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Inductor question





TL>I am still leaning towards the classic induction coil method of
TL>purchasing a spool of soft iron bailing wire, cutting the wire
TL>into sections, coating them, and tightly binding the cut sections
TL>into a bundled core.

TL>Any additional information by other experimenters would be
TL>appreciated.

TL>Richard Quick


I recommend using an old variac. If you cut the windings off an 8A 
variac, you then have a long magnetic path length which is easily 
utilised. You can hacksaw through the core in around 5-10 minutes. When 
you have done so it is an easy task to open up the sawcut with a bolster 
chisel, to give you a gap that is, say, half an inch wide.

It is then easy to wind a load of suitable enamelled Cu wire onto the 
core: you will end up with a core that will not saturate and has minimal 
eddy current losses. You can make it multilayer, or you can do what I am 
doing, and wind three inductors which can then be switched in 
series/parallel combinations to provide a variety of reactances. In my 
case, each one will be approx 18 ohms which will give me switchable VAs 
of  approx. 1kVA, 1.6kVA, ... upto 10kVA with three 57mH chokes in 
parallel.

One other method is to cut the variac core into two equal halves: the 
one half can have the windings whilst the other can be moved towards and 
away from the winding half. Or you could make a 1:1 transformer like a 
variometer whereby coupling between separate coils is performed by 
proximity to a common core. The neatest way, however (this was metioned 
sometime over the last week or so by someone on the list whose name I 
forget-sorry) is to use a DC current through a separate control winding. 
The problem with this is that you will saturate the core (seeing as the 
devise is a saturable reactor) so the 2nd harmonic powers will be 
significant. This will limit the charging ability of the pole 
transformer.

Richard Craven
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 CMPQwk #1.42 UNREGISTERED EVALUATION COPY