Looking for a round magnet

M

Minifig666

Senior Member
I've looked around e Magnets UK but they don't say where the poles are on each magnet. However they still look promising. Perhaps you could contact them?
 
J

John O

Senior Member
Thanks, I will.

I'm just looking at a transparent fan that I took out of my PC case yesterday and there's a metal ring set in the rotating hub, which "encircles" the windings. I'm just about to break it apart as it "feels" to me that it should be magnetic and have poles on opposite sides of the diameter!

John.
 
W

westaust55

Moderator
with poles across the flats readily available . . .

10 mm diameter x 3mm thick
http://www.jaycar.co.uk/productResults.asp?keywords=LM1622&keyform=KEYWORD&SUBMIT.x=0&SUBMIT.y=0

But eclectic or BB have recently indicated Jaycar UK mail out of Aust.

also on thE Bay:

6mm x 1.5mm on Ebay (50 for AUD$6)
http://cgi.ebay.com.au/50-x-Disc-Rare-Earth-Neodymium-Magnets-N50-6mm-x-1-5mm-/290512420988?pt=AU_Miniatures&hash=item43a3e3c07c

or 100 for AUD$11
http://cgi.ebay.com.au/100-x-Disc-Rare-Earth-Neodymium-Magnets-N50-6mm-x-1-5mm-/300504710628?pt=AU_Miniatures&hash=item45f779fde4

or in the UK


6mm diam x 3 mm (50 for £3.19)
http://cgi.ebay.co.uk/50-Neodymium-Disc-Magnets-6mm-dia-x-3mm-Free-Post-UK-/160535760720?pt=LH_DefaultDomain_3&hash=item2560ad4f50

5 mm diam x 2 mm (50 for £2.99)
http://cgi.ebay.co.uk/50-Neo-Magnets-3x2mm-Most-Powerful-N52-Grade-warhammer-/160535306113?pt=UK_Toys_Wargames_RL&hash=item2560a65f81

or smaller 4mm diam x 1 mm (100 for £3.69)
http://cgi.ebay.co.uk/100-Neodymium-Disc-Magnets-4mm-x-1mm-N40-models-craft-/150544984988?pt=LH_DefaultDomain_3&hash=item230d2e2b9c
 
J

John O

Senior Member
It's got a "ferrite" type ring inside the metal ring and it does seem to drag a compass needle at opposite sides. It's about 20mm across so, as you say, it's probably too big but it's probably worth a test when the chip arrives and I've had chance to set it up.

The magnetic units 45mT don't mean a lot to me so it will be a case of suck it and see anyway :)

John.
 
J

John O

Senior Member
westaust55 said:
with poles across the flats readily available . . .
Click to expand...
Thanks. Yeah, I've seen those but I need the poles across the diameter :(

I'll have a better idea of what's suitable once the chip arrives and I find out how to drive it. Initially I'd thought that a common button magnet with a countersunk hole through the middle would be ideal but, it's only when I got down to the detail that it became apparent that there's more to magnets than meets the eye :)

John.
 
techElder

techElder

Well-known member
A magnet polarized the way you want it would not be very common. In my previous experience with magnets (some time ago), I have forced multiple poles the way you want them, but never only a N-S. It isn't a good length to diameter ratio.

I must admit that the "super" magnets we use now could be manufactured to have poles the way you want them, but I've not kept up with that.

I would think you should be looking / designing for a magnet that is long compared to it's thickness and is not round like a disk. I have put bar magnets into molds and essentially molded a disk around them to make them "round".
 
J

John O

Senior Member
defi said:
These any use
http://uk.farnell.com/eclipse-magnetics/n807/neodymium-disc-magnets-6mm-x-3mm/dp/1800040?crosssellid=1800040&crosssell=true&in_merch=true&
If not try austria microsystems I got some from them last year
Click to expand...
I'm not sure if the Farnell ones are suitable or not. But the datasheet at least explains the proper term for what I want is 'diametral' !

Thanks for the suggestion to try austria microsystems directly - I'll get in touch to see what they say.

Hmm, austria microsystems want $31 for shipping.

Looks like I'll be trying a short bar magnet from the local hardware store for < $1 for two.


John.
 
Last edited:
Buzby

Buzby

Senior Member
This item on eBay 110638972607 is in Coventry, UK. It might be a bit big, but ask the seller if he's got any others not listed.
 
J

John O

Senior Member
Andrew Cowan said:
These look even better; from the UK, 6mm diamter, and 1mm thick (so you could put 3 on top of each other):

http://www.first4magnets.com/f306dm---6mm-x-1mm-magnets-diametrically-magnetised-pack-of-10-a9y-477-p.asp
Click to expand...
Ah, nice one :) I think the 1mm thickness will be fine. I can't really see why they specify 2.5mm. I've just ordered a bag of 10 anyway. Can't go wrong at that price. :)

..

Thanks to everyone for your suggestions and offers of help... much appreciated.

John.
 
C

clockwork

Member
Magnet Supplier

"first4magnets.com" is a UK company in Lincolnshire that sell every type of magnet you can think of. Well worth a look at their website. Quick delivery too.
 
J

John O

Senior Member
The more I think about that the more I think it could be a struggle. The three "like poles" would have to be aligned so I could end up chasing them all over the place :)

John.
 
B

BCJKiwi

Senior Member
John O said:
The more I think about that the more I think it could be a struggle. The three "like poles" would have to be aligned so I could end up chasing them all over the place :)

John.
Click to expand...

Yes that's the problem - maybe Andrew will wake up in due course :)
 
A

Andrew Cowan

Senior Member
<wakes>

Good point. I was thinking it would be like 'normal' neodinium magnets, which can be placed side by side, into a grid pattern. But with these, it makes sense that on top of each other they will fly apart.

So, the big (and unimportant) questions:
- If you glued three together in this manner, would the magnetic field be stronger or weaker? Stronger, as there is more flux, but maybe weaker, as they would be trying to force themselves apart.
- Would they stick together if you turned the centre magnet 180 degrees, so the poles on each side are NSN and SNS? I think they probably would stick, but I'd imagine the magnet would then have very little pulling power, as two would cancel each other out.

Let us know when they arrive, John!

Andrew
 
J

John O

Senior Member
You're wondering about the same questions as me! I'll let you know :)

It may be that the strength of a single magnet IS determined to some extent by its thickness because I can't see why the datasheet would specify "at least 2.5mm" otherwise.

How several stuck together would behave remains to be seen!

John.
 
W

westaust55

Moderator
Believe (if memory serves me correctly) that if you stack some identical magnets end to end N S N S N S
That the
Magnetic field strength will be the same as for 1 magnet.
 
fernando_g

fernando_g

Senior Member
John O said:
It's got a "ferrite" type ring inside the metal ring and it does seem to drag a compass needle at opposite sides. It's about 20mm across so, as you say, it's probably too big but it's probably worth a test when the chip arrives and I've had chance to set it up.

The magnetic units 45mT don't mean a lot to me so it will be a case of suck it and see anyway :)

John.
Click to expand...
1 milliTesla = 10 Gauss;
Both are measures of magnetic flux density.

The product of that value and the surface area gives your magnet's "strength"
 
Last edited:
E

eclectic

Moderator
John O said:
Ah, thanks. Without some reference, it's still difficult to "visualize" though.

John.
Click to expand...
John
Have I missed the datasheet / reference
requirementas to the size of the magnet?

Following Fernado's post, I was
just thinking about "bulking out" a magnet
with epoxy or other filler.

e
 
J

John O

Senior Member
The datasheet says it should be 6mm diameter and greater than 2.5mm thick.

Someone sent me a PM and pointed me in the right direction on the austria microcontroller website so, hopefully, a couple of free samples will be on their way soon :)

"Strength-wise", I don't have the same "feel" Gausess or millTeslas as I have for most other units.

John.
 
E

eclectic

Moderator
John O said:
The datasheet says it should be 6mm diameter and greater than 2.5mm thick.

Someone sent me a PM and pointed me in the right direction on the austria microcontroller website so, hopefully, a couple of free samples will be on their way soon :)

"Strength-wise", I don't have the same "feel" Gausess or millTeslas as I have for most other units.

John.
Click to expand...
Sorry, my poor question.
Can you supply the original data-sheet?

e
 
You must log in or register to reply here.
Top