Bill,
I was thinking of that when I typed that. The bodies and forms of those
large grid resistors may hold them too far apart to work. About the only
way to do it , maybe, would be to wind two alloy coils like this with a
short space, no more than two turns between the two. Tubing large enough
wouldn't require a form anyhow. I'm thinking about a large coil, maybe
8" to 12" in diameter, wound with 1/2"-3/4" alloy tubing, etc. But, If I
were to do it, I think I'd try that figure eight design first as it
cancels itself at each turn. This would probably require some sort of a
form, so a large diameter wire might have to be used or a smaller
tubing. One thing, it could be water or oil cooled and drop the size by
about 50%-80% according to the book. I was thinking about the diameter.
At 8" diameter, that would be 25" around the circumference so it would
take up that length of wire pretty quick. One might get by with about 14
turns per coil using that one alloy (807) I read about. It was available
in wire but tubing I don't know. If that wire was cheap enough, it sure
would be an interesting experiment.
Will Matney
Bill Fuqua wrote:
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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
__________ NOD32 1.817 (20040719) Information __________
This message was checked by NOD32 antivirus system.
http://www.nod32.com
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|