[Amps] Non-inductive resistors

[craxd]

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
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>
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