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Home -> Resources -> How To -> Bifilar Coil Winding

How To Wind a Bifilar Coil

Author: Mark Read
Created: Thursday 26 July 2007
Last update: Thursday 26 July 2007
Description: This mini-project shows you how to wind a bifilar (2 wire) coil. The 870 wind coil created using the below procedure took approx 20 minutes using our manual coil winding jig.
Instructions: View the photos and video to see how it's done.
Notes: This demonstration uses the manual coil winding jig as described in our mini project sheet How To Build a Simple Coil Winding Jig. The actual coil wound in this demonstration was used in our project Bedini SSG Battery Energizer - Build #1.

Materials List

In this "how-to" we are going to wind a bifilar coil for our Bedini SSG Battery Energiser project (however we shall not be placing the core material in the coil for this example).

The empty black plastic spool was a freebie from my local hardware store (the spool had link chain on it, which had been all sold, so I asked if I could have the spool). The spool dimensions can be seen here

The 2 spools of enameled copper wire was purchased from (July 2007).

  • 1 x empty plastic spool, approx 90mm high with 70mm to 90mm diameter flanges and a core hole 14mm to 20mm in diameter.

  • 1 x spool of enameled copper wire, 0.5Kg, 0.56mm (close to #23 AWG), approx 120m in length. RS Stock #357-750. A$36.80.

  • 1 x spool of enameled copper wire, 0.5Kg, 0.80mm (close to #20 AWG), approx 100m in length. RS Stock #357-772. A$35.40

  • Black electrical insulation tape. A$2.00 for a pack of 4 rolls.

Equipment Needed

  • Coil Winding Jig (optional). Our example coil could of been wound by hand but that process takes around 3-4 hours!


  • Diagram showing the winding process.


View the completed (wound) coil here.


View the winding videos, either streamed (in a new web browser window that opens automatically when you click on the link) via the YouTube website, or via downloading the Microsoft wmv files to your computer.

Watch here on YouTube (runtime: 5 minutes 35 seconds)

Tip: If you're accessing this site via a dialup link, we suggest you watch the low-bandwidth friendly streamed videos, available on YouTube.


Media Player
Windows WMV files (320 x 240 - 150 kpbs low bandwidth encoding)

Simply click on the video link below to watch in a new window (if you're on a Microsoft Windows platform, like Windows XP), or right click on the link and select 'Save Target as ...' to download the video to your computer & watch off-line.

Winding a Bifilar Coil (6.1Mb)

Winding Notes

  1. Ensure you've got all the parts and equipment you need (refer to the lists above) before starting.

  2. View all the drawings, photos and videos (above) to get an idea of what you're about to build. Print off any drawings and photos to help with the construction process.

  3. Set aside 30 minutes to complete your first wind (if using the recommended manual coil winding jig) or 3 to 4 hours if winding by hand. The remaining instructions apply to the manual winding jig only.

  4. Start by drilling 2 holes in the empty (coil) spool - 1 in the top flange, and 1 in the bottom flange. The 2 holes should be opposite one another. The holes need only be big enough to fit the 2 copper wires through (we used a 2mm drill bit).

  5. Stand (or sit) in front of the manual coil winding jig, so that the cranking end is closest to you, and the copper wire "feeder" end is furthest away from you. It might help to print off a copy of the spool winding schematic and place on top of the base plate underneath the coil spool as a winding reference guide.

  6. Place the empty spool onto our winding jig (undo the retaining screw on the "crank" or "winding" shaft, slide the shaft out of the left leg, slide the empty spool on to the shaft, push the shaft back through the left leg hold and reattach the retaining screw).

  7. Place the 2 copper wire spools (0.56mm and 0.80mm) onto the feeder shaft. It does not matter which spool sits on the left and which one sits on the right.

  8. Grab hold of both copper wires from the feeder spools and push them, both together, through the left hand flange hole we drilled earlier. Pull the 2 copper wires through the 2mm hole so that around 100mm (4 inches) of wire pokes through.

  9. Now, with your right hand, slowly wind the crank handle anti-clockwise (backwards) so the 2 copper wires slowly start to wrap around the spool. The 2 copper wires will come in over the top of the spool towards you and feed around and under. Use your left hand to keep the 2 copper "feeder" wires together.

  10. Keep a count of how many turns you are making with the crank handle. When you get up to a count of "100", stop winding and write "100" (or a single vertical stroke) on a piece of paper. Then begin counting from "1" again.

  11. After 10 to 20 winds, slide the copper wire on the spool to the left, so they sit side-by-side and give you more room to wind on more wire onto the spool.

  12. The copper wire will "move to the right" as you wind it on to the spool. For our example spool it took 50 winds to totally fill the black spool shaft. At this point our feeder wire is hard up against the right hand flange.

  13. Keep winding, but now start a second layer of copper, moving your hand slowly from right to left. Don't be too concerned if your 2 feeder wires want to start "parting company" a little as they wind on to the spool. This is natural, but do try your best to keep them perfectly parallel to one another as you wind them on to the spool. Keeping your left hand close to the spool will ensure greater accuracy.

  14. You'll find your "second layer" won't be the same number of turns as your "first layer" - your second layer will probably be a few shorter than the 1st layer. This is natural as we're not robots with precision winding skills :)

  15. When you back back to the left hand flange, you've completed your "second layer" of windings. Keep going - head towards the right hand flange again to complete your third layer.

  16. Keep doing this back-and-forth layer-by-layer system until you have completed all the turns you require. For example, the Bedini SSG bifilar coil calls for around 850 turns.

  17. When you've completed your winding, use a pair of pliers or wire cutters to cut the 2 feeder wires around 100mm (4 inches) away from the coil (front) spool. Then feed these 2 wires through the little hole in the right hand flange.

  18. Now, to finish off your spool, grab your black insulation tape and wind it around your front spool, covering the copper wire as you go. Just one or two layers of tape is sufficient.

  19. That's it - all done!!