# Single conductor inside hollow conductor

1. ## Re: Single conductor inside hollow conductor

50 Hz is way too low for 13 turns on an unknown core size

for ferrite Bpk < 0.3T Bpk = Erms /( 4.44 F. N Ae ) for sine wave. Ae = ferrite core area, N = turns, F = Hz

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area in m^2

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2. ## Re: Single conductor inside hollow conductor

It makes sense to characterize the transformer in terms of mains and leakage inductance plus large signal parameters.

In case of 50 Hz application, leakage inductance can be effectively neglected, but main inductance respectively magnetizing current can't. The voltage drop you are seeing isn't caused by insufficient coupling but voltage drop due to magnetizing current. It would be roughly the same with regular transformer windings and same number of turns.

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3. ## Re: Single conductor inside hollow conductor

13 Turns on a steel core will give you a much better indication @ 50Hz

4. ## Re: Single conductor inside hollow conductor

Originally Posted by Easy peasy
13 Turns on a steel core will give you a much better indication @ 50Hz
The core I used is hitachi amcc100. I mistakenly said that it was 13 turns on core. I initially had 6 turns on core and was seeing the lower voltage. When I went to 13 turns the coupling was much better. In both cases the current was higher when voltage was applied to outer conductor. My apologies for the misinformation. I work away from home 4 weeks at a time and trying to recall things from memory. When I get back home I will take measurements again and post them.

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5. ## Re: Single conductor inside hollow conductor

I applied 3 vac across center conductor and measured 1.4 vac on shield wire. When I applied 3 volts to shield wire I measure 2.71 volts on center conductor.
I do not have any direct explanation but these come to the mind:

1. The two conductors are not symmetrically places. Because the shield is floating, a large part of the electric field is blocked and a smaller part of the magnetic field is also blocked (more if the shield is solid). That I guess is the reason for case I. Correct way, in my opinion, is to twist two coaxes nicely, connect the shields to the ground (fixed voltage) and measure the effects between two core conductors. There are coaxes with foil shields and they may be used for more reliable results.

2. When the shield is used a primary, the electric field will be zero inside but the magnetic field will be not. But because of the gap (there will be some space), we shall have some leakage. Hence I expect higher voltage for case II.

You should carry out the experiment (i) without a core and (ii) with a simple rod (iron or ferrite) whose length is larger than the coil length.

3. By the way, did you measure the current?

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6. ## Re: Single conductor inside hollow conductor

if anyone wishes to continue he discussion of potential, emf and voltage, etc,
as this seems somewhat far afield from kajunbee's question

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7. ## Re: Single conductor inside hollow conductor

@cmitra I did measure input current, but I'm unable to say with certainty what it was. Will be another 5 days before I get back to house. I ordered a 16' roll of .026" Id soft copper capillary tubing and 23 gauge magnet wire. Hopefully I will be able to insert the wire in tubing. Since the copper tubing has no insulation do you think I could get away with using polyurethane spray varnish like used on furniture?

8. ## Re: Single conductor inside hollow conductor

Since the copper tubing has no insulation do you think I could get away with using polyurethane spray varnish like used on furniture?
If the voltages are small enough, there should be no problem.

In my student days, I have seen electromagnets made with copper tubes covered with cotton threads and heavily varnished. Water mixed with glycol (I think) used to be circulated with a pump in a closed circuit which is in turn cooled with chilled water...

To thread the wire in the tube: ensure there is no blockage by first blowing air. Then pass some light oil (paraffin oil is very good) to reduce friction. Then try to push the magnet wire slowly. I should not be difficult. If you wish to remove the oil, use water mixed with some detergent and finally use alcohol and air to remove the last traces of alcohol.

Finally, do not use very high frequency to do the final experiment because copper will block high frequency magnetic field also. A low frequency, the skin depth is large and you can get useful results.

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9. ## Re: Single conductor inside hollow conductor

Proving to be more difficult than I expected. The 23 gauge will start but just the slightest bend in wire or tubing will cause it to jam up. I will try with 24 gauge and see how that goes. If that doesn't work I may go with larger capillary tubing. Basically insert the smaller tubing inside a larger tube. It should not be as difficult to insert solid wire through the larger Id tubing. I can then solder the wire into the smaller tubing. And then use wire to pull small tubing through larger tubing.
I'm trying to keep as tight as possible to minimize air gaps and keep inner conductor centered. But not sure if worth extra effort. How might these things effect the output?

10. ## Re: Single conductor inside hollow conductor

After several attempts I was able to put something together. I was able to manage 40 turns on the same core I had used previously. The tubing ws .065" Id with 23 gauge wire inserted. These are a few measurements I took with tubing as primary.

Primary applied voltage- 2.28 vac amps - 1.98
Secondary voltage - 2.27 vac

Primary voltage - 3.96 vac amps - 2.31
Secondary voltage - 3.96 vac

Primary voltage - 4.94 vac amps - 2.63
Secondary - 4.93 vac

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11. ## Re: Single conductor inside hollow conductor

so you have made a 1:1 transformer - well done ...!

12. ## Re: Single conductor inside hollow conductor

To pull wire through a tube, first use a vacuum cleaner to s-u-c-k a string through the tube. (It works quickly whether the tube is coiled or straight.) Tie the wire to the string, then pull on the string which in turn pulls the wire.