Electromagnetic Coil Launcher Project
■ FIGURE 3. Transformer
bobbin and ferrite core.
■ FIGURE 4. Transformer parts
can be salvaged from an energy
saver compact fluorescent bulb.
All inductance measurements were
taken with the iron cores in place.
If you can’t locate a bobbin and
core of similar dimensions at your
local electronics store, then obtain a
dead or unused energy saver compact
fluorescent light bulb like the one
shown in Figure 4. Crack open the
lamp at the seam, being careful not to
break the glass tube, and remove the
circuit board. Locate the ferrite core
transformer and unsolder it from the
PCB (printed circuit board). Detach
the core parts by unwrapping any tape
that may be holding them together.
Use a knife or saw with a fine blade
to cut the glue at the points where the
core halves are in contact if the E-cores
are glued together. There will probably
be an air gap spacer on each side of the
cores and in the middle so that the
ferric material of each core does not
contact. Don’t worry about destroying
the gaps because we will be adding
our own later. Remove all of the wire
and tape from the bobbin.
It’s okay if your bobbin doesn’t
have terminal posts since connector
wires can be used instead. You should
now have a bobbin and E-cores similar
to the ones shown in Figure 5-A.
Start by numbering the bobbin
posts from 1 to 8 in the positions
shown in Figure 3. Solder one end of a
piece of #26 laminated magnet wire to
post number 2 and then wind the primary coil of 10 turns clockwise around
the top half of the bobbin as shown in
Figure 5-B. Solder the other end of the
primary winding wire to post number
3. Using another piece of #26 magnet
wire, solder one end of the wire to
post number 1 and then wind the
feedback coil of eight turns on the
bobbin clockwise below the primary
winding as shown in Figure 5-C.
Solder the other end of the feedback winding to post number 4. Next,
cover the primary and feedback windings with a layer of electrical tape as
■ FIGURE 6.
depicted in Figure 5-D. On the other
side of the bobbin, solder the end of a
piece of #34 AWG magnet wire on
post number 5 and then wind the secondary coil of 500 turns in even layers.
When hand winding the coil, you
probably won’t be able to get the layers perfect but it won’t be a problem;
just make them as neat as possible.
Solder the other end of the secondary
winding to post number 8 as shown in
Figure 5-E. Wrap the secondary winding with a layer of transformer tape
and then coat the solder connections
with silicone rubber or a similar insu-
■ FIGURE 5.
March 2008 53