Heating in 4-1/2 turn inductor
 

On Sun, 29 Aug 2010 14:37:49 -0500, "amdx" wrote:


"JosephKK" wrote in message
.. .
On Fri, 27 Aug 2010 14:23:13 -0700 (PDT), whit3rd
wrote:

On Aug 27, 1:30 pm, "Jeff Johnson" wrote:
"whit3rd" wrote in message

...

On Aug 27, 10:31 am, "Jeff Johnson" wrote:

The theory of ideal inductors does not give any reason why a 1/2 turn
should
at all be important.

Oh, yes, it DOES give a reason. A pot core (or E cores) has a pair of
return
flux arms flanking the central element, and a '1/2 turn' winding
imbalances
those return fluxes.

In the ideal case the fringe effects are usually ignored.

What 'fringe effects'? This is about the flux contained in the
magnetic arms of the core, not outside somewhere

That means the 3-d flux inside the core is very different in the
two cases, and if one return arm saturates, that flux distribution
alters
considerably during the cycle. That causes (1) the material to heat
due to remagnetization in an asymmetric way, (2) the forces of the
pole pieces to modulate as the field builds. The first effect (caused
by material hysteresis) might have been expected. The second
effect, though, will cause ultrasonic excitation of the core, maybe
creating cracks by mechanical stress.

...all the effects you describe should heat the central
windings more than the outside and have little to do with the end turn
amount.

Oh, this has nothing to do with ohmic heating in the windings. It
concerns
the B-H curve, which (for a hysteretic material) loops around some
area.
At 600 kHz, the area, multiplied by 6e6, is the power lost when the
magnetic material is forced to traverse that loop.
If part of the material saturates, its loop is of greater area than
the rest of
the material. A core that should handle 2A without overheating, then
would overheat.

You may be on to something. Maybe. At least it make physics sense to
me, but then i are enguneer. It does show a path to have thermal
non-uniformity that is regenreative.

Say Mike just how big is that pot core?

I think it may have been a 3622 but could have been a 4229.
MikeK

I take it that is dimensions in mm. What material? Minimum
"thickness" (cross section)

Heating in 4-1/2 turn inductor GOSH!
 

I tried reading and understanding most of the posts, but confess not
understanding all of them.
BUT, I cannot resist inserting my "two cents" worth:

In olden days, it was quite common (but unwelcome) to have parasitic
oscillations run away in large RF amplifiers. They would start all by
themselves and quickly begin roasting tubes, coils, even adjacent conductive
surfaces, whatever got in the way. The often encountered case would be a HF
amplifier running away (self-oscillating for the unwashed) at a VHF or UHF
frequency.

One common, but mysterious result was burned parts of RF chokes in the
plate circuit. (you do remember tubes, right?) I think there were a couple
of commercial RF chokes wound on long ceramic (steatite?) cores with
assorted winding spacings on the ceramic core. Burned spots would occur in
only one or two places on the length of the winding. Caused, supposedly by a
high current node on a VHF or UHF resonant portion of the winding.

4 1/2 turns at 600khz must be an awfully low impedance circuit, but
could be right down the alley for VHF.

Brian has my vote for barking up the right tree.

Old Chief Lynn, W7LTQ

Heating in 4-1/2 turn inductor
 

"JosephKK" wrote in message
...
On Sun, 29 Aug 2010 14:37:49 -0500, "amdx" wrote:


"JosephKK" wrote in message
. ..
On Fri, 27 Aug 2010 14:23:13 -0700 (PDT), whit3rd
wrote:

On Aug 27, 1:30 pm, "Jeff Johnson" wrote:
"whit3rd" wrote in message

...

On Aug 27, 10:31 am, "Jeff Johnson"
wrote:

The theory of ideal inductors does not give any reason why a 1/2
turn
should
at all be important.

Oh, yes, it DOES give a reason. A pot core (or E cores) has a pair
of
return
flux arms flanking the central element, and a '1/2 turn' winding
imbalances
those return fluxes.

In the ideal case the fringe effects are usually ignored.

What 'fringe effects'? This is about the flux contained in the
magnetic arms of the core, not outside somewhere

That means the 3-d flux inside the core is very different in the
two cases, and if one return arm saturates, that flux distribution
alters
considerably during the cycle. That causes (1) the material to heat
due to remagnetization in an asymmetric way, (2) the forces of the
pole pieces to modulate as the field builds. The first effect
(caused
by material hysteresis) might have been expected. The second
effect, though, will cause ultrasonic excitation of the core, maybe
creating cracks by mechanical stress.

...all the effects you describe should heat the central
windings more than the outside and have little to do with the end turn
amount.

Oh, this has nothing to do with ohmic heating in the windings. It
concerns
the B-H curve, which (for a hysteretic material) loops around some
area.
At 600 kHz, the area, multiplied by 6e6, is the power lost when the
magnetic material is forced to traverse that loop.
If part of the material saturates, its loop is of greater area than
the rest of
the material. A core that should handle 2A without overheating, then
would overheat.

You may be on to something. Maybe. At least it make physics sense to
me, but then i are enguneer. It does show a path to have thermal
non-uniformity that is regenreative.

Say Mike just how big is that pot core?

I think it may have been a 3622 but could have been a 4229.
MikeK

I take it that is dimensions in mm. What material? Minimum
"thickness" (cross section)

Here's the pdf on the core I think was used. The material was 3F3.
I don't know the gap size, I thought we generally used the 160 gap,
but I don't even see that listed. I decided it's more likely we used the
4229
than the 3622. It's been 10 years so details have faded.
http://www.ferroxcube.com/prod/assets/p4229.pdf

Heating in 4-1/2 turn inductor
 

Hey OT:

I stand by my proximity effect.

The Q is equal to Rl/Xc the half turn has twice as much Xc so the Q
for that turn is half as much as the other turns because of proximity
Thus the Pd in the half turn is 4 times the Pd in the other turns.

73 OT
de n8zu



On Aug 25, 12:09*pm, "amdx" wrote:
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

Heating in 4-1/2 turn inductor
 

A 12 bit insulator is 4/3 bytes a half turn is 1/X or 8 bits...

"amdx" wrote in message
...
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

Heating in 4-1/2 turn inductor
 

On Fri, 3 Sep 2010 10:01:03 -0500, "amdx" wrote:


"JosephKK" wrote in message
.. .
On Sun, 29 Aug 2010 14:37:49 -0500, "amdx" wrote:


"JosephKK" wrote in message
...
On Fri, 27 Aug 2010 14:23:13 -0700 (PDT), whit3rd
wrote:

On Aug 27, 1:30 pm, "Jeff Johnson" wrote:
"whit3rd" wrote in message

...

On Aug 27, 10:31 am, "Jeff Johnson"
wrote:

The theory of ideal inductors does not give any reason why a 1/2
turn
should
at all be important.

Oh, yes, it DOES give a reason. A pot core (or E cores) has a pair
of
return
flux arms flanking the central element, and a '1/2 turn' winding
imbalances
those return fluxes.

In the ideal case the fringe effects are usually ignored.

What 'fringe effects'? This is about the flux contained in the
magnetic arms of the core, not outside somewhere

That means the 3-d flux inside the core is very different in the
two cases, and if one return arm saturates, that flux distribution
alters
considerably during the cycle. That causes (1) the material to heat
due to remagnetization in an asymmetric way, (2) the forces of the
pole pieces to modulate as the field builds. The first effect
(caused
by material hysteresis) might have been expected. The second
effect, though, will cause ultrasonic excitation of the core, maybe
creating cracks by mechanical stress.

...all the effects you describe should heat the central
windings more than the outside and have little to do with the end turn
amount.

Oh, this has nothing to do with ohmic heating in the windings. It
concerns
the B-H curve, which (for a hysteretic material) loops around some
area.
At 600 kHz, the area, multiplied by 6e6, is the power lost when the
magnetic material is forced to traverse that loop.
If part of the material saturates, its loop is of greater area than
the rest of
the material. A core that should handle 2A without overheating, then
would overheat.

You may be on to something. Maybe. At least it make physics sense to
me, but then i are enguneer. It does show a path to have thermal
non-uniformity that is regenreative.

Say Mike just how big is that pot core?

I think it may have been a 3622 but could have been a 4229.
MikeK

I take it that is dimensions in mm. What material? Minimum
"thickness" (cross section)

Here's the pdf on the core I think was used. The material was 3F3.
I don't know the gap size, I thought we generally used the 160 gap,
but I don't even see that listed. I decided it's more likely we used the
4229
than the 3622. It's been 10 years so details have faded.
http://www.ferroxcube.com/prod/assets/p4229.pdf


Thanks, i will have to study some to be able to read that datasheet.