Today's Message Index:
----------------------
1. 12:40 AM - Re: detecting ground loops, was Re: Re: noisy 912 alternator (D L Josephson)
2. 06:14 AM - Re: Re: detecting ground loops, was Re: Re: noisy 912 alternator (Jim Kale)
3. 08:07 AM - Technique for DSub Pin / data breakout for RPM issue (plevyakh)
4. 09:26 AM - Re: Technique for DSub Pin / data breakout for RPM issue (ARGOLDMAN@aol.com)
5. 09:46 AM - Re: Technique for DSub Pin / data breakout for RPM issue (Robert L. Nuckolls, III)
6. 11:41 AM - Re: Newbie with PM alternator feed question (blues750)
7. 02:13 PM - Re: Re: Newbie with PM alternator feed question (Robert L. Nuckolls, III)
8. 04:37 PM - Re: Technique for DSub Pin / data breakout for RPM issue (Joe Dubner)
Message 1
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| Subject: | Re: detecting ground loops, was re: re: noisy 912 alternator |
On 10/12/15 11:59 PM, AeroElectric-List Digest Server wrote:
>> Hi Guy... just out of curiosity, can you explain how you test for
>> ground loops? Using an ohm meter, apparently, but hoe exactly? Thanks!
>
> A 'ground loop' is said to exist when a potential
> antagonist (most often an alternator, motor or
> sometimes a strobe) shares a ground path with a
> potential victim (most often an audio system or
> some instrument that responds to millivolt level
> signals).
>
> Hence, the victim's performance is compromised
> by the DC/AC components of the antagonist's
> functionality. Ground loops are avoided with
> judicious attention to architecture where failure
> to 'avoid by design' cannot be readily detected
> except for the victim's mis-behaviors.
>
> I'm not sure how any sort of instrument or
> other measuring process would be useful in
> detecting/analyzing a ground loop.
Some parts of the audio world are trying to get away from the name
"ground loop" because the wording is confusing (it's seldom a loop and
can be in the power lead, not just ground.) We are using the term
"common impedance coupling" because a common path is used for two
currents, variations in one being superimposed on the other. A
differential scope is actually quite useful in analyzing this condition
-- you look for AC signals with one probe connected to each end of the
"ground" wire.
David Josephson
Message 2
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| Subject: | Re: detecting ground loops, was re: re: noisy 912 |
alternator
I have heard the term "Ground Loop" used a lot and as I understand the
problem, it mostly occurs when a unit that is sensitive to very small
fluctuations in voltage is used and the common ground circuit is not a
single common point, but a lengthy circuit distributed around the airplane
using wires or airframe components. This can lead to small resistances
distributed along the common ground circuit. As current increases in the
common ground circuit, these small resistances develop voltages along the
common ground circuit. Electrical devices, (radios, etc.) that are
sensitive to very small voltage differences and that are connected at
different points along the ground circuit, sense the very small voltage and
behave as if they are not connected to a common ground point, but to
different values of ground.
The solution seems to be to have a very current hefty single point (robust
common Bus Bar) to connect each of the using devices to so that minor
voltages cannot develop across distributed resistance in a long common
ground path. A hefty bus bar (preferably near the alternator/battery
current source): and all using devices have the common ground lead tied to
that point. Is that a layman's description of the solution?
This seems to be what is being discussed below. I am just trying to get it
all straight in my brain.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of D L
Josephson
Sent: Tuesday, October 13, 2015 2:39 AM
Subject: AeroElectric-List: Re: detecting ground loops, was re: re: noisy
912 alternator
--> <dlj04@josephson.com>
On 10/12/15 11:59 PM, AeroElectric-List Digest Server wrote:
>> Hi Guy... just out of curiosity, can you explain how you test for
>> ground loops? Using an ohm meter, apparently, but hoe exactly? Thanks!
>
> A 'ground loop' is said to exist when a potential
> antagonist (most often an alternator, motor or
> sometimes a strobe) shares a ground path with a
> potential victim (most often an audio system or
> some instrument that responds to millivolt level
> signals).
>
> Hence, the victim's performance is compromised
> by the DC/AC components of the antagonist's
> functionality. Ground loops are avoided with
> judicious attention to architecture where failure
> to 'avoid by design' cannot be readily detected
> except for the victim's mis-behaviors.
>
> I'm not sure how any sort of instrument or
> other measuring process would be useful in
> detecting/analyzing a ground loop.
Some parts of the audio world are trying to get away from the name "ground
loop" because the wording is confusing (it's seldom a loop and can be in the
power lead, not just ground.) We are using the term "common impedance
coupling" because a common path is used for two currents, variations in one
being superimposed on the other. A differential scope is actually quite
useful in analyzing this condition
-- you look for AC signals with one probe connected to each end of the
"ground" wire.
David Josephson
Message 3
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| Subject: | Technique for DSub Pin / data breakout for RPM issue |
Folks,
I've come across this a few times in the System Test and Flight test of my GlaStar.
Can you please share a technique you've used to break into a DSub connector
pin and read the data going through that Pin/Wire?
Currently...I'm looking for something that will allow me to easily disconnect a
DSub 15 and DSub25 connectors, insert the data Breakout board, and then read
the data going through any Pin with a Voltmeter.
I found this on eBay, and it would work, but I'd have to also get a short pigtail
connector to enable the connections due to space.
http://www.ebay.com/itm/DIN-Rail-Mount-D-SUB-Interface-Module-DSUB-Header-Breakout-Board-/191703597826?var=&hash=item2ca26cc302
Here's my recent flight test issue. I have dual LightSpeed Ignition System Plasma
IIIs. The RPM sensor on Ignition #1 is working great! I feed this into
my Grand Rapids EIS4000 engine monitor and get reliable RPM readings.
My problem is with Lightspeed Ignition #2. When I switch to Ign #2 only, my RPM
goes to zero. So either my Lightspeed #2 signal tach reading voltage is
bad, or my connection to to the EIS4000 engine monitor is bad.
I need to break into the Dsub 15 connector on the Lightspeed Ignition #2, and read
Pin 6 (Signal Tach), and Pin 13 (Shield Ground) to confirm I'm getting 0V
at idle, and 5V or higher at higher throttle settings. If this checks good, then
I'll have to break into the EIS4000 DSub 25 connector and check Pin 24 (Tach
Input #2) and see if it's sensing a value.
Is there an easy way to break into a DSub and measure readings without having to
pull apart the connector and patch in a test wire?
Thanks for your experience'd inputs!
Howard
GlaStar N19HL (flying and loving every minute!)
--------
Howard Plevyak
GlaStar / North Bend, Ohio
hplevyak@mac.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=447881#447881
Message 4
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| Subject: | Re: Technique for DSub Pin / data breakout for RPM |
issue
One thing I have found helpful is to make a "jumper/diagnoser cable.
Use a flat ribbon cable (much longer than you think that you need) and get
several press-on sub d-s of both genders in vairous sizes (obviously the
largest one (probably a 25 pin)) but also 15 and 9 pin ones. Be careful to
keep the proper pin alignment as these press on things do not indicate pin 1.
Start with a 25 pin male, a few inches down put a 25 pin female (again
ascertain that pin 1 is correct then a few inches down put a 15 pin male then
a 15 pin female and then a 9 pin male and female. if you want to use only
1 size use that size only. now in the middle just put a male plug (of each
size for ease). At the other end of the wire put the same arrangement of
plugs that you originally used in the beginning of the harness.
What you now have is a jumper cable, usable for 3 or more sizes of sub-ds
with a male (pins exposed) sub-d in the middle( or males of vaarious
sizes)-- remember that the pin numbers (over 5, I believe) will be different as
the d-subs get larger-- .
With this cable, you can do invivo studies (all systems connected). this
jumper cable can be used for many other things. Since I have a Cozy with
rotary engine, I use tit to verify 9, 15 and 25 pin sub-ds from the IP to the
FW.
Just don't run over the cable with a chair (Don't ask me how I know the
damage that causes.)
Good luck (did I say make sure that the pins are on the appropriate wires
Rich
In a message dated 10/13/2015 10:10:07 A.M. Central Daylight Time,
hplevyak@mac.com writes:
--> AeroElectric-List message posted by: "plevyakh" <hplevyak@mac.com>
Folks,
I've come across this a few times in the System Test and Flight test of my
GlaStar. Can you please share a technique you've used to break into a
DSub connector pin and read the data going through that Pin/Wire?
Currently...I'm looking for something that will allow me to easily
disconnect a DSub 15 and DSub25 connectors, insert the data Breakout board, and
then read the data going through any Pin with a Voltmeter.
I found this on eBay, and it would work, but I'd have to also get a short
pigtail connector to enable the connections due to space.
http://www.ebay.com/itm/DIN-Rail-Mount-D-SUB-Interface-Module-DSUB-Header-Br
eakout-Board-/191703597826?var=&hash=item2ca26cc302
Here's my recent flight test issue. I have dual LightSpeed Ignition
System Plasma IIIs. The RPM sensor on Ignition #1 is working great! I feed
this into my Grand Rapids EIS4000 engine monitor and get reliable RPM
readings.
My problem is with Lightspeed Ignition #2. When I switch to Ign #2 only,
my RPM goes to zero. So either my Lightspeed #2 signal tach reading
voltage is bad, or my connection to to the EIS4000 engine monitor is bad.
I need to break into the Dsub 15 connector on the Lightspeed Ignition #2,
and read Pin 6 (Signal Tach), and Pin 13 (Shield Ground) to confirm I'm
getting 0V at idle, and 5V or higher at higher throttle settings. If this
checks good, then I'll have to break into the EIS4000 DSub 25 connector and
check Pin 24 (Tach Input #2) and see if it's sensing a value.
Is there an easy way to break into a DSub and measure readings without
having to pull apart the connector and patch in a test wire?
Thanks for your experience'd inputs!
Howard
GlaStar N19HL (flying and loving every minute!)
--------
Howard Plevyak
GlaStar / North Bend, Ohio
hplevyak@mac.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=447881#447881
Message 5
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| Subject: | Re: Technique for DSub Pin / data breakout for RPM |
issue
At 10:01 AM 10/13/2015, you wrote:
>
>Folks,
>I've come across this a few times in the System Test and Flight test
>of my GlaStar. Can you please share a technique you've used to
>break into a DSub connector pin and read the data going through that Pin/Wire?
here is a cheep/n/dirty that I've used many times
using a short chunk of ribbon cable and the appropriate
connectors. Of course, this is for signal/low-power
levels only. Limit this technique to wire currents
of 1A or less.
Emacs!
More robust techniques call for a specialized
break-out fixture not unlike this
Emacs!
Here's a breakout box I built in a few hours to explore
signals in a starter-generator controller. Your tool would,
of course, be fitted with d-subs.
Emacs!
Here's a specific application example for examining data at
altitude and 'from a distance'.
Connectors on the left tied into a system back in the hell-hole
of a Beechjet. The ribbon cable was routed through the gasket
on the baggage compartment door, taped to the side of the
fuselage and brought into the cabin through the passenger
entry door gasket. I sat in pressurized comfort watching
for an intermittent that had plagued the airplane for months.
It only occurred at altitude. Spotted the problem in the
DAS data which led to discovery of a pushed back pin in
a connector on the pressure bulkhead.
Your task DOES have a practical solution that lies somewhere
between the cheap-n-dirty to the high-altitude remote explorations
cited. But you will have to build something.
Bob . . .
Message 6
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| Subject: | Re: Newbie with PM alternator feed question |
[quote="nuckolls.bob(at)aeroelect"]
>
>
> > Trying to sort things out as I proceed and appreciate this forum and your literature!
>
> Pleased that you find it useful. I need to take
> care of some other pressing business. I'll see if I
> can sketch a diagram of what I've described above
> and post it later today.
>
I've posted a drawing that describes on/off control
of a 3-phase PM alternator with Over Voltage Protection
http://tinyurl.com/n9tottf
Bob,
After doing a more detailed electrical load budget / requirements study, it looks
like it will really be near the limits of the 30A rated PMA I currently have
in my build. I am considering increasing the 30A PMA to a 50A PMA by changing
to a 50A alternator stator the company has available. With that in mind, what
do I need to do with the components on the drawing you provided earlier.
Do I need to spec different relays or capacitor? Any other considerations? Your
thoughts and insight will be much appreciated
Thanks!
Dave
Bob . . .
> [b]
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=447895#447895
Message 7
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| Subject: | Re: Newbie with PM alternator feed question |
>
>Bob,
>
>After doing a more detailed electrical load budget / requirements
>study, it looks like it will really be near the limits of the 30A
>rated PMA I currently have in my build. I am considering increasing
>the 30A PMA to a 50A PMA by changing to a 50A alternator stator the
>company has available. With that in mind, what do I need to do with
>the components on the drawing you provided earlier. Do I need to
>spec different relays or capacitor? Any other considerations? Your
>thoughts and insight will be much appreciated
>
>Thanks!
A FIFTY amp PM alternator? Drops into the existing
stator space? What rectifier/regulator do they recommend?
Forgive my raside eyebrows . . . that's a BIG jump in
performance . . . which is physically possible
with bigger magnets, more iron, etc. But to make
it a drop-in replacement raises some questions.
Are there links to the company and to any data
they offer for this 'upgrade'?
Also, could you share your load analysis with
us? It would be interesting to see how you've
walled off the various requirements for the
alternator-out failure mode.
Bob . . .
Message 8
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| Subject: | Re: Technique for DSub Pin / data breakout for RPM |
issue
plevyakh wrote, On 10/13/2015 08:01:
>Can you please share a technique you've used to break into a DSub connector pin
and read the data going through that Pin/Wire?
Howard,
A technique I use is to make up some short pairs of wires with D-subminiature
pins like in the first attached image. The wires can be used to "bridge" a
D-subminiature connector pair and at the same time allow connecting a test lead.
http://www.mail2600.com/misc/D-subFixture1.jpg
This technique gets old fast if the mating pair contains more than about four
wires. :-( In that case, I use a fixture similar to the ones shown in the
second image (but with more connectors).
http://www.mail2600.com/misc/D-subFixture2.jpg
The ribbon cable can have any reasonable number of D-sub connectors attached
(they are easily crimped in a small vise). My favorite is to crimp on 5
connectors: a male and a female at each end and an additional connector for
probing. This makes a universal breakout fixture and can also function as a
temporary gender changer.
--
Joe
RV-8A
Independence, OR
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