Calculating Magnetic Field Strength (H) in Solenoid.

Hi AJ,

Instead of approaching these calculations from the B, H and u point of view, it is often easier to think in terms of the magnetic circuit, equivalent to the electric circuit that we electrical people are brought up on. i.e. Ohms law; and yes there is the magnetic circuit version of Ohms law, which it seems to me you are looking for:

I posted these some time back, hope they help:

http://cr4.globalspec.com/comment/26943

http://cr4.globalspec.com/comment/26953

NeilJ

If you got your formula right, because i haven't got my notes at hand, than i can assure you it is valid for any number of layers of winding.

I had been using it succesfully on solenoids ages ago.

This is why you can build a small strong electromagnet because you're trying to fit as many a turns on a short iron core as possible.

Adding/piling the number of turns over a shortest possible distance enable you to get a strong electro-magnet.

Note: It works like the electronic circuit; the shorter wire (shorter Core) offers less resistance to current flow (flux flow). To increase the current flow in a wire you can increase its cross-section (cross-section of Core), if you wanna keep the length of your solenoid and the power level to it.

Bear in mind it gets more complex as you keep making compromises about the Iron Core geometry:

1. Cross-Section
2. Length
3. Type of material

The last one may even sound a little dum but make sure you use the right material especially if the solenoid is subject to rapid switching!

regards.

Re: Calculating Magnetic Field Strength (H) in Solenoid.

What is the "right material" that you refer to below? In a 12DC solenoid, is it very much less efficient using common mild steel. If there is a significant difference, what should I specify as the "correct material" when ordering steel from a metal supplier.

Many thanks

If you got your formula right, because i haven't got my notes at hand, than i can assure you it is valid for any number of layers of winding.

I had been using it succesfully on solenoids ages ago.

This is why you can build a small strong electromagnet because you're trying to fit as many a turns on a short iron core as possible.

Adding/piling the number of turns over a shortest possible distance enable you to get a strong electro-magnet.

Note: It works like the electronic circuit; the shorter wire (shorter Core) offers less resistance to current flow (flux flow). To increase the current flow in a wire you can increase its cross-section (cross-section of Core), if you wanna keep the length of your solenoid and the power level to it.

Bear in mind it gets more complex as you keep making compromises about the Iron Core geometry:

1. Cross-Section
2. Length
3. Type of material

The last one may even sound a little dum but make sure you use the right material especially if the solenoid is subject to rapid switching!

regards.

Analogous to an electric circuit, you can think of H as battery voltage (emf) and B as current. Mu corresponds to conductance or the inverse of resistance. If you have an air gap, its like a resistor (mu much less than the iron). A good approximation is that all the potential drop (H=n*i) occurs across the air gap. Like a resistor in an electrical circuit, the air gap limits the flux (B).

Hi Guest,

The current is analogous to the TOTAL flux Phi [Webers], and the current density will then be analogous to flux density B [Webers / sq m]

The emf (is the Electro-Motive-Force) measured in [volts], and is analogous to the mmf (Magneto-Motive-Force) measured in [AmpTurns], H is the [AmpTurns per meter] around the magnetic circuit.

I know from personal experience that heat affects magnetic flux, but do not know why.

I would like to know, why is the magnetic flux of an energized solenoid coil affected by temperature? In other words why does the magnetic field change shape when exposed to ambient temperature versus 350+ F? I have observed 125 vdc solenoid operated valves in power plants which give different readings of internal position reed switches, actuated by magnetics, at different incremental temperatures.

Also, is magnetic flux affected by sub-zero temperatures?

You should use a femm program that will allow you to model it to get a very close answer. A good free femm program is the one by David Meeker:

http://femm.foster-miller.net

it has some examples and I think it has an example that's pretty close to what you're looking for