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randommscience117

Fri Jun 01 2012, 11:21PM

Registered Member #4274 Joined: Mon Dec 19 2011, 03:10AM
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I was wondering if it is possible to transmit DC current in 1 wire with both positive and negative. If one pole, say the positive pole, was a different frequency than the negative, wouldn't they travel in different depths of the wire and therefore not 'short circuit'? I know power companies use something similar to read your power meter by transmitting the usage back through the line at a different frequency, but is this possible with power transmission, and how would you do it?

Neet Studio

Fri Jun 01 2012, 11:24PM

Registered Member #4037 Joined: Fri Jul 29 2011, 03:13PM
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DC = 0Hz. How may 0Hz can you have?

>DC current
>different frequency

Also skin depth does not mean the actual depth the current travel at.

At DC = 0Hz, the whole cross section of the wire can carry current.

I'll do what Tesla did... No wires.

Pinkamena

Fri Jun 01 2012, 11:47PM

Registered Member #4237 Joined: Tue Nov 29 2011, 02:49PM
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Pretty sure that's not what skin depth means!

genious 7

Sat Jun 02 2012, 12:18AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
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Nope, it doesn't work like that as far as I know. You can have different frequencies on the same cable, yes, but you need a return path for that; it will not be on the same cable.

However, in my extremely nontechnical and nonprofessional experience, I think you could transmit power in one wire while using the earth as the other terminal;ej after an isolation transformer (or some type of transformer) , one end to earth, the other to the receiver end. In the receiver end, the second cable is again connected to ground. While I'm pretty sure this works, I have no idea how safe/unsafe (probably unsafe) this is.

Patrick

Sat Jun 02 2012, 12:53AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Data transmission over power wire and single wire power are different.

For example you can modulate HF over LF or DC, like the home automation X10 stuff used too.
And as for power, as others have said the ground path is the other wire, however tesla and others have always been facinated with single wire and wireless power transmission, which involve RLC circuits and or microwaves. Though there are many proposed methods.

I think your 0Hz and skin depth reasoning is flawed.

Also:

Michael Chen wrote ...

However, in my extremely nontechnical and nonprofessional experience, I think you could transmit power in one wire while using the earth as the other terminal;ej after an isolation transformer (or some type of transformer) , one end to earth, the other to the receiver end. In the receiver end, the second cable is again connected to ground. While I'm pretty sure this works, I have no idea how safe/unsafe (probably unsafe) this is.

You must realize that the dirt is of high resistance, and in traditional power circuits its used to hold two or more points at a common potential (near zero volts, for example) while a proper conductor is at that same potential as earth and functions as the high current return.

randommscience117

Sat Jun 02 2012, 01:07AM

Registered Member #4274 Joined: Mon Dec 19 2011, 03:10AM
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Sudden realization: No frequency will only travel on the inner-most part of the wire, therefore it would always 'short circuit'. Oops.
New question: Can DC and AC be transmitted on the same wire under any circumstances?

Patrick

Sat Jun 02 2012, 01:14AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

randommscience117 wrote ...

Sudden realization: No frequency will only travel on the inner-most part of the wire, therefore it would always 'short circuit'. Oops.
New question: Can DC and AC be transmitted on the same wire under any circumstances?

let me look at my college textbook it has a picture of what your asking.

EDIT: i cant seem to find it but i believe the magnitudes add and subtract in polarity, though source impedance matters since you would have atleast one DC source and one AC source, also series vs parallel mattters.

Neet Studio

Sat Jun 02 2012, 01:24AM

Registered Member #4037 Joined: Fri Jul 29 2011, 03:13PM
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A switch mode power supply that draws on DC power, but reflected back AC ripple current back to the supply on the same two wires.

If your power rail does not have low impedance (insufficient decoupling caps for example), you'll find AC voltage superimposed on top of the DC as the load draws on current.

Also read up on Superposition principle.

It is one of the most basic theories in electrical engineering...

Ben Solon

Sat Jun 02 2012, 01:30AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

You can have ac with a bias ie. 0-340v p-p rather than -170-170v p-p. but as said: dc is 0hz, and ac is >0hz. If current is alternating, then it's not dc and vice versa.

Mattski

Sat Jun 02 2012, 01:36AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Absolutely, it's just an AC signal with a DC offset. A bias tee allows you to separate them so that you can inject the DC without affecting the AC. Note that in the Wikipedia diagram the return path for both the AC and DC current is not drawn, but it must be there. I think some security cameras can be powered over their coax this way.

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