Remagnetising a tiny rod magnet

Many thanks for all the suggestions. I like the idea of giving it a belt with the mains; fairly easy to set up. But I have a couple of queries. Will an ordinary 13A domestic plug cartridge fuse in a standard plug be OK, or does it require something special? Bearing in mind the length of the bar (8mm), any suggestions as to what wire I should use? Insulated, obviously, to avoid shorting between turns, but I only have bits and pieces of 1mm^2 and 2.4mm^2 cable handy that I can strip out a single wire from (although I could probably find some similar sized flex). The thickness of the insulation will limit the number of turns I can get over 8mm, but if I go for the thinner wire (i.e. the 1mm^2 stuff), it will not have such a low resistance and may reduce the peak current. Any suggestions as to how many turns are necessary?
If that doesn't work, RM's suggestion of a much smaller Nd magnet is a good idea, although I will have to compensate for the lower weight in order to keep the correct calibration of the rain gauge, but that shouldn't be difficult.
If all else fails, I'll try Harry's suggestion of stroking it with a Nd magnet, although the small size and the technique will make it fiddly. Still, if it works.....
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 04/08/13 14:11, Chris Hogg wrote:

I think at that size I'd be inclined to use teh coil and car battery approach. essentially get a small cardboard tube and wind a couple of hundred turns of simple pvc covered wire over it, and hold it all in place with masking tape and just 'flash' that across a car battery.with the magnet thing inside
--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Buy a magnetic door switch for an alarm? They are cheap - one part contains the reed switch, the other the magnet. If you'd like the dimensions of the actual magnet, I'll measure one for you.
--
*No sentence fragments *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 04 Aug 2013 14:47:30 +0100, "Dave Plowman (News)"

If that wouldn't be any trouble, then yes please, although I'd be surprised if it was anything like the same size. If by chance it is, would you let me know details of the door switch please?
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

One I have here - there are other types - has a rectangular bar magnet measuring 25.5 x 8.5 x 8.5mm
--
*To be intoxicated is to feel sophisticated, but not be able to say it.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 05 Aug 2013 12:19:09 +0100, "Dave Plowman (News)"

Many thanks for doing that, but too big in all dimensions to be immediately useful. ATM I'm pursuing other solutions. If I ever get it right, I'll post here. Thanks again.
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Might be worth giving the dimensions of your one - may ring a bell with someone. Although a reed switch usually doesn't need much in the way of magnetic field to work - depending on distances.
--
*If horrific means to make horrible, does terrific mean to make terrible?

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 05 Aug 2013 14:15:05 +0100, "Dave Plowman (News)"

You missed it in my OP? A circular rod 4mm dia. x 8mm long.
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 05 Aug 2013 14:54:15 +0100, Chris Hogg wrote:

I wonder if the shank of a 4 mm steel wood screw or a bit of 4 mm wire nail would be easier to magnatise to a suffcient strength than the orginal ferrite? Stroking with the neodynium one you have.
--
Cheers
Dave.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 05 Aug 2013 14:54:15 +0100, Chris Hogg wrote:

There's a magnet of around that dia in this kit:
(Amazon.com product link shortened)
Can't be sure how long the magnet is because of the brass mounting.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The other way you can do it is to stick your duff magnet on the neodymium magnet and put on hard (ideally non-magnetic) surface and tap the (duff) magnet with a hammer. Hammering ferrous materials in a magnetic field was how permanent magnets were made in days of yore.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/08/2013 21:00, Chris Hogg wrote:

How about chipping a flake off the small brittle Nd magnet and putting it at one end. You can get Nd magnets 1-2mm thick with self adhesive on one side and N or S pole on the other. I'd suggest buy one shatter it and stick a piece just big enough to induce the right level of magnetism in the host. Neater job if you buy round ones the right size.

What you want is a tiny Nd magnet attached to a soft iron nail!

Probably didn't get it above the Curie temperature.

Try this lot and hope that one is the goldilocks solution:
http://www.first4magnets.com/mdmsp---micro-disc-magnet-selection-pack-24-magnets-f6y-333-p.asp
Or a ferrite one and hope you can patiently cut it down to size
http://www.first4magnets.com/rectangular-ferrite-magnets-175-c.asp
--
Regards,
Martin Brown
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A RESULT!
Initially I tried TNP's method of a few turns of thick wire (actually about 20 turns and 1mm^2) on a small plastic bobbin (a wheel 'borrowed' from one of the trays in the dishwasher!), connected it via a 'Quicktest' connector (see http://tinyurl.com/qffkxxs ) to a cooker type panel supplying a 7.5 kW pottery kiln. Banged down the lid, quick flash from the neon, blew the 13A fuse, tripped the 50A MCB and the RCD in the dedicated CU, recovered the little magnet, but zilch! Not a Gauss (or should that be an Oersted), well, nothing significant, anyway!
On to plan F (or is it plan G now?) Whichever, it was a combination of Bob Minchin's and Martin Brown's suggestions of getting a much smaller Nd magnet and/or chipping a bit off one that I'd got. The Nd magnets I had were 4mm dia. and 6mm long, and I'd bought a pack of 10 from First4Magnets so plenty to play with. I chopped one into three more-or-less equal lengths by holding it in the wire-cutting section of a pair of pliers at the point I wanted it to break (2mm) and then squeezed the pliers in a small bench vice. They snapped/cleaved perfectly in just the right place, pretty much straight across. So I now had three Nd magnets, ~2mm long. I tried two together, but they were still too strong, but one on its own, with a couple of short bits of mild steel rod to provide the extra length and weight, and Bingo! it works perfectly, and the gauge calibration is still OK.
I'm delighted. Many thanks to everyone for their helpful suggestions.
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.