# Electromagnet calculator

Discussion in 'General Electronics Chat' started by Sceadwian, Sep 1, 2007.

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Does anyone know of any electro magnet calculators? I'd like to be able to estimate the amount of force produced between a solenoid electromagnet and a static magnet next to it, the current required to produce a given force heat dissipation voltage drop, basically anything that can give me a better idea of what the optimal size/winding for the force desired.

2. ### ClydeCrashKopWell-Known Member

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Last edited: Sep 2, 2007

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5. ### tmedapNew Member

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Whre from find WORKING electromagnet calculator or -formula

I need make normal working electromagnet for my daughter school project. I am electric and not like 100 turn coil, current 100A - keep 1V5 Duracell with gloves. But cannot find simple formulas for calculations for electromagnet. I have
10mm ferrum centre
3V school battery maybe max current 0.5A
Item for raise 2g
temperature 20C

6. ### duffyNew Member

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I've been using Quickfield with good results. They have a "student version" which is free.

7. ### jasonbeNew Member

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Do you know of the magnetic properties of the item? I think that it may be that the magnetic field of the item interacts with the magnetic field of the electromagnet to produce a force. I don’t know how to calculate the height that the item will be raised based on the upward force produced by these interacting magnetic fields and the downward force of gravity. However, I imaging that the surface of the shapes – such as whether these surfaces have round or concave shapes – would be important. You question seems uniquely different from the content of this thread to me, and if it hasn’t already been asked in another thread, you might consider making a new thread. I think that you might have to figure out the magnetic properties of your item and the way that magnetic properties of two items suspended in air interact to produce a force. I looked briefly for a database of the magnetic field of materials without success – though I imagine such databases are readily available. There is some information at Magnetic field - Wikipedia, the free encyclopedia about fields. However, I don’t know if you can just add the strength of the fields together to find the overall field - because I don’t think that the strength of these two fields can be considered independently from the height of the item. I imagine that all three variables – representing the fields and distance between the electromagnet and the item, are interrelated.

You could start off by calculating the downward force of gravity on your item. The equation for this is force, F = ma, can be found at Force - Wikipedia, the free encyclopedia. m = mass = kilograms = 1000 grams. Your item is about .002 grams. a = gravity = about 9.8 m/s2.

8. ### duffyNew Member

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If you want to calculate it instead of measure it, you are going to need to plot cross sections and calculate field lines using finite element analysis. It's too complicated for one simple equation because it's dependant on the geometry.

9. ### jasonbeNew Member

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Were you referring to tmedap’s post? One way of measuring the field strength might involve drilling a hole from a region on the surface of the item – where the magnetic field of the item was strongest and had a polarity opposite of the top of the electromagnet, through the center of mass of the item – so that the item could move freely up and down a support – such as a nonmagnetic rod. Then the rod could be temporarily secured to the electromagnet in such a way that the items movement in response to magnet field of the electromagnet was along an axis that was coincident with the long concentric axis of the rod. The distance from the item to the magnet could be measured. Then the electromagnet connected to the rod could be replaced with different combinations of magnets having known magnetic fields until the same distance was measured between 1) these magnets and the electromagnet and 2) the item and the electromagnet. Then, then the magnetic field of the electromagnet could be equated with that of the different combinations of magnets. Temporarily connecting the rod to the electromagnet and performing a similar experiment might result in measurements approximating the field strength of the item. These two figures could then be plugged into equations to test if the height of the item above the electromagnetic is comparable with theoretical expectations.

Last edited: Jan 16, 2009
10. ### duffyNew Member

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Yes, just a supplemental remark to tmedap and Sceadwian. Although I'm not sure about the right way to do it, I agree with you that trying to measure it would be better for this kind of thing.

Last edited: Jan 17, 2009
11. ### tmedapNew Member

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Only manual is about 300 pages.

Thank You! ...

12. ### user_88Member

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... a magnet equation ... for your review

Attached is a simple approximation of the magnetic model which you have described. The main simplifying assumption is that most of the MMF ... resulting from the coil turns ... is established across the air gap, and that the magnetic reluctance of the iron core material is not as important.

The equation will allow the computation of a value for Ni, the product of the number of coil turns times the electrical amperes in the coil.

Once you have wound the coil on the rod, use a DC ammeter ... and see it you have a sufficient Ni magnitude. .... If the resulting current is too large for your battery, then insert a resistor of appropriate value.

For an initial object distance of 1 cm, I calculated the value of Ni to be about 141. If you could wind several hundred turns of #30 AWG magnet wire around your 1cm dia. iron rod, you might achieve the necessary Ni quantity.
...

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13. ### duffyNew Member

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Doesn't look right. Where's his permanent magnet? I don't see anything in there for the coercive force of the permanent magnet, or geometry terms for the armature.

It's true than an air gap drops most of the magnetomotive force (like a big resistor in magnetic ohm's law) but it says nothing about the total flux. Force is proportional to flux density, and you need to factor in the permeability of the core material with an "m" curve (B-H curve) to get that.

Last edited: Jan 20, 2009
14. ### user_88Member

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... The equation presented is only for tmedap's problem specification. The problem posted by the original poster is not within the scope of the equation.:
"for electromagnet. I have
10mm ferrum centre
3V school battery maybe max current 0.5A
Item for raise 2g"

It should be possible to wind a coil on a 1 cm dia. rod, and see what value of NI is required, using an initial 1 cm object distance. .... The given equation should provide at least an 'upper bound' on the value of NI that is required to generate a force to equal the weight of the object.... The actual experiment value requiring a smaller NI magnitude.

If you would care to examine the derivation of the equation .... see
Amazon.com: Electromechanical Energy Conversion: David Brown: Books
... see chapter 2, section 2.3, example 2.7
... one or two assumptions are necessary to meet tmedap's problem description.

Also, there is some material here: