Safe way to test my unknown larger neo magnet strength?

[Airstream]

I just got a secondhand bundle of 'unknown' sourced 1x2x0.5 neodymium magnets.

They are the fine grain ceramic style,  sloppy-clay-like bricks with thin dull metal plating.

And on examining one of them I am not very impressed with its pull & push. The attraction to a steel plate through my fingers was milder than I thought it would be.

I was expecting some scary repulsion - attraction, amplified up from the 1" x 1/8" 30 lb lift curiosities I have had laying around.

Since there is exactly the number for a dual rotor and no spares I was reluctant to experiment too much without knowing exactly what I was looking for.

How can I tell if these are worthy to continue with? Thanks!

[Norm]

 Bathroom scales

Adjust screw so magnet almost touches plate.
Norm.

[ChrisOlson]

Usually you'll want to know how much gauss you have the air gap to calculate the number of turns of wire required.  The pull force of the magnet is related to the size as well as internal gauss, and it varies between a large magnet and a small magnet of the same strenght.

The best way to check them to see what you have is with a gauss meter.  Those meters can be purchased relatively inexpensively, or you could go to a motor rewinding shop and see if they have one you can test them with.  If they are N42 neo they will be about 6200 gauss at the surface of the magnet.

--
Chris

[Airstream]

gauss meter... be purchased relatively inexpensively... hah!

And, I should have e-mentioned I don't own a bathroom scale in the first post

Any other folk-wisdom out there to test one of these? 

See if it tears the sheet metal off a tool box lid like a spot weld would? (just kidding)

[ChrisOlson]

If neither of the above is going to work, then maybe get out a magnifying glass and examine the magnet closely.  Maybe the "rating" is stamped on it someplace.

Or put them on a set of rotors, run a test coil and see what you get.

Magnets are rated by pull force with a test on a thick steel plate (the bathroom scale method) or gauss (the gauss meter method).  Period.  There is no other way to tell.
--
Chris

[Rover]

The previous answers were all the best, diging deep.

On of my favorite shop tools is a run of the mill "Berkley" digital fish scale... available at walwar for not so much.  Has a little hook, hang stuf from it. I use it for blade weight , etc, think its good to 50Lbs.

I have no idea on how to figure out magnet strength using the scale method though.

[Rover]

...Adding.. its also a good way to weigh luggage, before boarding a plane to make sure you don't get hammered with extra fees.

Oh yeah.. it will also weigh fish

[kurt]

...Adding.. its also a good way to weigh luggage, before boarding a plane to make sure you don't get hammered with extra fees.

Oh yeah.. it will also weigh fish

i have one of those mostly use it for weighing the wife's cat... comes in handy now and then. paid $20 for it at Walmart.

[silentblue1987]

well I like the more adventurous approach when testing magnets, hand it to my 2 year old niece and tell her to put it on the fridge. If she starts screaming because it pinned her hand to the door they're worth keeping.  j/k of course   

take 2 magnets and stick them to eachother.
find some boards and do a sort of slicing motion to seperate the magnets.
the amount of weight needed to seperate them should tell you what their worth.

http://www.youtube.com/watch?v=befbUmDsBok

1in x 2in x 1/2in  N42 grade magnets need roughly 70 lbs to seperate them... good luck

[Tritium]

I received two 2" diameter by 1" thick N50's that had shifted in shipment and were stuck together (had been packed with thin Styrofoam between them which crushed into a paper thin layer). It took all my strength and several tries at a table edge to get them apart.

Thurmond

[ChrisOlson]

1in x 2in x 1/2in  N42 grade magnets need roughly 70 lbs to seperate them... good luck

From the MDFA Standard for testing magnet pull force:

5.0 Apparatus

5.1 A test plate made of 1018 cold rolled steel, ASTM A794 (current edition), with a surface area large enough for the magnet-working surface to make 100% contact. A surface roughness of 63 micro inches, and a flatness or 0.001 " over the contact surface is required. Plate thickness must be such as to absorb all lines of magnetic flux emanating from the magnet, i.e., remains unsaturated.

5.2 Gauss meter to check for saturation of test plate.

5.3 Surface roughness and flatness measuring devices.

5.4 Fixtures to hold the magnet and the test plate evenly through the magnet center of force while a load is applied to separate the magnet from the test plate.

5.5 A method or device to provide a gradually increasing pulling or pushing force against the magnet and the test plate.

5.6 A device which provides a measure of the total force being exerted between the magnet and test plate.

5.7 A method for recording the peak force at which breakaway occurs.

Suggested apparatus for measuring breakaway force:

Test plate mounted on roller bearings to allow self-alignment so that load is applied to magnet through magnet's center of force. Load cell (strain gauge) that relies on resistance change with force applied. Resistance change leads to change in current flow, which can be measured. Output can be read by device calibrated to give results in appropriate units of measure. Output devices should, as a minimum, be able to retain peak readings. Many standard commercial devices are available.

http://www.intemag.com/MDFA_Pull_Test.html

--
Chris