Today's Message Index:
----------------------
1. 07:33 AM - Re: Ammeter reading oddly (Robert L. Nuckolls, III)
2. 07:33 AM - What did I do wrong? (Fergus Kyle)
3. 07:34 AM - Re: proper cable for engine instrument (Robert L. Nuckolls, III)
4. 08:04 AM - Re: What did I do wrong? (Ron Quillin)
5. 08:06 AM - Re: Ammeter reading oddly (Hinde, Frank George (Corvallis))
6. 09:37 AM - What did I do wrong? (Fergus Kyle)
7. 07:32 PM - Re: What did I do wrong? (Robert L. Nuckolls, III)
Message 1
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Subject: | Ammeter reading oddly |
At 09:56 PM 9/7/2008 +0100, you wrote:
><peter@sportingaero.com>
>
>You probably don't really want to hear this, but Van's gauges aren't the
>best quality items on the planet. I have found that the temperature and
>pressure gauges are not that accurate (+/- 15%), so no reason why the
>ammeter should be any better! I've always found a voltmeter very
>comforting to tell the alternator is still at work.
>
>Regards, Peter
I have a Van's battery ammeter which I've confirmed does
have a sensitivity to strong RF fields. I disassembled
the gage and was pleasantly surprised at the level of
technology used in this particular instrument. I'll
direct the reader's attention to the suite of photos
at:
http://aeroelectric.com/Pictures/Instruments/Vans/
In particular, note the potentiometers (blue)
in this view . . .
http://aeroelectric.com/Pictures/Instruments/Vans/VAM10_05.JPG
I suspect these adjustments are included in all
the Vans instruments in this style.
In general, I found them well assembled and
artfully designed. These use a 4-quadrant,
moving-magnet motor to drive a pointer. This
is the technology of choice in most mechanical
instrumentation used throughout the automotive
industry. They're inexpensive, rugged and capable
of exemplary accuracy.
They DO require some signal conditioning electronics
and the electronics are subject to the usual
snakes and gremlins. Long term drift (calibration
stability) and RF susceptibility are the
biggest issues. Indeed, the instrument I have
exhibits a characteristic I've never seen before
in an instrument.
A hand-held transceiver waved around the
powered up instrument will drive the pointer
either direction depending on position of
the antenna. See:
http://aeroelectric.com/Pictures/Instruments/Vans/VAM10_09.JPG
http://aeroelectric.com/Pictures/Instruments/Vans/VAM10_10.JPG
Mechanically, I was surprised that they use
thru-hole parts . . . this is NOT the most economical
way to assemble a complex device in volumes.
The largest disappointment was components
that stand up on their lead wires. These instruments
might be at risk for loosing a component under
qualification vibration.
Generally speaking, this series of instrument
appear to be of good value . . . particularly
if they ALL have calibration pots. I can live
with long term changes in calibration as long
as I can RECALIBRATE as necessary.
I hadn't planned to write about these devices
until I've solved the RFI problem . . . but I
didn't want this thread to move forward without
making folks aware of useful details about
how they're built.
The two potentiometers probably adjust offset
(zero) and scale (calibration). They may be
interactive meaning that one has to rock back
and forth between zero and full-scale readings
so that the pots can be set dead-on.
Bob . . .
Message 2
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Subject: | What did I do wrong? |
Bob,
You said:
" It's a study in trade offs. If the electrics of Ferg's jumper
are higher loss than 4AWG equivalent, how bad is the temperature
rise during a cranking event? Keep in mind that the flat strap
sheds heat faster than a round, insulated wire. How bad is
the voltage drop during a cranking event? We KNOW that the
system total loop resistance is significant. See:
http://aeroelectric.com/Pictures/Schematics/Voltage_Drop_Study_2.pdf
Gee . . . it may well be that the thin brass strip originally
proposed might be okay in the grand scheme of things.
I mention all this only because the elegant solution
considers ALL the ingredients that go into a recipe for
success . . . of which getting the math right for deducing
equivalency is but one part."
Well, I went there, and behold a neat resistance diagram - good
stuff...... Did you do this with a "megger"? I remember my mentor (lo
those many years) going over all my work with his megger to confirm - I
thought - good connections and no shorts. Is that still the routine?
Ferg
PS: My main purpose in brass was to establish the shape and size while
looking for a copper source.
Message 3
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Subject: | Re: proper cable for engine instrument |
At 08:54 PM 9/7/2008 -0700, you wrote:
>
>I need to run the cables for the engine monitor. Which is the better cable
>to run I want to have at least 20 leads for a 6 cylinder engine with turbo
>and fuel flow. I'm thinking to get the G3 from
>http://www.insightavionics.com/g3.htm
>any suggestion
>
>Thanks for the advice
In the big iron birds, this kind of instrument
would be installed using factory bundles of
individual wires . . . ESPECIALLY when part
of that installation is thermocouple wire.
See what the installation manual calls for
first. I suspect it will suggest built-up
bundles. Use 22759 for the copper, and
the good stuff . . .
http://www.omega.com/ppt/pptsc.asp?ref=XC_K_TC_WIRE&Nav=temh06
for thermocouples.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 4
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Subject: | Re: What did I do wrong? |
At 07:26 9/8/2008, you wrote:
>PS: My main purpose in brass was to establish the shape and size while
>looking for a copper source.
Try McMaster-Carr.
8964K271 is a 0.125 x 12" Alloy 110 Electronic-Grade Copper for $7.33.
Many other sizes available.
http://www.mcmaster.com/
Ron Q.
Message 5
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Subject: | Ammeter reading oddly |
It's the gauge...The fact the ammeter swings high for a few seconds then returns
to normal indicates that everything is working normally.
Explanation....
You have a battery that spits out hundreds of amps in 3 to 5 second burst to run
the starter...Now think of that energy as a tank of water...You sunddenly opened
a big valve at the bottom and let a lot of water out...Now the ballvalve
opens and it gradually gets topped up by the small filler pipe until its full
then the valve closes and then it stops.
Well the alternator is is the small filler pipe and the ammeter is measureing the
flowrate back into the tank..I mean battery.
That few seconds of +20A is the alternator topping the battery off.
Now if the ammeter goes to -10A and stays there in flight you got a problem.
Realistically ammeters are a bit of a waste of time, My Dynon has one and I never
look at it..But I do have an alarm on battery volts..if it drops to 12.5V I
get an audible alarm...Then I look at the amps.
Frank
RV7a IO360 electric fuel pumps only. Now featuring mogas+ 10% ethanol.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Peter Pengilly
Sent: Sunday, September 07, 2008 1:56 PM
Subject: RE: AeroElectric-List: Ammeter reading oddly
--> <peter@sportingaero.com>
You probably don't really want to hear this, but Van's gauges aren't the best quality
items on the planet. I have found that the temperature and pressure gauges
are not that accurate (+/- 15%), so no reason why the ammeter should be any
better! I've always found a voltmeter very comforting to tell the alternator
is still at work.
Regards, Peter
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Neil Clayton
Sent: 06 September 2008 22:50
Subject: AeroElectric-List: Ammeter reading oddly
<harvey4@earthlink.net>
When I first start the engine, and then engage the alternator, the Van's ammeter
flips over to +20 for a few seconds.
Then it gradually descends to zero and settles a needle's width on the -ve side
of zero, where it sits for the duration.
If I turn the alternator off, the ammeter goes to -10 so I know it's sensing something,
but the slight -ve reading in flight bothers me.
Do you think it's just an adjustment issue on the gauge, or is something else going
on?
Thanks for ideas.
Neil
Message 6
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Subject: | What did I do wrong? |
Cheers,
At the risk of flogging this dog of a topic, I consulted an old
friend, "Handbook of
Applied Mathematics" in stumbling through several attempts to assimilate
Ron's excellent
application. I quote:
"Wires are often grouped in smaller ropes for ease of use. The group of
wires is called a
"strand"; the term "wire" being reserved for the individual wires of the
strand. Strands are
usually built of wires of such a size that the cross-section of the
metal in
the strand is the
same as the cross-section of the solid wire having the same gage (sic)
number."
This book also gave me a value of 204 mils in diam.
Half that, squared, times pi, gave me 32781 square mils. Divide by a
thickness of
125 mils gives 261-odd mils or =BC inch. So, .25 by .125 inches seems
correct
but 1/16 by
=BD inch seems easier, in copper.
I must remember pie are round, cake are square.
Ferg
Message 7
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Subject: | Re: What did I do wrong? |
At 10:26 AM 9/8/2008 -0400, you wrote:
>Bob,
> You said:
>" It's a study in trade offs. If the electrics of Ferg's jumper
> are higher loss than 4AWG equivalent, how bad is the temperature
> rise during a cranking event? Keep in mind that the flat strap
> sheds heat faster than a round, insulated wire. How bad is
> the voltage drop during a cranking event? We KNOW that the
> system total loop resistance is significant. See:
>http://aeroelectric.com/Pictures/Schematics/Voltage_Drop_Study_2.pdf
> Gee . . . it may well be that the thin brass strip originally
> proposed might be okay in the grand scheme of things.
> I mention all this only because the elegant solution
> considers ALL the ingredients that go into a recipe for
> success . . . of which getting the math right for deducing
> equivalency is but one part."
> Well, I went there, and behold a neat resistance diagram - good
>stuff...... Did you do this with a "megger"? I remember my mentor (lo
>those many years) going over all my work with his megger to confirm - I
>thought - good connections and no shorts. Is that still the routine?
>Ferg
A 'megger' is what the name implies, a meg-ohmmeter
usually with a capability of reading thousands of
meg ohms. This device would be used to measure insulation
resistance while powered up at hundreds if not 1000 volts.
The diagram was a hypothetical based on experiences. Although
there are micro-ohmmeters that can be used to measure very
small resistances directly. The one I have is like this
http://www.avtron.com/pdf/ate/t477w.pdf
While the 'megger' uses very high voltage to detect and
quantify very large resistances the micro-ohmmeter
or bonding meter uses high currents to detect and
quantify very low resistances.
>PS: My main purpose in brass was to establish the shape and size while
>looking for a copper source.
Did we get you covered? There was a lot of 'stuff' flying
around there for awhile. 4awg is 0.2 dia, 0.1 radius.
0.1(squared) x 3.14 or 0.031 square inches cross section. This
means that a .032" piece 1" wide copper has the same cross
section and conductivity.
I may have some .032" or 22 gage (.025") sheet stock
in M.L. I'll check tomorrow when I'm there.
Bob . . .
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