There would be too little magnetic coupling from two series resistors wound
opposite directions for the field to cancel.
Some N.I. wire wound resistors have two opposite direction wound coils such
that they cross and connect twice each turn. This simulates a uniform
cylinder. I have had some of these in the past but even these sometimes do
not work well above 5 or so MHz.
73
Bill wa4lav
At 03:43 PM 9/28/2004 -0400, craxd wrote:
Mike,
For smaller loads, I'd use a Globar resistor also. For the 20 Kw load, and
to homebrew one with limited resources, they might look into this. I was
thinking about those large grid resistors. If one had two of them, 25 ohms
each, but wound in opposite directions, it might work somewhat by
seriesing them. This would be the same as that dual wound resistor in two
sections with the different hand coils. The bifilar has a lot of
capacitance due to the potential difference between the incoming and
outgoing resistance wire. But, if this was broken up like the mentioned in
sections, it may work also. One would have to use some sort of alloy
tubing with the highest resistance you could get. For 20 Kw, were probably
talking something like 3/4" diameter tubing with maybe a 1/8" thick wall
or larger. Inco Alloys (Now named Huntington Alloys), has both the alloy
mill (Huntington, WV.), and the tubing plant just down the road in
Burnaugh, Kentucky. They make about every nickel alloy, (Inconel, Monel,
etc.), and others you could mention. I had a friend who retired there and
he may know about this, I'm not sure. Even using that figure eight pattern
might be better. It has a figure eight wound every other turn so to
continuously reverse the current flow from one turn to the next. With
stiff enough tubing, this might be done without using a coil form.
I'd like to experiment with this some myself just to see what will work
and what will not. For loads of 5 Kw and down, I'd stick with the Globar
resistors.
Will Matney
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