"Jeff Johnson" wrote in message
...


"amdx" wrote in message
...

"Jeff Johnson" wrote in message
...


"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



Resonance? (I assume by 1/2 you mean the 4.5 inductor?)
Yes, a 4 and 1/2 turn inductor had the 1/2 turn overheat.


huh?

The half turn and the other turns were ok? This is impossible!?!?! One
has the same current through the whole coil and if the wire was uniform
then it should heat heally well. Not only that copper is a good heat
conductor so if the 1/2 turn was heating up then he heat should spread
pretty quickly.

This assumes everything else is uniform along the coil. Something has to
be going on that your not telling us? Ideally the heat should be uniformly
distributed along the coil.

By "HOT" I assume you mean much much hotter than the other coils?

Heat is generated by the current, is it not? and the current should be
uniform throughout the wire? The resistance of the wire itself should also
be uniform. This suggests that the heat dissipated per unit length is
independent of position.

Were both ends hot? If not then something else is going on. Because you
are saying the .5 end of a 4.5 coil got HOT. Yet which end? the 4.5 coil
has two .5 ends and should in theory be symmetric and hence both get
equally HOT. If they wern't then something is aloof.

I got some confirmation from my collaborator, The 1/2 turn as were
describing it
was the LAST 1/2 turn wound on the bobbin.
MikeK

"amdx" wrote in message
...
I got some confirmation from my collaborator, The 1/2 turn as were
describing it
was the LAST 1/2 turn wound on the bobbin.

It doesn't happen to be nicked, forming a shorted turn perhaps?

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"amdx" wrote in message
...

"Jeff Johnson" wrote in message
...


"amdx" wrote in message
...

"Jeff Johnson" wrote in message
...


"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



Resonance? (I assume by 1/2 you mean the 4.5 inductor?)
Yes, a 4 and 1/2 turn inductor had the 1/2 turn overheat.


huh?

The half turn and the other turns were ok? This is impossible!?!?! One
has the same current through the whole coil and if the wire was uniform
then it should heat heally well. Not only that copper is a good heat
conductor so if the 1/2 turn was heating up then he heat should spread
pretty quickly.

This assumes everything else is uniform along the coil. Something has to
be going on that your not telling us? Ideally the heat should be
uniformly distributed along the coil.

By "HOT" I assume you mean much much hotter than the other coils?

Heat is generated by the current, is it not? and the current should be
uniform throughout the wire? The resistance of the wire itself should
also be uniform. This suggests that the heat dissipated per unit length
is independent of position.

Were both ends hot? If not then something else is going on. Because you
are saying the .5 end of a 4.5 coil got HOT. Yet which end? the 4.5 coil
has two .5 ends and should in theory be symmetric and hence both get
equally HOT. If they wern't then something is aloof.

I got some confirmation from my collaborator, The 1/2 turn as were
describing it
was the LAST 1/2 turn wound on the bobbin.
MikeK

What you describing is,

L1 V L2
V1--/\/\--+--/--0

on the same core?

L2, the 1/2 turn part of the coil is behaving wildly different than expect?

After all, ideally L2 has resistance in direct proportion to the total
winding which in this case 0.5*/4.5 ~ 11% of the total resistance of the
coil.

In a single coil the power dissipation of the 1/2 turn would also be ~ 11%
and this is quite easy to see. You are saying that it is much more than this
as if the ratio's were turned up side down. Something like the 1/2 part
dissipating 90% and the 4 turns part dissipating 10%?

if you agree with the layout of

L1 V L2
V1--/\/\--+--/--0

Then it is easy to see that in ideal circumstances the current through L1
should equal that of L2 and the I^2R heating would produce the results I
described first.

Instead of assuming the two inductors are on the same core we can assume
they are on different cores. This will help us understand if differences in
flux could cause such problems.

You mentioned in another post that you were using AC to drive the coil? Did
the effect happen with DC?

Did you measure the voltage on the 1/2 turn?

Was the core itself generating the heat or was it due to the 1/2 turn?

What was the total current through the coil?

Was it possible the coil could have been shorting out on another turn or the
core?

Was it really 1/2 a turn getting hot or "just the end of it"?

Was the coil tested by itself outside the circuit? If so did it exhibit the
same phenomena?

What was the end of the coil that generated the heat connected to? Was the
connection itself possible cause for the heat?

Was the coil reversed in the circuit? If so did it exhibit the same problem
with the ends switched?

You mentioned that you tried 4 turns and 5 turns and the problem went away.
Did it go away completely or partially? Was those two coils made exactly the
same way and connected the same or were they in any way different besides
just the turn difference?

Was the coil one continuous piece? the 1/2 turn was not spliced on?

Did you try a 5.5 and/or 6 turn coil?

Did the 1/2 turn end get hot very quick or did it take a while? Basically
seconds or minutes?

Did you try to change the direction of the core relative to the coil? If so
did it make any difference?

Is there any possible way the core itself could have been generating the
heat at the 1/2 turn and the effect you experienced was just the core
heating up that 1/2 first?

Did you allow the inductor to run a long time? If so, What was the effect
still? Was the whole coil hot or still just the 1/2 turn?

Hopefully you can answer some of these questions. It sounds to me like you
didn't do much troubleshooting so I expect most of them can't be answered so
the true reason probably will not be known.

On Wed, 25 Aug 2010 11:09:35 -0500, "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


I think it's forcing a substantial portion of the flux to pass through
half of the core and thus increasing the core losses.

There's a half turn technique used in transformer design that ends up
with two half turns in parallel IIRC. Maybe you could use that.

On 8/25/2010 11:09 AM, 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



This kind of odd-ball result can be caused by "parasitics" - in other
words, a high overtone excited by just the right length of inductor
paired with just the right stray capacitance, and energized by something
that can hit the high notes....

Brian W

"brian whatcott" wrote in message
...
On 8/25/2010 11:09 AM, 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



This kind of odd-ball result can be caused by "parasitics" - in other
words, a high overtone excited by just the right length of inductor
paired with just the right stray capacitance, and energized by something
that can hit the high notes....

Brian W

Maybe, but we had it confirmed by someone else and I doubt very much
they developed the circuit we were using to do the test. We used it to
cancel
out the capacitance of a piezo transducer. Driving about 250 watts into a
20 ohm load, at about 600 khz.
MikeK

On 8/26/2010 6:41 AM, amdx wrote:
"brian wrote in message
...
On 8/25/2010 11:09 AM, 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



This kind of odd-ball result can be caused by "parasitics" - in other
words, a high overtone excited by just the right length of inductor
paired with just the right stray capacitance, and energized by something
that can hit the high notes....

Brian W

Maybe, but we had it confirmed by someone else and I doubt very much
they developed the circuit we were using to do the test. We used it to
cancel
out the capacitance of a piezo transducer. Driving about 250 watts into a
20 ohm load, at about 600 khz.
MikeK



You don't have to guess whether I am right or wrong: you just have to
hang a 200MHz bandwidth scope on the hot end, and see what you get.

Brian W

Hey OM:

First how many newsgroups do you have this thread cross posted on?

Second: A 1/2 turn is equal to 1 turn in a pot core so 4 and 1/2 turns
is the same as 5 turns.

Lastly OM: I think you are looking at a classic case of proximity
effect.

73 OM
de n8zu





On Aug 25, 4:09*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

"raypsi" wrote in message
...
Hey OM:

First how many newsgroups do you have this thread cross posted on?

How many do you see it on?

Second: A 1/2 turn is equal to 1 turn in a pot core so 4 and 1/2 turns
is the same as 5 turns.

I don't think so. If I put 4-1/2 turns on a potcore and measure inductance,
then unwind the 1/2 turn, do you think the inductance will measure the same?

Lastly OM: I think you are looking at a classic case of proximity
effect.

It may be, but I can't explain to myself how that would happen. I do think
it has
something to do with the flux through the coil though.
Thanks, MikeK


73 OM
de n8zu





On Aug 25, 4:09 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

In article , "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

** Is it a 5-turn inductor with 1/2 turn shorted?

--
Richard L. Measures. AG6K, 805-386-3734, www.somis.org