# magnet strength...educated guess most welcome

Discussion in 'General Electronics Chat' started by Kermit2, Feb 15, 2010.

1. ### Kermit2 Thread Starter AAC Fanatic!

Feb 5, 2010
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I'm building a small generator and would like to get an approximate guess for the number of force lines. They are N42 Neo's. Sized 1inch by 2inch by 1/2 thick. Poles through thickness. Stacked in a pile of 3. For a total pole length of 1.5 inches.

It is a consequent pole frame and there are two of the three piece magnet stacks, one on each side. I've been using 90,000 lines/sq.in. but I think this might be to high.

The core is compressed iron powder and epoxy and the air gap distance to the core is .092". So total gap of .184" , call it 3/16 inch.

I can post some pictures of the rotor and magnet frame if they would help. I ask because I understand small generators and consequent pole types especially have more field leakage than other types or sizes. Is 90,000 lines to high with the gap and type of generator?

Any educated guesses would be welcome, facts will be given front row seats.

Kermit

2. ### Kermit2 Thread Starter AAC Fanatic!

Feb 5, 2010
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a picture to help visualise the arrangement.

3. ### kubeek Expert

Sep 20, 2005
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I always thought that the force lines are just a tool for imagining the magnetic filed´s density and shape?

Or is there something I was not told during the physics course? I never heard of any kind of equation that would be even remotely connected to lines density or force lines whatsoever.

ETA: looks like the unit lines/cm2 really exists, and are comparable to Teslas.
I know that magnetic filed creates these lines when being applied to a bunch of iron filings, but is their position determined by the field, or is it more or less random based on the original structure of the filings and how they connect when being magnetised?
So my question is, do these lines really exist and can be counted, or are they more like some old bogus meaurement unit?

Last edited: Feb 15, 2010
4. ### Kermit2 Thread Starter AAC Fanatic!

Feb 5, 2010
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This is unexpected. I've seen evidence of some great minds, with much wisdom on display here. To think such a simple question could somehow 'stump' these fountains of accumulated knowledge is really quite shocking.

I will of course accept an answer(or guess) that is in Guass or Weber or Maxwells or Tesla or whatever unit you think is required.

I would hope to be proven a hopeless worrier and will keep my fingers crossed that a simple answer will be forthcoming in a less than a fortnight?

Sep 26, 2009
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6. ### 3ldon Active Member

Jan 9, 2010
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Try modeling it in FEMM. http://www.femm.info/wiki/HomePage

90,000 lines isn't nessisarly too high, but this depends on the powdered iron and its specific losses, what you consider minimum efficiency to be and what is the RPM?

7. ### Kermit2 Thread Starter AAC Fanatic!

Feb 5, 2010
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3ldon, thank you for that input. I thought 90,000 might be just a little too much. I'll run with 80,000 and find my ampere-turns based on that. A large deviation from my calculated values should indicate which way I'm off.

Kermit