# Reverse Bifilar Coil vs Bucking Coils

Discussion in 'General Electronics Discussion' started by Mr Ed, Mar 18, 2018.

1. ### Mr Ed

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Oct 6, 2017
Can somebody point out the difference between these coils? Because to me they seem to do the same thing.
The reverse wound bifilar coil is wound in such a way that in any one position on the coil the current is flowing both ways which results in a zero net magnetic field.
Bucking coils consist of two coils. One wound CW and the other CCW. The coils are positioned end to end in a magnetic poles opposing configuration ie. NN or SS. This also results in a zero net magnetic field.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
The former would generate very little magnetic field because conductors carrying current in opposing directions are nearly concident.

In the latter case, each coil could quite easily generate a substantial magnetic field, it's just that they are of the same magnitude but opposite direction, they mathematically cancel. It doesn't mean that there isn't a magnetic field at some points.

Consider forcing two magnets together so that their like poles connect. Because, at best the magnets can be placed end on end, not coincident to each other, their fields will be distorted (greatly) but not cancelled out.

Electrically, the former can't store significant energy, but the latter can (i.e. it is inductive).

3. ### Mr Ed

16
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Oct 6, 2017
If the bifilar coil was the secondary coil of a transformer, would a current be induced? In the case of bucking coils I think it would.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
If it was wired such that each part of the bifilar winding was in opposition to the other, then no.

For bucking could, the answer is yes. It's no different than any other 2 coils.

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Oct 13, 2019
Depends on whether you are inducing an electrical current through the 2 counter wound bifilar coils from another coil or whether you are driving an electrical current through those coils directly. In the case of an induced magnetic field upon two coplanar coils. One CW and the other CCW, the induced magnetic field is the same orientation through both coils and they’re electrical polarity will simply be reversed at the ends of the coils.
No opposing of fields here. However if you directly drive a current through these coils in series,such as a split coil upon the same form they’re own magnetic fields will oppose. NN, SS. If one feeds a current through a bifilar coil that loops back on itself at one end travels back to the start, then they’re magnetic fields cancel. If one loops the first wire of a bifilar coils end back to the start of the 2nd wire and takes the output off the 2nd wires end then the magnetic field is not cancelled and the coil as a whole can store more energy due to the added capacity. Wind 2 coplanar coils one CW and CCW. Connect the 2 coils to each coils opposite ends, they will be same electrical polarity. Cross connected. Now induce upon this coplanar bifilar coil a magnetic field by driving it with an input coil. The coplanar bifilar Does not cancel its magnetic field but is mutual and in proper alignment thru both coils. Use a 3rd coil for ouput or use this arrangement through a spark gap to pulse an ordinary transformer.