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progress report (ballast)



Hi All,
       I have been experimenting with one of my inductor cores and the
windings from an old auto transformer I found at the Scrapyard. I carefully
read Richies excellent article on his new  ballast inductors, and checked
the turns ratio to core size to my core . My core area turned out to be 6
Square Inches to Richies 8.75" . As Richie had 134 turns  I worked out I
would need about 200 to maintain the same ratio. I checked the auto tranny
coils and they had 200 turns of 3.5mm square magnet wire.  I  dragged the
whole  tranny home, all 60 KGs of it, and set about removing the laminations
one by one so as not to damage the windings . Also I was reluctant to take
it out of the back of the van as I knew I couldn't move it once it was on
the floor. This only took a day or so. Once I had the coils off I checked
that they fitted my core . They fitted perfectly.! ah a miracle. I then
coupled  up an ammeter and volt meter to the variac, and tried various air
gap sizes while checking the current at  10 volt intervals. I started with
no gap ,and got 1.5 amps at 250 volts. I tried larger and larger gaps and
noted the current up to 10 amps. The lines look really smooth with no sign
of saturation.  I had to stop at 10 amps as it was 2.00 AM and it was rather
loud with all the loose laminations. This evening I tried the ballast out
with my 2.2 kW radar tranny  running a Jacobs ladder, and it works fine and
draws 12 amps with everything running cool except my meter leads. I have
made a current probe by winding 100 turns of 22 AWG around a small ferrite
ring with a 1 ohm resistor across it, and looping  one turn of the lead  to
the ammeter  though it. This gives a nice 100 millivolt signal to the scope
at 12 amps. When I find my 10 x scope probe I will see what the phase angle
between the voltage and current looks like with different air gaps. It all
seems to be working out fine at the moment. I  have put four lengths of
threaded rod though the angle brackets holding the core together so all  I
have to do to adjust the air gap is slacken off 4 nuts  and fit in different
thickness' of poly  depending on the current required. I did try the welder
under the same conditions but it gets very hot at 12 amps. I might try using
the welder after the ballast for fine tuning but It is so easy to just
change the gap spacing I might not bother. I was worried about circulating
currents around the threaded rod but no sign of warming  after 10 minutes of
Jacob's ladder at 2800 watts. Can't wait to try it out on the coil. Any help
on  calibrating the current  probe  welcome. It would be nice if it had a
linear response between 1.5 and 15 amps. I  will write this all up with
photos and put it up on a web site when I have more time.

cheers
bob golding