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If I wound 2 solenoids with current in opposite direction (wound into each other like in the 1st photo) will I cancel the magnetic field ? Or did I made it stronger ?

Is it better having a twister pair cables, with current in opposite direction? Or is it better to have 2 solenoid wound in opposite direction? Which one gives the lower emf to nearby components (the best emf cancelling effect) ?

Thank you.

(I run the wires with 9VAC 2A psu)

EDIT : Clarifications : In the green wire I have -4.5V and in the red I have +4.5V. The current flow in different directions. The cables feed a load. The green wire is the current return path (conventional). enter image description here enter image description here enter image description here

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2 Answers 2

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enter image description here

Figure 1. The right-hand rule for polarity of a solenoid. Source: Commons.

If you apply the right-hand rule twice, once for each direction of the current you will see that the result is zero flux. They cancel out. No inductance. No magnetic field.

Which one gives the lower emf to nearby components (the best emf cancelling effect)?

Contra-currents will minimise EMF but gives you no inductance so it is no use.

All of this assumes that your winding direction is the same for both coils as shown in your diagram. If wound opposite rotation then the contra-current would end up adding to the first coil.

Note: I once had to create a 1 Ω test load for a 30 A current controller. We wound the right length of 1.5 mm2 insulated wire into a foot diameter coil. When powered with 50 Hz it would vibrate severely on the table top. We unwound it, folded it in half and rewound it. There was then no vibration from the coil. We had cancelled out any magnetic field almost completely.

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  • \$\begingroup\$ Thank you. The main goal is not to create useful solenoids, it is to cancel the magnetic fields created by heavy currents in the wires. Zero inductance is fine. This arrangement is better than twisted pairs ? \$\endgroup\$ Commented Dec 8, 2019 at 15:42
  • \$\begingroup\$ No magnetic field gives no magnetic attraction meaning it's not a solenoid. \$\endgroup\$
    – Transistor
    Commented Dec 8, 2019 at 15:46
  • \$\begingroup\$ I understand now. You completely cancel any emf since there is no inductance anymore. So you cancel better than a mere twister pair cables arrangement ? \$\endgroup\$ Commented Dec 8, 2019 at 16:15
  • \$\begingroup\$ It doesn't have much to do with inductance. It has to do with current and those cancel out. Are you clear that you can't make a solenoid this way? \$\endgroup\$
    – Transistor
    Commented Dec 8, 2019 at 16:21
  • \$\begingroup\$ … it is to cancel the magnetic fields created by heavy currents in the wires. Just run a single wire carrying the same current in the opposite direction next to it then. \$\endgroup\$
    – Janka
    Commented Dec 8, 2019 at 16:42
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If I wound 2 solenoids in opposite direction (wound into each other like in the photo) will I cancel the magnetic fied ? Or did I made it stronger ?

You made it stronger because, if you analyse the current flow in the red wire and the green wire, they are in the same direction.


For the visually impaired, I've taken the original drawing, shortened it to concentrate on the wire turns and superimposed current direction lines: -

enter image description here

So, using the red wire exiting on left (because it is unambiguous in its current direction), I've projected magenta current direction arrows for each red turn. For the green wire exiting on the right (because it is unambiguous in its current direction), I've projected bright green current direction arrows.

Clearly the red current and the green current are in the same direction and therefore produce additive magnetic fluxes.

If they were wound in the same direction (in order to cancel the magnetic fluxes), the OP should have shown it like this (but he didn't): -

enter image description here

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$
    – Dave Tweed
    Commented Dec 9, 2019 at 12:00

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