Winding a strong electromagnet

[Kator01]

Hey capthook,

Ah, great idea. I like your random way of thinking. A side-effect with this idea is that you reduce the capacity between the windings as well. Some time ago member pese was speaking of a transformer-design
build in germany in the 50 ´s or 60 ´s. They used only iron-wire-windings and by this there was no need of a core because the permeability was built in - so to say.  Of course this design had heat-losses. But it would be intersting to rebouild such a transformer.

Another thing I found some time ago - and I was not sucessfull to find it in my files - but I rememer this :

They said - and this was backed by calculation and tests - that once a load ( weight ) drawn to the coil-core-surface and has come to rest and is in close contact - you can reduce the current to a certain percentage to hold it in place.
So you can try this with your test-rig you already have.

There is another effect where you could combine magnetic-attraction with electrostatic-attraction-forces to hold a load-weight in place if this is needed.By  this combination you can switch off your electromagnet and only have a few miliamps at 200 Volt DC left to to hold the load in place.
It is called Johnson-Rahbeck-Effect ( dicovered in 1920 ) I only have a german description and will provide this here but it will take some time as I have to scan this from an  old german physics-book ( 1940)  and translate it for you.

In the meanwile you can try to find it via different search-engines. One of my favorites is this one here :

http://clusty.com/search?input-form=clusty-simple&v%3Asources=webplus&query=

Best Regards

Kator01

[Xaverius]

The welding wire idea was just a new/odd idea I thought I'd share - thinking it's probably not a real solution.

Glad you got your ferrite - looking forward to your results! Odd it is 2 pieces - hopefully they are even a better size now to work with.

I ordered mine from where I did because I didn't want that plastic tubing, wanted different sizes, was cheaper, and quicker delivery.  It should be here tommorrow 

What are your winding dimensions?
How are you going to test?  1 or 2 "D" batteries (1.5v or 3v) may be easier for testing than 9v?

The "strength" tests I've done are holding strength - as in a traction style EM.  It should be relative to an airgap EM.  They have been geared towards wire size, winding depth and length, and power consumption. 
Using a 5/16" hex bolt as weight and adding nuts and washers to add/subtract to that weight to determine the holding power.  Then weighing it to determine ounces/lbs of pull.
It could also be expressed as: 5/16" x 4" hex bolt with 5 nuts and 3 washers.

Is this a testing method you will pursue?  What other options/methods have you considered?
Anyone else with comments?

The earlier tests were add hock - and I didn't take adequte notes.

Once I get the ferrite - I will perform the above method with various cores and windings and post results.

You're wise to avoid the plastic coated ferrite, a real pain in the neck to remove the plastic, LOL!

Winding dimensions are 80 feet of 26 guage wire which is approximately 300 turns at 4 ohms resistance, 2 layers.  I'm testing with a 9V battery, I can use alligator clip jumper wires, connect one clip to the wire, the other clip to the battery terminal.

My test method consists of an eye bolt approximately 1/2 inch diameter with a nut threaded flush on the end giving an approximate surface diameter of 1 inch.  The eye on the other end is a ring of metal, I place an S hook on it and attach a bucket to the S hook.  While the EM is energized I pour water into the bucket until it breaks loose and falls.  Then I weigh the bucket with water and the hardware(eye bolt and S hook) for pounds of force.  I then multiply that number by 4.4 to obtain the force in Newtons.

BTW, Stormwise advertises their rods as easy to wind wire on the plastic, while keeping the ferrite weather proof.  However, no magnetic field is set up if you try it that way.  Sounds like deceptive advertising to me.

[Xaverius]

@ CapnHook

No luck with the Ferrite.  A 3 inch core wound with 300 turns of wire and 1.5 amperes yielded 1/10th of a pound of force.  Essentially useless.  I'm going to query some manufacturers for some electric steel samples.  Hope I have better luck, next time.

[capthook]

Your weight/pull testing idea is a good one.  It's much easier and more accurate to pour water than my method with the nuts and washers.  It's time consuming to add some nuts, then remove a nut, add some washers, etc..
Thanks!!

No luck with the Ferrite. 

What?!!?  Really?  DAMN!  It SEEMS it would make a great core.  I have a little piece laying around, and when I attach a magnet (large or small), the flux pours right through it like it was the magnet itself.

...............................

once a load ( weight ) drawn to the coil-core-surface and has come to rest and is in close contact - you can reduce the current to a certain percentage to hold it in place.

Good point. The effect of an air-gap is almost exponential.  So the smaller the airgap, the flux is x².  A close approximation is: half the pull for every 1/8" increase of airgap.
However - I wouldn't know how to design a circuit/process for automatically/accurately  adjusting the power draw to take advantage of this effect.  And in real time - it happens very quickly!
Or how to apply it to a (short) pulse/repulsion style EM.

[Xaverius]

Your weight/pull testing idea is a good one.  It's much easier and more accurate to pour water than my method with the nuts and washers.  It's time consuming to add some nuts, then remove a nut, add some washers, etc..
Thanks!!

What?!!?  Really?  DAMN!  It SEEMS it would make a great core.  I have a little piece laying around, and when I attach a magnet (large or small), the flux pours right through it like it was the magnet itself.

...............................
Good point. The effect of an air-gap is almost exponential.  So the smaller the airgap, the flux is x².  A close approximation is: half the pull for every 1/8" increase of airgap.  Of course it depends on the strength of the flux to begin with and the material being affected.

However - I wouldn't know how to design an circuit/process for automatically/accurately  adjusting the power draw to take advantage of this effect.  And in real time - it happens very quickly!
Or how to apply it to a pulse/repulsion style EM.

That small piece of ferrite you have, is it soft or hard?  The one that I ordered is soft.  Is the one you have already magnetized?  Could be I have a defective core.  Perhaps you'll have better luck with the Amidon material.    If you do I might try some.