough. it is labeled as "Heavy Duty Welding cable 600V -50
> degrees C to 105 degrees C.
Yup, it will be just fine . . .
> I will use a crimp on ring terminal, I have the tool from ACS for
> this but should I solder the end before crimping, there are a lot
> of fine wires in this cable. I will have to check the AEC Bible, I
> seem to remember reading something on this subject.
If your crimp tool produces the proper crush, then
crimping is as good as solder. The two processes
are essentially interchangeable. If you solder at
all, then crimping adds no value.
http://www.aeroelectric.com/articles/big_term.pdf
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
Message 5
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| Subject: | Why have a switch on ALT Field? |
I am brain storming here while I work on my electrical system design (Z12). I wonder
why there is a switch for the Alt Field. From my reading on the forums internally
regulated alternators get their life shortened if one turns them on
under load, (they should be on before start until after start to get the most
life out of the alternator). The B&C alternator is externally regulated and can
handle the switching under load. But operationally there is no reason to switch
the alternator on and off, if you have an abnormal situation and need to turn
the alternator off you can do that just as easily with a circuit breaker as
you can with a switch. So why not leave the switch out of the loop and wire
the alternator field directly to circuit breaker so it is always on, in case of
alternator problem, pull circuit breaker. On less switch a few ounces and dollars
saved. So, am I missing something obvious here?
I have posted this on VAF, but thought since this forum is more on point I should
post it here.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=264938#264938
Message 6
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| Subject: | Re: Mounting BATT/START Relays |
>The holes on the two relays work out so that one could just use 2
>bolts and two normal nuts (not anchor nuts) and mount the two relays
>through common holes in the firewall.
> The only drawback I can see is that if one or the other needs to
> be replaced then both you can't remove one without disturbing the
> other, this does not seem like a big deal to me as they are fairly
> long lasting devices. Can anyone see why my idea is a bad one?
The TC aircraft guys do things like this all the time . . .
> I though of heat transfer from the hot side of the firewall, but
> bolts into nut plates would do that to some degree, and all of the
> relays could be mounted forward of the firewall like many factory
> airplanes have them.
??? not sure of the rationale here. The
battery relay should be as close to the battery
as practical and certainly positioned so that
the battery(+) lead doesn't penetrate the firewall
before reaching the relay's fat terminal.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
Message 7
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| Subject: | Re: Why have a switch on ALT Field? |
At 10:22 AM 9/25/2009, you wrote:
I am brain storming here while I work on my electrical system design
(Z12). I wonder why there is a switch for the Alt Field. From my
reading on the forums internally regulated alternators get their life
shortened if one turns them on under load, (they should be on before
start until after start to get the most life out of the alternator).
Bob Nuckolls replies:
An urban (or perhaps hangar) legend. I've been
working with alternators and generators for 40+
years. There is no basis in physics to support
the legend. In fact, it has always been a design
goal of every TC aircraft electrical system to
offer any time, any conditions, positive ON/OFF
control of alternators and/or generators without
concern for degradation of performance or damage
to equipment.
The B&C alternator is externally regulated and can handle the
switching under load.
As can ALL other skillfully designed alternators. One
of the foundations upon which the hangar-myth was
built had to do with alternators ostensibly
wired per Z-24 . . .
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z24-Interim.pdf
. . . and apparently switched off (B-lead
broken) while the alternator was under load.
This started a hysterical kerfuffle about "turning
alternators on or off under load". Numerous
authors have posited the same hypothesis before.
However, the special case presented by a b-lead disconnect
contactor energized efforts by the in-experienced
and un-informed to stoke the fires anew and stir
the pot of misunderstanding.
I enjoyed a two-day tour of a LARGE scale alternator
remanufacturing operation about a year ago. Details
of this visit can be discovered at:
http://aeroelectric.com/R12A/03_Alternator_12A1.pdf
During that visit I witnessed a demonstration
of a full load, max rpm, hot-alternator b-lead
disconnect that liberated kilojoules of energy
in the ensuing arc . . . 5 times in a row. The
flash of fire was so great that it was impossible
to photograph or record on video. Their chief engineer
asserted that all of their reman products (2800+
line items) were tested to the same design goals.
These alternators were demonstrably immune from
self-induced load dump damage.
But operationally there is no reason to switch the alternator on and
off, if you have an abnormal situation and need to turn the
alternator off you can do that just as easily with a circuit breaker
as you can with a switch.
Suppose you have two alternators like Z-12 or
Z-13? Is it not useful to test the two alternators
independently of each other irrespective of all
other conditions?
Suppose you have smoke in the cockpit? How
about an unruly regulator? Our brothers in
the TC aircraft world have adopted any-time,
any-conditions, ON/OFF control as a design
goal.
So why not leave the switch out of the loop and wire the alternator
field directly to circuit breaker so it is always on, in case of
alternator problem, pull circuit breaker. On less switch a few ounces
and dollars saved. So, am I missing something obvious here?
Perhaps not obvious . . . but certainly not
'secret'. Any student of contact physics for
things like relays, switches and CIRCUIT BREAKERS
will understand that depending on a breaker
like . . .
http://aeroelectric.com/Pictures/Breakers/Klixon_1.jpg
. . . to open the 100 volts plus, b-lead of a runaway
alternator is quite likely to experience a hundreds-of-
kilojoules arc in the gap of relatively slow moving
contacts that are guaranteed to produce a lot of smoke
in the cockpit. BREAKERS are not intended to serve
as commanding manual control devices. Breakers for
aircraft are designed to break faults of several
thousand amps at 32 VOLTS or less. See paragraph
4.7.14 of . . .
http://www.aeroelectric.com/Reference_Docs/Mil-Specs/5809G.pdf
Since the first generators (and then alternators) went
aboard an airplane, the pilot has been offered positive
control of those electrical energy sources by breaking the
FIELD lead. At no time did anyone consider the main power
output feeder protection to be a control device. In fact,
b-lead protection on TC aircraft isn't even on the panel . . .
http://aeroelectric.com/Pictures/Wiring_Technique/A36_Firewall_A.jpg
I have posted this on VAF, but thought since this forum is more on
point I should post it here.
Please post this reply to VAF. Thanks!
Bob . . .
Message 8
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| Subject: | Re: Why have a switch on ALT Field? |
Bob,
Thank you for the explanation, this really helps me understand the design better.
I did post your reply on the VAF for all to read. I think this will add to
everyones education.
So if I understand what your post, the gist is that there is potential for excess
voltage in some situations as to make a CB fail if used to cut the field to
the alternator. I have heard others say CBs are not meant to be switches, but
at my airline we routinely pull CB on certain items while the airplane sits
between flights for several hours. Things like the radar, TCAS, VSI indicator.
This use of the CB as a switch happens several times a day for each aircraft.
It this an accepted practice since these are low voltage items.
You have given me the data i was looking for, I now understand why the switch is
needed, it is due to potential high loads.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=265058#265058
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