How are magnets rated

[Xairman]

I am looking at buying magnets for some of my cars.

There seems to be an enormous amount of them on the market.

How does the average guy decide what to get?

I see that they are sold by length, width and thickness but that doesn't really tell me how strong they are.


Can any body shed some light on this matter?

[LegoPete]

I pulled the following off the net from a Google search...

How do you measure the strength or power of a magnet?

Most commonly, Gaussmeters, Magnetometers, or Pull-Testers are used to measure the strength of a magnet. Gaussmeters measure the strength in Gauss, Magnetometers measure in Gauss or arbitrary units (so its easy to compare one magnet to another), and Pull-Testers can measure pull in pounds, kilograms, or other force units. Special Gaussmeters can cost several thousands of dollars.

I know that some slot companies, like Ninco, advertise their magnets' strength using mass (ie. 1500 g*). I assume, after reading above, that this is using some sort of pull-tester. I'm not sure how these correlate to Gauss or any other units.

Pete



*Ninco brochure actually uses the term "GM", which is NOT the way to specify grams. The term GM actually doesn'y make sense as it, literally, means "gigamega". Sorry, this is just something that bugs the heck out of me, and if you think I'm anal about it check out www.nist.gov

[MG Brown]

From wondermagnet.com

How are your magnets measured and graded for strength, quality, etc.?

Magnet Strength Measurements (B)--The units for measuring the field strength (flux density) of a magnet are Gauss or Tesla. 1 Tesla = 10,000 Gauss. The Earth's magnetic field is on the order of 1 Gauss. There are different ways to classify and measure field strength:

B (flux density): This is the measurement (in Gauss or Tesla) you get when you use a gaussmeter at the surface of a magnet. The reading is completely dependant on the distance from the surface, the shape of the magnet, the exact location measured, the thickness of the probe and of the magnet's plating. Steel behind a magnet will increase the measured 'B' significantly. Not a very good way to compare magnets, since B varies so much depending on measurement techniques.

Br (residual flux density): The maximum flux a magnet can produce, measured only in a closed magnetic circuit. Our figures for each magnet are provided to us by the magnet manufacturer. They are a good way to compare magnet strength...but keep in mind that a magnet in a closed magnetic circuit is not doing any good for anything except test measurements.

B-H Curve: Also called a "hysteresis loop," this graph shows how a magnetic material performs as it is brought to saturation, demagnetized, saturated in the opposite direction, then demagnetized again by an external field. The second quadrant of the graph is the most important in actual use--the point where the curve crosses the B axis is Br, and the point where it crosses the H axis is Hc (see below). The product of Br and Hc is BHmax. If we have these measurements available, they are provided to us by the magnet manufacturer--very complicated and expensive equipment is needed to plot a B-H curve.

Magnet Quality (BHmax): The quality of magnetic materials is best stated by the Maximum Energy Product (BHmax), measured in MegaGauss Oersted (MGOe). This is because the size and shape of a magnet and the material behind it (such as iron) have a large effect on the measured field strength at the surface, as does the exact location at which it measured. All of our Nickel-plated NdFeB magnets are grade N35 (BHmax=35 MGOe) and all of our Gold-plated NdFeB magnets are grade N45 (BHmax=45 MGOe). This gives about a 5% difference in strength, and a 150% difference in cost...it is wise to balance your magnet strength needs by cost too. Other magnets are measured the same way -- a grade 8 ferrite magnet (grade C8) has BHmax=8 MGOe.

Coercivity (Hc): This measures a magnet's resistance to demagnetization. It is the external magnetic field strength required to magnetize, de-magnetize or re-magnetize a material, also measured in Gauss or Tesla.

[bov]

er....

Now I feel like I'm full of flux.....

But I'm sure that'll be helpfull to someone....

Good searching, Mick

Cheers, Tony

[oldstromguy]

No idea how "strong" these are.....

but 1 added to Carrera cars improves braking and handling greatly.

http://cgi.ebay.com/50-MAGNITACKS-RA...QQcmdZViewItem

[MG Brown]

Tony: I have purchased surplus magnets from wondermagnet in the past. I would recommend them.

[Guest]

Holy smokes MG Brown!!!! I feel like I just stepped out of my college Physics class. Maybe you could help me, I have a question concerning how magnetism effects the fluid dynamics of certain....


Oh forget it, I was just kidding anyway.

[RichD]

Magnet Strength

Measuring the strength of the magnets themselves will not tell you very much, it is what they do in the car that matters. The magnets used in 1/32nd scale cars are a neodymium alloy that comes in two different grades. Neo is the strongest magnetic material. The only real reason to worry about the strength of the individual magnets is if you are trying to save a little weight. Generally if you need more downforce you can use a bigger magnet, add extra magnets or move the magnet you have closer to the rails. Conversely you can get less downforce by using a smaller magnet or shimming the one you have. One thing to remember is that the size of the magnetic footprint is just as important as the absolute downforce. A big bar magnet can give you a more forgiving car than a couple of dot magnets that exert the same downforce. We use this scale setup to measure the total downforce and we also specify where the magnet is located. We have calibration magnets so all of the scales will read the same.

[Robert Livingston]

You can buy a DS Pro "Pocket Checker 90" tachometer with a built in Gauss meter, with which you can read the magnetic force at the outside surface of your slot car motor's case. The directions in the box say not to measure neodymium traction magnets directly. But you can measure them at a fixed distance, in order to compare one magnet with the other. Magnetic fields fall off rapidly as distance from the magnet increases. I have not yet tried this, but will soon enough.

manufacturer:

http://www.ibbautoracing.com

diistributor:

http://www.mrrc.com

Fred at Port Angeles sells the DS 90 in the USA. I know you can call or e-mail to check on price and availability. Try this: http://www.132slotcar.us/

The rig shown above by RichD is a good one. Instead of the solid steel bridge which spans the scale and provides the magnetic downforce, you could substitute a wooden bridge with a length of Magnebraid, or a sample of whatever magnetic track rails you like, in order to directly measure the car's downforce on your track.

[PeteN95]

I have seen a secret prototype of a pocket magnet tester just for 1/32 scale slot cars, which will be available very soon. It is simple, compact, and works very well. It should also be very reasonably priced and make magnet racing much easier to police.

[MG Brown]

I have a question concerning how magnetism effects the fluid dynamics of certain....

If you get to the wondermagnet site... they have this cool "magnetic fluid" stuff that they sell! That will keep you entertained for a while.

[Dennis David]

Magnut

Ironic that there is a thread in the HO forum where the posters are arguing about the legality of certain magnets.

[BWA]

I have a very simple and super reliable test. I just measure how much junk they will hold on my Fridgerator door.

[Xairman]

Magnet mania

Thanks for the replys guys.
I think you covered everything there is to know about magnets, right from the north to south poles.

I guess the ultimate test for a magnet would be,
" will the magnet hold a brand new Scaley F1 to the refrigerator door?"

Let me know if anybody tries this.