Winding a strong electromagnet

[gyulasun]

Hi capthook,

Thanks for your P.Message. I think most of the aspects of making a good electromagnet have been included in this and in some other threads, I cannot add much new ideas unfortunately. Thanks also for quoting one of my earlier text on this subject earlier in this thread.
Some additional thoughts: I agree with Honk by saying that solid pure iron should be used with caution because of the eddy currents (unless you do not pulse-operate your EM),  see his thoughts: http://www.overunity.com/index.php?topic=2222.msg135629#msg135629 and here:
http://www.overunity.com/index.php?topic=5279.msg118679#msg118679
Also an important thing on response timewhen you do pulse the EM: http://www.overunity.com/index.php?topic=4948.msg105636#msg105636

You maybe noticed member DMMPOWER electromagnet offer? see here http://www.overunity.com/index.php?topic=4624.msg96814#msg96814
This reminds me to Jack Hildenbrand magnet valve but unfortunately DMMPOWER does not give any hint on the construction...   By the way, there is (I think) a valid argument against combining an EM with a permanent magnet to increase the flux by saying you can make the same increased flux by choosing a core with bigger permeability...
Well, this can be true up to a limit in the budget or fast switching speed or simply using already the highest exotic permeability core above which there is no higher and still you can increase the flux by including the flux from a perm. magnet too...

Thanks,  Gyula

[capthook]

Gyula-

Thanks so much for the reply!  As always - your input is HIGHLY valued and most excellent!

By the way, there is (I think) a valid argument against combining an EM with a permanent magnet to increase the flux by saying you can make the same increased flux by choosing a core with bigger permeability...
Well, this can be true up to a limit in the budget or fast switching speed or simply using already the highest exotic permeability core above which there is no higher and still you can increase the flux by including the flux from a perm. magnet too...

Thanks,  Gyula

Agree.  From several text-books, as well as recent hands-on tests, adding a permanent magnet(PM) is helpful in that the PM can greatly multiply the relative force of the EM.
I can't provide exact figures, but...

Example in non-exact terms:
Supply an EM with 5 watts you get 1000 gauss.
Now take a permanent magnet with 1000 gauss and attach to the far end of the EM.
Apply the same 5 watts to EM.
You now end up with (1000+1000)x4= 8,000 gauss.
So you have greatly increased the efficiency of that 5 watts of power.

"If we have a certain number of magnetic lines, N, the pull is proportional to N(squared).
So the more powerful the pull to begin with, the greater is the change of pull when you produce a small change in the number of magnetic lines."

I see it as: it takes A watts to produce the needed flux from the EM.
Attaching a PM provides B watts of equivalent flux.
A-(Bx2)= C, the watts now needed to produce the needed flux.
The PM has 'pre-charged' the EM for free by 'pre-aligning' some of the magnetic domains.

Once again - I don't know the exact relative effect - is it 4x or 8x or x²?  Wish I knew - but it is large.  One reference book states it as x².

Also - as in my project - if you are (only) repulsing a PM with the EM, it is an additional benefit by nullifying/reducing the attraction of the PM to the EM core.

Honks points are good ones on eddy currents and hysteresis losses (which points again to laminated electric steel as the core of choice), and I still need to learn more about these as well as reactance.

As to powdered cores, what I've found thus far is that most have them have low permability (20-150u) and saturation points and would be inferior in most designs over laminated electrical steel.

I'm still reading through the full threads of the links you gave....
Still reading the interesting Hilden motor thread: http://www.overunity.com/index.php?topic=2222.0
and this: http://www.overunity.com/index.php?topic=3456.0

- -
As to metglas, permalloy etc... it seems the super high permeabilities translates into excellent shielding - but not as EM or generator cores.  As Xaverius mentions, I think it has to do with low saturation points, as well as their 'orientations'.

It seems the practical/efficient core solution is electrical steel - grain-oriented even being the best.
Ferrite cores might also be a good choice, depending on the application.  I'll know more first hand info next week...

- -
Ways to source scrap laminated electrical steel:

Old microwave: http://www.overunity.com/index.php?topic=4047.msg101636#msg101636 \

"You can also get good laminations from junked alternators." wattsup


So much to learn - so little time!  One little step after the other 

[Kator01]

Hi capthook,

I would be very interested in reading this electromagent-book. Can you please review your link ?
It is no valid. No such book exists in this library.

http://books.google.com/books/pdf/The_Electromagnet__and_Electromagnetic_M.pdf?id=CLmFTg_j0pwC&output=pdf&sig=ACfU3U3SDSRbaHhRwpQzx6pb7kwk3pCBuA

Do you have a copy saved ?


Regards

Kator01

[mondrasek]

Kator01,

Link works for me.  Book is ~11.8Mb which is over my outgoing e-mail limit here at work or I'd offer to send it to you.

M.

[Kator01]

Hi mondrasek,

thank you anyway... but this is strange. Must be somthing wrong with the german-google-books-database.

Regards

Kator01