If I wanted to make a electromagnet with .5 tesla at the face with the dimensions of 2.5 inches wide and 5 inches tall, depth will be determined on what is needed to achieve desired gauss. What gauge wire with how many windings would be required.
Paul
The gauge is determined by the current that you will need. It has no effect on your inductance though.
You didn't specify core material.
I have wondered this myself, but not looked into it in any great depth. Inductance is the easy part, but how to convert to gauss is not so evident.
Lets say it's a soft iron core.
Paul
It will be problematic to get 0.5 tesla at the face of an electromagnet, unless it has a return path or very narrow airgap.
There are so many factors that define the outcome. Here's some.
1) It is easy to calculate the magnetizing force at any known windings, currents and depth
but the final flux result is mostly determined by the airgap, then current and permeability of the core.
2) The shorter the depth, the stronger the magnet, due to a smaller airgap between faces.
3) But a shorter magnet will also have less winding space and will be harder to cool.
4) Using a big core (not depth) will increase the strength of the electromagnet.
5) Oersteds Formula for magnetizing force: 0,4 * 3,14 * Turns * Amps / Centimeters depth = H Oersteds
6) What you need is the strongest magnetizing force possible at resonable cooling rate.
Knowing the formula you can calculate this yourself and then you should use the highest permeability core material one can get.
But if you are trying to reach the same strength as a strong Ndfeb magnet you really need to use liquid cooling.
Good luck
I'm sure someone here with better math skills than I can point out the relationship between amp-turns and gauss output.
That's what it comes down to I believe.
That will be impossible to calculate unless the exact airgap distance is known.
Honk,
Surely knowing the number of turns, the current (DC), the core permeability, and the core length, one can determine what the Gauss reading would be at one end of the coil?
There must be a relationship?
I know it could be determined empirically, so why not mathematically?
Isn't the air-gap distance just the length of the solenoid?
No, one must also calculate especially on the airgap to get to know the flux, but the formula just show average flux, not face flux.
And yes, the length of the solenoid is part the airgap, but the total size and area matters to.
This is why a long solenoid have less face flux compared to a short solenoid, but inside the core the flux will be extremely high.
If you bend a solenoid into a C, with a very narrow opening between ends, then it is easy to reach high flux levels.
Actually, in a closed electromagnetic system (no airgap) it just takes a few hundred milliwatts to reach really high flux levels.
But as soon a an airgap is introduced the flux levels drop like a rock.
If you look at the cores used for switched power supplies you can get them at various permeabilities and inductances.
But increased permeability gives less power throughput due to easier saturation of the material.
This is why I on daily basis calculate the cores I use to fit the chosen design perfectly, but I never calculate face flux
because there is no need for me to know this when I design my electronics. It is very difficult to calculate this when using
an open solenoid electromagnet. There's just to many uncertain parameters to get an accurate result.
The best I can do is to maximize the magnetizing force, then use the best core possible and measure the face flux using a gaussmeter.
metalspider,
This may help. Shows you how to calculate the field strength both inside (in the middle) of the solenoid, AND at the end (which is the one you want).
I was confident there would be a formula out there...just had to find it. I hope it is accurate.
Have fun.
http://www.physics.rutgers.edu/ugrad/276/21-Ampere-S00.doc
uo is the permeability of free space (4Ãâ,¬ x 10-7), but I think you want to use the ur of your core material. Soft iron is about 5000 (I've seen anything from 1000 to 7000)
B is in Tesla (T). 1T = 10,000 Gauss
Yes, this is right, but the solenoid Paul wants has a rectangular metallic core, not circular.
This complicates the calculations. A rectangular metallic core and a return air gap of "uncertain" proportions.
But I don't know if this affects the formula. Kind of hard to calculate. But I wish Paul the best of luck.
(My bet is to go for the strongest magnetizing force possible at manageable cooling)
Quote from: Erfinder on December 23, 2007, 03:13:32 PM
.....snip
It is possible that someone on this forum may be able to provide you with an answer to your question, but I believe that the men of a bygone era understood more and had more to say about the issue than all the learned individuals of today. It is for this reason that I tip my hat to Peter Lindemann for recommending the text.
SOLENOIDS ELECTRO-MAGNETS and ELECTRO-MAGNETIC WINDINGS 1914
ISBN: 1-55918-096-X
Regards
Hi Folks,
Here is an earlier edition of this book from 1910, by the same author, Charles R. Underhill:
http://www.archive.org/download/solenoidselectro00underich/solenoidselectro00underich.pdf
This pdf file is of good quality scan of the original and about 35MB of file size, 388 pages, freely downloadable.
Merry Christmas!
Gyula
Thanks Gyula! ;)
Merry xmas.
Quote from: metalspider on December 22, 2007, 04:03:30 PM
If I wanted to make a electromagnet with .5 tesla at the face with the dimensions of 2.5 inches wide and 5 inches tall, depth will be determined on what is needed to achieve desired gauss. What gauge wire with how many windings would be required.
Paul
You also want a time constant of about 1 ms which determines the inductance to resistance ratio:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indtra.html
:-)
Terry
Yes Terry that is right. So what is the answer?
Paul
Reaching 1ms charge time is virtually impossible in the type of electromagnet you want to design.
In order to reach low charge times you need really low impedance, but at the same time you want
high fields by using high permeability core alloys and this increases the inductance greatly.
The only "easy way" to lower the inductance is to wind your electromagnet using really thick gauge
wire at very low resistance and then run heavy currents through your magnet, something like 150-200 amps.
But this will require some really good & heavy duty power electronics......
Tom Schum posted an interesting chart which shows the effect of various parameters on winding an EM:
http://mysite.verizon.net/vzesfls5/sitebuildercontent/sitebuilderfiles/coil_comparisons.pdf
Terry
Honk,
What do you think is the fastest rise time I can hope for?
Paul
P.S. Merry Christmas :)
Honk,
What do you think is the fastest rise time I can hope for?
Paul
P.S. Merry Christmas :)
Merry Xmas.
That is a tough question.
It depends totaly on the final inductance of the solenoid.
I'm sorry, but I can't give you a straight answer on this question due to the many unknown variables.
But I believe you will have a hard time getting down to one 1ms. The Solenoid is just to big to have a low inductance.
You should really aim for a high current solenoid to reach your goal. This is your best shoot.
(I guess this electromagnet is going to be used in your fine E.M.I.L.I.E. Looking forward to see it)
If we look at Tom's chart, we find that you can have thick wire, high current and relatively low voltage to result in a given EM field. Alternatively, you and have a thin wire with lots of windings, high voltage, lower current and give the same relative field.
Since time is of the essence, it would be prudent to choose a very small wire with a very large breakdown voltage on the insulator (say teflon) and create many windings. With a breakdown voltage of, say 2000 V, and a IGBT gate, one could achieve the required field with a small L/R ratio.
But, as Honk says, it requires a lot of trade-offs to optimize such a design.
Merry ?mass to all and to all a good nite!
Terry