Today's Message Index:
----------------------
1. 05:56 AM - Re: Capacitor for Z-13/8 (Robert L. Nuckolls, III)
2. 06:02 AM - Re: External Power and electrical system (Robert L. Nuckolls, III)
3. 07:09 AM - Re: Ammeter Shunt (Speedy11@aol.com)
4. 07:13 AM - Re: Re: Grounding lugs and transponder radiation (Brian Lloyd)
5. 07:39 AM - Re: Re: Ammeter Shunt (Ralph E. Capen)
6. 08:16 AM - Mic audio ground - PMA8000B (John Tvedte)
7. 11:28 AM - Re: Re: Ammeter Shunt (Brian Lloyd)
8. 11:28 AM - Re: Mic audio ground - PMA8000B (Brian Lloyd)
9. 11:39 AM - Re: Re: Ammeter Shunt (Brian Lloyd)
10. 11:51 AM - building a hall-effect ammeter (Brian Lloyd)
11. 12:06 PM - FW Bell RSS-100-A hall effect sensor (Brian Meyette)
12. 12:22 PM - Re: building a hall-effect ammeter (Dale Ensing)
Message 1
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| Subject: | Re: Capacitor for Z-13/8 |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 10:28 PM 7/13/2006 -0400, you wrote:
>Where can I purchase the capacitor (20-50KuFd) called out in Z13/8? I
>cannot find it on the B&C site and wondered if the automotive variety
>would work?
>
>TIA
>
>Bret Smith
>RV-9A (91314)
>Mineral Bluff, GA
>www.FlightInnovations.com
B & C has a kit that includes all of the SD-8 filter, control
and ov protection parts cited in the drawing. You can give
them a call and see what the thing costs. I wasn't able to find
it quickly on their website either and don't have the time right
now.
If you just want the capacitor, check out Digikey
http://dkc3.digikey.com/PDF/T062/1099.pdf
The P10078 22KuF/40V is a good part for the task.
Also, look at 95F4431 at http://newark.com
This is a smaller diameter and much less expensive
part that would also do nicely.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
Message 2
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| Subject: | Re: External Power and electrical system |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 09:47 PM 7/13/2006 +0200, you wrote:
>--> AeroElectric-List message posted by: =?iso-8859-1?Q?Mich=E8le_MS?=
><michele.delsol@microsigma.fr>
>
>Listers,
>
>I have been planning on adding external power to my system (one alternator,
>one battery, PMag IO360). My original design was pretty simple, hook it
>straight onto the battery such as one does when jump starting a car.
That works.
> Then I
>added a relay so that the external power terminals would not be hot when not
>connected to external power.
What is the added value? What risks are mitigated by this?
Is your external power INTENDED to crank an engine with a
compromised battery . . . or just to run electro-whizzies on
the ground, or just charge a battery, or just maintain a battery?
Settling on one of these design goals drives the size of your
hardware ranging from a tiny wall-wart charger and 24AWG connecting
leads up to 2AWG welding cable plugged in through a very fat connecto.
>Then some knowledgeable fellow builders told me
>that I should only use external power for starting the engine nothing
>else.
If that was their design goal, that's correct. What's your design
goal?
> Then some other knowledgeable builders told me that I could install a
>cigar lighter jack in parallel as an external power connector for recharging
>the battery.
Yup, that's another achievable design goal . . .
> Then there was the issue as to external power not being clean
>DC current and consequently liable to play havoc with some of my sensitive
>equipment.
If you have a battery on the bus any time ground power is
applied, then externally conducted noises are not an issue.
The battery is the airplane's best firewall against any and
all perturbations of bus voltage.
>Based on this I proceeded to design a circuit which would
>automatically disconnect all electricals except for the starter solenoid,
>current to the PMags and current to my fuel pump. Whereupon another
>knowledgeable person suggested that I should remember the KISS principle I
>may be over designing my system.
Again, depends on your design goals. What do YOU want this
ground power system to do for you?
>What do you guys suggest isolate my electrical system when external power
>is hot or just hook it up onto the battery via a relay?
Start with the article at:
http://aeroelectric.com/articles/grndpwr.pdf
This is typical of ground power jacks installed on
type certificated aircraft with a few AEC enhancements
added as described in the text.
This installation may be used for just about every purpose
other than battery maintenance because you need to close
a contactor to get connection between external power and
the battery.
Let's start with what you want the connection to do and
then tailor it to that task. Most of what you were told
is inaccurate and/or incomplete.
Bob . . .
Message 3
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| Subject: | Re: Ammeter Shunt |
Brian,
I'm one of those ignorant pilots who believes that an ammeter can provide
useful information while in flight, so I intend to install one along with a
voltmeter. I'm crafting my electrical system to do what I want it to do.
Do you, or anyone, know of one that is a digital center-zero meter? How
about a combo digital ammeter-voltmeter?
I plan to use hall effect devices and I'm going to mount them in at least
three places in the electrical system. I also plan to sample the voltage at the
same locations in the electrical system. I'm still deciding where those
locations will be, but they will likely be on the alternator lead, at the main
battery and at the standby battery. Other potential locations are the main bus
and the standby bus. I plan to route the sensor wires to a rotary selector
switch so as to be able to view any of the sensor locations on a single ammeter
and voltmeter. Too much effort and expense for little or no gain? Perhaps, but
it's the way I want it.
I believe that by using HE devices instead of shunts I would not have to
worry about making the shunt beefy enough to handle the starting loads. Is there
any advantage to using a shunt that I'm overlooking?
Has anyone found a good source for donut HE devices?
Thanks,
Stan Sutterfield
www.rv-8a.net
1. You can put one in series with any source of power (alternator,
generator, dynamo) and find out how much current it is delivering.
2. You can put one in series with a battery and see either its
charging current or loads when the charging current is insufficient
to carry all the loads (as in when the alternator is turning too
slowly or is off-line).
3. You can put one in series with a load or loads and see how much
current that device or devices demand from the system.
If you change the path so that the current no longer travels through
the shunt then you won't get any reading. Heck, you can put the shunt
permanently in the path to the battery so it always shows battery
current, even starting current. Then you can always see what is going
into and coming out of your battery. Just make sure your shunt is
beefy enough to handle the starting currents.
The above is true regardless of the number of alternators or
batteries in your system.
Bob makes a point that all this discussion is so you can craft your
electrical system to do what YOU want it to do. You may have
different reasons to measure current than Bob or I do. Bob doesn't
like the center-zero battery ammeter and I understand that. I have
developed new respect for this instrument in applications where one
will be running from battery power.
Here is another way of looking at it. If you have two sources of
power (alternators/dynamos) you are never going to be running your
loads off your battery. It is only needed to start the airplane. The
center-zero battery ammeter is almost useless in that system. OTOH if
you have a single alternator system and will depend on the battery to
get you to your destination should the alternator fail, you might
want to know what the loads are so you can estimate remaining battery
capacity. Now the center-zero ammeter is useful.
I have a boat with a 1000AH battery bank. That battery bank provides
all of the boat's power when I am at sea. I have to periodically
recharge it. I want to know how much capacity I have consumed so I
know how much is left and I want to know when it is fully charged. In
this application the battery ammeter/shunt is critical. No other tool
will suffice.
Message 4
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| Subject: | Re: Grounding lugs and transponder radiation |
--> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
On Jul 13, 2006, at 6:50 PM, europa flugzeug fabrik wrote:
> --> AeroElectric-List message posted by: "europa flugzeug fabrik"
> <n3eu@comcast.net>
>
>
> brian wrote:
>> ...If your transponder puts out a peak power of 200W we have:
>>
>> 200 = V^2 / 2000
>>
>> If we do the algebra we get:
>>
>> V = sqrt (200 * 2000) or 632V....
>>
>>
>
> That could be for what I know, but I thought we worked on 50 ohms
> by fiat. I have a musty, ancient xponder service manual I eBayd
> cheap for maybe giggles. To measure power, they had you kludge a
> commercial voltage detector together with a special diode, IN23B.
> Then you observed reply pulse trains on any whatever scope and
> counted P-P volts by graticule divisions. Volts squared, divided by
> 50 (into a dummy 50-ohm load) and thems peak watts. So only 100V
> P-P would work out to 200W.
You are correct for measuring the power at the output of a
transponder as the impedance there is 50 ohms. But we were not
talking about the impedance at the output of the transponder or of
the feedline. We were talking about the voltage at the tip of the
antenna.
The impedance of an antenna changes depending on where you feed it.
In a quarter-wave monopole (a "whip" antenna) the feedpoint impedance
at the base (the part nearest the ground plane) is something close to
50 ohms. (It is actually 36 ohms but that is close enough for
government work.) The impedance at the other end, where the little
ball is, is around 2000 ohms. The current in the conductor is at a
maximum near the base and a minimum at the end. Conversely the
voltage is at a minimum near the base and at a maximum near the free
end. If you consider the impedance to be the ratio of voltage to
current you can see that the impedance is constantly changing along
the shaft of the antenna. (This RF stuff is *WAY* different from the
DC stuff as voltage and current vary along a conductor or antenna
unlike DC were they stay the same.)
BTW, your comment about peak voltage caught a mistake of mine in that
I did my calculations in RMS volts when I should have done the
calculations in peak volts (RMS volts X 1.414 for a sine wave). So
the peak voltage at the tip of our transponder antenna with 200W
input is quite near 900V.
> Thats the purists approach, and funny that around 1990, I had my
> xponder check done by a crotchety old-timer. Hed ramp check
> also Mode C by observing similarly kludged, detected xponder output
> on what looked like his Dads old scope -- on wheels. For his
> selected altitude test points per Part 43, he had sketched the bit
> pattern on little index cards. Head cocked skyward to use his
> bifocals, holding said card up to the scope with round display.
> Pump vacuum at the plane, then run to the scope to check. He had
> to work fast, as permissible leak-down in the static sys at higher
> alts can cause up to multiple bits to flip Grey-code style (he
> seemed to rely on an observed time lag). Who needs very expensive
> equipment, when all you need are FAA-approved index cards? Worked
> for him and me, a priceless observance of an actual FAR Part 145
> repair facility at work, worth every penny for the log entry.
> Purists impress me.... Had the temptation to hit the IDENT butt!
> on whilst he was straining through bifocals, but dared not!
It is pretty cool that you can do it that way. You are just looking
at the pulses (RF on/off) and reading the code. I have done that as a
quick-and-dirty test with a cheap scope, a wire probe, and a crystal
diode configured as a shunt detector. You can get a pretty good
feeling for whether your transponder is working or not (assuming
there is an ATC RADAR close enough to interrogate the transponder
into a reply while on the ground).
> How 50-ohm impedance became the norm, where impedance of the
> atmosphere is etched in stone by a higher power, and a 1/4-wave
> straight element is natural at 37, well I beg off. Perhaps cuz it
> all works, or perhaps you know....
Ah, you have discovered the difference between physics and
philosophy. Physics just tells us that the feedpoint impedance at the
center of a dipole is 72 ohms. (A monopole being half a dipole is why
its impedance is 36 ohms.) It doesn't tell us *why* it is 72 ohms.
Philosophy is supposed to tell us why. The easiest answer is,
"because God wanted it that way," but that is too hard to get my tiny
brain around. I will just settle for trying to understand a few of
the relationships between the how, what, and where.
> 75 works for video hi-def TV with 2-way for nefarious purpose.
The answer is, "because the feedpoint impedance at the center of a
dipole is 72 ohms." Once you make a wire intended to feed that
impedance you may as well use it for something else too. If you have
a coax with a characteristic impedance of 75 ohms you have to
terminate it at 75 ohms to minimize reflections. Everyone else may as
well use that impedance as well. And then people started playing with
monopole antennas and found 50 ohms to be more convenient so we got
another kind of coax we could use with lots of different things.
> The history of the decibel may be similar whimsy? Not the
> convenient, additive/subtractive nondimensional math, but Dr. Bell
> didn't get recognized as did Watt, Ohm, etc., and his employer
> allegedly thought dividing by 10 (deci) was more practical.
No, the official unit is the Bell, just like the other official units
are things like the watt, volt, ampere, coulomb, etc. It is just that
sometimes it is easier to measure things with multipliers in the
units like micro-volt, milliampere, kilowatt, and decibel.
> Purists like me write "dB,"not "db." :D
Well, that is the way it is supposed to be written. Just like Hertz
is Hz, not hz. Mega-Hertz is MHz, not mhz.
> It's like in very current cell phone technology, where despite
> awesome cleverness to me at least, nobody's been memorialized for
> nuthin'. :x
There hasn't been a lot that is new in radio theory. The "new" stuff
is just clever application of what we have known for a long time. It
is now with digital signal processing we can do some things that we
knew could be done but couldn't do effectively using the technology
at hand back when the math showed the possibility.
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
Antoine de Saint-Exupry
Message 5
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| Subject: | Re: Ammeter Shunt |
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Message 6
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| Subject: | Mic audio ground - PMA8000B |
--> AeroElectric-List message posted by: "John Tvedte" <JohnT@comp-sol.com>
Say - on the PMA7000, 8000 or GMA340 audio panels...none of them have a
dedicated return (ground) for the Mic Gnd (used on SL30/40 & GNS480). I
would assume the 'dedicated' returns are all connected together
internally - and are there for ease of install - i.e. to pin 10,11.....
Anyone have some advice as to what to hook up the Mic Gnd to on a
PMA8000 series audio panel?
-------------------------
Say - I noticed that the PMA7000 vs the PMA8000 and GMA340 have opposite
convention on the tip and middle tip of the audio plugs - for L/R use.
Obviously the input tip/middle tips are changed as well - so pass thru
is just fine.
Is there actually a convention used? - just curious....
Message 7
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| Subject: | Re: Ammeter Shunt |
--> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
On Jul 14, 2006, at 10:37 AM, Ralph E. Capen wrote:
> --> AeroElectric-List message posted by: "Ralph E. Capen"
> Vision Microsystems uses one for their current detection (uses four
> wires and a shield).......I have one installed and was thinking
> about something along the lines of what you're doing......
>
> My question is where are you getting the rotary switch to switch
> the four wires? (I would gang all of the shields)
You may find that you only need to switch one or maybe two wires. At
least one wire is power in and one other is power ground. You can
probably leave those hooked up all the time and not switch them. I
would guess that one of the other wires is output and one is signal
ground or maybe it has a differential output.
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
Antoine de Saint-Exupry
Message 8
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| Subject: | Re: Mic audio ground - PMA8000B |
--> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
On Jul 14, 2006, at 11:11 AM, John Tvedte wrote:
>
> Anyone have some advice as to what to hook up the Mic Gnd to on a
> PMA8000 series audio panel?
Insulate the mic jack from the airframe. Return the shell to the
ground at the audio panel. All your mic inputs will return to this
same common ground at the audio panel.
Do not return your mic grounds to the single-point power ground at
the firewall.
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
Antoine de Saint-Exupry
Message 9
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| Subject: | Re: Ammeter Shunt |
--> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
On Jul 14, 2006, at 10:03 AM, Speedy11@aol.com wrote:
> Brian,
> I'm one of those ignorant pilots who believes that an ammeter can
> provide useful information while in flight, so I intend to install
> one along with a voltmeter. I'm crafting my electrical system to
> do what I want it to do.
Well, if only ignorant pilot believe that an ammeter provides useful
information then I am an ignorant pilot too.
> Do you, or anyone, know of one that is a digital center-zero
> meter? How about a combo digital ammeter-voltmeter?
There are a lot of companies that make volt/ammeter combination
gauges. I have not seen an analog center-zero ammeter that is also a
combination volt/ammeter. The digital ones will usually show a sign
on the current indication thus allowing you to see the magnitude of
both charge and discharge. You should be able to find either analog
or digital to suit your taste.
> I plan to use hall effect devices and I'm going to mount them in at
> least three places in the electrical system. I also plan to sample
> the voltage at the same locations in the electrical system. I'm
> still deciding where those locations will be, but they will likely
> be on the alternator lead, at the main battery and at the standby
> battery. Other potential locations are the main bus and the
> standby bus. I plan to route the sensor wires to a rotary selector
> switch so as to be able to view any of the sensor locations on a
> single ammeter and voltmeter. Too much effort and expense for
> little or no gain? Perhaps, but it's the way I want it.
Then that is how you should do it. It is your airplane and you should
equip it the way you like.
> I believe that by using HE devices instead of shunts I would not
> have to worry about making the shunt beefy enough to handle the
> starting loads. Is there any advantage to using a shunt that I'm
> overlooking?
Shunts are more accurate. When there is zero voltage across the
terminals of a shunt there is definitely no current through the
shunt. Hall effect devices exhibit offset error and can be affected
by other nearby conductors carrying current. But in most cases they
are just fine.
Bipolar hall effect sensors usually have their output midway between
ground and the supply voltage (typically +5V) when they are sensing
zero current. So +2.5V really means zero current. You just need to
calibrate your indicator accordingly.
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
Antoine de Saint-Exupry
Message 10
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| Subject: | building a hall-effect ammeter |
--> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
FYI: http://www.siliconchip.com.au/cms/A_30551/article.html
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
Antoine de Saint-Exupry
Message 11
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| Subject: | FW Bell RSS-100-A hall effect sensor |
--> AeroElectric-List message posted by: "Brian Meyette" <bmeyette@gmail.com>
Does anyone know a source of this sensor, or an equivalent? I need it for
current flow measuring on BMA EFIS/One. Newark no longer lists them - just
the 200a. Allied lists them, but none in stock and they tell me 18 week
delay to get one. None of the other places I checked list them at all;
DIgikey, Mouser, onlinecomponents, and several others listed on the FW Bell
site. I realize BMA has theirs, but it's $100 and these FW Bell ones are
$43; quite a difference.
--
Message 12
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| Subject: | Re: building a hall-effect ammeter |
--> AeroElectric-List message posted by: "Dale Ensing" <densing@carolina.rr.com>
Brian,
Is this available as a kit?
Dale Ensing
> --> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
>
> FYI: http://www.siliconchip.com.au/cms/A_30551/article.html
>
> Brian Lloyd
>
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