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Old 04-01-2011, 03:48   #76
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A pair of wires running a DC load will cause a compass card to swing if the wires run close to the compass.It is wise when routing wires near a compass to twist them with an electric drill before installation to cancel out any magnetic effect on the compass.This turning motion is the same as happens in a permanent magnet electric motor but there is only one winding acting on the card.

My 2cents(Cdn)

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Old 05-01-2011, 01:12   #77
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a constant voltage dc current with a fixed wire shouldnt cause problems.. when you moved / swung the wire it and the magnetic flux moved with it, and that is what caused the reaction.. when you mount the wire the problem should be gone...

twisting th wire will make the job look kinda neat / professional, but I would like to see the wires seperated in case you need to replace just one conductor..

but, I dont know the code or common practice..
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Old 05-01-2011, 01:25   #78
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a constant voltage dc current with a fixed wire shouldnt cause problems.. when you moved / swung the wire it and the magnetic flux moved with it, and that is what caused the reaction.. when you mount the wire the problem should be gone...

twisting th wire will make the job look kinda neat / professional, but I would like to see the wires seperated in case you need to replace just one conductor..

but, I dont know the code or common practice..

DC current in a wire makes a magnetic field. A constant magnetic field will create deviation in your compass, it doesn't have to move.

From: Electric current - Wikipedia, the free encyclopedia


According to Ampère's law, an electric current produces a magnetic field.

Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire.


If two wires are close to each other with currents flowing in opposite directions, they make opposite magnetic fields that tend to cancel each other. Twisting them does the job better. The worst thing you can do is run the positive and negative wires far apart if you're trying to minimize the magnetic field.

John
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Old 05-01-2011, 03:50   #79
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yes, like i said the flux will be constant with the current being constant and the wire not moving.

if the current is so high that it affects your compass then you might have a nuclear reactor onboard...

if you have otehr devices that turn the current on and off fairly rapidly, that may make a difference too. (if it is within close enuf proximity to the nav hardware)

any wires that conduct fast oscillation would be shielded (braided) and grounded...

a simple twisted wire will not do much for cancelling out the flux generated... unless it too was shielded..
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Old 17-01-2011, 14:06   #80
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if the current is so high that it affects your compass then you might have a nuclear reactor onboard...
Some compass manufacturers provide and recommend that the wires supplying power to the lighting of the compass be twisted. Not much current is required for the lighting of a compass. Wires carrying current in opposite direction tend to cancel each other.
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Old 17-01-2011, 14:20   #81
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although i understabnd the concept of cancling out, the wires are so much larger and the twist is so 'far apart' with relation to ATOMS and ELECTRONS that it jsut wont matter.


think about shielded cable and how tight they are woven together to keep rf and interference, and you think that a simple twist of the wires would do the same thing?

I just saw a special on Stephen Hawking and the indicated that if an atom had a nucleus the size of a marble, the electron would be two miles away... (making the electron the width of hair...

anyways, electrons and radiation waves will slip thru any twist you can give a wire...
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Old 17-01-2011, 17:43   #82
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although i understabnd the concept of cancling out, the wires are so much larger and the twist is so 'far apart' with relation to ATOMS and ELECTRONS that it jsut wont matter.
Have you tried that old lab demonstration of passing an electric current in a wire near a compass?
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Old 17-01-2011, 17:47   #83
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yes, and what is the difference between that 'experiment' and how anything is wired in the real world?

the wire moves!!!! if the wires doesnt move then nothing is going on...

the other 'difference' could be that instead of DC voltage, that AC is flowing throw a fixed wire and that could/would have an affect... Or RF frequency in the wire could have similar affect...

but per this discussion it has been DC...

but per the experiment, are you suggesting that if we twist the wires and pass it by the magnet that there wont be an affect?
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Old 17-01-2011, 17:54   #84
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If two wires are close to each other with currents flowing in opposite directions, they make opposite magnetic fields that tend to cancel each other. Twisting them does the job better. The worst thing you can do is run the positive and negative wires far apart if you're trying to minimize the magnetic field.
John
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Old 17-01-2011, 18:07   #85
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yes, and what is the difference between that 'experiment' and how anything is wired in the real world?

the wire moves!!!! if the wires doesnt move then nothing is going on...

the other 'difference' could be that instead of DC voltage, that AC is flowing throw a fixed wire and that could/would have an affect... Or RF frequency in the wire could have similar affect...

but per this discussion it has been DC...

but per the experiment, are you suggesting that if we twist the wires and pass it by the magnet that there wont be an affect?
I don't think you remember the experiment very well. The video linked below doesn't have a nuclear reactor, the wire isn't moving, and the battery in the little box isn't AC.



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Old 17-01-2011, 18:13   #86
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Impressive how seriously some are taking electrical theory here on a boating forum,
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Old 17-01-2011, 19:56   #87
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Impressive how seriously some are taking electrical theory here on a boating forum,
Useless theory for those who pay to have all the work done on their boat. Useful for someone thinking about routing wires near their compass.

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Old 17-01-2011, 20:04   #88
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hang on, I might have to call you on this one...if the conductor is a straight wire, (no coil), andit has current flowing thru it, and you are saying it gives off a magnetic field, i would have to disagree...

is the current direct current? or AC?

If it is AC, then yes, you will get the same magnetic field as if the 'coil' had one loop...

so, hang on, did i just contradict myself? let me read... um, why, yes, i did... hmmm

i hate that


sorry
I stand Corrected, on a miserable and basic issue!!!

God, I hate it when that happens.. i start thinking about something and go off and then try to defend it... what a putz!

anyways, thanks for the video, and making me go back and review basics


and sorry

but, I would like more info on the twisted wire thing as i still dont think twisting two or three wires would complete cancel out the em field, maybe at exactly 180 degree positions but not at other angles of the wire... not sure that makes sense


but in light of my prior basic err, i would default to beleiving my position is more then WEAK... heheheh
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Old 18-01-2011, 04:25   #89
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edited it all out when I decided it just didn't matter
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Old 23-01-2011, 10:15   #90
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i still dont think twisting two or three wires would complete cancel out the em field,
You are right.
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If two wires are close to each other with currents flowing in opposite directions, they make opposite magnetic fields that tend to cancel each other.
John
If we accept the above then we may also accept that the wire the closest to the compass will have the greatest effect on the compass than the other wire that is further away. Now if we rotate (twist) 180 degrees the two wires then the wire that was the further away become the closest with an opposing effect on the compass. More the twist.
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does the job better.
John
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Impressive how seriously some are taking electrical theory here on a boating forum,
It all depend how much accurate someone like his boat compass.
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