Re: Heating in 4-1/2 turn inductor
amdx
"amdx" <am...@knology.net> wrote in message
news:7baf9$4c754008$45013905$14...@KNOLOGY.NET...
> Several years ago while making inductors for tuning a class E amplifier we
> end up with a 4-1/2 turn inductor. The inductor used a 3F3 potcore, gapped
> I think,
> but it has been awhile. The inductor was driven hard but below saturation.
> The problem; the 1/2 turn got HOT. Four turns or five turns were ok.
> My physicist friend had an EE verify the problem 2000 miles away.
>
> So, can anyone tell me why 1/2 turn would make such a difference in the
> heating?
>
> Thanks, MikeK
>
Salmon Egg
"amdx" <am...@knology.net> wrote:
How do you make a half turn inductor?
Bill
--
An old man would be better off never having been born.
John Larkin
Bring wires out opposite slots on a pot core. I've seen it do strange
stuff, too.
John
glen herrmannsfeldt
Not so obvious to me. The current has to be the same through
the whole inductor. The half turn likely has less flux linkage,
and so lower inductance. The I**2*R loss should be the same, though.
One that I can think of, is that some heat goes into the core, and
so heats the wire less. If the half is not in contact with the core,
then it would be different.
-- glen
Scott
Half a circle, as used at say 450 MHz and up (the one end is soldered to
one point on a circuit board, goes straight up say 1/4", bends over 180
degrees and the other end soldered to another pad on the PC board...just
like this "U" but flipped over (upsidedown U)...
Paul Hovnanian P.E.
It may have something to do with the magnetic path handling the half
turn. The core may be saturating sooner.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
A mathematician is a machine for converting coffee into theorems.
glen herrmannsfeldt
> John Larkin wrote:
(snip)
>> >> > The problem; the 1/2 turn got HOT.
>> >> > Four turns or five turns were ok.
(snip)
> It may have something to do with the magnetic path
> handling the half turn. The core may be saturating sooner.
But the current, and I**2*R loss (per unit length) is the same
in any case. Isn't it?
-- glen
Salmon Egg
glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:
A circuit must have a whole number of turns based upon topology. That
is, if it is wound on some multiply connected core, you cannot take a
closed circuit and deform it intto a single turn without cutting through
a core. This is independent of the magnetic magnetic properties of the
core. The point is that the Maxwell flux equation integrates over a
closed contour. One may argue whether the flux is the same through each
turn or not, but there are complete turns.
I cannot picture how a piece of wire (part turn} can heat up differently
tyhan another piece of wire in series will. If anything, wire in the
iterior would heat up more because of proximity effects increasing
resistance. If the observation is correct it may be because there is a
hidden shorted turn. Another possibility, if really high frequencies are
involved, That there are hidden resonances that cause the inductance to
be distributed rather than lumped.
I am highly skeptical of the report. ARe we being put on?
Szczepan Białek
"Salmon Egg" <Salm...@sbcglobal.net> wrote
news:SalmonEgg-9506B...@news60.forteinc.com...
> >>
>> >> >> > The problem; the 1/2 turn got HOT.
>> >> >> > Four turns or five turns were ok.
>
> tyhan another piece of wire in series will.
You are right. But there not "the 1/2 turn got HOT" but the "a 4-1/2 turn
inductor" got hot. The "Four turns or five turns inductor do not got hot.
> If anything, wire in the
> iterior would heat up more because of proximity effects increasing
> resistance. If the observation is correct it may be because there is a
> hidden shorted turn. Another possibility, if really high frequencies are
> involved, That there are hidden resonances that cause the inductance to
> be distributed rather than lumped.
>
> I am highly skeptical of the report. ARe we being put on?
Report is O.K. :
"Several years ago while making inductors for tuning a class E amplifier we
end up with a 4-1/2 turn inductor.
So, can anyone tell me why 1/2 turn would make such a difference in the
heating?"
S*
John Polasek
The coil would probably draw 20 amps DC but in RF may be only 10 mA.
The reason is that in RF there is a back voltage due to Lentz' law
that bucks nearly all of the input voltage, but it's missing in that
half turn. So I would have to guess that that 1/2 turn had a very
large voltage across it if it didn't couple with the magnetic field
with its counter voltages.
I think you are acquainted with the fact that a DC motor has a huge
inrush stall current that could burn out the winding but is massively
reduced when it's running due to the induced back voltages.
John Polasek
glen herrmannsfeldt
(snip, I wrote)
>>Not so obvious to me. The current has to be the same through
>>the whole inductor. The half turn likely has less flux linkage,
>>and so lower inductance. The I**2*R loss should be the same, though.
>>One that I can think of, is that some heat goes into the core, and
>>so heats the wire less. If the half is not in contact with the core,
>>then it would be different.
> The coil would probably draw 20 amps DC but in RF may be only 10 mA.
> The reason is that in RF there is a back voltage due to Lentz' law
> that bucks nearly all of the input voltage, but it's missing in that
> half turn. So I would have to guess that that 1/2 turn had a very
> large voltage across it if it didn't couple with the magnetic field
> with its counter voltages.
Yes, but in the configuration, as I understand it, it can
be treated at least as inductors in series.
> I think you are acquainted with the fact that a DC motor has a huge
> inrush stall current that could burn out the winding but is massively
> reduced when it's running due to the induced back voltages.
One way is to drill a hole through the core such that one turn
only goes through half the core. That only works to the extent
that the flux divides evenly, and it likely won't in that case.
I do wonder, though, if the half turn saturates part of the
core then, yes, the back voltage will be reduced. Well, it
is pretty much that the inductance is reduced if the core
saturates.
-- glen