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pats4p(at)sbcglobal.net
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 Posted: Tue Nov 21, 2006 5:04 pm Post subject: 24V 12V grounds |
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I have a question and I'm in search of an answer. I have a 24V system with a 24/12 volt 15A converter . Can the output ground of the converter (12V) use the same single point ground as the 24V, or is it necessary to supply a second dedicated ground point for the 12V ?
Thanks,
Pat
[quote][b]
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nuckollsr(at)cox.net
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| Posted: Tue Nov 21, 2006 7:41 pm Post subject: 24V 12V grounds |
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At 05:02 PM 11/21/2006 -0800, you wrote:
| Quote: | I have a question and I'm in search of an answer. I have a 24V system with
a 24/12 volt 15A converter . Can the output ground of the converter (12V)
use the same single point ground as the 24V, or is it necessary to supply
a second dedicated ground point for the 12V ?
|
Tie them all together . . . preferably at carefully
crafted locations designed to minimize the number of
grounds and risks for ground-loop noise. See Figure
Z-15 in . . .
http://aeroelectric.com/articles/Rev11/AppZ_R11J.pdf
Bob . . .
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flyadive(at)aol.com
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| Posted: Wed Nov 22, 2006 3:06 pm Post subject: 24V 12V grounds |
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One more time!
There is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
If you truly believe there is Design one so I can build it and you can prove me wrong.
OR tell the poor questioning soul how to "carefully crafted locations designed to minimize the number of
grounds and risks for ground-loop noise."
Ya CAN'T because each plane is different the wire runs vary and there is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
Barry
Yes - I am still monitoring the list, if for no other purpose than to BUST MYTHS!
=====================================================
--
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mprather(at)spro.net
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echristley(at)nc.rr.com
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| Posted: Wed Nov 22, 2006 4:04 pm Post subject: 24V 12V grounds |
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flyadive(at)aol.com wrote:
| Quote: | One more time!
There is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
If you truly believe there is Design one so I can build it and you can prove me wrong.
OR tell the poor questioning soul how to "carefully crafted locations designed to minimize the number of
grounds and risks for ground-loop noise."
Ya CAN'T because each plane is different the wire runs vary and there is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
Barry
Yes - I am still monitoring the list, if for no other purpose than to BUST MYTHS!
=====================================================
You say to-may-to, I say to-mah-to.
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I've always known a ground-loop as a situation where two devices share
an unsymmetrical supply or ground path. The arrangement is such that
the voltage across one device will fluctuate due to the operation of the
other.
+12V -------------------------------/----\-
/ \
/ \
Load 1 Load 2
/ \
GND-------/\/\/\/----------/------------/\/\/\/\/------\
I hope the ASCII art come through unscathed. Please use a monospaced
font for email.
If a high powered strobe were used as Load 1, it's operation would
present a residual voltage where it's wiring connected back into the
ground line when the light is turned on. This is caused by the fact
that all conductors have some resistance (represented by the squiggly
lines). The voltage goes away when the light is extinquished. This
would change the voltage perceived by Load 2 as the strobe flashes,
which would be a bad thing if it were an audio line, because then you'd
hear every flash.
It's called a ground-loop, because power lines tend to be pulled from a
central location, while local grounding is the norm. You may have a
different term for this, and use ground-loop to refer to a different
phenomena. Please share your point of view, but also be aware that I'm
an ignorant American who thinks that my English measurement system
serves me just fine, so I'm unlikely to change terminology this week.
[quote]
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nuckollsr(at)cox.net
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| Posted: Wed Nov 22, 2006 4:11 pm Post subject: 24V 12V grounds |
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At 06:05 PM 11/22/2006 -0500, you wrote:
| Quote: | One more time!
There is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
If you truly believe there is Design one so I can build it and you can
prove me wrong.
OR tell the poor questioning soul how to "carefully crafted locations
designed to minimize the number of
grounds and risks for ground-loop noise."
Ya CAN'T because each plane is different the wire runs vary and there is
NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
Barry
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I don't need to hypothesize about one because there are countless
examples of DC ground loops and the techniques developed to avoid them.
All of our temperature measurement devices aboard an airplane used
dedicated outbound and return wires so that both signal and ground
leads can convey good data to the system having and interest
in remote temperatures. To ground the sensor locally would inject
voltages not related to the measurement task which are related
to airframe resistance combined with ground currents of other systems
that flow on the airframe.
Very early on in my association with the OBAM aircraft community
I got a phone call from a Longez pilot who reported that his
CHT, OIL TEMP and OIL Pressure gages read just fine with the
alternator off . . . but differed wildly from true readings
when the alternator was first turned on and then wiggled around
as other accessories were turned on and off. This anecdote
is described on pages 5-5 and 5-6 of the 'Connection. Seems
the senders for these instruments were locally grounded to
crankcase while the instruments were grounded to battery(-)
at the nose. The airplane didn't have a starter so the 10AWG
ground wire the builder ran from battery(-) to crankcase
was sufficient for alternator return . . . but offered a substantial
voltage difference between crankcase and battery(-) due to alternator
output currents flowing in the wire.
This small voltage in a DC GROUND LOOP was responsible for
upsetting the ship's engine instruments. Adding a dedicated
ground wire for instruments that returned all the way to the
crankcase broke the loop and eliminated the problem.
Starter generator controllers on all our bizjets feature
remote sense conductors for both bus and ground signals
that are extended from the controller all the way to
to generator's terminals under the nacelle. The use of
remote as opposed to local sensing for both bus and ground
eliminates any errors of measurement that might be introduced
by currents flowing on the airframe. We do this to avoid
the DC GROUND LOOP that would most certainly exist were
the practice not observed.
These are but a handful of dozens of examples of DC
Ground Loops that we choose to avoid by judicious architecture
of vulnerable systems.
| Quote: | Yes - I am still monitoring the list, if for no other purpose than to BUST
MYTHS!
|
I don't know what you would choose to call the system
design errors that would introduce the problems cited
above. Perhaps we have a misunderstanding of definitions.
The venue in which I've made my living all these years
calls these phenomenon "ground loops" and because they're
DC signals being upset by DC currents flowing on the
airframe, we call them DC GROUND LOOPS. Do you have
another name for them?
Bob . . .
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Thu Nov 23, 2006 8:02 am Post subject: Re: 24V 12V grounds |
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| Quote: | One more time!
There is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
If you truly believe there is Design one so I can build it and you can prove me wrong.
OR tell the poor questioning soul how to "carefully crafted locations designed to minimize the number of
grounds and risks for ground-loop noise."
Ya CAN'T because each plane is different the wire runs vary and there is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
Barry |
Barry is absolutely correct.
Unfortunately, we don't use real grounds in real things. Theoretically-real grounds are hard to carry around since they weigh...oh let's see....INFINITE. Your fuel economy would be terrible.
So we use "ground" as slang to indicate where all the (usually) negative conductors are connected (mostly). It is perfectly possible to have no DC ground in an airplane, and in fact, composite airplanes just use a second conductor to borrow those little electrons from the battery.
The problems occur when we share conductors (AC, DC, Negative, Positive, or jumping-around-a-lot), because then old Devil Mr. Ohm demands his due.
PS: A DC circuit is only DC if it sits perfectly still. If you turn it ON or OFF it is AC if only for an instant. Managing that instant is the whole career of some engineers.
Hope this helps.
"Every act of conscious learning requires the willingness to suffer an
injury to one's self-esteem...."
-Thomas Szasz
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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nuckollsr(at)cox.net
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| Posted: Thu Nov 23, 2006 7:29 pm Post subject: 24V 12V grounds |
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At 08:02 AM 11/23/2006 -0800, you wrote:
| Quote: |
> One more time!
>
> There is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
>
> If you truly believe there is Design one so I can build it and you can
prove me wrong.
> OR tell the poor questioning soul how to "carefully crafted locations
designed to minimize the number of
> grounds and risks for ground-loop noise."
> Ya CAN'T because each plane is different the wire runs vary and there
is NO SUCH FREEKEN thing as a GROUND LOOP in a DC circuit.
>
> Barry
Barry is absolutely correct.
Unfortunately, we don't use real grounds in real things.
Theoretically-real grounds are hard to carry around since they weigh...oh
let's see....INFINITE. Your fuel economy would be terrible.
So we use "ground" as slang to indicate where all the (usually) negative
conductors are connected (mostly). It is perfectly possible to have no DC
ground in an airplane, and in fact, composite airplanes just use a second
conductor to borrow those little electrons from the battery.
The problems occur when we share conductors (AC, DC, Negative, Positive,
or jumping-around-a-lot), because then old Devil Mr. Ohm demands his due.
PS: A DC circuit is only DC if it sits perfectly still. If you turn it ON
or OFF it is AC if only for an instant. Managing that instant is the whole
career of some engineers.
Hope this helps.
|
Golly gee Eric. Talk about slicing and dicing the dictionary.
An alternating current system is one that changes polarity,
I.e. like positive for 1/2 cycle and reverses for another
half cycle. I.e., it ALTERNATES. Stating that DC becomes
something other than DC just because it is dynamic suggests
a vernacular from another planet.
Okay folks. Where Eric (and I presume Barry) lives. Any
DC system that is not absolutely rock stable is no longer
a DC system but . . . what? Oh yes, at what point do you
draw the line on stability sir? 1-volt "wiggles"? 1-millivolt
wiggles . . . how about microvolt wiggles? Taking this notion
to the molecular extreme, one might say that, "There is no such
thing as a DC system." Even a battery generates some
"wiggles" in output voltage as electrons within the chemistry
jump from ion to ion.
My teachers would disagree with your definitions sir as
do I. For the purposes of common language and understanding
here on the List and just so we're all on the same page, let
us stipulate: That (1) alternating current power distribution systems
are likened to that which comes out of your wall sockets and
(2) direct current power distribution systems are likened to that
which runs our automobiles. Further, DC systems that are less
than stable are still DC systems with distortion (noise). AC systems
suffer distortions too (mini-brownouts, switching transients and yes,
the effects of GROUND LOOPS). To argue differently may impress the
neophyte but it borders on bizarre in the venue where I work.
| Quote: | "Every act of conscious learning requires the willingness to suffer an
injury to one's self-esteem...."
|
-Thomas Szasz
What a bummer idea! I'll suggest a alternative:
"Every act of conscious learning requires a willingness to
seek out and understand the simple-ideas (fundamentals)
for the systems of interest. One's self-esteem is enhanced
by the ability to use those simple-ideas in ways that
are useful. One's self-esteem is really bolstered when
CUSTOMERS are willing to support your livelihood by
PURCHASING inventions you SUPPLY based on your understanding
of those fundamentals."
-Bob Nuckolls
I've read some of Szasz's work. He posits some interesting
and even attractive ideas but he's obviously not grounded
in reality. For example. He suggests, "abolition of involuntary
hospitalization: No one should be deprived of liberty unless
he is found guilty of a criminal offense. Depriving a person
of liberty for what is said to be his own good is immoral.
Just as a person suffering from terminal cancer may refuse
treatment, so should a person be able to refuse psychiatric
treatment."
I've had a lifetime experience with a mother who has suffered
from paranoid schizophrenia since her teens. I've witnessed
a virtual miracle of productive integration into family
and society when interventions were working along with her
suffering in a 24/7 living hell of nightmares when she
decided she was cured and dumped her protocols. Szasz speaks
a language attractive to amoral passivists but as your
chosen quotation illustrates, he does not philosophize in
simple-ideas. May I suggest more forward-looking philosophers
who have demonstrated the value of their philosophies for
living many times over? Try Charles Kettering, Ayn Rand,
Virgil Elings, just to name a few. These folks do not wallow
in self-deprecating ideas and nostrums for living. Not
one bummer quote from the lot!
Bob . . .
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FLYaDIVE(at)aol.com
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| Posted: Fri Nov 24, 2006 5:43 am Post subject: 24V 12V grounds |
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In a message dated 11/23/2006 10:31:05 PM Eastern Standard Time, nuckollsr(at)cox.net writes:
| Quote: | "There is no such
thing as a DC system." Even a battery generates some
"wiggles" in output voltage as electrons within the chemistry
jump from ion to ion. |
============================================
Hi Bob:
I do live on my own planet, but unfortunately I have to share it; I would even accept a planetoid.
GREAT statement above Bob. That is what I learned also. We must have read the same books at one time or another.
But, why in your GROUND explaination/seranio (your post explaining ground loops) did you pick thermocouples and group them under the DC Ground umbrella?
If you recall thermocouples when first produced were done so as a floating (non-grounded) device. And in many cases as a non-shieled device. This led to may erroneous reading on the gages ESPECIALLY when digital read-outs with low voltage sensing circuits came into play. So the method of correcting and stabilizing became a GROUNDED thermocouple. But, in this case you are talking Fruit Salad ... You know ... Apples & Oranges. They are close, but throwing them into the same bowl, I feel does not truly explain the issue. I think it is only confusing to many out there. Too much Tech-Know-Babble, sounding too much like Professor Irwin Cory.
The topic is DC GROUNDS. And you know me I keep things SIMPLE ... K.I.S.S. M.E. SIMPLE.
And for those that just might still be interested in the basics and how to eliminate about 98% of your electronical issues and NOISE issues here is the short version of the basics:
GROUND at the SOURCE (Alternators, Batteries, Avionics and the like).
CLEAN YOUR GROUNDS
ADD MORE GROUNDS to DC Circuits - Battery to Engine, Battery to Firewall, Firewall (after additional grounds have been added) to Panel and YES I strongly believe in a nice heavy gage Ground Terminal Block. Or at least a Brass Nut & Bolt.
[I believe my above statement is what started this debate - MORE Grounds do HELP]
DC Circuits Ground at BOTH ENDS
AF (Audio Frequencies) Ground ONLY at the Source
RF (Radio Frequencies) Ground at BOTH ends
Crazy thing here ... Alternators produce BOTH AF & RF, so what do you do? GROUND at BOTH Ends. YES! GROUND!
After you do the grounding THEN you can start playing with Inductors & Capacitors and Transient Suppressors.
This is the short list. I very seldom need to do more than that to prevent or remove a problem.
Barry
[quote][b]
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