Today's Message Index:
----------------------
1. 12:20 AM - Re: Why have a switch on ALT Field? (rvg8tor)
2. 03:16 AM - Re: Re: Why have a switch on ALT Field? (Jay Hyde)
3. 06:47 AM - Re: Why have a switch on ALT Field? (rckol)
4. 06:50 AM - Why have a switch on ALT Field? ()
5. 07:41 AM - Re: Re: Welding cable (Robert L. Nuckolls, III)
6. 07:47 AM - While on the topic of alternators (Robert L. Nuckolls, III)
7. 08:07 AM - Re: Why have a switch on ALT Field? (Joe)
8. 08:57 AM - Re: Re: Why have a switch on ALT Field? (Kelly McMullen)
9. 11:27 AM - Re: Re: Why have a switch on ALT Field? (Tony Babb)
10. 02:18 PM - Re: Why have a switch on ALT Field? (Robert L. Nuckolls, III)
11. 02:26 PM - Re: Re: Why have a switch on ALT Field? (Robert L. Nuckolls, III)
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Subject: | Re: Why have a switch on ALT Field? |
Bob,
I know you are trying to help but, this last post does not seem to help me, it
actually confuses me. I respect your experience but I am not trying to design
an electrical system from scratch, much like I did not design my RV-8A from
scratch. I picked a plane from a good designer (Van's). While building I study
the plans and try to understand how the parts relate to be a better builder,
if I have a question I call builder assistance and I ask questions on the forum.
When it came to the electrical system, I went with a design from an expert in the
field, in studying the design I asked a simple question,
'why is the alternator field switch needed". There have been a lot of words written,
much of which my little brain doesn'tunderstand how it relates to the very
simple question. The possible answers I was expecting were:
1. It has always been done that way
2. It doesn't matter the non-switch method will work but has these limitations
(fill in the blanks)
3. You need the switch because if you don't have one it will cause XYZ.
Some of what you wrote I get but I really just need the simple short answer, not
a run down on design philosophy. Since you designed the systems I thought of
all people you could provide the best explanation. I thank you for attempting
to answer my questions, if nothing else you have convinced me not to deviate
from the Z diagram. I can't say that I understand fully why the alternator
field switch is a requirement other than to provide a convenient way to turn off
the field. I look forward to the simple answer if there is one.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=265184#265184
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Subject: | Re: Why have a switch on ALT Field? |
Hi there Mike,
Perhaps I can shed a bit of light on your questions. The switch is used as
it switches a smaller current than would be required on the B-lead; thus you
can use a switch and not a contactor. By switching off the field you have
effectively switched off the alternator in its entirety, not just its
output.
Now its just a spinning mechanical device. If you switch the output (B
lead) then you have a live spinning device and if the fault is inside the
alternator then you're still feeding it...
Utilising the field to switch the alternator also allows you to fit in
overvoltage protection that will quickly detect and clear any overvoltage
fault that would fry all your avionics leaving you with a damaged alternator
AND no instruments (electrically powered ones in any case); whereas, if the
overvoltage fault is detected and cleared you can still run the instruments
on the battery.
If you have an internally regulated alternator then you need to switch the
output by using a contactor close to the alternator, because you cannot
access the field winding wire. Protecting the alternator by using a panel
mounted CB means that you lead a fat wire into the cockpit to the breaker in
your panel, which in turn means that there is a long bit of fat wire that is
unprotected- that long bit from the alternator to the CB. Personally I
don't like that.
If you use a contactor that is close to the source (alternator or battery)
then the only unprotected bit of fat wire is that bit between the source and
the contactor. A short bit of fat wire is unlikely to fault, or has a
higher reliability because it is short and mechanically robust. The closer
a contactor is to the voltage source the better your chances of removing the
power source from a fault.
Jay
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of rvg8tor
Sent: 27 September 2009 09:15 AM
Subject: AeroElectric-List: Re: Why have a switch on ALT Field?
Bob,
I know you are trying to help but, this last post does not seem to help me,
it actually confuses me. I respect your experience but I am not trying to
design an electrical system from scratch, much like I did not design my
RV-8A from scratch. I picked a plane from a good designer (Van's). While
building I study the plans and try to understand how the parts relate to be
a better builder, if I have a question I call builder assistance and I ask
questions on the forum.
When it came to the electrical system, I went with a design from an expert
in the field, in studying the design I asked a simple question,
'why is the alternator field switch needed". There have been a lot of words
written, much of which my little brain doesn'tunderstand how it relates to
the very simple question. The possible answers I was expecting were:
1. It has always been done that way
2. It doesn't matter the non-switch method will work but has these
limitations (fill in the blanks)
3. You need the switch because if you don't have one it will cause XYZ.
Some of what you wrote I get but I really just need the simple short answer,
not a run down on design philosophy. Since you designed the systems I
thought of all people you could provide the best explanation. I thank you
for attempting to answer my questions, if nothing else you have convinced me
not to deviate from the Z diagram. I can't say that I understand fully why
the alternator field switch is a requirement other than to provide a
convenient way to turn off the field. I look forward to the simple answer
if there is one.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=265184#265184
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Subject: | Re: Why have a switch on ALT Field? |
Mike,
Here is a response without embellishment.
You need the alternator field switch because there is no alternator field breaker
in Z-12. A fuse is used instead.
You could substitute a breaker for the fuse and use it instead of a switch, but
I wouldn't because:
1. You will be switching the field on and off at least once on every flight and
a normal breaker is not designed to be a robust switch.
2. You could use a "switch-breaker", but I have heard so many stories about these
having short life spans (at least the reasonably priced ones) that I would
not put one in my aircraft.
3. I don't think you will save any money or weight using a breaker instead of
the more reliable switch and fuse.
Regards
--------
rck
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=265200#265200
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Subject: | Why have a switch on ALT Field? |
9/27/209
Hello Ian, Thanks for reading my post and responding. Please let me make an
attempt at reducing your confusion. You wrote:
1) "As I understand it, the switch is on the alternator field low-current
12V line (called IGN on my alternator) ........"
Can you both turn ON (activate) and turn OFF (deactivate) your alternator's
electrical output with this alternator field switch?** This is generally
considered a desireable design goal.
There are some internally regulated alternators that, once activated, draw
their field current from inside the alternator and it is not possible to
deactivate those alternator's electrical output by turning OFF an external
field switch. While this subject has been hotly debated several times on the
aeroelectric list it is generally considered that the feature of not being
able to shut down the alternator's electrical output with an external field
switch is an undesirable design goal.
2) "..........the circuit breaker protects the output side (B lead)."
The primary purpose of a CB or fuse in the B lead is to protect the wiring
in the B lead. This wiring normally goes from the positive terminal of the
battery to a main battery contactor and then onto the B output terminal of
the alternator. If this wiring should encounter a short to ground the
BATTERY could dump a huge amount of amperage into the wiring and cause a
fire. Therefore the primary purpose of the CB or fuse in the B lead wiring
is to protect the wiring from BATTERY electrical output.
But since there are alternators that could "run away" and not be shut down
by a switch in the circuit providing electricity to the alternator's field
some people who have those kinds of alternators look upon the CB in the B
lead as a means of cutting off the excess electrical flow from the
alternator.
Depending upon the manual pulling of a circuit breaker in the B lead as the
only means of terminating an over voltage situation or a "run away"
alternator is generally not considered a desirable design goal.
Does this help?
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
**PS: I'd be interested in knowing how your alternator field switch does
work and if you have an externally or internally regulated alternator?
======================================================
Time: 10:45:24 AM PST US
Subject: Re: AeroElectric-List: Why have a switch on ALT Field?
From: Ian <ixb@videotron.ca>
OK, now here's one more vote for "confused". I thought the circuit
breaker was supposed to be rated at the output amperage of the
alternator because it's that current that one wants to limit. My 40A
circuit breaker would do nothing for me on the alternator field circuit.
As I understand it, the switch is on the alternator field low-current
12V line (called IGN on my alternator) and the circuit breaker protects
the output side (B lead). Mine is wired this way because it made
sense.
Ian Brown,
RV-9A, Bromont, QC
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At 06:22 PM 9/26/2009, you wrote:
>Well I guess you see why I asked, I spent some time googling and
>didn't find much whioch actually called out the epdm
>insulation. Guess I should have mentioned that. I did find
>this place and I sent an email to ask what brand it is they carry,
>hopefully they will respond Monday and I'll report back. Its
>finding that EPDM insulation that seems tricky, I had some stuff
>locally but it had a paper inner liner and I didn't find the outer
>stuff to be very tough, it seemed easy to nick and penetrate.
I looked at some wire in the junk box that
I think came from an installation kit for
an automotive super-sound system. The insulation
was decidedly plastic looking (shiny) and
also had a paper liner.
>
>
><http://www.wesbellwireandcable.com/Welding.html>http://www.wesbellwireandcable.com/Welding.html
Hey, good find on the web-source! Looks like
their prices are really good too. As you can
see from their offerings, there are MANY different
kinds of insulation . . . EPDM is not the magic
material, just one of many that would be
suitable. I didn't intend that one zero in
on EDPM in that manner. The fact that a reel
of wire (or a catalog page) cites EDPM says
that you KNOW what's being offered. That reel
of shiny stuff with unknown and/or questionable
insulation material MIGHT be okay. Without
identification or other qualification data
like materials or temperature ratings, it's
good to move on and consider other sources.
Looks like the WesBell folks are an excellent
source of wire suitable for use as fat wires
in your airplane.
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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Subject: | While on the topic of alternators |
I've had a number of private e-mails on the alternator
field switch thing. I want to thank those who have
joined the discussion with lucid and accurate offerings
of their own.
I recalled an article that was sent to me about spring
time of last year where the author attempted to explain
the simple-ideas upon which the battery/alternator power
system works in our airplanes. Seems that many folks on the
'net were citing this article as a valuable reference.
http://www.aeroelectric.com/articles/Know_Your_Charging_System.pdf
Those who are interested in expanding their understanding
of what alternators do (and don't do) are encouraged
to review this piece wherein I've endeavored to screen
out the 'chunks' of misinformation.
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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Subject: | Re: Why have a switch on ALT Field? |
This is the way I understand it. Please correct me if I am wrong.
The alternator output current does not need to be limited by a circuit
breaker because the alternator output is self-limiting. If one were to
add more loads to a fully loaded alternator, the voltage would drop,
thus limiting the current automatically. It is not desired to
unnecessarily run the alternator B lead into the cockpit. The B-lead
circuit breaker is not necessary, and adds weight, cost and complexity.
The purpose of an ANL fuse on the alternator output is not to protect
the alternator or to prevent it from producing more than its rated
current. The purpose of the ANL fuse is to protect the wires between
the battery and alternator from 400+ amps of battery current in the
event that the alternator shorts out, most likely from shorted diodes.
In the event that an over-voltage condition occurs (due to a faulty
regulator), an over-voltage module will short out the supply voltage
that goes to the alternator field. If that happens, an alternator-field
circuit breaker will trip, thus protecting the wires from excessive
current resulting from this short circuit.
Joe
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Subject: | Re: Why have a switch on ALT Field? |
rckol wrote:
>
>
> 1. You will be switching the field on and off at least once on every flight and
a normal breaker is not designed to be a robust switch.
Why?? Is there a need to turn the alternator on/off separate from the
master if it is functioning correctly?
> 2. You could use a "switch-breaker", but I have heard so many stories about these
having short life spans (at least the reasonably priced ones) that I would
not put one in my aircraft.
The Klixon switch breakers in my Mooney are almost all OEM from 45
years/6000 hours ago. A couple have been replaced from springs getting weak.
Message 9
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Subject: | Re: Why have a switch on ALT Field? |
Jay,
Thank you so much. Spelling out what may be obvious or intuitive to
experienced hands is a great assistance to us neophyte electron herders.
Tony
Velocity SEFG 62% done, 78% to go
www.alejandra.net/velocity
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Jay Hyde
Sent: Sunday, September 27, 2009 3:04 AM
Subject: RE: AeroElectric-List: Re: Why have a switch on ALT Field?
--> <jay@horriblehyde.com>
Hi there Mike,
Perhaps I can shed a bit of light on your questions. The switch is used as
it switches a smaller current than would be required on the B-lead; thus you
can use a switch and not a contactor. By switching off the field you have
effectively switched off the alternator in its entirety, not just its
output. Now its just a spinning mechanical device. If you switch the output
(B
lead) then you have a live spinning device and if the fault is inside the
alternator then you're still feeding it... Utilising the field to switch the
alternator also allows you to fit in overvoltage protection that will
quickly detect and clear any overvoltage fault that would fry all your
avionics leaving you with a damaged alternator AND no instruments
(electrically powered ones in any case); whereas, if the overvoltage fault
is detected and cleared you can still run the instruments on the battery. If
you have an internally regulated alternator then you need to switch the
output by using a contactor close to the alternator, because you cannot
access the field winding wire. Protecting the alternator by using a panel
mounted CB means that you lead a fat wire into the cockpit to the breaker in
your panel, which in turn means that there is a long bit of fat wire that is
unprotected- that long bit from the alternator to the CB. Personally I
don't like that.
If you use a contactor that is close to the source (alternator or battery)
then the only unprotected bit of fat wire is that bit between the source and
the contactor. A short bit of fat wire is unlikely to fault, or has a
higher reliability because it is short and mechanically robust. The closer
a contactor is to the voltage source the better your chances of removing the
power source from a fault.
Jay
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of rvg8tor
Sent: 27 September 2009 09:15 AM
Subject: AeroElectric-List: Re: Why have a switch on ALT Field?
Bob,
I know you are trying to help but, this last post does not seem to help me,
it actually confuses me. I respect your experience but I am not trying to
design an electrical system from scratch, much like I did not design my
RV-8A from scratch. I picked a plane from a good designer (Van's). While
building I study the plans and try to understand how the parts relate to be
a better builder, if I have a question I call builder assistance and I ask
questions on the forum.
When it came to the electrical system, I went with a design from an expert
in the field, in studying the design I asked a simple question,
'why is the alternator field switch needed". There have been a lot of words
written, much of which my little brain doesn'tunderstand how it relates to
the very simple question. The possible answers I was expecting were:
1. It has always been done that way
2. It doesn't matter the non-switch method will work but has these
limitations (fill in the blanks) 3. You need the switch because if you
don't have one it will cause XYZ.
Some of what you wrote I get but I really just need the simple short answer,
not a run down on design philosophy. Since you designed the systems I
thought of all people you could provide the best explanation. I thank you
for attempting to answer my questions, if nothing else you have convinced me
not to deviate from the Z diagram. I can't say that I understand fully why
the alternator field switch is a requirement other than to provide a
convenient way to turn off the field. I look forward to the simple answer
if there is one.
--------
Mike "Nemo" Elliott
RV-8A QB (Fuselage)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=265184#265184
Message 10
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Subject: | Re: Why have a switch on ALT Field? |
At 09:58 AM 9/27/2009, you wrote:
>This is the way I understand it. Please correct me if I am wrong.
>
> The alternator output current does not need to be limited by a
> circuit breaker because the alternator output is self-limiting.
correct
> If one were to add more loads to a fully loaded alternator, the
> voltage would drop, thus limiting the current automatically.
yes
> It is not desired to unnecessarily run the alternator B lead into
> the cockpit.
yes
> The B-lead circuit breaker is not necessary, and adds weight,
> cost and complexity.
> The purpose of an ANL fuse on the alternator output is not to
> protect the alternator or to prevent it from producing more than
> its rated current. The purpose of the ANL fuse is to protect the
> wires between the battery and alternator from 400+ amps of battery
> current in the event that the alternator shorts out, most likely
> from shorted diodes.
Yup . . .
> In the event that an over-voltage condition occurs (due to a
> faulty regulator), an over-voltage module will short out the supply
> voltage that goes to the alternator field. If that happens, an
> alternator-field circuit breaker will trip, thus protecting the
> wires from excessive current resulting from this short circuit.
Yes . . . this is a property unique to the
crowbar philosophy for opening the alternator's
field supply after an ov condition is detected.
There are other designs that do not open the
field supply breaker . . . and can be considered
as a potential player in your design goals.
The reason that Z-figures featuring crowbar
ov protection -AND- fuseblocks have a field
supply breaker is to accommodate the crowbar
ov control philosophy. If non-crowbar shutdown
products are considered, then one could easily
supply alternator field through one of the
fuses and leave the circuit breaker out.
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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Subject: | Re: Why have a switch on ALT Field? |
Why?? Is there a need to turn the alternator on/off separate from
the master if it is functioning correctly?
Depends on your architecture. Does the MASTER control
the alternator too? Is the MASTER a progressive transfer
two-pole switch or classic "split rocker". Then indeed,
the alternator field breaker may never need to be touched.
But if the MASTER is a simple two-pole switch that controls
alternator and battery at the same time, then you could
use the field breaker to shut the alternator down for
battery-only ground-ops.
2. The Klixon switch breakers in my Mooney are almost all OEM from 45
years/6000 hours ago. A couple have been replaced from springs getting weak.
But the Potter-Brumfield W31 style breakers installed in
many other airplanes for about the same length of time
have been identified has having a safety of flight
failure mode that is prompting an AD to replace about
80,000 of the critters. Not all switch breakers are
alike. All are much more expensive than the fuse/switch
architecture featured in the Z-figures.
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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