magnetic field size question

[mbrownn]

I have no means of getting reliable measurements of the size of magnetic fields or their strength, is there some info available on the net that I can look up?

The things I am interested in are as follows:-

1) Assuming the resistance does not change, When we double the number of turns in a coil we increase the power of the pulling force. Does this double the pulling force or is it less? Is the size (volume) of the field doubled?

2) We know that increasing current increases the strength of a magnetic field in a coil. Assuming the current is constant, does increasing voltage without an increase in current, increase the size (volume) of the field created?

[gyula]

Hi mbrownn,

On your 1st question, I assume you mean the coil's DC resistance does not change, right? :

So when you double the N number of turns for an electromagnet coil to 2N, then the magnetic field, B also doubles (assuming the same input current) and the force, F exerted by the magnetic field increases 4 times (provided the core of the coil does not saturate either). Electromagnet - Wikipedia, the free encyclopedia

In practice, whether the 4 times force can manifest or not, depends on some factors, including air gap, heat loss in the wire, core losses if you have core etc, the 4 times force is a theoretical maximum I believe.
By the way, when you increase the number of turns while you keep the DC resistance of the wire the same, you can only do this by using a thicker wire, right? This inherently increases the total volume of the coil with respect to the earlier coil with the N number of turns. I do not mean the increased volume area is always a drawback but one factor you have to consider in many cases.

On your 2nd question: I do not fully understand your question. Please explain how you can increase input voltage across a coil without an increase in current?

Perhaps you think of a pulsed coil when you control and restrict the ON time of the input voltage i.e. you start with a higher amplitude DC voltage than earlier and switch it off at a time moment the current is the same like in the earlier case, well within the 5 times the coil's L/R time constant, 5*(L/R). Is that what you mean?

Gyula

[mbrownn]

Thankyou for your reply. Its a hypothetical question.

What I am thinking about is the size of magnetic fields from coils.

We know a ceramic magnet has a large field and relatively small pull when compared to a Neo magnet. The neo has huge pulling force, but its range is small when compared to a ceramic magnet.

Can these field sizes ie range be replicated by a single coil by changing voltage alone?

Imagine we have a variable DC voltage source with a fixed current, say 1A. No matter what voltage we dial up we can only get 1A flow. We apply this to a low resistance coil at say 10v and measure the size (volume, not strength) of the field. Now we apply 20v and measure the size of field again. Im assuming that the current does not change and that by some means we are able to raise the voltage, Ohms law does not allow this, hence hypothetical. At 1A the pulling force, or strength should be constant, but would the volume of the field be bigger?

It does trouble me that voltage has no influence on a magnetic field. We know current influences pulling force, as does the number of turns, but increasing current usually means increasing voltage. Under this situation the volume or size of the field does increase. Its like there is something missing.

If it is only current that causes a magnetic field then no power is required other than that consumed in ohms law. Do you see what I am getting at?

[MagnaMoRo]

What I am thinking about is the size of magnetic fields from coils.

We know a ceramic magnet has a large field and relatively small pull when compared to a Neo magnet. The neo has huge pulling force, but its range is small when compared to a ceramic magnet.

Can these field sizes ie range be replicated by a single coil by changing voltage alone?

Both magnetism and gravity have infinite volume but variable strength. The strength is determined both by cumulative quantity and density of matter. Think of a neo magnet as being much more densely packed than a ceramic of equal size. The neo will definitely be detectable from further away.

[gyula]

Hi mbrownn,

you wrote: "We know a ceramic magnet has a large field and relatively small pull when compared to a Neo magnet. The neo has huge pulling force, but its range is small when compared to a ceramic magnet."

Unfortunately, I have a different view on the fields of a ceramic and Neo magnets: I found Neos have large fields and ceramic magnets have much smaller fields. When I spinned a Neo magnet in front of an old computer monitor which had a cathode ray tube display, it influenced the picture of the monitor from about 45-50 cm distance (it was a N35 cylinder, OD=18 mm, thickness 5 mm) while a 2 cm x 3 cm ceramic rectangular magnet I had (thickness was also 5 mm) influenced the picture from only 15-20 cm when spinned. BOTH magnets were magnetized through their thickness.
If you did not mean the large or small fields like in this test, then please describe a situation.
I think the fields from magnets depend also on the magnets shape and thickness, besides their material type.
I agree with you on the huge pull force for the Neo and a small pull force for the ceramic magnet.

I believe the different fields in strength (large and small) can be reproduced by a single coil (preferebly with similar size and shape than a permanent magnet in question) whose input current is adjustable to get fields (at certain distances) with similar strength. When such coil has a ferromagnetic core, then the shape and the permeability of the core can also influence the strength of the field created.

You wrote:

"If it is only current that causes a magnetic field then no power is required other than that consumed in ohms law. Do you see what I am getting at?"

Well, this could be close to reality with (electromagnet) coils receiving DC current which is not interrupted with a frequency higher than a few Hertz. This is because the inductive reactance, XL of the coil will start to block input current as the frequency of the switching increases. To compensate this, you would need to increase the input voltage to arrive at a needed input current, say the 1 Amper from your hypothetical example.

On the other hand, you would wish to reduce the wire resistance to as low as possible for a given coil, to reduce its heat dissipation as per Ohm's law. However, the question to be solved is that whether the amount of the input current is enough or not to maintain a needed field "size" and at the same time you keep the heat loss of the coil at a minimum.

Gyula

[mbrownn]

I think we are unable to answer the role of voltage in magnetic fields, but I can't help thinking there must be one.

For example, we know high voltage charges its surroundings electro statically. This can be measured. I wondered if there was a relationship between electrostatic charge and magnetism. Would that manifest as the size of the field?

Yes, we have to have current to cause a magnetic field, but permanent magnets show us we can have small intense fields or large less intense fields. Permeability could well be a factor in this.

In the area of free energy research, much has been made of voltage without current as a method of reducing input power, but we know current produces magnetism. It seems logical to investigate current without voltage as this gives magnetism as well as the other electrical effects. I believe field size, as well as strength, could be important when it comes to efficiently harvesting mechanical power. I know it is impossible to totally eliminate the need for voltage, but what are the disadvantages of making the voltage requirements so small?

[charly2]

I think you are correct mbrownn, I had the same question weeks ago while I was replicating the magnetic valve of Jack Hildenbrand.
I found that a flat coil made of thick wire produces more force at lower watts, yes at lower volts and higher amps than a long one, the reason for volts in the equation is because of the resistance in the wire of the coil.
Resistance is the enemy that limits the current. So an increase of volts is a must if you want more amps.
I have not finished yet what I'm doing but I made two valves different desing each, one wired with 28awg and another with 18awg, the first one was feed at 7.5v 1.5amps, the second one at 1.5v 7amps, I could no measure the force as I would like but the second one surprised me.
Now, if we could have a coil made of superconductor wire (cero resistance) we would not need to rise the voltage in order to get more amps running in the coil. This way the magnetic field can be created at very lower watts.
I think a good coil (or electromagnet) design could be made finding the equilibrium point between wire thickness and number of turns preferable in layers more like the pancake coils.

[gyula]

Hi mbrownn,

you wrote: "I think we are unable to answer the role of voltage in magnetic fields, but I can't help thinking there must be one."

I think there is "only" an indirect role of the voltage: when you close the circuit of a voltage source, current starts and magnetic field is created. Without any voltage amplitude, no current and no field.

you wrote: "I know it is impossible to totally eliminate the need for voltage, but what are the disadvantages of making the voltage requirements so small?"

Low voltage level involves high currents to achieve a needed Amper*Turns (At) excitation. The strength of the magnetic field created linearly depends on current and on the number of turns. High current involves high losses so if you do not use very good conductors with ample surface area, including the connection points too then you waste power. I am sure you are aware of this of course.

If you recall the Babcock lecture on his motor some years ago, he mentioned examples on flux strength of a conductor driven from a voltage source of 1 V, from which a given length of the conductor with 1 Ohm DC resistance consumed 1 A and it created a certain amount of flux. Then he stated the use of an 0.1 Ohm resistance conductor (instead of the 1 Ohm) with the same lenght and using a voltage source of only 0.1 V to consume 1 A again, the created flux is the same amount like before. So just using a thicker wire (of the same length than the thinner wire) resulted in a ten times decrease in DC resistance, hence the input energy can be dropped from 1 Joule to 0.1 Joule, as Babcock expressed it.
I think it is always good to find means for reducing input power to achieve a certain goal like getting a given amount of flux with a minimum input energy possible but we have to find means also to harness this "cheaply" created flux with a COP>1 result. This is what has not been shown.

Gyula

[mbrownn]

I think a good coil (or electromagnet) design could be made finding the equilibrium point between wire thickness and number of turns .....

I totally agree. Most motors today are built with a relatively high resistance. there is a good reason for this as it prevents burn out if the device is operated outside its design specs and it also means we can have smaller, cheaper motors. I dont know what the optimum would be, but I use very low resistance pancake coils, typically 6 turns. These are found in starter motors and also golf cart motors. The resistances can be as low as 0.01Ohms.

Another reason for asking about field size is because in a motor the field has to bridge air gaps which cause losses.

[mbrownn]

Hi mbrownn,

I think there is "only" an indirect role of the voltage: when you close the circuit of a voltage source, current starts and magnetic field is created. Without any voltage amplitude, no current and no field.

you wrote: "I know it is impossible to totally eliminate the need for voltage, but what are the disadvantages of making the voltage requirements so small?"

Low voltage level involves high currents to achieve a needed Amper*Turns (At) excitation. The strength of the magnetic field created linearly depends on current and on the number of turns. High current involves high losses so if you do not use very good conductors with ample surface area, including the connection points too then you waste power. I am sure you are aware of this of course.

If you recall the Babcock lecture on his motor some years ago, he mentioned examples on flux strength of a conductor driven from a voltage source of 1 V, from which a given length of the conductor with 1 Ohm DC resistance consumed 1 A and it created a certain amount of flux. Then he stated the use of an 0.1 Ohm resistance conductor (instead of the 1 Ohm) with the same lenght and using a voltage source of only 0.1 V to consume 1 A again, the created flux is the same amount like before. So just using a thicker wire (of the same length than the thinner wire) resulted in a ten times decrease in DC resistance, hence the input energy can be dropped from 1 Joule to 0.1 Joule, as Babcock expressed it.
I think it is always good to find means for reducing input power to achieve a certain goal like getting a given amount of flux with a minimum input energy possible but we have to find means also to harness this "cheaply" created flux with a COP>1 result. This is what has not been shown.

Gyula

It does seem the only answer on the voltage is as you suggest, but something in my head says there is more to know on this. For now, I am following a gut instinct that tells me that voltage is required for other reasons, although I don't know what they are. There is something about comparing different types of magnets and their fields that is shouting "voltage" at me.

At the end of the day we have to compromise, Just as the guys that use high voltage have to use some current, I will have to use some voltage.

Why does high current involve high losses? lowering the resistance reduces losses according to ohms law. Yes we end up with a big heavy motor so we get more friction but it seems a good compromise.

As I see it, resistance is loss, inductance gives us an opportunity to recover and recycle.

I have a lot of respect for Mr Babcock, his lectures have pointed me in a few different directions with good results.

My biggest problem with resistance now is the brushes as they account for about 90% (a guess) of the resistance in my motors. I think I need to go to some sort of brush like Tesla used on his devices as carbon brushes are just too high in resistance. I tried using spring steel but had a lot of problems, having said that I was getting good speed and torque at 3v 8A on a modified 12v motor.

[charly2]

I use very low resistance pancake coils, typically 6 turns. These are found in starter motors and also golf cart motors. The resistances can be as low as 0.01Ohms.

Depending on the wire thickness, it would be possible to feed a current near and bellow the limit of the awg# at very low volts.
The problem I found is a source of low volts and high amps, the way I tested my coil at 1.5v and 7amps was several alkaline batteries in parallel until reach the amps needed.
Is there any other way to get 1.5v or even lower DC voltage with a decent amps?, diodes have a limit for this purpose.

[gyula]

Hi Charly2,

you wrote: "Is there any other way to get 1.5v or even lower DC voltage with a decent amps?"

Yes, there are the switch mode power supplies with higher than 90% efficiency in most cases. IF you think of microprocessors running in computer motherboards, they run with plenty of Ampers at a low output voltage and for this purpose the step down high current DC-DC converters have been developed.

Here is a link to one manufacturer to see the choices what is it like if you are not much familiar with them, there are several other manufacturers (Texas Instruments, Onsemi etc) of course:

LTM4649 - 10A Step-Down DC/DC ?Module Regulator - Linear Technology
LTM4627 - 15A DC/DC uModule Regulator - Linear Technology
LTM4630 - Dual 18A or Single 36A DC/DC ?Module Regulator - Linear Technology etc etc


Or if you prefer off the shelf DC-DC converters, you can find some on ebay:

DC DC CC CV Buck Converter Step Down Power Supply Module 7 32V to 0 8 28V 12A EC | eBay

http://tinyurl.com/kd9e686

Gyula

[charly2]

Great!!!, thank you gyula.
I have never paid attention to these modules, definitely great options.
0.6v @ 12 or more amps incites to play with it .

[mbrownn]

Depending on the wire thickness, it would be possible to feed a current near and bellow the limit of the awg# at very low volts.
The problem I found is a source of low volts and high amps, the way I tested my coil at 1.5v and 7amps was several alkaline batteries in parallel until reach the amps needed.
Is there any other way to get 1.5v or even lower DC voltage with a decent amps?, diodes have a limit for this purpose.

A single cell from a lead acid battery will give around 2v under load, but if we get things working in the mV range we can use earth currents, basically stick two copper rods into the ground.

In nature, electricity tends to come in two forms, high voltage pulses such as lightning, and low voltage such as earth currents. It is available in other ranges too but we haven't been so successful in tapping it yet.

[mikrovolt]

You can make a magnetometer and amplify it to 2x 10x 100x
using an op-amp.
https://www.youtube.com/watch?v=RDAHTKLeQSc

Some classic physics demos are beginning to use animation to help visulize.
https://www.youtube.com/watch?v=NWE9SCRgBv0

We can try to define some terms to make this easier to understand.
This paper 1998 by Bill Beatty suggest the concept needs improvement :
Electrical curriculum: What is Voltage?

I would like to see more progress in this area.