- #1

jschwartz6

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First, as I understand it, the flux density in a round solenoid is basically

B = μnI.

One of my solenoids (square plunger) is about 9300 turns/m with plunger area 1E-4 m[itex]^{2}[/itex] running 1.5A. I'm using a mild steel core with a rough estimate of μ[itex]_{r}[/itex]=50. By the above equation, the field from my solenoids is predicted about 0.88 T. Does that sound logical?

Also I have found a force equation that I don't know whether to believe:

F = B[itex]^{2}[/itex]A/(2μ[itex]_{0}[/itex])

(the force exerted on the solenoid plunger). Does anyone have a correction for this? This equation is predicting ~28 N and I'm getting ~0.35 N from that particular solenoid. Having an accurate force equation would be a huge help.

I tested my solenoids on an Instron tester machine. The peak forces for the highest-aspect-ratio solenoid were highest, followed by my medium-aspect-ratio solenoid, and then the one with the square plunger was the least. I'm pretty sure this is because the higher-aspect-ratio solenoids have a larger length of wire per coil. So I think the field for these rectangular-core solenoids might be:

B = μnI + (2)μ[itex]_{0}[/itex]I/(2πr)

where the latter term is the field about a straight length of wire, and each wrap of the coil has two lengths (one above and one below the plunger).

Then, for the force of the rectangular-core solenoids, I would add the term NILB to the regular force equation. Does that seem right?

Thanks for the help; sorry for the long post.