Today's Message Index:
----------------------
1. 03:09 AM - Re: Diodes versus switches 101 ? (Robert L. Nuckolls, III)
2. 03:19 AM - Re: Re: Diodes versus switches 101 ? (Robert L. Nuckolls, III)
3. 05:19 AM - Electrical Question ()
4. 09:10 AM - Re: B&C S895-1 as start button for 20A/14VDC ciruit? (Robert L. Nuckolls, III)
5. 09:29 AM - Re: Re: High density D-sub crimper (Robert L. Nuckolls, III)
6. 09:31 AM - Re: High density D-sub crimper (Robert L. Nuckolls, III)
7. 09:45 AM - Re: Diodes versus switches 101 ? (ZuluZephyr)
8. 11:06 AM - Re: Diodes versus switches 101 ? ()
9. 11:53 AM - Re: High density D-sub crimper (rampil)
10. 01:29 PM - Re: Diodes versus switches 101 ? (Robert L. Nuckolls, III)
11. 02:17 PM - Re: Diodes versus switches 101 ? (Matt Prather)
12. 07:26 PM - Re: AeroElectric-List Digest: 13 Msgs - 03/12/08 (Lee Logan)
13. 11:07 PM - Re: High density D-sub crimper (Ed Holyoke)
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Subject: | Diodes versus switches 101 ? |
At 10:57 PM 3/12/2008 -0500, you wrote:
><billschlatterer@sbcglobal.net>
>
>Thanks Bob, that tells me what I need to know. Wasn't planning on taking
>the diode out anyway but it's good to understand the why and why not? My
>only regret about my building process is that once I'm done, I won't have
>much use for the things I have come to understand from this list. Education
>is a good thing but practical use makes it excellent. In my case, I have
>learned just enough from this list to recognize what I don't know yet? That
>may be the reason I become a repeat builder ;-)
Correct . . . presuming that you do not take what
you've learned and share it with others. Knowledge and
understanding are commodities that grow in value the more they
are given away. We all benefit every day from associations
with individuals who are willing to share what they've learned.
After your airplane is finished, you can satisfy your debt
to all the teachers who participated in your success by
"paying it forward". See:
http://en.wikipedia.org/wiki/Pay_it_forward
http://tinyurl.com/32cfym
Bob . . .
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Subject: | Re: Diodes versus switches 101 ? |
At 09:50 PM 3/12/2008 -0700, you wrote:
>
>I have followed the switch vs diode controversy on a number of forums with
>interest since I am building a Sportsman with a Subaru H6 Engine. I am
>aware of crash involving a failed diode. I believe the diode was not
>rated for the actual amp load which was the most likely reason for the
>diode failure and the ensuing controversy.
Due diligence in design cannot be discounted. It
could just as easily have been a failure due to an
improperly tightened nut. Had it been a fastener failure,
is there value in responding to that knowledge by
replacing all the fasteners in our machines with
grade 8 hardware and metal locknuts?
The real issue is to understand what suite of
components are available to arrive at at an elegant
solution and then properly apply those components
to the task.
>There is another design recommending the elimination of the diodes and
>using one switch to supply the fuel pumps, ECU and EFI. This provides a
>single point of failure which I think violates the design goals of the Z19
>drawing of providing redundant paths, components and circuits.
Consideration of design goals and failure mode
effects are important components of the process . . .
>Being a committed party ( I have the engine) and wanting the simplest most
>reliable electrical system possible, I have designed a variation of the
>Z19 drawing using the same parts count with diodes (rated for the load)
>than includes a bypass circuit in case of diode failure (unlikely).
It's unfortunate that your lack of confidence leads
you to conclude that there is value in "backing
up" a diode. On the other hand, it's far better that
you fly this airplane free of worry about it. Worries
do not enhance your piloting skills and should be
assuaged irrespective of the physics and/or probabilities.
Bob . . .
Message 3
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Subject: | Electrical Question |
3/12/2008
Hello Tom, You wrote:
1) "For clarification, the NC switch means that I press the button to
actually cut the power. Why would this be used on an old military
helicopter stick? What is the reason for cutting the power on a switch?"
We used to say that having helicopter time in your logbook was like having
an STD entry (Sexually Transmitted Disease -- it was called venereal
disease back then) in your health record.
So I will reluctantly admit that I did fly a helicopter (CH-46) for a year
in Viet Nam. The cyclic grip had a button on it that when pressed would
disconnect the electronic flight stability / attitude positioning system so
that one could manually reposition the stick and the helicopter's attitude
then releasing the button would reengage the electronic attitude positioning
system.
Maybe you have a control stick grip that does something similar.
2) "Again, is there any way I can wire it to work with my remote ident
operation?"
I am not the right guy to answer that question, but I am sure that by using
two of the small "ice cube" type relays that ident operation could be
accomplished. It might be a pretty awkward way of doing it though from an
electrical viewpoint.
I'll forward your question to the Matronic's aeroelectric-list and maybe one
of the electrical experts there (even the great guru Bob Nuckolls) would
take a shot at it.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
PS: You can subscribe to this list here -- the daily digest is a great deal.
One email inbound each day puts you in contact with the living beating heart
of the homebuilder's electrical world.
http://www.matronics.com/Navigator/?AeroElectric-List
--------------------------------------------------------
----- Original Message -----
From: "Tom Gibbons" <TomisFlyingby@comcast.net>
Sent: Wednesday, March 12, 2008 12:25 AM
Subject: Electrical question
On my military surplus control stick I have 4 push buttons, 2 wired normally
opened (NO) and 2 wired normally closed (NC). I really do not have access
to these switches so I have to make due but can I use the NC switches
somehow?
I have plans for comm flip/flop, nav flip/flop, and Ident for my
transponder. I actually have a "hattie" switch in the middle for trim which
is not hooked up. The stick is installed with the ptt and intercom trigger
switches working good. All kinds of switches on this guy. Was not going to
use it but hey, it felt so comfortable, why not.
For clarification, the NC switch means that I press the button to actually
cut the power. Why would this be used on an old military helicopter stick?
What is the reason for cutting the power on a switch? Again, is there any
way I can wire it to work with my remote ident operation?
Tom
Paint this summer???
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Subject: | Re: B&C S895-1 as start button for 20A/14VDC ciruit? |
At 01:11 AM 3/9/2008 -0800, you wrote:
>
>Hi Bob,
>
>Hope all is well with you :)
>
>I have a B&C S895-1 push button originally intended as a start buton;
>however, the Eggenfellner recommendation for the starter circuit is for a
>switch or push button capable of 20A/14VDC (switch will be connected to
>the internal contactor on the Subaru H6 starter solenoid).
>
>I have been reviewing both your Switch_Rating.pdf and the chapter in the
>Connection, and I'm coming to the conclusion that this switch is probably
>too light for this application. Would it work? Sure. For how long? Who
>knows... But what would be the risk that I could fuse this switch closed
>or just plain heat it up too much? Also, the connection leads on this
>switch seem a bit small/light for 12AWG wire...
>
>Please advise when you have a moment.
The S895-1 switch would probably give a good service
life in this application. See:
http://www.aeroelectric.com/articles/Switch_Ratings.pdf
the REAL stress on this device will be the arcing
that takes place during release -AND- the openings
that occur during contact bounce at closure. Make
sure there's a diode from contactor (+) to ground.
I think B&C is supplying that switch with an MOV
already mounted. I recommended that about 10 years
ago during my brief love affair with MOVs . . .
turns out the diode is a MUCH more effective
solution to inductive energy management.
I'm wondering if the starter solenoid supplied
is the two-stage configuration described in
http://www.aeroelectric.com/articles/strtctr.pdf
If so, the 20A rating request by Eggenfellner
is probably an acknowledgement of the short term
energizing inrush unique to this design. The
wires supplied on that switch were tailored
to the starter contactor supplied in tht B&C
starter installation kit. Your application
would be better served with 16AWG wire and
a 15A fuse.
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: | Re: High density D-sub crimper |
At 07:16 AM 3/9/2008 -0700, you wrote:
>
>If you crimp connectors without the specific dies, you would
>be well served by soldering the wire strands to the crimps as
>well or the wires might just fall out!
>I have an AMP ProCrimp II with all the dies for the CPC
>Series I connectors, and they still sometimes fail the tug test when I
>don't oversolder them!
Your talking about the open-barrel, sheet metal pins.
I just went to the shop and pulled three 24AWG wires
from pins installed with my generic open-barrel crimp
tool. I got pullout forces that ran from 8 to 11 pounds.
If your pulling these off with your fingers you may have
the wrong tool or are not closing it hard enough.
I put some high density machined pins on with the $low$
d-sub crimp tool and produced crimps that I could not
pull off with the fingers. I don't have any of these
pins on hand right now but as soon as I can, I'll do
a calibrated pull-test and look at the cross sectioned
wire grips under the microscope. But I'm betting that
we'll find the crimps to be satisfactory on the HD
pins too.
Bob . . .
Message 6
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Subject: | Re: High density D-sub crimper |
At 10:08 PM 3/8/2008 -0800, you wrote:
>
>Howdy,
>
>I've got to crimp about 30 machined high density d-sub pins on an ACU
>install and I don't think my standard density crimper (B&C) is gonna work.
>I'd hate to spend $800 on a Daniels and postitioners for one little deed.
>Any ideas?
>
>I thought about getting a $30 crimper and some of the fold over pins. Are
>those pins as reliable as the machined ones? Will the crimper (fold over
>style, also B&C) do those little pins in one of it's slots?
Your risks for process error are lower with the machined
pins. I thick Steinair can sell you some. I also believe
the 20AWG crimper from B&C will properly install the
22AWG pins. I'll see if I can get a considered confirmation
in the next few days. I have come connectors on order with
my favorite local connector guy but he's a 15 mile drive from
here. When my order comes in, I'll pick up some 22AWG HD
pins for the experiment.
Bob . . .
Message 7
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Subject: | Re: Diodes versus switches 101 ? |
Bob,
I appreciate your comments, thoughts and efforts in helping all the builders develop
more reliable and better electrical systems. A worrier I am not, but a
simple change to the design that provides backup to a potential component failure
makes logical sense to me. I plan on flying in remote places and reliability
is high on my list of design goals. That is why I am here to learn and listen,
ask questions and share if I think something is worthy of the groups time.
Keep up the great work. Your work has been invaluable to me in the building process.
Bob, Thanks!!
Rocky Morrison
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=169589#169589
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Subject: | Diodes versus switches 101 ? |
Bob,
Thanks for the background and scope of the diode. That said and given
the intended reliability of the diode, I would hope my e-bus capacity
remains below 20A in my Z19 setup. Assuming the use of the B & C cooled
diode setup, should I fear any continuous load up to the 25A suggested
rating?
Thanks too for the tips on switching. I can see a few 2-10's in my
future for saving valuable panel space. Some great examples through 8-9x
in your book.
Glenn
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Bill
Schlatterer
Sent: Wednesday, March 12, 2008 11:57 PM
Subject: RE: AeroElectric-List: Diodes versus switches 101 ?
--> <billschlatterer@sbcglobal.net>
Thanks Bob, that tells me what I need to know. Wasn't planning on
taking the diode out anyway but it's good to understand the why and why
not? My only regret about my building process is that once I'm done, I
won't have much use for the things I have come to understand from this
list. Education is a good thing but practical use makes it excellent.
In my case, I have learned just enough from this list to recognize what
I don't know yet? That may be the reason I become a repeat builder ;-)
Thanks Bill S
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Robert L. Nuckolls, III
Sent: Wednesday, March 12, 2008 9:41 PM
Subject: Re: AeroElectric-List: Diodes versus switches 101 ?
--> <nuckolls.bob@cox.net>
There was some discussion about Z19 using diodes in a critical ECU
circuit and the question arose as to what kind of failure modes apply to
diodes and their reliability as compared to switches. I think the trust
of that thread (sub list) and post below is that diodes might be
"automatic" but switches are safer and less likely to fail? ( I have no
opinion but would like to understand the rationale ) This was posted
and I was just wondering what the thought might be on the AE list since
most of Bobs diagrams "suggest" a diode in the E-Bus circuit as opposed
to a switch. That might not be AS critical as the ECU/EFI circuit on an
all electric engine but the same concerns still apply?
Posted to the Sub list:
"After 30 years in the industrial electrical construction and
maintenance field I can say without equivocation that a robust switch is
much less likely to fail than a robust diode. The science of the switch
is much simpler - use a lot of good conducting material that is not
likely to corrode and support it with stout mechanical parts that hold
tightly.
Now, by contrast, the science of the diode starts with getting good
silicon material and contaminating it in just the right proportion with
just the right material at just the right temperature for just the right
time. THEN you can start on building the junctions onto some sort of
heat dissipating holder. I have replaced dozens of solid state devices
that failed (always failed open)
Interesting! Most solid state failures I've observed were
shorted devices (overheated and or voltage spiked). The
devices that did go OPEN were transistors that shorted first
and then opened their emitter bond-wires due to over current.
. . . and I never found the root cause of failure. I put in an exact
replacement and the circuit worked just fine for years. The trade off
you get for the "automatic" switching of a diode vs. the manual switch
is in the area of RELIABILITY. I'll be using manual switches for all
critical loads."
Not wanting to stir anything up, just want to understand the thinking
and factual matter in the post above?
About 1980 I was designing a new solid state speed
controller and runaway monitor system for the Lear 55
and ultimately the entire fleet of 30 series aircraft.
It was the first time I was tasked with doing a formal
failure mode effects analysis and mean-time-between-failures
(MTBF) study on a new product.
I dug out Mil-HDK-217 and began slogging through the
part-by-part service life prediction algorithms.
By the time some 200+ items of solder joints, transistors,
resistors, capacitors, etc were all accounted for, I was
pleased to turn the crank and a really nice MTBF number
on the order of 10,000 hours fell out. But wait, there
was this really expensive, mil-spec, hermetically sealed
25A power relay used as a last-ditch backup disconnect.
After factoring this device into the grand scheme
of things, my shinning MTBF number fell to something
on the order of 900 hours!
Several times over the last 25 years I've asked the
guys at Electromech's field service shop how the Lear
trim controllers are holding up. The failure items
they have to report were surprising. MOST of the field
failures were in mass-terminated ribbon cable connectors
followed by loss of ground through the mounting hardware
that held the two boards together. Seems this was before
I learned about having solid, on-purpose wiring grounds
and NOT to depend on mountings that loosen and/or corrode.
Electronically, most failures were the usual gang of
jelly bean components, solder joints, etc. Most failures
were in the monitor boards that had 3x the parts count
of a controller board. There were NO failures of the
controller that caused a runaway and a tiny fraction
of the failures incapacitated the system. There had
been no failures for that piece-o-#@@$, high-dollar
relay that crashed my MTBF study.
Bottom line: Was this relay badly misjudged? No,
I had a pretty good understanding of contact physics
and designed the electronics such that relay contacts
were closed before electronics actually caused the motor
to run. Similarly, electronics shut the motor down and
waited some tens of milliseconds before opening the
relay. Hence, the relay was never required to actually
switch any power. No current was flowing when the relay
contacts opened or closed and current was not allowed to
flow until contacts stopped bouncing on closure.
This is why Lear bought my design with the somewhat
distorted MTBF numbers because in thousands of hours
of flight, the relay never really saw any switching
service. Nowadays, there are more accurate considerations
of how a part is used that will provide a more realistic
prediction of failure rates.
Does this mean that the very robust, mil-spec relay
is the golden child of the design and the electronics
were left holding the bag for all the failures?
No, most failures were due to bonding/connection
issues. This controller resides in the vertical fin,
just under the leading edge of the stabilizer. This
has to be the worst environment in the airplane for
environmental extremes. For the most part, the electronics
seem to be living up to predictions for a long and
quite satisfactory service life in thousands of hours.
My personal experience since supports an assertion
that the silicon rectifier diode has an expected
service life that will far outpace any electro-mechanical
device (relay or switch) that is tasked with controlling
current flow.
Some of my most vexing field failures problems to solve
involve relays or switches. I've never had to chase down
root cause for failures of energy steering diodes
in an airplane.
Now, let us consider the gentleman's contrary assertion.
No doubt he has replaced blown diodes and perceives them
to be less robust than a switch. I cannot help but wonder
if his problem children were not subject to overheating
and or over-voltage due to industrial line transients
or local lightning. Whatever the root cause of his
observed failures, there is nothing in my experience
or that of my colleagues in the aircraft industry that
parallels his experience. I'm not suggesting that he is
being untruthful; only that we're probably observing
an apples/oranges situation. The environments
in which our diodes live and the manner in which they
are applied in airplanes are sufficiently different
from his industrial environment to prevent a useful
comparison.
So please folks, don't rip out your diodes and put
in switches. There are two reasons to support this
suggestion:
First, we design for failure tolerance.
What are the risks if a diode DOES fail? How will
the pilot know it? Is it pre-flight detectable? Will
the failure cripple the system such that it becomes
a hazard? If the answers to any of these questions
give you cause for concern about comfortable termination
of flight, then redesign the system to eliminate
the potential for stress. Consider his statement:
"I'll be using manual switches for all critical loads."
Our common usage of steering diodes for power is
one of TWO power paths to an e-bus. So even if it
does fail open, it has backup. If it fails shorted,
we can detect this during pre-flight.
Second, there is nothing in the service history of
diodes (or any other solid state device) to suggest
they are recognized problem children waiting for a
chance to ruin your day or drive up your cost of
ownership.
Bob . . .
Message 9
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Subject: | Re: High density D-sub crimper |
Hi Bob,
I was responding to Ed's comment that he might get some stamped
pins. I still think soldering crimped open barrels is the way to go.
The reason is that to meet specs on the pull test you must have
a connector pin specific to both the wire size and insulation along with
accompanying crimp dies. Since available wire may have unpredictable
insulation thickness in a homebuilder's shop, soldering is just extra assurance.
--------
Ira N224XS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=169619#169619
Message 10
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Subject: | Diodes versus switches 101 ? |
At 02:02 PM 3/13/2008 -0400, you wrote:
>
>Bob,
>Thanks for the background and scope of the diode. That said and given
>the intended reliability of the diode, I would hope my e-bus capacity
>remains below 20A in my Z19 setup. Assuming the use of the B & C cooled
>diode setup, should I fear any continuous load up to the 25A suggested
>rating?
>
>Thanks too for the tips on switching. I can see a few 2-10's in my
>future for saving valuable panel space. Some great examples through 8-9x
>in your book.
You're welcome. I would hope your endurance bus is below
20A too. I get about 2 or 3 drawings a month from builders
who are asking for a review of their particular implementation
of a Z-figure. The majority of these drawings have too much
stuff on the e-bus.
A review of the endurance bus philosophy might be useful here.
If one is flying one alternator and one battery, the e-bus is
intended to offer a minimum power load on a battery of known
capacity for the purpose of NOT turning an alternator failure
into an emergency. How much 'stuff' is necessary to stay on-course
for say 1 to 2 hours with the airplane configured for en route
phase of flight?
This list boils down to one nav receiver, transponder, minimal
panel lighting, etc. The nicely crafted e-bus for a one-alternator
airplane should be reduced to 4A or less total load. Now, other
things can drive from the e-bus but should be capable of being
switched off during alternator out operations.
If you have an auxiliary 8A alternator then the e-bus loads can
be elevated to 8A total. Likewise, a 20A aux alternator would
support a 20A e-bus . . . and perhaps there's little if any value
in even having an e-bus.
The 25A diode bridge recommended since day-one for the e-bus
normal feedpath diode was selected for its MECHANICAL convenience
of mounting and making connections via fast-on terminals. In
no way was it intended to imply that e-bus loads could total up
to that value. Anything over 10A should prompt a review of the
diode installation for the purpose of deducing thermal adequacy
of the mounting in carrying away heat.
Most of my fused feeders to the e-bus in the Z-figures are protected
at 7A. If you have an SD-8 second alternator, perhaps that fuse
should go up to 10A. But if your suite of proposed equipment
combined with an evaluation of how you plan to fly causes you
to pile everything but the kitchen sink on the e-bus, then
we need to talk.
If your e-bus loads are more than 10x the battery contactor
load then the advantages of shedding the contactor as a
battery only load are diminished considerably.
If most of the stuff you really need to run exceeds 8A then
you need an SD20 aux alternator and Figure Z-12 is probably
your minimum parts count approach to managing alternator
out conditions. Z-12 cannot fully exploit the design goals
for an e-bus so it would not be unreasonable to eliminate
it entirely and run the whole airplane from the main bus
with the SD-20 backing up the main alternator.
That takes care of the worries about diodes and e-bus
switches and makes the airplane simpler to operate.
Bob . . .
Message 11
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Subject: | Diodes versus switches 101 ? |
snip
> A review of the endurance bus philosophy might be useful here.
> If one is flying one alternator and one battery, the e-bus is
> intended to offer a minimum power load on a battery of known
> capacity for the purpose of NOT turning an alternator failure
> into an emergency. How much 'stuff' is necessary to stay on-course
> for say 1 to 2 hours with the airplane configured for en route
> phase of flight?
>
> This list boils down to one nav receiver, transponder, minimal
> panel lighting, etc. The nicely crafted e-bus for a one-alternator
Plus any devices required to remain upright (in an all-electric airplane)
- aviate, then navigate? An EFIS (or an electric attitude indicator).
>
> Bob . . .
>
Regards,
Matt-
Message 12
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Subject: | Re: AeroElectric-List Digest: 13 Msgs - 03/12/08 |
Does anyone know where I can download the installation manuals for the
Garmin GNC300, SL-30, and a PS Engineering PMA6000MC?
Thanks for the help!
Lee...
Message 13
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Subject: | Re: High density D-sub crimper |
Thanks Bob,
I'm interested in how the experiment comes out.
Ed Holyoke
Robert L. Nuckolls, III wrote:
> <nuckolls.bob@cox.net>
>
> At 10:08 PM 3/8/2008 -0800, you wrote:
>
>> <bicyclop@pacbell.net>
>>
>> Howdy,
>>
>> I've got to crimp about 30 machined high density d-sub pins on an ACU
>> install and I don't think my standard density crimper (B&C) is gonna
>> work. I'd hate to spend $800 on a Daniels and postitioners for one
>> little deed. Any ideas?
>>
>> I thought about getting a $30 crimper and some of the fold over pins.
>> Are those pins as reliable as the machined ones? Will the crimper
>> (fold over style, also B&C) do those little pins in one of it's slots?
>
> Your risks for process error are lower with the machined
> pins. I thick Steinair can sell you some. I also believe
> the 20AWG crimper from B&C will properly install the
> 22AWG pins. I'll see if I can get a considered confirmation
> in the next few days. I have come connectors on order with
> my favorite local connector guy but he's a 15 mile drive from
> here. When my order comes in, I'll pick up some 22AWG HD
> pins for the experiment.
>
> Bob . . .
>
>
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