Today's Message Index:
----------------------
1. 01:51 AM - Re: Advice about 24V systems (Nigel Harrison)
2. 07:03 AM - Re: Coax crimper / stripper question (Robert L. Nuckolls, III)
3. 07:23 AM - Re: How do you carry the braid from a shielded (Eric M. Jones)
4. 07:40 AM - Re: LSE Ign Power Wire (Matt Prather)
5. 08:14 AM - Re: Coax crimper / stripper question (cgalley)
6. 09:09 AM - Re: Taxi/Landing Lights (Robert L. Nuckolls, III)
7. 09:09 AM - Re: Advice about 24V systems (Robert L. Nuckolls, III)
8. 09:10 AM - Re: LSE Ign Power Wire (Robert L. Nuckolls, III)
9. 09:40 AM - Re: AeroElectric-List Digest: 23 Msgs - 02/12/05 (Jay Brinkmeyer)
10. 10:35 AM - Re: Re: How do you carry the braid from a shielded (N1deltawhiskey@aol.com)
11. 10:52 AM - Light Switch (Tinne maha)
12. 12:05 PM - Re: Coax crimper / stripper question (John Schroeder)
13. 01:13 PM - Re: How do you carry the braid from a shielded (Eric M. Jones)
14. 02:46 PM - Re: 11937 Besing (Robert L. Nuckolls, III)
15. 03:05 PM - Fuel Pressure Gauges (Tinne maha)
16. 03:28 PM - Re: Fuel Pressure Gauges (Denis Walsh)
17. 05:34 PM - Garmin Antenna (F. ILMAIN)
18. 05:52 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Fiveonepw@aol.com)
19. 07:24 PM - Re: static wicks (Robert L. Nuckolls, III)
20. 07:39 PM - Re: Light Switch (Robert L. Nuckolls, III)
21. 07:43 PM - P Static (was Re: Re: 11937 Besing (David Carter)
22. 08:27 PM - Re: Re: How do you carry the braid from a (Robert L. Nuckolls, III)
23. 09:06 PM - paranormal resistance (sarg314)
24. 09:34 PM - Re: P Static (was Re: Re: 11937 Besing (Robert L. Nuckolls, III)
25. 10:00 PM - Fuse links (TimRhod@aol.com)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Advice about 24V systems |
--> AeroElectric-List message posted by: "Nigel Harrison" <naharrison@manx.net>
Thank you Bob for your thoughts and recommendations. I will stay with
aeroelectric. I've ordered the aeroelectric book too. It looks as if I would
be best to go for 12 V with the addition of a second battery as a back up.
Am I correct in thinking that if they were connected in parallel this would
allow the generator to charge both? Some sort of switching mechanism could
then allow the back up to be used once the main battery power was used up.
Best wishes
Nigel Harrison
Isle of Man
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Robert
L. Nuckolls, III
Subject: Re: AeroElectric-List: Advice about 24V systems
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<b.nuckolls@cox.net>
At 09:38 PM 2/12/2005 +0000, you wrote:
>--> AeroElectric-List message posted by: "Nigel Harrison"
><naharrison@manx.net>
>
>
>Dear All,
>I am a Europa builder and am planning to install an all-electric set up
with
>a Grand Rapids EFIS etc. Reading Greg Richter's artlcle on Aircraft wiring,
>he is of the opinion that a 24V electrical system will provide much more
>safety margin tha a 12V system in the event of generator failure.
With all due respect to Greg's accomplishments as a manufacturer
of EFIS systems, the article you cited is rife with errors and
offers no understanding of the simple-ideas in physics that support
good design decisions. If you're interested in the details you can
check out:
http://aeroelectric.com/articles/richter/richter.html
>My aircraft will have a Rotax 912S. The engine manufacturers have advised
me
>that "Unfortunately the Rotax electrical system is only 12 V DC.The
internal
>alternator gives an AC voltage above 24 V at a speed of about 3000 rpm,
>which may possibly be suitable, but you would have to design or procure a
>rectifier/regulator for 24 V." Can someone advise me whether this
alternator
>would be suffiiciently powerful to charge 2 x 12V 16Ah batteries in series.
>Rotax also mention a rectifier/regulator. Advice on this too would be
>useful.
I aware of no compelling explanation of system operation
and design that makes a case for 24 volt systems replacing
12 volt systems in small aircraft. The owner built and maintained
aircraft industry is seeking best return on investment
(i.e. VALUE) for component selection and system architecture.
The automotive world provides us with many low cost,
robust alternatives to 24 volt devices which are uniquely
aircraft in nature. The high cost of certification and relatively
low production numbers makes aircraft parts a very poor
value.
>I have little in the way of electrical knowledge/knowhow, so simple
>explanations would be most helpful.
May I suggest a source of information on a variety
of small aircraft electrical systems topics? Look
over the offerings at:
http://aeroelectric.com/articles.html
Further, please stay with us here on the AeroElectric-List.
There are many folks among the 1300+ subscribers who
will be pleased to share their experiences and insight
as they apply to your task.
Bob . . .
*************************************************************
This email has been scanned by the Manxnet Mail Plus anti-virus system.
http://www.manx.net/mailplus
*************************************************************
*************************************************************
This email has been scanned by the Manxnet Mail Plus anti-virus system.
http://www.manx.net/mailplus
*************************************************************
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Coax crimper / stripper question |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 10:05 PM 2/12/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: Jay Brinkmeyer
><jaybrinkmeyer@yahoo.com>
>
>Would this tool crimp RG-142/400? Perhaps -400 is size equivalent to
>others? If
>so, which size?
>
>http://www.mytoolstore.com/klein/t1720.html
This tool doesn't have the proper die sizes. You need a
.213" hex and .068 round or hex for most connectors used
on RG142/400. See BNC Crip tool at:
http://bandc.biz/cgi-bin/ez-catalog/cat_display.cgi?9X358218#RCT-2
>Also, would someone be so kind as to recommend a good coax stripper?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4693&item=5751327980&rd=1
This tool says RG-59/6 but the three blades are individually
adjustable for cut depth and it's easily set up for RG-142/400
Bob . . .
--------------------------------------------------------
< Throughout history, poverty is the normal condition >
< of man. Advances which permit this norm to be >
< exceeded -- here and there, now and then -- are the >
< work of an extremely small minority, frequently >
< despised, often condemned, and almost always opposed >
< by all right-thinking people. Whenever this tiny >
< minority is kept from creating, or (as sometimes >
< happens) is driven out of a society, the people >
< then slip back into abject poverty. >
< >
< This is known as "bad luck". >
< -Lazarus Long- >
<------------------------------------------------------>
http://www.aeroelectric.com
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: How do you carry the braid from a shielded |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "Wayne Sweet" <w_sweet@comcast.net>
>Don't quite get the picture. Is this equivalent; bare the shield around the
>circumference, letting it retain it's structure and form, then soldering a
>bare wire around that shield's circumference and taking that wire to the
>ground lug? >Wayne
Wayne,
That's a negative. Bob's published way is also....ahem....problematic. The
right way of running a shield through a D-Sub is with a shield--not a
pigtail. The problem can be summarized as follows (and what I say goes for
higher frequencies, not DC):
1) The shield does what it does because of its geometry. Changing its
geometry changes its response to charges in motion. There is a very big word
to describe this but if I told you.....well....you know!
2) Changing the impedance by pigtailing the carefully-constructed coaxial
shield wrecks the impedance and adds a spurious antenna at frequencies
described by the particulars of the pigtail.
3) Taking care to make the coax think it's still a coax takes special care.
4) Little of this was common practice before 1980, due somewhat to the
introduction of higher frequencies but moreover DIGITAL stuff since then.
The EMC approvals that became required simply changed common practices.
From Kimmel Gerke (EMC) Associates---"....all penetrations, such as shields
or cables, be bonded or decoupled at the point of penetration...NO PIGTAILS
or long leads. This is a leading cause of FCC/VDE failures, with poorly
terminated wiring acting as undesired antennas."
"Cables and Connectors....metal connectors with a full circumferential
termination of cable shield to connector for any cable shield that must work
above 1 MHz...NO PIGTAILS."
(Emphasis mine)
The connection of conductors is barely taught in electronics classes, but
consider---
What's the difference between a 10A connector and a 100A, 1000A, or a
million-Amp connector?
What's the difference between a DC connector and a 10 MHz connector?
What's the difference between a microvolt connector and a Megavolt
connector?
What's the difference between a gold connector and an aluminum
connector?
Well...so is there a difference between a coaxial connector and a
pigtail?
Does it matter? Maybe not. Do you have an aircraft that barely has any
electronics and rarely strays far from the home field or rack full of stuff?
Would like the best quality signals you can get? Do you want radio signals
in that long dark patch between Bandahatchie and Huatabampo? Do you want to
ask the Aeroelectric list how to quiet all the hums and buzzes in your
intercom?
As for the right way to terminate shielded wire---there are a myriad of
ways. Check AMP "Braid-Pic" terminations. Or just browse thru Digikey
section A. Or conceptually--imagine a fat ring-tongue connector. The shield
goes into the sleeve and is soldered there. The center conductor is not
teased out. This is not perfect but is way better than a pigtail.
And there is still a lot to be said for a good twisted pair below a few GHz.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
Teamwork: " A lot of people doing exactly what I say."
(Marketing exec., Citrix Corp.)
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: LSE Ign Power Wire |
--> AeroElectric-List message posted by: "Matt Prather" <mprather@spro.net>
I used 18g in my Varieze - partly because the run from the nose
(battery location) to the firewall (ign module location) is kind
of long.
Regards,
Matt-
VE N34RD
> --> AeroElectric-List message posted by: "Tinne maha"
> <tinnemaha@hotmail.com>
>
> I installed a single LSE ignition in my project a while back and, for
> some unknown reason, ran an AWG 14 wire from the battery bus to the
> control module. Two hours ago, I'd have sworn up & down that the
> installation manual required that big of a wire, but now I can't find
> any reference to it in the manual or on the web page.
>
> The web page shows a current draw of 1.2 amps @ 13.8 volts for my Plasma
> II/4 cylinder set up: This would only require an AWG 20 or so wire.
>
> Will listers with operating LSE systems please tell me if I'm cracking
> up? How did you size the power wire on your project?
>
> Thanks,
> Grant
>
>
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Coax crimper / stripper question |
--> AeroElectric-List message posted by: "cgalley" <cgalley@qcbc.org>
I have a Model 59500 Amp crimper but no dies. Where can anyone find just
the dies at a reasonable cost?
Cy Galley - Bellanca Champion Club
Newsletter Editor-in-Chief & EAA TC
www.bellanca-championclub.com
Actively supporting Bellancas every day
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Taxi/Landing Lights |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 11:31 PM 2/12/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Tinne maha" <tinnemaha@hotmail.com>
>
>Bob/List,
>
>I finally found the time/equipment/etc. needed to measure the current used
>by my taxi & landing lights. 4.4 amps each. Thanks for your suggestions on
>that. The measurement may not have been necessary, but I couldn't calculate
>theoretical values 'cuz I didn't have any data: 'Sides that, I'm a 'seeing
>is believing' kinda guy & it was a good exercise for me. Satisfied my
>curiosity.
Good for you!
>Now the question becomes how to wire these two lights (together in one
>housing, but able to be controlled separately) for optimum use. I'm
>inclined to set it up with a 3 position switch - down is 'Off', middle is
>taxi light only & up is both landing & taxi lights on. I've thought of
>other possble set ups (2 separate, 'on-off' switches or a 3 position switch
>that doesn't allow both lights to be on at the same time), but I can't think
>of a reason NOT to have the taxi light on whenever the landing light is on.
>The only difference between the two lights, as far as I can tell, is the
>angle at which the light is directed.
This is a common feature on OBAM aircraft. A signle S700-2-10 or
equal is wired per Figure 11-17 in the 'Connection to function
just as you've described.
Bob . . .
Message 7
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Advice about 24V systems |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 09:49 AM 2/13/2005 +0000, you wrote:
>--> AeroElectric-List message posted by: "Nigel Harrison"
><naharrison@manx.net>
>
>
>Thank you Bob for your thoughts and recommendations. I will stay with
>aeroelectric. I've ordered the aeroelectric book too. It looks as if I would
>be best to go for 12 V with the addition of a second battery as a back up.
What is it that you want to "back up"? Most aircraft with
a 912 engine are relatively simple. What systems do you plan
to carry and what flight operations do you anticipate that
demand extra-ordinary power supply reliability?
>Am I correct in thinking that if they were connected in parallel this would
>allow the generator to charge both? Some sort of switching mechanism could
>then allow the back up to be used once the main battery power was used up.
You can have as many batteries as you wish and run them in
parallel for all normal operations. Active notification
of low voltage heralds failure of an alternator whereupon
the pilot separates each battery from the others to accomplish
their respective tasks. Let's talk about the equipment you
plan to carry, how much energy each system requires and how
you plan to us the airplane.
Bob . . .
Message 8
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: LSE Ign Power Wire |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 11:05 PM 2/12/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Tinne maha" <tinnemaha@hotmail.com>
>
>I installed a single LSE ignition in my project a while back and, for some
>unknown reason, ran an AWG 14 wire from the battery bus to the control
>module. Two hours ago, I'd have sworn up & down that the installation
>manual required that big of a wire, but now I can't find any reference to it
>in the manual or on the web page.
>
>The web page shows a current draw of 1.2 amps @ 13.8 volts for my Plasma
>II/4 cylinder set up: This would only require an AWG 20 or so wire.
>
>Will listers with operating LSE systems please tell me if I'm cracking up?
>How did you size the power wire on your project?
22AWG is electrically robust enough to do the task. Some manufacturers
have a policy that no wiring on the engine for control or insrumentation
is less than 20AWG for mechanical robustness . . . but there's no
good reason I can deduce for 14AWG wire to feed this accessory.
Bob . . .
Message 9
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: AeroElectric-List Digest: 23 Msgs - 02/12/05 |
--> AeroElectric-List message posted by: Jay Brinkmeyer <jaybrinkmeyer@yahoo.com>
Am I out of luck? I trimmed by shielded wing strobe wires with the idea of
running them to a connector at the wing root. What sort of connector to use?
Can I splice or should I punt and run only a single wire run between power
supply and strobe? (Wheelen only gives you one big hunk of wire...)
Jay
>I need to carry the braid from a shielded wire past the molex connector.
>What is the correct way to do this?
>Just carry it through as one of the pins in the connector?
>Cecil
Okay so I had a triple espresso........
Almost nobody does shield termination correctly. Allow me to explain:
A shield-- braid, tape or foil is a kind of perfect partner--a little
Faraday cage around the wires that acts as a ground plane in reference to
the wires running through it. When some charge moves on the internal wires,
the shield supplies the opposite charge--on loan from ground. Well sort
of......
The right way of terminating the shield is coaxially--like a coaxial
bulkhead connector does. The absolutely wrong way is to separate the inner
wires from the shield and twist the shield into a wire and attach it to
ground as if it were just another wire. Holy Moley! Now that you have
strangled the little baby shield it develops a bad case of impedance at
frequencies that otherwise would have been grounded--depending on the fine
and random details of the high impedance "pigtail".
This makes terminating a shield a task that calls for special care. A way to
understand how to do this properly is to imagine a grounded metal wall that
the wire goes through. The shield is teased open and electrically bonded to
the wall around the circumference of the hole. That's the way to do it. Any
technique that approximates this is better than a "pigtail"
Oink,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
=====
__________________________________
http://my.yahoo.com
Message 10
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: How do you carry the braid from a shielded |
--> AeroElectric-List message posted by: N1deltawhiskey@aol.com
Eric,
Interesting comments. Not necessarily an "infidel," but perhaps a slightly
confused skeptic.
Your comments for coax makes sense when it comes to low energy RF signals.
And coax connectors are designed to do just as you suggest.
Allowing that I may be wrong in my perspective/assumptions, the rest of the
wiring in our aircrafts are carrying much lower frequency currents, so we use
shielded wire where the impact of external electro-magnetic energy could set up
unwanted currents in our wire, usually referred to as "noise" if it is at
audio frequencies.
Where it may be an issue, the unshielded part of our wire becomes sort of an
antenna to pick up these stray EM fields. The shorter the unshielded wire,
the less opportunity to pick up this EM energy. Where shielded, the EM may set
up currents in our shield and shielded wire equally, but since the latter is
grounded, the net effect is 0.
So, I would deduce that the shorter the unshielded wire, the lower the
currents that the EM can set up. While these are not 0, they may be low enough
to
not be audible. Hence, the pigtail solution.
I looked at Bob's article and found it interesting he was using single
conductor shielded for his demo. I have none of that in my A/C, they are all 2-
or
3-conductor shielded, twisted internally. In this case, I should think the
pigtail method would work fine in most cases. I also noted is was recommended
for my Apollo GX-60/SL-70 interconnections with the caveat that the unshielded
portion of the wire be as short as possible, and the pigtail no longer than
1-1/4". So these do, apparently, and usually, provide satisfactory performance.
Not as quiet as concentric pass-throughs, but a lot better than unshielded.
On the other hand, I have trouble imagining a pass-through using D-sub
connectors that would be concentric. What you seem to suggest is that all shielded
wires be connected using some other kind of connector. What do you have in
mind that would allow us to do what you suggest?
Regards, Doug Windhorn
In a message dated 13-Feb-05 7:24:17 Pacific Standard Time,
emjones@charter.net writes:
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "Wayne Sweet" <w_sweet@comcast.net>
>Don't quite get the picture. Is this equivalent; bare the shield around the
>circumference, letting it retain it's structure and form, then soldering a
>bare wire around that shield's circumference and taking that wire to the
>ground lug? >Wayne
Wayne,
That's a negative. Bob's published way is also....ahem....problematic. The
right way of running a shield through a D-Sub is with a shield--not a
pigtail. The problem can be summarized as follows (and what I say goes for
higher frequencies, not DC):
1) The shield does what it does because of its geometry. Changing its
geometry changes its response to charges in motion. There is a very big word
to describe this but if I told you.....well....you know!
2) Changing the impedance by pigtailing the carefully-constructed coaxial
shield wrecks the impedance and adds a spurious antenna at frequencies
described by the particulars of the pigtail.
3) Taking care to make the coax think it's still a coax takes special care.
4) Little of this was common practice before 1980, due somewhat to the
introduction of higher frequencies but moreover DIGITAL stuff since then.
The EMC approvals that became required simply changed common practices.
From Kimmel Gerke (EMC) Associates---"....all penetrations, such as shields
or cables, be bonded or decoupled at the point of penetration...NO PIGTAILS
or long leads. This is a leading cause of FCC/VDE failures, with poorly
terminated wiring acting as undesired antennas."
"Cables and Connectors....metal connectors with a full circumferential
termination of cable shield to connector for any cable shield that must work
above 1 MHz...NO PIGTAILS."
(Emphasis mine)
The connection of conductors is barely taught in electronics classes, but
consider---
What's the difference between a 10A connector and a 100A, 1000A, or a
million-Amp connector?
What's the difference between a DC connector and a 10 MHz connector?
What's the difference between a microvolt connector and a Megavolt
connector?
What's the difference between a gold connector and an aluminum
connector?
Well...so is there a difference between a coaxial connector and a
pigtail?
Does it matter? Maybe not. Do you have an aircraft that barely has any
electronics and rarely strays far from the home field or rack full of stuff?
Would like the best quality signals you can get? Do you want radio signals
in that long dark patch between Bandahatchie and Huatabampo? Do you want to
ask the Aeroelectric list how to quiet all the hums and buzzes in your
intercom?
As for the right way to terminate shielded wire---there are a myriad of
ways. Check AMP "Braid-Pic" terminations. Or just browse thru Digikey
section A. Or conceptually--imagine a fat ring-tongue connector. The shield
goes into the sleeve and is soldered there. The center conductor is not
teased out. This is not perfect but is way better than a pigtail.
And there is still a lot to be said for a good twisted pair below a few GHz.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
Teamwork: " A lot of people doing exactly what I say."
(Marketing exec., Citrix Corp.)
Message 11
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
--> AeroElectric-List message posted by: "Tinne maha" <tinnemaha@hotmail.com>
Hello Bob/List,
I've read Bob's shop notes about 'Switch Ratings, What's it all mean?',
including Bob's conservative rule of thumb that the 115 Volt AC current
rating stamped on most switches can be substituted for the 12 Volt DC
current rating.
Literature on the switch I hope/plan to use on my taxi/landing light gives a
4 Amp rating for 30 Volts DC. Does it follow that the same switch can carry
8 amps at 15 Volts DC?
(BTW, the literature gives AC Ratings as follows: 3 amps @ 250 Volts, 6 amps
@ 125 Volts. So, my question re-phrased is: Does this apparently linear
relationship also apply to DC ratings?)
Thanks in advance,
Grant
Message 12
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Coax crimper / stripper question |
--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
Jay -
That tool seems to be a tad high priced for doing a very few crimps on an
airplane. It also illustrates the variety of coax's there are and choosing
the right tool makes it hard.
Here is one way to decide which die set to buy for the coax work. Decide
on the brand of connector: AMP, Amphenol, etc. ... . Amphenols cost more,
but I have yet to run into any trouble using them. Another brand we used
gave us trouble getting the ferrule down over the insulation and flush to
the outer case of the BNC to crimp it. They were commercial grade from
Digi-Key as I recall. The extension the goes between the insulated inner
conductor and the shielding is a tad too fat. It was also hard to get the
center connector/pin to snap into place. In the catalogs, go to the coax
number you intend to use and get the mfg.'s product number. Then get the
specs and it will tell you what size crimp for the center pin and for the
ferrule. Then buy a die set for the crimper frame. This info should be
available on line in the DigiKey and Mouser catalogs.
For a stripper, Bob Nuckolls looked at this one and liked it a lot. We
have a different one, but the important thing is that you can do all the
cutting and stripping in one use of the tool, and when you adjust it
right, it will not cut any ot the shield stranding or the center conductor.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4693&item=5722575929
I bought a Paladin 1300 series ratcheting crimper frame and 2 sets of
dies. One set (#2082) has a slot for 24-30 AWG open barrel and another for
18-22 AWG open barrel. This combo does Molex Mini-Fit Juniors, AMP CPC
Type I, AMP Mate 'N Lock (the kind that Whelan sends along with their
light and strobe kits) and the older Molex connectors.
The other set of dies (no number) for the Paladin has slots for 22-18,
16-14 and 12-10 open barrels. I used this set to crimp a few AWG16 and a
couple of AWG 12 wires to Molex Mini Fit Senior connectors (landing/taxi
lights and pitot heat, respectively). The Paladin is a medium quality
crimper and the dies are good quality. You will not wear them out on one
airplane's wiring project. The frame and both sets of dies were $76. I
bought them from GreatCables.com. You can also get a Paladin die set for
crimping Red, Blue and Yellow PIDG terminals for another $22.
The machined pin crimper from B&C is specially modified to do perfect
crimps on the AMP brand machined pins. They set the depth so that the
diamond crimp is at the right position on the pin. You do Dsubs and AMP
CPC Type 2 CPC's with these pins and crimper. I have done about 80 percent
of all crimps with these two crimpers and the 8082 die set for the
Paladin. The wire range for these pins are AWG 20 to 24. We went to CPC
Type 1's or Molex Mini Fit Juniors when we had AWG 18 wires to put into
connectors along with AWG 20 & 22 wires. In one particular Type 1, we had
AWG 18's, 20's 22's and a couple of 16's and 14's. But, remember they take
different size open barrel pins hence we used both dies sets.
One lesson we learned is: Dsubs are great for computers, but hard to hook
up when joining two cables. They mate OK, but securing them with those
4-40 screws and hex standoff nuts is a pain in cramped places (that's damn
near everywhere in an airplane). We converted several of ours to AMP CPC
Type 2's and the machined pins. Much easier to mate and lock to each
other. You use the same pin extractor and crimper for both DSubs and CPC
Type 2's. The other connector we used a lot of were the AMP Mini-Fit
Juniors. They carry more amps than a DSub (up to 9), are nice to crimp and
lock together easily. They make a pin for this connector that is very easy
to crimp to those beastly thin wires that RAy Allen (MAC) uses on their
trim servo components. We also used several AMP CPC Type 1's.
Steinair also sells a frame and some dies, a machined pin crimper and the
machined pins & sockets. I don't know what brand they are or the size of
the dies. And I have not used them.
This was a long answer to your question, but I hope it helps in other
aspects of the wiring.
Cheers,
John
> Would this tool crimp RG-142/400? Perhaps -400 is size equivalent to
> others? If so, which size?
>
> http://www.mytoolstore.com/klein/t1720.html
>
> Also, would someone be so kind as to recommend a good coax stripper?
Message 13
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: How do you carry the braid from a shielded |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: N1deltawhiskey@aol.com
>Your comments for coax makes sense when it comes to low energy RF signals.
>And coax connectors are designed to do just as you suggest.
>Not as quiet as concentric pass-throughs, but a lot better than unshielded.
>On the other hand, I have trouble imagining a pass-through using D-sub
>connectors that would be concentric. What you seem to suggest is that all
shielded
>wires be connected using some other kind of connector. What do you have in
>mind that would allow us to do what you suggest?
>Regards, Doug Windhorn
Hi Doug,
The issue of what power levels and what frequencies require proper
connections is fraught with peril. You might think that audio frequencies
are easy, but a square wave is made up of ALL frequencies. (Fourier Series:
Signals can be composed by a superposition of an infinite number of sine and
cosine functions. The coefficients of the superposition depend on the signal
being represented and are equivalent to knowing the function itself.....I
bet you already knew that!)
All D-sub connectors have matching covers to which the shield may be
grounded. I would not be going very far out on the limb to say that all
coaxial and common shielded cables have matching connectors. There are of
course ungrounded shields--but you can get pretty much anything--so there's
no accounting for taste. My description of how coaxial cable and shielded
cable should be terminated would be helped by illustrations--none of which I
have. But I assure you that this has been the standard technique since the
1980's.
I expect many builders to say, "Well...it's good enough." This is my second
favorite invitation to disaster right after, "Watch this...Hold my beer."
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"...as we know, there are known-knowns; there are things we know we know. We
also know there are known-unknowns; that is to say, we know there are some
things we do not know. But there are also unknown-unknowns; the ones we
don't know we don't know." Donald Rumsfeld
Message 14
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: 11937 Besing |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 03:21 PM 2/13/2005 +0000, you wrote:
>Below is the result of your inquiry. It was submitted by
>Paul Besing (paul@kitlog.com) on Sunday, February 13, 2005 at 07:21:13
>
>Sunday, February 13, 2005
>
>Paul Besing
>
>,
>Email: paul@kitlog.com
>Comments/Questions: Bob, what are your thoughts on static wicks? There
>has been some debate on an RV-10 list about them. Knowing your thoughts
>on how much more reliable radios are nowadaws, I'm surprised to hear so
>many people that want to now put them on airplanes.
Static wicks have nothing to do with radio quality or reliability.
EVERY time dissimilar materials slide across each other, there is
a tendency for one material with a stronger affinity for electrons
than the other to acquire a negative charge. Common manifestations
include sparks that jump between fingertip and doorknob after
walking across carpet. In the winter especially, I have to remind
myself to keep part of my body touching the frame of my 1" vertical
belt stander while sculpting a piece of metal . . . the Van DeGraff
like nature of the belt sander will charge the ol' bod with a
significant kick if I don't bleed it off during the sanding operations.
Precipitation static is unique to airborne particles sliding past
any conductor. Radio receivers can be severely affected by dust
storms usually associated with high winds. I used to work with
an amateur radio repeater installation 1200 feet up on KTVH-TV
in Hutchinson, KS. A blowing snow storm would severely de-sense
our receivers.
Airplanes have unique problems in that they generate their
own wind. Airplanes flying through dust, rain or snow can
pick up significant charges. When the charge reaches sufficient
magnitude, it begins to form coronas at the sharp (usually
trailing edges) of wings and flight control surfaces.
The static wick is a sharp-ended conductor (enhances tendency
for charge to concentrate and form corona) connected to the
airframe through some nominal but rather high resistance. The
idea is to put sufficient static wicks in the right places
so that they force lots of small, low current discharges to form
and dissipate the energy at much lower (read less noisy)
levels than if the wicks were not present.
The faster the airplane flies, the more likely it is to
experience the effects of p-static. Further, the finish
and skin materials have an influence on tendency to build
and concentrate static charges. These effects are present
and potentially troublesome irrespective of the vintage
of radios carried aboard the airplane.
VHF radios are less susceptible than HF or ADF
receivers. Grounded antennas are quieter than isolated
antennas. There are some modern digital signal processing
techniques that can reduce the audible effects of
p-static but ultimately, locally generated static noises
will overwhelm a receiver looking for weaker signals.
The number, style and placement of static wicks on
our bizjets is as much an art as a science. We spent
a great deal of $time$ selecting the right products
and installations. Further, there's a comprehensive
incoming inspection of static wicks . . . seems that
a performance of a static wick is very sensitive to
production variability.
If your airplane suffers from the effects of p-static,
it may take a lot of effort over a long period of time
to deduce the optimum solution.
Bob . . .
Message 15
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Fuel Pressure Gauges |
--> AeroElectric-List message posted by: "Tinne maha" <tinnemaha@hotmail.com>
Hello again list,
I am hoping/planning to install an Ellison throttle body on my Lycoming
O-235 powered Kitfox. I will have an electric boost pump for priming as
well as for take-off and landing, but there is no engine driven pump. As
planned, there will be only about 0.8 PSI of fuel pressure in the normal
flight attitude (i.e. boost pump off). The Throttle body I plan to use
requires a minimum 0.5 PSI of fuel pressure. Normally I would not be
comfortable with this narrow a margin of error, but I will have the boost
pump to use should the pressure drop and, more importantly, I know this has
already been done on a nearly identical Kitfox/engine combination.
The owner & the builder of that particular airplane each have encouraged me
to install a fuel pressure gauge, but I'm not convinced it will add any
benefit other than confirming my electric fuel pump is working (I think I
can determine that with my ammeter during run-up.) My reasoning is as
follows: As a 0-10 PSI gauge is the lowest range I can find, the 'normal'
reading for my plane will only be 10% of the range. Thus, any change in the
normal condition will almost certainly be un-detectable unless it's already
too late (e.g. engine roughness or fuel starvation set in.)
Any experience, comments or criticisms on this?
Thanks again,
Grant Krueger
Message 16
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Fuel Pressure Gauges |
--> AeroElectric-List message posted by: Denis Walsh <denis.walsh@comcast.net>
I use my direct reading psi gage for a couple other things. When it
dances, it shows you are getting bubbles and about to get vapor lock.
Nice to make sure it is steady before take off. Also when it reads
high after a burger stop it means you have vapors building up and
require hot start procedures. Lastly, when it drops to zero in flight
it is a clear sign to change tanks before the motor quits.
I agree with putting one in, but it does not seem absolutely necessary
to me either.
Hope this helps.
Denis (non mechanic, non expert, non kitfox, and non 235 owner)
On Feb 13, 2005, at 4:03 PM, Tinne maha wrote:
> --> AeroElectric-List message posted by: "Tinne maha"
> <tinnemaha@hotmail.com>
>
> Hello again list,
>
> I am hoping/planning to install an Ellison throttle body on my Lycoming
> O-235 powered Kitfox. I will have an electric boost pump for priming
> as
> well as for take-off and landing, but there is no engine driven pump.
> As
> planned, there will be only about 0.8 PSI of fuel pressure in the
> normal
> flight attitude (i.e. boost pump off). The Throttle body I plan to use
> requires a minimum 0.5 PSI of fuel pressure. Normally I would not be
> comfortable with this narrow a margin of error, but I will have the
> boost
> pump to use should the pressure drop and, more importantly, I know
> this has
> already been done on a nearly identical Kitfox/engine combination.
>
> The owner & the builder of that particular airplane each have
> encouraged me
> to install a fuel pressure gauge, but I'm not convinced it will add any
> benefit other than confirming my electric fuel pump is working (I
> think I
> can determine that with my ammeter during run-up.) My reasoning is as
> follows: As a 0-10 PSI gauge is the lowest range I can find, the
> 'normal'
> reading for my plane will only be 10% of the range. Thus, any change
> in the
> normal condition will almost certainly be un-detectable unless it's
> already
> too late (e.g. engine roughness or fuel starvation set in.)
>
> Any experience, comments or criticisms on this?
>
> Thanks again,
> Grant Krueger
>
>
Message 17
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
--> AeroElectric-List message posted by: "F. ILMAIN" <f_ilmain@hotmail.com>
Does anyone knows if a Garmin GPS antenna can be used with 2 receivers (a
pannel mount and a handheld for example) with a split coax cable
Thanks
Message 18
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Size of Fuse vs. Circuit Breaker - Corrected |
--> AeroElectric-List message posted by: Fiveonepw@aol.com
In a message dated 02/11/2005 10:01:40 PM Central Standard Time,
jschroeder@perigee.net writes:
We didn't get to go for barbecue
this time!!
MEGA bummer- hate when that happens...
Mark do not archive
Message 19
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: static wicks |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 05:37 PM 2/13/2005 -0700, you wrote:
>As always, your responses are detailed and helpful. Thanks again for taking
>the time to respond. I gather from your response, that for the experimental
>airplane, randomly installing static wicks on control surfaces probably
>wouldn't do as much benefit?
Just no way to tell. You have to start some place. The BIG
problem with deducing static wick effectiveness is
quantification. It's nearly impossible to duplicate both
conditions that produce the noise and very difficult to
gage magnitude of the noise. I'll ask around out at RAC
and see if I can get some first hand guidance from folks
who have done this.
In any case, if you've had a problem at some point in time
it certainly doesn't hurt to try SOMETHING. It may be
"pink elephant" repellant (haven't seen any pink elephants
around here in a long time . . . it must be working!), or
it may just do the trick. The hard part is knowing when
you've truly done a good thing. Fortunately, our customers
fly around in p-static territory with some regularity . . .
we get feedback pretty fast. If I were to task you with
a development program to optimize the wicks installation
on an RV, just how would you go about it?
Let me see what the pros have to say.
Bob . . .
Message 20
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Light Switch |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 10:50 AM 2/13/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Tinne maha" <tinnemaha@hotmail.com>
>
>Hello Bob/List,
>
>I've read Bob's shop notes about 'Switch Ratings, What's it all mean?',
>including Bob's conservative rule of thumb that the 115 Volt AC current
>rating stamped on most switches can be substituted for the 12 Volt DC
>current rating.
>
>Literature on the switch I hope/plan to use on my taxi/landing light gives a
>4 Amp rating for 30 Volts DC. Does it follow that the same switch can carry
>8 amps at 15 Volts DC?
>
>(BTW, the literature gives AC Ratings as follows: 3 amps @ 250 Volts, 6 amps
>@ 125 Volts. So, my question re-phrased is: Does this apparently linear
>relationship also apply to DC ratings?)
No . . . it's not linear. If the switch is 6A at 125 it will perform
well at 6A and 14v as well. By "well" I mean thousands of cycles.
Most switches are rated in tens of thousands of cycles at full ratings,
some as high as 50,000 cycles. Suppose DOUBLING the current through the
switch cuts your rating by 90%, how long will it take to put 1,000-5,000
cycles on any switch in your airplane?
Use whatever switch you like and don't loose any sleep over it. The
switch you use is more likely to die of old age (weather and other
environment cycles over decades) than it is to die of electrical
overstress.
I used to fly a friend's C-150 that was fitted with some really
cheesy plastic rocker switches. One night Dee and I were coming
back from Hutchinson where there's an excellent steakhouse on the
airport. The venerable ol' 150 suffered it's first known switch
failure that night . . . the DOME LIGHT switch. It was used so
seldom and at such a LOW current level, there was not enough
total activity to keep the contacts clean.
I swapped the dome light and landing light switches and everything
was still working fine several years later when he sold the airplane.
Don't get wrapped around the axle of switch ratings. They seldom
have a direct correlation for prediction of performance in owner
operated light aircraft. If this were a working airplane that flies
100 hours a MONTH in all kinds of environments as opposed to 50
hours a YEAR in nice VFR days like most lightplanes, then we might
take more notice of switch quality and ratings. But given how you're
likely to use your airplane, it's not worth the effort to be concerned.
Bob . . .
Message 21
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: 11937 Besing |
--> AeroElectric-List message posted by: "David Carter" <dcarter@datarecall.net>
Some, not all, of our 26 A-7s at Des Moines, Iowa in 1980s would have UHF
and VHF incapacitated by P static between 20 and 25,000 feet at .8 Mach in
cirrus clouds. We couldn't find any specific fixes (had lots of static
wicks already on all the planes). Depot at Tinker eventually paid a
$million bucks for a contractor to take over a hanger at Sioux City, Iowa
(also flying A-7s then) and use high voltage generatorsto induce lots of
static electricity in an airframe in the hanger.
Determined that the "rolling flow" of electrons from nose to tail was mostly
going along the exterior skin panels rather than being carried back on the
"stringers". As it flowed aft, it would jump the small air gap between
panels and make noise. When a plane was known to be a bad actor, we'd add
extra grounding straps to connect adjacent skin panels so the static elec
wouldn't jump the slight air gap between panels and make noise. Worst
thing, though, was the UHF/VHF antenna in top of vertical stab (swept) -
static flowing by those panels near the antennae were the most predictable
sources of P static. We put extra grounding straps in that area on all
planes. Problem went away - never had another writeup after going through
the fleet one time.
David
----- Original Message -----
From: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
Subject: AeroElectric-List: Re: 11937 Besing
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net>
>
> At 03:21 PM 2/13/2005 +0000, you wrote:
> >Below is the result of your inquiry. It was submitted by
> >Paul Besing (paul@kitlog.com) on Sunday, February 13, 2005 at 07:21:13
> >
> >Sunday, February 13, 2005
> >
> >Paul Besing
> >
> >,
> >Email: paul@kitlog.com
> >Comments/Questions: Bob, what are your thoughts on static wicks? There
> >has been some debate on an RV-10 list about them. Knowing your thoughts
> >on how much more reliable radios are nowadaws, I'm surprised to hear so
> >many people that want to now put them on airplanes.
>
>
> Static wicks have nothing to do with radio quality or reliability. [ but
everything to do with static electricity jumping air gaps in the airframe
The radio is fine - just picks up part of the multi-spectrum static being
produced. DCC]
Message 22
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: How do you carry the braid from a |
shielded
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
shielded
At 10:29 AM 2/13/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
>--> AeroElectric-List message posted by: "Wayne Sweet" <w_sweet@comcast.net>
>
> >Don't quite get the picture. Is this equivalent; bare the shield around the
> >circumference, letting it retain it's structure and form, then soldering a
> >bare wire around that shield's circumference and taking that wire to the
> >ground lug? >Wayne
>
>Wayne,
>
>That's a negative. Bob's published way is also....ahem....problematic. The
>right way of running a shield through a D-Sub is with a shield--not a
>pigtail. The problem can be summarized as follows (and what I say goes for
>higher frequencies, not DC):
>
>1) The shield does what it does because of its geometry. Changing its
>geometry changes its response to charges in motion. There is a very big word
>to describe this but if I told you.....well....you know!
>
> 2) Changing the impedance by pigtailing the carefully-constructed coaxial
>shield wrecks the impedance and adds a spurious antenna at frequencies
>described by the particulars of the pigtail.
>
>3) Taking care to make the coax think it's still a coax takes special care.
>
>4) Little of this was common practice before 1980, due somewhat to the
>introduction of higher frequencies but moreover DIGITAL stuff since then.
>The EMC approvals that became required simply changed common practices.
>
> From Kimmel Gerke (EMC) Associates---"....all penetrations, such as shields
>or cables, be bonded or decoupled at the point of penetration...NO PIGTAILS
>or long leads. This is a leading cause of FCC/VDE failures, with poorly
>terminated wiring acting as undesired antennas."
I've taken a Kimmel-Gerke course and yes, shielding issues are
a big deal . . . at HF frequencies and up . . . especially for
enclosures. Shielding in airframes is intended to deal with
rise-times in the microsecond world, all the faster stuff
is filtered off inside the appliances at the connectors. Shielding
is used in airplanes for the relatively slow signals allowed by
DO-160 and MIL-STD-704 for noisy devices and never for frequencies
wherein a pigtail length becomes an issue.
>"Cables and Connectors....metal connectors with a full circumferential
>termination of cable shield to connector for any cable shield that must work
>above 1 MHz...NO PIGTAILS."
>
>(Emphasis mine)
>
>The connection of conductors is barely taught in electronics classes, but
>consider---
>
> What's the difference between a 10A connector and a 100A, 1000A, or a
>million-Amp connector?
> What's the difference between a DC connector and a 10 MHz connector?
> What's the difference between a microvolt connector and a Megavolt
>connector?
> What's the difference between a gold connector and an aluminum
>connector?
>
> Well...so is there a difference between a coaxial connector and a
>pigtail?
>
>Does it matter? Maybe not. Do you have an aircraft that barely has any
>electronics and rarely strays far from the home field or rack full of stuff?
>Would like the best quality signals you can get? Do you want radio signals
>in that long dark patch between Bandahatchie and Huatabampo? Do you want to
>ask the Aeroelectric list how to quiet all the hums and buzzes in your
>intercom?
>As for the right way to terminate shielded wire---there are a myriad of
>ways. Check AMP "Braid-Pic" terminations. Or just browse thru Digikey
>section A. Or conceptually--imagine a fat ring-tongue connector. The shield
>goes into the sleeve and is soldered there. The center conductor is not
>teased out. This is not perfect but is way better than a pigtail.
>
>And there is still a lot to be said for a good twisted pair below a few GHz.
Yeah but . . . we're wrestling with victims and antagonists
here that are 100-1000 times more likely to be hosed by magnetically
or ground loop coupled noises than electro-static. I cannot recall
a single noise problem in 30 years where adding (or fixing existing
shields) was the issue. I've worked radiated issues that shielding
would not fix but lumped-constant filters did. The problem I worked
over the Xmas holidays on a Beechjet and now working on a Hawker
are magnetically coupled . . . one case involves a a wire that was
shielded trying to fix the problem! I'm also working a problem on
T-6 that is 95% sure to be ground loop coupled.
Yes, shield pigtails CAN be important but in very rare circumstances
on airplane interconnection harnesses . . . this is because of the
suggestions offered by DO-160 testing that make most of our accessories
relatively robust IRRESPECTIVE of effects of external wiring. One of
the first questions I get from a technically founded reviewer is
"did you consider ways to eliminate the need for shielded wires
you're calling out in the diagrams?" We are encouraged to minimize
the use of shielded wire for weight and labor considerations. Once
I've jumped the DO-160 hurdles, there are VERY FEW cases where
shielding is necessary or even noticeably beneficial.
Case in point . . . the wires running from strobe power supplies
are twisted trios with all outbound electrons matched by inbound
electrons. I'll bet that the shielding of that wire offers no
demonstrable benefits other than insurance against an invasion
of pink elephants . . . but yes, there is a sharp rise time
trigger pulse of 300 volts or more that runs out that wire . . .
having a shield is not a bad idea but it's certainly not going
to stand or fall on the length of a pigtail that carries it
through a connector.
I did work a relay life issue where shielding was part of root
cause of the problem. Seems that the transmission line effects
of 30' of shielded wire with a high quality, dynamic dead short
at the far end (filter capacitor) was exacerbating the tendency
of perfectly good relay contact to stick. Simply opening the shield
grounds cause relay life to jump 10x or so. I'll send you the report
on this if you'd like to see it . . . this was a situation that
cost us a ton of dollars and was based on a design issue that's
never considered when it comes to deciding whether or not a wire
should be shielded.
I'm not trying to say that shield pigtails never make a difference
but in the aircraft world, they're not an issue. Remember
that the guys at K-G work the whole spectrum of RFI/EMI issues
where the vast majority of their clients are consumer products
customers. DO-160 conducted emissions and susceptibility requirements
reduce wire shielding to a very low order of probability for noise
issues and we NEVER depend on wire shielding for performance at
RF.
Bob . . .
Message 23
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | paranormal resistance |
--> AeroElectric-List message posted by: sarg314 <sarg314@comcast.net>
Here's one for electric Bob: This is not really relevant to building a
plane, but I observed something when making my battery cable that I
cannot explain. I used Bob's method for soldering lugs onto a #02 cable
using a propane torch. The soldering went as expected. Maybe 20
seconds after I was finished, with the cable still pretty hot, I used my
multi-meter to measure the resistance of the cable. I have no sensible
reason for doing this. The odd thing is that the resistance showed as 3
ohms. As the minutes went by the indicated resistance dropped
steadily. The meter is a Fluke model 11 and seems to have an accuracy
of about 0.1 ohm at the low end of the scale. After the cable was just
warm to the touch - probably 80 or 90 deg. F - it still showed 1 ohm,
which is 1000 times too much. The resistance continued to drop over the
next 5 or 10 minutes until it got down to 0.1 ohm which, I think is as
good as 0 with this meter. That's what it usually shows when you short
its leads together.
Elevated temperature will increase the resistance of a wire, but the
resistance was significantly different from 0 when the cable appeared to
be nearly at room temperature. Further, I made 2 cables and they both
showed the same effect.
Could it be some thermocouple effect that is confusing the resistance
measuring circuit in the meter? I did noticed that it demonstrated
polarity, which points to something like that. That is, if it was
indicating 0.8 ohms and I reversed the leads, it would then indicate
-0.8 ohms. Negative resistance indicates the meter was pretty
confused. Any ideas what was going on here?
--
Tom Sargent, RV-6A, engine.
Message 24
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: 11937 Besing |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 09:43 PM 2/13/2005 -0600, you wrote:
>--> AeroElectric-List message posted by: "David Carter"
><dcarter@datarecall.net>
>
>Some, not all, of our 26 A-7s at Des Moines, Iowa in 1980s would have UHF
>and VHF incapacitated by P static between 20 and 25,000 feet at .8 Mach in
>cirrus clouds. We couldn't find any specific fixes (had lots of static
>wicks already on all the planes). Depot at Tinker eventually paid a
>$million bucks for a contractor to take over a hanger at Sioux City, Iowa
>(also flying A-7s then) and use high voltage generatorsto induce lots of
>static electricity in an airframe in the hanger.
>
>Determined that the "rolling flow" of electrons from nose to tail was mostly
>going along the exterior skin panels rather than being carried back on the
>"stringers". As it flowed aft, it would jump the small air gap between
>panels and make noise. When a plane was known to be a bad actor, we'd add
>extra grounding straps to connect adjacent skin panels so the static elec
>wouldn't jump the slight air gap between panels and make noise. Worst
>thing, though, was the UHF/VHF antenna in top of vertical stab (swept) -
>static flowing by those panels near the antennae were the most predictable
>sources of P static. We put extra grounding straps in that area on all
>planes. Problem went away - never had another writeup after going through
>the fleet one time.
>
>David
Excellent anecdote sir. I appreciate it. This perfectly
underscores the nefarious nature of p-static.
Bob . . .
Message 25
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
--> AeroElectric-List message posted by: TimRhod@aol.com
Bob: I am using duel light speed electronic ignitions. One I am running
off of a battery fuse block with a 5 amp fuse. The second I want to run off a
second battery using a fuse llnk as described in your book. The wire run is
a 20AWG which I understand would normally be linked with a 24AWG. This is
rated for only 3 amps though. I need a 5 amp protection. Can I fuselink a
20AWG with a 22AWG? I dont really want to change the wire run to 18AWG which
you recomend in your book to fuse link with 22AWG If not what about an in
line fuse of 5Amp? Thanks Tim
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|