Charles Proteus Steinmetz in the Space Orthogonal to Real - Foucault or Eddy Currents

[Joe Gwinn]

Some time ago, I speculated that Steinmetz (a very big early name in electrical engineering) had done the analysis of eddy currents upon which most or all later treatments depended. It turns out that this is likely true, and Steinmetz also turns out to be a very good writer. He explains every major equation in words, term by term, and explains what they mean physically. It's clear why he is famous. (I wish my college textbooks were all this clearly written.)

Charles Proteus Steinmetz - Wikipedia, the free encyclopedia

Anyway, eddy currents (also known as Foucault Currents) are described in at least two of Steinmetz's books.

For the energy-loss effects on transformers and motors, see "Theory and Calculation of Alternating Current Phenomena", first published in 1900, third edition in 1916. The treatment (starting on page 136) here is simplified, and Steinmetz points the reader to more complete analyses in other of his books.

The full text is available gratis as a pdf download from Google Books: Alternating Current Phenomena - Google Books.

For the full analysis of eddy currents, addressing the effects on inductance and phase shifts acquired while passing through shields, see Section III of "Theory and calculation of transient electric phenomena and oscillations", first published in 1909, third edition published in 1920.

Again, the full text is available from Google Books: Transient Electric Phenomena and Oscillations - Google Books.

[David Schwab]

You gotta love Google Books!

[Joe Gwinn]

If you are going in for some self-study, the following may also be useful:


"Theory and calculations of electrical circuits", Steinmetz, 1st edition, 1917.

Electrical Circuits - Google Books.


"General lectures on electrical engineering", 5th edition, 1918.

General lectures on EE - Google Books.


Our grandfathers were pretty smart after all. And very industrious.

The old books very often were more clearly written than those of today.

[ken]

Cool!

Steinmetz was one of my favorite scientists, I had a book about his life story when I was 10. He also invented the lightning arrester after his cottage was hit by lightning, which melted his mirror.

I had no idea that Google Books had anything like this.

Thank you,
Ken

[Joe Gwinn]

Steinmetz was one of my favorite scientists, I had a book about his life story when I was 10.

I must confess that I had never heard of Steinmetz until I undertook electrical engineering in college.

He also invented the lightning arrester after his cottage was hit by lightning, which melted his mirror.

Only got a mirror? Can't have been much of a lightning bolt.


I can't say that I ever expected to see musicians and pickup makers undertaking the study of complex variables and the theory of alternating-current circuits, not to mention phasors, but here we are.

[Possum]

....

My understanding of eddy currents has changed recently. I always thought they were going to kill the high trebles, 'dem trebles better git outa town before the brass cover gang shows up heah...

I have been trying to kill some of the very highest treble in some prototypes and what I thought would work didn't. I made a brass plate that sits under the magnet and coils, it DID reduce the peak resonance, it did boost the readings at 1khz on the LCR meter. It DIDN'T affect the high trebles at all, and made the pickup sound harsh. So I tried wrapping the magnet in copper tape along the longitudinal axis and soldered it shut. It did the same thing and left the highest trebles alone. There is something happening in the highest ranges beyond the peak rez that only using some shellac with water in it affected in the coil itself. Now, is it because the water is conductive or is it because of its dielectric effect or are those two things the same? Nothing's easy is it....

[Mike Sulzer]

My understanding of eddy currents has changed recently. I always thought they were going to kill the high trebles, 'dem trebles better git outa town before the brass cover gang shows up heah...

I have been trying to kill some of the very highest treble in some prototypes and what I thought would work didn't. I made a brass plate that sits under the magnet and coils, it DID reduce the peak resonance, it did boost the readings at 1khz on the LCR meter. It DIDN'T affect the high trebles at all, and made the pickup sound harsh. So I tried wrapping the magnet in copper tape along the longitudinal axis and soldered it shut. It did the same thing and left the highest trebles alone. There is something happening in the highest ranges beyond the peak rez that only using some shellac with water in it affected in the coil itself. Now, is it because the water is conductive or is it because of its dielectric effect or are those two things the same? Nothing's easy is it....

A baseplate acts as a resistive load on the pickup up to some frequency. The coupling between the pickup and the plate decreases at high frequencies because of the leakage flux. That is, there is in effect an inductor (the leakage inductance) in series with the resistor. This isolates the resistance from the pickup coil at high frequencies. I showed a plot of this effect a while ago.

Why are you using brass and water-logged shellac to control high frequency loss? Since these things are (roughly) equivalent to circuit components, why not just use an actual resistor and capacitor?

[Joe Gwinn]

I have been trying to kill some of the very highest treble in some prototypes and what I thought would work didn't. I made a brass plate that sits under the magnet and coils, it DID reduce the peak resonance, it did boost the readings at 1khz on the LCR meter. It DIDN'T affect the high trebles at all, and made the pickup sound harsh. So I tried wrapping the magnet in copper tape along the longitudinal axis and soldered it shut. It did the same thing and left the highest trebles alone.

I would try a brass cover. Make the music pass through the metal.

There is something happening in the highest ranges beyond the peak rez that only using some shellac with water in it affected in the coil itself. Now, is it because the water is conductive or is it because of its dielectric effect or are those two things the same? Nothing's easy is it....

The dielectric constant (around 80) will sharply increase self-capacitance, and the conductance will increase damping. Waterlogged shellac won't make for very stable characteristics. Elimination of the unstable effects of moisture in the coil is why Leo invented wax potting.

[Possum]

...

Brass didn't affect the high frequencies at all, neither did the closed copper loop around the magnet. They affected the upper midtones in an unpleasant way. PUtting a brass cover on a $500 set of pickups isn't going to fly with anyone :-) For one, thing when the nickel plate wears off you get ugly yellow on your expensive pickups, bad.

I don't want to use shellac because the alcohol has water in it, but while it was wet it DID do exactly what I wanted, it was perfect. I'm not convinced though that the shellac itself had anything to do with the effect, more likely it was the alcohols, because when it dried the effect was gone. The ideal is to find some substance that can soak into a coil and do the same thing after it completely dries out. You can't add say metal powder to shellac because that stuff can't penetrate, I know that from the black potting wax Leo used, the powder stays on the surface and the wax penetrates. Capacitors I don't want to use becuase the next tone up down is .047uf, for one thing its not what was used and the other is it really makes buckers sound dull. I know one pickup maker who says he's found a formula that works on coils but he signed a deal with the devil down at the crossroads and won't talk :-) I've been scrounging around in the dielectrics list which I'll attach, but haven't come upon anything useful yet. I'll attach it here. Also note this list seems to have been made in the early 1900's, as there is a substance called "kent wax" that doesn't exist now. Anyway, maybe the "science and engineering" dept. might have some ideas here I wonder if there are conductive glues that can be thinned and would penetrate...

[Mike Sulzer]

Capacitors I don't want to use becuase the next tone up down is .047uf, for one thing its not what was used and the other is it really makes buckers sound dull. ..

I do not mean the tone control cap; it cannot have the effect you want. I am referring to an additional resistor and capacitor in series across the pickup. The value of resistor would be chosen to introduce enough loss to achieve the effect you want. The value of the capacitor would be chosen so that the effect does not extend down in frequency where you do not want it. Its value would be smaller than that of the tone cap.

You can try this outside of the guitar and get the same effect as inside as long as the volume pot is on ten.

[Peter Naglitsch]

this list seems to have been made in the early 1900's

Maybe, maybe not. I can spot both "Coke" and "Cocaine" in that list... Ever tried soaking a pickup in Cocaine?

Sorry, OT

[Joe Gwinn]

Brass didn't affect the high frequencies at all, neither did the closed copper loop around the magnet. They affected the upper midtones in an unpleasant way. Putting a brass cover on a $500 set of pickups isn't going to fly with anyone :-) For one, thing when the nickel plate wears off you get ugly yellow on your expensive pickups, bad.

For the experiment, put a sheet of brass between strings and pickup.

I don't want to use shellac because the alcohol has water in it, but while it was wet it DID do exactly what I wanted, it was perfect. I'm not convinced though that the shellac itself had anything to do with the effect, more likely it was the alcohols, because when it dried the effect was gone.

I think you are right here. Dry shellac will have a constant in the range 2-4, which is in the same range as wax. By contrast, ethanol is 24 and water is ~80.

The ideal is to find some substance that can soak into a coil and do the same thing after it completely dries out. You can't add say metal powder to shellac because that stuff can't penetrate, I know that from the black potting wax Leo used, the powder stays on the surface and the wax penetrates.

Well, all the cyanide compounds and some arsenic compounds have nice high dielectric constants.

Metal dust won't do anything at all.

One common solid material with a very high dielectric constant is titanium dioxide, which is widely available as a paint pigment, and can be ball milled in shellac to be fine enough to easily penetrate a coil.

Titanium dioxide is proposed and possibly used to raise the dielectric constant of plastic films used in capacitor manufacture. ScienceDirect - Ceramics International : Synthesis and dielectric properties of polyaniline/titanium dioxide nanocomposites. This is behind a paywall, but the abstract gives the game away.

I know one pickup maker who says he's found a formula that works on coils but he signed a deal with the devil down at the crossroads and won't talk :-)

What color are his coils? I wonder if he is using paint pigments.

Silver crosses are supposed to help while negotiating devil deals.

I've been scrounging around in the dielectrics list which I'll attach, but haven't come upon anything useful yet. I'll attach it here. Also note this list seems to have been made in the early 1900's, as there is a substance called "kent wax" that doesn't exist now.

That list is from a nondestructive-test company, and they usually collect every published bit of data, old plus new, so the presence of old data does not prove that the list is obsolete. Many of the substances in that list were not available in 1900. Nor have dielectric constants changed much over the centuries.

Capacitors I don't want to use because the next tone up down is 0.047uf, for one thing it's not what was used and the other is it really makes buckers sound dull.

One can buy film capacitors in 2% steps, and one can parallel large and small capacitors, so you ought to be able to hit any desired target.

[Possum]

.....

I don't think anyone would buy a pickup and an extra cap and resistor to "fix" what shouldn't be there in the first place :-) The titanium thing sounds interesting, I wonder if it would really penetrate though, cheap enough to try. White coils? :-)

[Joe Gwinn]

I don't think anyone would buy a pickup and [add] an extra cap and resistor to "fix" what shouldn't be there in the first place :-)

But it's a perfectly valid way to experiment. One can also buy capacitor substitution boxes to speed things up.

The titanium thing sounds interesting, I wonder if it would really penetrate though, cheap enough to try. White coils? :-)

Now that I think about it, titanium dioxide in shellac is commercially available in paint stores as a primer. The standard is BIN by Zissner.

B-I-N Shellac Base Primer Sealer

Be sure to get the shellac based kind, not the water based kind. Thin with denatured alcohol.

The white pigment is only about 25% titanium dioxide, as revealed by the MSDS, but the test is easy.

[Mike Sulzer]

I don't think anyone would buy a pickup and an extra cap and [add} resistor to "fix" what shouldn't be there in the first place :-)

I agree, and in any case you know what will sell. But you could build in the R and C (or whatever network is required) yourself.