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 Post subject: Iron wire inductor
PostPosted: Sat Oct 28, 2017 9:09 am 
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What if insulated iron, or silicon steel, for that matter, was made into an inductor so that the wire was to act as both the windings and the magnetic core? It seems like it probably was tried sometime within the past 200 years or so. The reasons it doesn't work, if it doesn't, could be a bit complicated, but I'd like to try to see what they are, like besides copper in standard-type inductors being a better conductor and being pretty corrosion resistant.


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 Post subject: Re: Iron wire inductor
PostPosted: Sun Oct 29, 2017 5:27 am 

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Ever thought you knew something till you tried to explain it?

After almost an hour I came up with:

E field is 90 degrees from the M field (in space at transformer, not phase)

Your iron wire idea tries to give a low magnet field impedance (reluctance?) in the same geometric plane as the electric field. It would make a very low efficiency transfer of power from primary to secondary.

On a different tack. The M field of the primary created by the E field of the primary has to "cut across" the connductors of the secondary to induce an E field in the soconday. There is no (or very poor) "cutting" when in the same plane. This goes along with why AC instead of DC. DC "cuts" twice; once at power on, and once at power off. AC continuously "cuts".

I'm not really satisfied with those explanations, but it has been a lllooonnnggg time since college.

Cheers,

P.S. If someone has a better explanation please give it.



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 Post subject: Re: Iron wire inductor
PostPosted: Sun Oct 29, 2017 3:18 pm 
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As Dale said, the magnetic flux (field) is perpendicular to the flow of current. And yes, there is some magnetism from even a single wire passing current, but it is "fairly weak" all by itself.

Think of it this way:
A single conductor produces one perpendicular magnetic field per unit of length, for demonstrative purposes let's just say mm. Now think of how this works, you apply a votage and current to the conductor and it flows from one end to the other producing the magnetic field as long as power is supplied. This field radiates out and away from he conductor, falling off at a rate determined by distance squared. The initial strength of the field is determined by the amount of current the conductor can and is passing at that time. Obviously a 1Amp current will produce a significantly less strong field than a 30,000 amp current. You can see this demonstrated by taking a fluorescent bulb to the high tension power lines and watching it light up, yet have no reaction when placed directly next to your home power lines within your walls.

Now to your query.

What you see above is the raw power being radiated and you'll notice it is quite inefficient. Now, if you take that conductor and wrap it around a form, the lines of flux from each wrap of the wire will add to the previous one, building up a larger field. Now here's the fun part. An object which has properties related to the magnetic spectrum, for example, iron, can be used to strengthen and or redirect those lines of flux. In the case of, let's say, a standard steel or even cut iron nail, it acts as a core that absorbs, concentrates, and re-radiates those lines of flux. Can't visualize it? Try the old iron filings experiments.

In the case of transformers, the cores are designed to work most efficiently at a particular center frequency or range. Above and below that and the efficiency drops off.

So ultimately, what you posit has some merit, but at the same time, the reality is that there are much more efficient ways to do what you are asking.

CeaSaR



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 Post subject: Re: Iron wire inductor
PostPosted: Sun Nov 12, 2017 11:30 am 
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Hi,

You can break this down into two or more separate questions.

The first question is what happens when we try to use iron for wire.
The first thing we notice is that the resistance is much higher than with copper wire. That is a deterrent, but maybe you can get away with it.
The second thing is that the active magnetic area is so small that it probably saturates, making it just like plain wire with higher resistance than copper.

The other part is what happens when it is wound into a coil.
It probably works just like a higher resistance coil.
The thermal conductivity of iron or steel is not as good as copper either, so it would not be able to be used for a very higher power. In fact, if the electrical resistance is higher it gets naturally hotter and since that heat might escape by less than 25 percent as well as with copper that might mean the effective power rating of the unit could be as low as 1/16 as that of a copper wound coil.

Another point is that steel is stronger than copper so it is used for component leads sometimes. You can find resistors with steel leads for sale. These can be detected by placing a magnet near the resistor and the leads stick to the magnet. The resistor leads are stronger because they are steel, and apparently dont affect anything else too much.

Another point is the skin depth. The skin depth is most likely less deep, so there is higher AC resistance (not reactance but AC resistance) as compared to copper of the same gauge. This also impairs the usability of wire made from steel or iron that is used an an AC circuit.

So there are a lot of drawbacks, but the one good thing is the lead strength.



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 Post subject: Re: Iron wire inductor
PostPosted: Mon Nov 13, 2017 8:25 pm 
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I had an inductor coil in mind that had a small inner diameter, and enough Iayering to make the outer diameter about ten times the inner, or more. Say ¼" inside, 2" outside diameter, and maybe something like 3" long.

I haven't been a fan of iron or steel leads because of concerns about corrosion and loss of solderability or circuit connection if the outer skin gets compromised, and I like the more bendable copper. I would tend to convert the iron or steel to copper by crimp or some other contact means similar to that.

The application in my mind was a 60Hz choke for dropping power a bit to an appliance, particularly, my microwave oven for smoother cooking.


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 Post subject: Re: Iron wire inductor
PostPosted: Tue Nov 14, 2017 12:35 pm 
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A note about microwave ovens...and stuff!

The magnetron is an all on, or all off device. The power is cycled to it with a varying duty cycle to control the cooking power.
If the supply voltage were reduced, the magenetron would probably function outside it's design limits and it may fail, or simply not oscillate properly. With it's cooling reduced it may overheat, and and if the oven has a has a digital control it could also get weird.

Reducing power to synchronous motors is usually a bad idea since the available torque is reduced, the motor 'slips' and it labors to drive the load.
DC motors can be controlled by the reduction of voltage, and the most common AC motor speed control uses a variable frequency drive.

Reducing input power works for lighting and resistance heating but usually not much else.

Just saying....



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 Post subject: Re: Iron wire inductor
PostPosted: Wed Nov 15, 2017 7:33 am 
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Lenp wrote:
A note about microwave ovens...and stuff!

The magnetron is an all on, or all off device. The power is cycled to it with a varying duty cycle to control the cooking power.
If the supply voltage were reduced, the magenetron would probably function outside it's design limits and it may fail, or simply not oscillate properly. With it's cooling reduced it may overheat, and and if the oven has a has a digital control it could also get weird.

Reducing power to synchronous motors is usually a bad idea since the available torque is reduced, the motor 'slips' and it labors to drive the load.
DC motors can be controlled by the reduction of voltage, and the most common AC motor speed control uses a variable frequency drive.

Reducing input power works for lighting and resistance heating but usually not much else.

Just saying....


Hi there Len,

Well, your reply begs the question, "Did you ever actually try this at home" :smile:

I ask because not only have i been doing this for years by pure coincidence of having very low line voltage during the summer months and with independent research with a variac and run of the mill microwave oven and by pure design using a Panasonic Inverter type microwave oven. Let me elaborate a little.

First, for many years i used a regular microwave oven and during the summer the power would go down as i would notice the food cooking much slower and sometimes not at all. I realized that lowering the input voltage would reduce power in a more linear fashion than having the oven pulse on and off as most do today.

Second, i bought a Panasonic Inverter microwave oven that has a built in inverter that actually lowers the continuous power NOT pulsing it on and off as most do.

Third, i got a regular run of the mill cheap mic oven on sale and used a variac to vary the input voltage and thus get slower cook times on the highest power setting. This meant that the oven was not pulsing but still had the cooking power reduced considerably. I found that i could cook food with as little as 300 watts input power (not cooking power) which means less than that cooking power.

So the first was by accident, the second by design, and the third by experiment because i wanted to see if i could do this with a regular mic oven too.

What i found out in the third case is that the power reduces significantly from about 120v down to about 80v or something like that, so that at some point it runs but stops cooking altogether. Before that point though i could get any power i wanted to get, for example low power to defrost a chicken pot pie.

Besides that i have read articles on the web about reducing voltage to the heater of the magnetron. There are some that suggest that the heater coating gets damaged with reduced voltage, however they dont seem to provide any time line for this supposed problem. What i noticed with my older oven was that even after several years it still worked even with reduced voltage in the summer months, so it cant be extremely bad. Also, modern ovens may have a better coating than the older ovens too so that might help.

The benefit i have seen to continuous low power cooking vs pulsed low power cooking seems to be more tender meats and more even cooking. It is hard to put a number on this though so you'd have to try it yourself.

So in general i agree that turning down the input voltage to all devices is not a good idea but with some it does work. I've been doing it for so long now that when someone says you cant do it i cant help but contradict that notion.



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 Post subject: Re: Iron wire inductor
PostPosted: Wed Nov 15, 2017 8:28 am 
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I have two microwave ovens, one on power pulsing and the other also on that, but also given voltage reduction. I noticed some of my things needed much more pulsing and for much longer than ovens were set up for. My first oven ended up with stuck timer contacts from too much cycling.

I made an external pulser that helped yet still was having some trouble with overheating split peas and leafy greens. I was concerned about cycling even more than I already was for good results. That was when I went to lowering the voltage some also.

I noticed that the oven with the bit of voltage reduction worked a bit better. Before, it was showing signs of transformer core saturation, and now it turns on much more smoothly, particularly more quietly and gently.


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 Post subject: Re: Iron wire inductor
PostPosted: Wed Nov 15, 2017 1:22 pm 
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Well, I was basing the post on my repair experience for older ovens. The transformer supplied both the filament and the high voltage, so to lower the filament voltage was a major redesign because the two windings were interconnected. I am sure, with an inverter design, the voltages could be adjusted until some of the electrons went to sleep, then a lower power may be obtained.


Consider these articles..
7. POOR EMISSION
Rejection due to insufficient electron emission from the cathode will show a sharp drop in the output power and moding during operation. Poor emission is due to residual gas in the tube, improper cathode temperature, etc. An increase in the residual gas contaminates the cathode and quickly deteriorates emission quality. Too high cathode temperature also contributes to poor emission by reason of excessive evaporation. Too low cathode temperature, on the other hand, not only produces insufficient electron emissions but also represents temporary degradation of the thoriated tungsten filament. The filament or heater voltage must be maintained within the specifications. As emission rejection actually includes such deceptive reasons as poor contact and increased resistance of the filament circuit, care must be taken.The electric power supply voltage must be carefully monitored. Variation of the supply voltage leads to excessive anode current (greater than the maximum ratings), which shows the same phenomenon as emission failure It is advisable to minimize any potential changes in the supply voltage greater than 2.5%.


Source https://www.thermex-thermatron.com/wp-content/uploads/2015/11/FailureOfMagnetrons_v3.pdf

Here is an article about using short pulses to control the magnetron output:
https://www.scribd.com/doc/119132766/Variable-Power-Short-Pulse-Microwave-Magnetron



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 Post subject: Re: Iron wire inductor
PostPosted: Wed Nov 15, 2017 2:42 pm 
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I think I am probably in the knee region of figure 4 right now (at the last linked site).

Yet after further looking at the graph, I think that isn't right. Since power is still a little over half of the rated output by my reckoning, operation has to be on the red (safe part) of the curve.

I did notice with greater voltage lowering than I'm using now (several years ago) that the magnetron got hot if too much reduction was used.

However, that was continuously powered. Presently, when pulsing the whole oven, the fan also is off in between pulses. That tends to keep the cathode temperature higher at the lower voltage.


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 Post subject: Re: Iron wire inductor
PostPosted: Thu Nov 16, 2017 6:55 am 
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Lenp wrote:
Well, I was basing the post on my repair experience for older ovens. The transformer supplied both the filament and the high voltage, so to lower the filament voltage was a major redesign because the two windings were interconnected. I am sure, with an inverter design, the voltages could be adjusted until some of the electrons went to sleep, then a lower power may be obtained.


Consider these articles..
7. POOR EMISSION
Rejection due to insufficient electron emission from the cathode will show a sharp drop in the output power and moding during operation. Poor emission is due to residual gas in the tube, improper cathode temperature, etc. An increase in the residual gas contaminates the cathode and quickly deteriorates emission quality. Too high cathode temperature also contributes to poor emission by reason of excessive evaporation. Too low cathode temperature, on the other hand, not only produces insufficient electron emissions but also represents temporary degradation of the thoriated tungsten filament. The filament or heater voltage must be maintained within the specifications. As emission rejection actually includes such deceptive reasons as poor contact and increased resistance of the filament circuit, care must be taken.The electric power supply voltage must be carefully monitored. Variation of the supply voltage leads to excessive anode current (greater than the maximum ratings), which shows the same phenomenon as emission failure It is advisable to minimize any potential changes in the supply voltage greater than 2.5%.


Source https://www.thermex-thermatron.com/wp-content/uploads/2015/11/FailureOfMagnetrons_v3.pdf

Here is an article about using short pulses to control the magnetron output:
https://www.scribd.com/doc/119132766/Variable-Power-Short-Pulse-Microwave-Magnetron



Hi Len,

Yeah it's amazing that i can get such contradictory results to many articles i have read. If i read them before i did anything, i would think that it was not possible and probably would have never done this. It's only through accidental experience that i started to think about it in the first place.

It's just a guess why there is such a conflicting result. It may be that they were dealing with older ovens or perhaps they put a bigger number on the number of years a microwave is supposed to work at maximum like-new capacity. Maybe they are talking 20 years while i am talking about 5 years. I stick to the 5 year number because that's about how often i buy a new microwave oven anyway. I had one for maybe 10 years though a long time ago.

So it could be that if you are looking for the maximum lifetime of the oven then linear power down is not good, but for the 5 year stretch it seems to work good enough.

Also, the articles could be based on maximum input power but reduced heater voltage only, whereas when i reduce power it is to both the heater and the power to the magnetron, or at least the voltage anyway. That may make a difference because the tube does not have to work with the full voltage now.

And then we also have to ask how does Panasonic do it. They power down linearly too using a built in inverter.



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 Post subject: Re: Iron wire inductor
PostPosted: Thu Nov 16, 2017 8:51 am 
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Never allow the facts to stand in the way of a good theory!
If the facts and the theory conflict, dispose of the facts.



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 Post subject: Re: Iron wire inductor
PostPosted: Fri Nov 17, 2017 2:40 pm 
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Lenp wrote:
Never allow the facts to stand in the way of a good theory!
If the facts and the theory conflict, dispose of the facts.


Hi,

Yeah sounds like a good rule (he he) :smile:



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