Heating in 4-1/2 turn inductor

It may have something to do with the magnetic path handling the half turn. The core may be saturating sooner.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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A mathematician is a machine for converting coffee into theorems.

I don't know what to say. Just not enough information. If your looking from some exotic possibility I don't think you'll find one.

The reason is that the current through the wire will almost be surely the same through out all points along the wire. That precisely means that the heat generated per unit length will be the same. Even if you have some crazy resonance or core flux/transformer effect going on, that current in the wire has to be the same through the whole wire(assuming no shorts).

You can't have electrons bunch up on part of the wire and not on any other part. Even if you could, that bunch would have to flow through the wire from one part to another and on average it would heat it up uniformly.

The reason is simple, We all know that for a power supply when one electron is supplied on the wire one electron leaves it so there really is no way to "bunch" it up.

Now, if the wire is not uniform in size or resistance then the heating effect is not uniform. As smith mentioned about the joint connecting the coil. In this case it is possible that the joint could be heating up and it was being passed along to the 1/2 turn and it just happens that you didn't let it run long enough to heat up any more turns.

The 1/2 turn was really a point at the joint and the heat just spread about about 1/2 turn.

To me this is the most plausable case. I'm not sure if it's physically possible any other way that involves the coil itself generating generating the heat. (I gave a good reason about about electron flow being uniform in the wire)

It may be possible using some type of standing wave or transformer like effect but even here I can't see it possible if the wire's restance per unit length is constant.

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

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ikeK

I'm sure it was not a bad connection. I know all about heat caused by I^2 x R at connections. In fact just yesterday I was checking for bad connections on my electric gokart and I burned my finger! I found a loose connection between a

5/16" post and a ring terminal connected to a 6 gauge wire. It was some oddity about the 1/2 turn in a potcore. I suspect the low turns count is also important to the phenomena. I thought I'd ask and see if anybody else ever had the problem. Closest I got was when John Larkin said, "I've seen it do strange stuff, too." John, would you care to elaborate? MikeK

One of my engineers, a real magnetics guy who used to work for Signal Transformer, designed a push-pull forward dc/dc converter using a pot core. This was in the power supply of a laser controller [1] where the customer, for reasons never rationalized, wanted our +24 power to be isolated. One center-tapped winding included a half turn on each side, and efficiency was terrible. Going to full turns, and wasting a bit more power in a downstream linear regulator, worked much better. Neither of us understood why.

John

[1] The controller is still in production. It manages the firing of a series of deep-UV MOPA lasers that expose some fraction of the fine-pitch ICs made in the world.

How many do you see it on?

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?

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

Hmmm...it is easy to demonstrate two coils in series, loaded with two caps to provide two (different Fx) resonant paths - the coil in the part that resonates carries way more current than the path that is not resonating...

Brian w

And I think these is exactly why you are pursing it. You believe it must be due to some fanciful effect because of the "1/2" turn as if 0.5 was more special than 0.73524 or 1.0.

You have the mindset to those people that think 3.141592... is special. This causes you to overlook the obvious. First, pi in another base is not

3.1415.... but in any case it must have been some number. In some alternate universe we could imagine it being 5.43524. In is only special in the sense that we make it special because it seems different than most other decimals. In fact though there are a ton of "special numbers".

The theory of ideal inductors does not give any reason why a 1/2 turn should at all be important. Tim mentioned the promixity effect which would produce heating throughout the windings and more so for inner windings so it is not the correct effect here.

Most other phenomena that stand any chance of creating the effect would do it symmetrical. Why? Because both ends have no special preference for the heat. This should be completely obvious.

The only chance is if you wrapped the windings in such a strange and crazy way and a totally screwed up core as to make a retard jealous of your work.

We think of other possibilities that would work in a non-symmetric way but they just don't seem to gel with physics. No one can say for sure since you obviously don't have any good investigative information to provide about it.

Almost always things that seem phenomenal are due to simple mistakes. If you are really serious about it then I would suggest you attempt to reproduce the result then do a bit more investigation. Until then you might want to drop it because we don't need another cold fusion story circulating around. (I'm being facetious)

OH, you think I might have some overunity thing going on? Let me get my magnet motor out!

Me to. MikeK

If you were using a proper newsreader, rather than Google, you would know, it would tell you at the top of the message.

Answer - 2. The mninmum possible to crosspost.

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"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

uld

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.

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.

In the ideal case the fringe effects are usually ignored. Atleast every book I've read about inductance supposes the fringe effects can be ignored. Remember, we are talking about the inductive effects on heating those ends and not the inductance itself.

In all causes if the the ends are relatively symmetric then both should heat up equally. Also the fringe effects tend to reduce the heat on the ends and not increase it. Also all the effects you describe should heat the central windings more than the outside and have little to do with the end turn amount. Again, In all cases it would be symmetric unless the core or windings themselfs were wound in some weird way. 99.99999% of all inductors are wound to be symmetric.

So if there is some effect that is due to the reasons you describe then it must be because they let a 2 year old create the winding.

Now, you'll have to excuse me if I make some assumptions about what is going on. When he says inductor I think of basically something that looks like an inductor and acts like one. So if he did something non-standard then he should include that information.

I cannot totally exclude some physical reason why such a thing could happen because I don't know all the possibities. Given the assumption that what they created was very much inductor like no one has presented any reason why only one side would heat up and the rest of the coil would be fine that is due to the coil/core.

The most likely effect is that the connection on that one end was bad or was shorting out. This is the best guess given the little amount of information that was provided.

Since he said the same result was produced independently then this possibly suggests something else but the same mistake could have been made twice.

It would be quite easy to create a partially laminated core that was not laminated near one end. The core would heat up due to eddy currents which would heat up the 1/2 turn first. Who the hell would use such a core? Such behavior is to be expected when someone doesn't know what they are doing.

f

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

d

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.

Yes , that is what I did, however on my second post I tried to add on sci.physics.electromag. It didn't work the way I thought it might. If you do a search you will find the thread has been picked up by,

science.niuz.biz/re-t367297.html I thought maybe that is what he saw. MikeK

Some may find interest in this. A turn around an outside leg of an E-core is called a half-turn because it encloses only one-half of the cross-sectional area of a turn around the center leg. It is well known that a half-turn in a secondary winding of a power transformer greatly increases the leakage inductance between windings, thus causing an adverse effect on cross-regulation. However, the increased leakage inductance of a half-turn can be very beneficial in tapped inductors for boost circuits and in coupled output chokes. This paper explains some of these little-known applications of a half-turn. The theory and formulae for prediction of leakage inductance added by such a half-turn are presented

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

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

I vote for fringing flux of the wire near the gap (if the hot piece was near the gap) because of eddy current heating.

I would think that proximity effect would be there if partial turn or integer number of turns.

Second vote? not sure...

I had a multiple in-hand winding of an inductor (12 E-cores) in a buck converter where each individual wire was not necessarily a triangle of current but all the wires taken together certainly were. That, I could only think was also due to fringing gap effect, except there were no partial turns. I'm still not sure that's what that was.

This is useful information I think. Hopefully there is a definitive answer eventually. Build another one maybe and try again ??

boB

Only two ideas from me, and they seem weak.

A half turn means the current goes in and out on separate sides. That makes one turn of inductance perpendicular to the rest of the turns that would skew the magnetic field.

If it is a powdered iron core, the volts per turn could be high enough that it conducts electricity.

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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?