Today's Message Index:
----------------------
1. 04:28 AM - (bob noffs)
2. 04:28 AM - Re: Re: Why are wire strands tinned ? (Ken)
3. 05:57 AM - Re: (Robert L. Nuckolls, III)
4. 08:34 AM - Re: capacitor and music jack help needed (Eric M. Jones)
5. 08:34 AM - Re: (Roger Evenson)
6. 09:00 AM - Vacuum pad alternator options for Rotax (Jon Goguen)
7. 09:17 AM - Re: Vacuum pad alternator options for Rotax (Bill Denton)
8. 10:47 AM - Re: Vacuum pad alternator options for Rotax (Jon Goguen)
9. 11:28 AM - Re: XCOM 760 (Eric M. Jones)
10. 11:31 AM - 5vDC Power Supply... (Greg Campbell)
11. 01:53 PM - New to List (Will N. Stevenson)
12. 02:18 PM - Re: Xcom 760 Redux (Eric M. Jones)
13. 03:32 PM - Re: Re: Xcom 760 Redux (Matt Prather)
14. 04:16 PM - Re: (Robert L. Nuckolls, III)
15. 04:21 PM - Re: Re: capacitor and music jack help needed (Robert L. Nuckolls, III)
16. 04:22 PM - Re: New to List (Eric M. Jones)
17. 04:25 PM - Re: Re: XCOM 760 (Robert L. Nuckolls, III)
18. 07:05 PM - Re: New to List (rv-9a-online)
19. 08:50 PM - Fox tails anyone? (Robert L. Nuckolls, III)
Message 1
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--> AeroElectric-List message posted by: "bob noffs" <icubob@newnorth.net>
hi bob, can i benefit from using your audio isolation amp board with just a transceiver
and headsets[ no music system]
bob noffs, woodruff, wi
Message 2
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Subject: | Re: Why are wire strands tinned ? |
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
As someone who has occasionally worked on 10+ year old cars in the
rust/salt belt, I would agree that there should be a "special place" for
manufacturers who install untinned wire in automobiles as well. I've
seen every strand badly corroded for the entire length of the wire.
Presumably moisture wicks its way many feet up the wires.
Ken
>An airplane is typically in a much more benign environment unless it is
>based near salt water. Nonetheless, I think tinned wire is a real good
>idea.
>
>
Message 3
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 06:23 AM 10/3/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: "bob noffs" <icubob@newnorth.net>
>
>hi bob, can i benefit from using your audio isolation amp board with just
>a transceiver and headsets[ no music system]
> bob noffs, woodruff, wi
Very simple audio systems are illustrated in Chapter 18:
http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf
. . . specifically in Figure 18-7 and associated text.
An airplane with one or two sources of audio does not
benefit from an isolation amplifier.
Bob . . .
Message 4
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Subject: | Re: capacitor and music jack help needed |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: luckymacy@comcast.net (lucky)
>What if I just got something like the one at
>http://www.sphere.bc.ca/test/inductors.html
>Fair Rite Snap-It RFI Ferrite Suppressors....Fits wires/bundles up to
>10mm/0.390
>inch in diameter, easily opens and snaps shut, fantastic for quenching
>EMI/RFI
>emissions from already existing equipment, power cords, cables, and
>connections.
>Type 0443167251, approx. 225 ohms impedance at 100Mhz, very efficient and
>inexpensive emission solution.
>Seems like it would be easy to install and remove if it didn't work.
>Lucky
Lucky,
It won't do anything for you. The snap-on ferrites are good for very high
frequencies only--like MegaHertz and GigaHertz. We need a "Very Low Pass
Filter"
The thing we need for kiloHertz noise is an inductor that is a substantial
physical size and in the milliHenry range. The capacitors we need are also
much smaller than 22kuF. There are a zillion prescriptions for noise
filters. Radio Shack used to carry suitable chokes. But the choices are
slimmer now. If you know a little about the subject you can design filters
with many available online calculators like the excellent free one from
www.nuhertz.com . The newest noise filters are "active" filters, which means
they have electronics that vary the filter response as needed.
I recommend getting noise filters from J.C. Whitney or Crutchfield or any
big car-audio place. They have good ones for short money. Just Google "noise
filters".
Remember-- you are way ahead if you stop the noise at the source. My
airplane will have a high current B+ noise filter near the alternator, and
one or more low current devices on the "avionics bus" or associated with
radios and intercoms wirings.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
(508) 764-2072
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
--Leonard Cohen
Message 5
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--> AeroElectric-List message posted by: "Roger Evenson" <revenson@comcast.net>
How about three sources of audio? Will three sources work with resistors
only and no isolation amp?
----- Original Message -----
From: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
Subject: Re: AeroElectric-List:
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> <nuckollsr@cox.net>
>
> At 06:23 AM 10/3/2005 -0500, you wrote:
>
>>--> AeroElectric-List message posted by: "bob noffs" <icubob@newnorth.net>
>>
>>hi bob, can i benefit from using your audio isolation amp board with just
>>a transceiver and headsets[ no music system]
>> bob noffs, woodruff, wi
>
>
> Very simple audio systems are illustrated in Chapter 18:
>
> http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf
>
> . . . specifically in Figure 18-7 and associated text.
> An airplane with one or two sources of audio does not
> benefit from an isolation amplifier.
>
> Bob . . .
>
>
>
Message 6
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Subject: | Vacuum pad alternator options for Rotax |
--> AeroElectric-List message posted by: Jon Goguen <jon.goguen@umassmed.edu>
Does anyone have experience with the modified Densei alternators that
mount on the vacuum pad of Rotax engines (esp. 912S) and are sold by
Flight Crafters, Lockwood aviation, and perhaps some others? As I
understand it, these are essentially standard automotive devices with
internal regulation mechanically modified to fit the vacuum pad. I'm
particularly interested in their current capability. I'm told by the
vendors that they'll provide 40 amps at 2800 rpm, a speed compatible
with the 912S vacuum pad rpm in cruise. I had originally intended to
use the B&C Systems SD20, but--as pointed out to me by Paul Wilson on
the list and confirmed by B&C--the output of the SD20 is only 12 amps
due to the low rpm at the pad. Lockwood says the Densei alternative is
especially popular in Europas. Anyone know how well these things work
in real life?
Thanks!
Jon
Jon Goguen
jon.goguen@umassmed.edu
Central Massachusetts
Kitfox Series V Rotax 912S / N456JG (reserved)
Complete except for electrics and avionics
Message 7
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Subject: | Vacuum pad alternator options for Rotax |
--> AeroElectric-List message posted by: "Bill Denton" <bdenton@bdenton.com>
Rotax also offers an external alternator for the 912; part number: 887254.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Jon
Goguen
Subject: AeroElectric-List: Vacuum pad alternator options for Rotax
--> AeroElectric-List message posted by: Jon Goguen
<jon.goguen@umassmed.edu>
Does anyone have experience with the modified Densei alternators that
mount on the vacuum pad of Rotax engines (esp. 912S) and are sold by
Flight Crafters, Lockwood aviation, and perhaps some others? As I
understand it, these are essentially standard automotive devices with
internal regulation mechanically modified to fit the vacuum pad. I'm
particularly interested in their current capability. I'm told by the
vendors that they'll provide 40 amps at 2800 rpm, a speed compatible
with the 912S vacuum pad rpm in cruise. I had originally intended to
use the B&C Systems SD20, but--as pointed out to me by Paul Wilson on
the list and confirmed by B&C--the output of the SD20 is only 12 amps
due to the low rpm at the pad. Lockwood says the Densei alternative is
especially popular in Europas. Anyone know how well these things work
in real life?
Thanks!
Jon
Jon Goguen
jon.goguen@umassmed.edu
Central Massachusetts
Kitfox Series V Rotax 912S / N456JG (reserved)
Complete except for electrics and avionics
Message 8
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Subject: | Re: Vacuum pad alternator options for Rotax |
--> AeroElectric-List message posted by: Jon Goguen <jon.goguen@umassmed.edu>
Bill,
Thanks. Unfortunately, that option doesn't fit under the cowl without
a lot of modification.
Regards,
Jon
Jon D. Goguen, Ph. D.
Department of Molecular Genetics and Microbiology
University of Massachusetts Medical School
55 Lake Avenue North
Worcester, MA 01655
Phone 508.856.2490
Fax 508.856.5920
On Oct 3, 2005, at 12:16 PM, Bill Denton wrote:
> --> AeroElectric-List message posted by: "Bill Denton"
> <bdenton@bdenton.com>
>
> Rotax also offers an external alternator for the 912; part number:
> 887254.
>
>
> -----Original Message-----
> From: owner-aeroelectric-list-server@matronics.com
> [mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Jon
> Goguen
> To: aeroelectric-list@matronics.com
> Subject: AeroElectric-List: Vacuum pad alternator options for Rotax
>
>
> --> AeroElectric-List message posted by: Jon Goguen
> <jon.goguen@umassmed.edu>
>
> Does anyone have experience with the modified Densei alternators that
> mount on the vacuum pad of Rotax engines (esp. 912S) and are sold by
> Flight Crafters, Lockwood aviation, and perhaps some others? As I
> understand it, these are essentially standard automotive devices with
> internal regulation mechanically modified to fit the vacuum pad. I'm
> particularly interested in their current capability. I'm told by the
> vendors that they'll provide 40 amps at 2800 rpm, a speed compatible
> with the 912S vacuum pad rpm in cruise. I had originally intended to
> use the B&C Systems SD20, but--as pointed out to me by Paul Wilson on
> the list and confirmed by B&C--the output of the SD20 is only 12 amps
> due to the low rpm at the pad. Lockwood says the Densei alternative is
> especially popular in Europas. Anyone know how well these things work
> in real life?
>
> Thanks!
>
> Jon
>
> Jon Goguen
> jon.goguen@umassmed.edu
> Central Massachusetts
> Kitfox Series V Rotax 912S / N456JG (reserved)
> Complete except for electrics and avionics
>
>
Message 9
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--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
(do not archive)
XCOM has refused to send me schematic of the power input section of the XCOM
760 radio.
What are they hiding???
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
(508) 764-2072
Message 10
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Subject: | 5vDC Power Supply... |
--> AeroElectric-List message posted by: "Greg Campbell" <GregCampbellUSA@comcast.net>
Hi,
I'm going to wire in a Garmin GPS 18 5Hz backup GPS receiver to my EFIS.
http://www.garmin.com/products/gps185hz/
and it requires 4.0 to 5.5 vdc input, drawing 65 mA @ 5vdc.
http://www.garmin.com/products/gps185hz/spec.html
For initial testing, I'm using 4 AA NiCd's (in series, 4.8vDC) rated at 2300mAh
each.
This is fine as long as I remember to charge them up, and turn the GPS off
between uses. (It's just a backup GPS Input for the EFIS & Autopilot).
For the final installation, I'd like to power it off 12vdc Ships Power.
I bought a 5vDC "Fixed Voltage Regulator" that supplies up to 1 Amp.
http://www.radioshack.com/product.asp?catalog%5FnameCTLG&product%5Fid276-1770
The one I got didn't have any instructions, and there is no spec sheet at www.RadioShack.com
Do these typically require external resistors? Heat sinks? etc ?
Any advice on wiring up the voltage regulator?
Then, to make things a bit fancier - I was hoping to run it from Ships Power
AND have a small AA or AAA battery backup pack for the GPS receiver.
The "ideal" battery backup system would:
1) Automatically charge up the NiCd's whenever the ship's power is ON
2) Not "overcharge" the NiCds or charge them at more than about 0.8 Amps.
3) Automatically power the GPS from the NiCds whenever the 5vDC power is "lost"
4) Automatically shut off the GPS after 6 to 8 hours so the NiCds don't drain completely.
Any advice on wiring up a simple and elegant backup battery?
Thanks in advance,
Greg
Message 11
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--> AeroElectric-List message posted by: "Will N. Stevenson" <will@wavecable.com>
Eric,
I'm new on this list and am overjoyed to find both you and Bob as sources of
future advice. I am building an experimental plane and plan on using your
Fatwire to move my battery aft in order to eliminate the tailcone ballast
weight req'd when the battery is hung in its usual place on the firewall. I
bought a copy of Bob's Aeroelectric Connection and have begun the journey to
electrical literacy, so that I can install an all-electric panel in the
aircraft myself.
You mentioned "My airplane will have.......,etc." --I wanted to ask
you--what plane are you interested in or building? Also, can you recommend
any reading for a person who wants to self-teach avionics and aircraft
electrical stuff other than Bob's book? I already have a good background in
basic automotive electrical troubleshooting but want to go further.
Thanks,
Will
> My airplane will have a high current B+ noise filter near the alternator,
> and
> one or more low current devices on the "avionics bus" or associated with
> radios and intercoms wirings.
> Regards,
> Eric M. Jones
> www.PerihelionDesign.com
Message 12
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Subject: | Re: Xcom 760 Redux |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
(do not archive)
Naw..shucks....the very nice people at XCOM came around and sent me their schematic.
I really appreciate it and give them a gold star for their service.
The internal design of the device is first rate. Ken Luxford disclosed an important
point:
XCOM writes---
There seems to be some confusion regarding the requirement for the 22kuF capacitor.
This is a Rotax requirement and NOT necessarily a requirement for the XCOM.
We have seen multiple Rotax installations here which have not had the recommended(
by Rotax) 22kuF capacitor fitted. The Rotax regulator appears to be quite
noisy without it. In some circumstances we have also seen cases where high
current strobes and similar have caused some fairly nasty transients on the
supply. In these cases, a fairly large capacitor on the supply line can be advantageous.
Regards
Ken Luxford
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
(508) 764-2072
"Hey, it ain'tt rocket surgery!"
--anonymous
Message 13
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Subject: | Re: Xcom 760 Redux |
--> AeroElectric-List message posted by: "Matt Prather" <mprather@spro.net>
This makes perfect sense and completes the picture. Thanks for bugging
them about this Eric.
Regards,
Matt-
> --> AeroElectric-List message posted by: "Eric M. Jones"
> <emjones@charter.net>
>
> (do not archive)
>
> Naw..shucks....the very nice people at XCOM came around and sent me
> their schematic. I really appreciate it and give them a gold star for
> their service.
>
> The internal design of the device is first rate. Ken Luxford disclosed
> an important point:
>
> XCOM writes---
>
> There seems to be some confusion regarding the requirement for the 22kuF
> capacitor. This is a Rotax requirement and NOT necessarily a requirement
> for the XCOM. We have seen multiple Rotax installations here which have
> not had the recommended( by Rotax) 22kuF capacitor fitted. The Rotax
> regulator appears to be quite noisy without it. In some circumstances
> we have also seen cases where high current strobes and similar have
> caused some fairly nasty transients on the supply. In these cases, a
> fairly large capacitor on the supply line can be advantageous.
>
> Regards
> Ken Luxford
>
> Regards,
> Eric M. Jones
> www.PerihelionDesign.com
> 113 Brentwood Drive
> Southbridge MA 01550-2705
> (508) 764-2072
>
> "Hey, it ain'tt rocket surgery!"
> --anonymous
>
>
Message 14
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 08:33 AM 10/3/2005 -0700, you wrote:
>--> AeroElectric-List message posted by: "Roger Evenson"
><revenson@comcast.net>
>
>How about three sources of audio? Will three sources work with resistors
>only and no isolation amp?
Probably. Try it and see. You can always add the iso-amp
later if the resistor-mix method doesn't work for you.
Bob . . .
Message 15
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Subject: | Re: capacitor and music jack help needed |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 11:46 AM 10/2/2005 -0600, you wrote:
>--> AeroElectric-List message posted by: "Matt Prather" <mprather@spro.net>
>
>The thing that is slightly frustrating about this whole discussion is that
>when you buy the XCOM (or whatever else), presumably you are buying a comm
>transceiver that is designed to be installed in an aircraft. And that it
>will be wired into the aircraft power buss. Why the heck wasn't the radio
>designed to perform correctly in that environment (without adding
>additional "stuff")??
I'm pretty certain that the XCOM (like it's predecessor in the market -
Microair 760) will work just fine on typical light aircraft bus fed by
an automotive alternator. Many ultra-light owners like these tiny
radios too and they're almost always fitted with PM alternators that
are NOISY without additional filtering.
Check the instructions carefully, is the large cap ALWAYS recommended
or a suggested solution in case you do have noise? Unless you're flying
behind a Rotax, you won't need the cap. If you are flying a PM alternator,
then I presume one will begin with one of the appropriate Z-figures where
this capacitor is always included. The XCOM is not the only accessory that
will appreciate the presence of the extra filtering.
Bob . . .
Message 16
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--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "Will N. Stevenson"
<will@wavecable.com>
>Eric,
>I'm new on this list and am overjoyed to find both you and Bob as sources
>of
>future advice. I am building an experimental plane and plan on using your
>Fatwire to move my battery aft in order to eliminate the tailcone ballast
>weight req'd when the battery is hung in its usual place on the firewall.
>I
>bought a copy of Bob's Aeroelectric Connection and have begun the journey
>to
>electrical literacy, so that I can install an all-electric panel in the
>aircraft myself.
>You mentioned "My airplane will have.......,etc." --I wanted to ask
>you--what plane are you interested in or building? Also, can you recommend
>any reading for a person who wants to self-teach avionics and aircraft
>electrical stuff other than Bob's book? I already have a good background
>in
>basic automotive electrical troubleshooting but want to go further. Thanks,
>Will
Welcome Will,
I am building Glastar N5EJ with a Sube 2.5L and I intend to finish it this
century. Starting a business has taken funds and time from the building.
You didn't say what you're building. (?)
(do not archive)
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
(508) 764-2072
"The man who carries a cat by the tail learns something that can be learned
in no other way."
- Mark Twain
Message 17
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 02:27 PM 10/3/2005 -0400, you wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
>(do not archive)
>
>XCOM has refused to send me schematic of the power input section of the XCOM
>760 radio.
>
>What are they hiding???
King, Narco, and most other folks wont send them out either. If you're
an authorized service station and pay money for service manuals, you
get all the schematics. They're not "hiding" anything, just complying with
what has been an industry practice since day-one. I work for a BIG user
of products from the major suppliers and I don't get schematics without a
lot of bother (I go to their local service shop and borrow them to copy).
Bob . . .
Message 18
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--> AeroElectric-List message posted by: rv-9a-online <rv-9a-online@telus.net>
Will:
There is a series of presentations on aircraft electrical system design
at http://b4.ca/raa_85/story/index.html .
These presentation were designed for the non-EE types who have to build
or maintain their own aircraft. They are not the definitive training
course, but may be of use as an introduction in conjuction with Bob's
book (which is referenced along with some other publications).
Vern Little
-9A in the paint shop.
Will N. Stevenson wrote:
>--> AeroElectric-List message posted by: "Will N. Stevenson" <will@wavecable.com>
>
>Eric,
>I'm new on this list and am overjoyed to find both you and Bob as sources of
>future advice. I am building an experimental plane and plan on using your
>Fatwire to move my battery aft in order to eliminate the tailcone ballast
>weight req'd when the battery is hung in its usual place on the firewall. I
>bought a copy of Bob's Aeroelectric Connection and have begun the journey to
>electrical literacy, so that I can install an all-electric panel in the
>aircraft myself.
>
>You mentioned "My airplane will have.......,etc." --I wanted to ask
>you--what plane are you interested in or building? Also, can you recommend
>any reading for a person who wants to self-teach avionics and aircraft
>electrical stuff other than Bob's book? I already have a good background in
>basic automotive electrical troubleshooting but want to go further.
>
>Thanks,
>Will
>
>
>
>
>>My airplane will have a high current B+ noise filter near the alternator,
>>and
>>one or more low current devices on the "avionics bus" or associated with
>>radios and intercoms wirings.
>>
>>
>
>
>
>>Regards,
>>Eric M. Jones
>>www.PerihelionDesign.com
>>
>>
>
>
>
>
Message 19
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Subject: | Fox tails anyone? |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
> > My airplane will have a high current B+ noise filter near the alternator,
> > and one or more low current devices on the "avionics bus" or associated
> with
> > radios and intercoms wirings.
A few weeks ago, we had some discussions about the value
of applying certain prophylactic measures to the installation
of devices in light aircraft with the notion that the
additions were of some value in standing off spikes and
noises (their intended purpose) and that a generous sprinkling
of these devices about the system (while not harmful) were
recommended just to make sure the offending stimulus, should
it manifest itself, would be managed with dispatch and aplomb.
In the very early days of publishing the 'Connection, a Longez
builder called me one evening to explain that, "I've wired the
whole airplane with shielded wire. I filtered the fuel pumps,
alternator, mags and defog blower. What else do I need? I was
taken aback by his story and asked, "Gee, I don't know. What
kind of a noise problem do you have?" "Oh, no problem", replies
he, "I haven't flown the airplane yet but I'm just trying to be
sure that noise isn't going to be a problem."
Similarly, I've noted that certain purveyors of quick-install
bus and switch products are fond of citing extra noise filters
and/or spike catchers as built in features worthy of elevating
their product's return on investment.
Just for grins, I went out to the driveway with trusty 'scope
and took this picture off the cigar lighter in my '95 Safari
with a 90A alternator, all loads turned on, engine over 2000
RPM so that the bus voltage was over 14.0 volts:
http://www.aeroelectric.com/Pictures/Safari_Bus_Noise_1.gif
Note that the major noise components are bounded by pk-pk
excursions on the order of 300 millivolts. There were some
narrow, higher voltage transients which I expanded out in
this picture:
http://www.aeroelectric.com/Pictures/Safari_Bus_Noise_2.gif
Hmmm . . . about a millisecond wide and excursions on the
order of 600-800 millivolts. Interestingly enough, the
general appearance of these noises did not seem to be affected
much by what was turned on or by engine RPM. It was difficult
to see what I hoped to identify as alternator ripple . . .
typically 1.5 volts peak-to-peak from an unfiltered
3-phase rectifier.
The reason that these noise are so small is because the
system is already fitted with a very effective filter called
a BATTERY. In the spam can business, we tell prospective
suppliers of electro-whizzies to EXPECT and be TOLERANT
of noises as described in:
http://www.aeroelectric.com/Pictures/MSTD704_28V_Noise.jpg
This is for a 28v system, we're working with a 14v system
so the values are cut in half. In the frequency range of
1000 to 8000 Hz, expect noises in a 14v system of 0.5 vrms
or 1.5 v pk-pk. Outside this band, the energy of expected
noises falls off at 10 to 40 db per decade.
At first blush, my '95 Safari's electrical system complies
with the spirit and intent of Mil-Std-704 for allowable noise.
In fact, it's much quieter. I can tell you that unless the
battery is VERY soggy, light aircraft with automotive
alternators have similar noise energies.
Now, let's consider a conversation of a few hours ago wherein
a builder was understandably miffed by the need to add
external noise filtering in the form a hefty capacitor
as recommended by the radio's manufacturer. I suggested
that this requirement made sense for small aircraft with
single-phase, PM alternators where the rectified output
was VERY trashy. Most accessories would benefit from
having the large capacitor added to the battery in terms
of overall system noise reduction. Indeed, this capacitor
was shown in all Z-figures illustrating PM alternator
installations.
I'm quite certain that makers of the XCOM (along with
the vast majority of professional suppliers to industries
featuring DC powered vehicles) fully understand the nature
of the world they're expected to live in as do all of RACs
suppliers by specification. The idea that there is benefit
to adding extra filtering . . . just for good measure . . .
does not drive toward the elegant solution. It drives up
parts count concentrated in the supply line to a suite of
accessories and probably adds no operational value except
to accommodate poorly designed products that need the extra
filtering. In the later case, it's more prudent to add
needed filtering to that one system only so as to avoid
adding unnecessary complexity in series with systems that
never needed extra filtering in the first place.
I recall a crusty ol' mechanic I worked beside in one
of my earliest jobs in two-way radio. He had a fox-tail
on his car's radio antenna. He called it his "go fast
ornament". When I inquired about its title, he offered
that once the fox tail was added to the antenna, it could
be observed increase the speed of his car. Since the antenna
laid back so much further the car was obviously going faster.
The siren song of gee-whiz features is seductive. Folks
at OSH sell all kinds of products with ad hype bolstered
by claims having no or poor foundations in practice or
physics. Any time a claimed feature increases parts
count without adding operational value, the elegance of design
is degraded. Additionally weight, volume, and cost of ownership
go up.
We have lots of filters and fixes applied to various
systems and devices in our production aircraft . . . all
of which are incorporated to mitigate a known performance
problem. We work up to the boundaries of DO160/MS704
but no further. This judicial application of remedy
in response to real problems avoids unnecessary and
reliability reducing over-design. It also avoids addition
of no-value-added "go fast" features.
One's risk of encountering a noise problem after good practice
for grounding and manufacturer's recommendations for shielding.
Any residual noise problems will be relatively easy to find
and fix and will probably demonstrate a design flaw that the
"fox-tail" wouldn't have helped with anyhow.
Bob . . .
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