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Coil Construction
1. Take a small piece of tape or paper and attach it to the end of the roll of 28 gauge magnet wire. Write the number '1' on the piece of tape or paper. This will be used later to identify the electromagnet's leads.
2. Mark a point on the shaft of the 5/8" hex bolt that is 2 1/4" away from the hex cap. Begin wrapping the 28 gauge magnet wire around the shaft of the hex bolt from this point. Do not start wrapping the coil from the very end of the wire. Give yourself a foot or so of 'extra' wire at the beginning of the coil. This extra wire should posses the label you created in Step 1. As you wrap the coil around the shaft, you should be working your way towards the hex cap end of the bolt. The coils should be wound as neatly and as tightly as possible.
The coil should begin 2.25" from the hex cap and should be wound towards it.
A few layers of masking tape have been wrapped around the shaft of the bolt
to help support the free end of the coil.
3. When the windings reach the hex cap, begin a second layer atop the first layer. Work will now progress up the shaft but the direction of the windings will remain unchanged. For example, if the wire was being wound about the bolt in a clockwise fashion on the first layer, the clockwise motion would continue on the second, and all subsequent, layers.
4. When the windings reach the 2 1/4" mark, begin wrapping the third layer, working towards the hex cap.
5. When the third layer is complete, create a center tap by running the magnet wire directly up the shaft of the bolt. Extend the wire about a foot beyond the end of the bolt. Label this outgoing wire '2.'
Three layers of wire have been wrapped around the core. Before continuing with
the fourth layer, the wire was brought back up the length
of the bolt's shaft in order to create a center tap.
6. Bend the wire back upon itself and run it directly down the shaft of the bolt to the hex cap. Label this in going wire '3.'
Bend the wire back upon itself in order to complete the center tap.
7. Wind the fourth layer of the coil. It will start at the hex cap and work its way up the shaft. Make certain that the fourth layer is wrapped in the same direction (clockwise or counter-clockwise) as the rest of the coil.
Continue wrapping the fourth layer as if the center tap never happened.
Use small bits of tape to hold the center tap wires in position.
8. When the fourth layer is complete, add a fifth layer.
9. When the fifth layer is complete, add a sixth layer. This is the coil's final layer of wire. When the sixth layer is complete, cut the wire from the spool, giving yourself about a foot or so of 'extra' wire. Label this final lead '4.'
10. Cover the coil with epoxy and let it set.
11. Use a strip of clear packing tape to secure the portion of the lead wires near the coil to the shaft of the bolt. This gauge wire is relatively thin and solid core wire has the nasty habit of breaking in the most inconvenient locations. The packing tape will act as a strain relief so, if a wire does snap, it will not snap at the surface of the coil.
12. Cut the loop of wire that was formed when you created the center tap in steps 5 and 6. Make the cut between the labels you placed on that section of wire. When complete, your coil will have four leads protruding from it, labeled 1, 2, 3 and 4. Each of these leads should be a foot or so long. Leads 1 and 2 control the inner three layers of the coil while leads 3 and 4 control the outer three layers. The full coil consists of about 1,000 turns of wire and has a total resistance of about 12 ohms.
The completed coil.
13. Use a medium grit sandpaper to scrape away the enamel insulation from the last inch of each of the four lead wires. If the labels are in the way, move them but keep them on their respective leads. It is in your best interest not to lose track of which lead is which.
14. That's a wrap!
This page is maintained by Steve Gagnon. |