Restoring a magnet's strength

[robgraham]

My brother has become a model railway geek - making money at it too, so I shouldn't be too rude about him !!

Any way he was on the phone to ask about restoring the strength of small dc electric motor magnets - seemingly the motors from older model railway engines (1960's etc) have detachable magnets and he reckons they've lost their strength.

Googling "make a magnet" seems to suggest that all that is required is to put them for a period into a strong magnetic field - ie a coil with a dc supply. Anyone anyone any experience of this ?

Thanks Rob

[John Williamson]

That's about it. If he can find a model shop that's been round a while, they *may* still have their Triang/Hornby remagnetiser sitting in a storeroom.

Handy links here:-

look for a source of new magnets that will fit, and live with the slower maximum speed and higher torque caused by the higher field strength.

[Graham.]

Yes, and also by orienting a rod to the current magnetic deviation angle and whacking the end with a hammer, but I doubt I could use either method to make a strong permanent magnet without some specialised equipment.

While clearing my garage yesterday I found my Labgear degaussing coil so if you want to destroy any magnets I'm yer man :-)

[Terry Casey]

As anyone whose finger has ever slipped of the sprung switch used on most deguassing coils will know, they work very well in reverse ...!

Don't think well enough for what you want, though ...

how about putting them near - but NOT touching! - on the the magnets in the "What the

****? (OTish)" thread? Just put something non-magenic between the two and leave for a while - then slide the smaller maget off. Repeat as required ...

[Man at B&Q]

If it's Hornby Dublo, buy new

Far better than you'll ever achive DIY.

MBQ

[Nightjar]

ISTR that the detachable magnet motors never were the best to begin with.

I had magnets made for me some years ago and I got the impression from the manufacturer that there is quite a gap between that theory and what happens in practice.

Colin Bignell

[Skipweasel]

Easier would be to plant another magnet on the surface.

Stick one or two of these on each side of the can...

you'll see the difference. I've done it with other small motors and it works quite well.

Cheap, too.

[Man at B&Q]

Yeah right.

Have you actually seen the motor in a 1960s model loco?

MBQ

[Andrew Gabriel]

11:00:36 -0000

What might work would be to use a couple of really strong rare earth magnets, and to hit the old magnet a couple of times or vibrate it whilst in the strong field.

I remember the very early Sun 2 Colour monitors we imported into this country before Sun was known here, which came with a separate mains degaussing coil. It worked extremely well, and one day someone noticed it was rated 120V 60Hz...

[Andy Dingley]

I've got a magneto remagnetiser in the shed. I don't think I'd bother with it though - these days it's easier to slip a thin piece of a rare earth magnet into the field circuit somewhere. A couple of mm of that will give more field strength than you need. Make a simple mild steel (or soft magnet iron, if you have it) spacer to fill the rest of the gap.

Don't overdo it. If the field is excessive, you'll lose more from simple attraction to the armature core than you'll gain from extra torque from the windings. I've seen some model motors lock up solid after they've had modern magnets inserted.

[Chris Hogg]

I'm probably wrong, but AIR the shaped pieces that surrounded the armature were actually just soft iron pole pieces, and the magnet itself was a small near-cube that the ends of the pole pieces were clamped on to. Heating it to a dull red heat and then allowing it to cool in a strong magnetic field (either from a DC coil or simply in contact with a rare-earth magnet from an old HDD) would be what I'd try. I think the heating bit is important, but Googling for re-magnetising doesn't mention it very often.

[Tim Streater]

Heating any iron magnet to dull red will destroy any magnetism it has. You can then re-magnetise it as described.

[Andy Dingley]

These magnets weren't iron though, they were Alnico. Heating them, long before a "dull red", is likely to cause them to shatter and spall.

Nor is there any reason to wish to demagnetise them before remagnetising. Even if you add a new magnet and just keep the old magnet as part of the field circuit, there's little need to demagnetise it beforehand.

[Skipweasel]

Not for about 40 years, no.

[Skipweasel]

Actually - a picture might really help.

[John Williamson]

The problem with sticking stuff onto them is the way that the body usually fits very tightly round the motor. To get room, you'd need to grind away most of the existing magnet. There's often only about a millimetre to spare.

Modern motors are much smaller for the same output, due to advances in magentic materials. One way out could be to put an entire new motor into the space occupied by the old armarture and you'll still have room for packing and a DCC unit.

[Chris Hogg]

You may well be right about the spalling, but in general, heating a magnet to dull red heat demagnetises it because the orientation of the magnetic domains become thermally randomised (see Curie point,

But IIRC at high temperatures, the same domains are more easily aligned by an external magnetic field, so as it cools you end up with a stronger magnet than doing the same at room temperature, for example.

[John Williamson]

$(KGrHqYOKjQErzNs)YHmBK+VL-P+Mw~~_35.JPGOr Google for Triang X04 motor.

After a bit of abuse, they looked like this:-

's actually one from a Scalextric car, the train ones had a worm gear, but they went the same shade of singed plastic.

[Skipweasel]

The magnets I posted a link for are only about that thick.

[Skipweasel]

Take it apart and replace the sugar-lump with a modern magnet. The sort I posted a link for are powerful and you can just add or remove them to get the size right.