Restoring a magnet's strength
robgraham
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
they *may* still have their Triang/Hornby remagnetiser sitting in a
storeroom.
Handy links here:-
http://www.modelrailforum.com/forums/index.php?showtopic=3526
Or 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.
--
Tciao for Now!
John.
Graham.
"robgraham" <robkg...@btinternet.com> wrote in message news:2b21322b-74a6-4b2a...@d16g2000yqd.googlegroups.com...
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 :-)
--
Graham.
%Profound_observation%
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 ...
--
Terry
Man at B&Q
> 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.
If it's Hornby Dublo, buy new http://www.superneomagnets.com/ Far
better than you'll ever achive DIY.
MBQ
Nightjar
> 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.
ISTR that the detachable magnet motors never were the best to begin with.
> 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 ?
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
6c6d99...@d16g2000yqd.googlegroups.com>, robkg...@btinternet.com
says...
> 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.
Easier would be to plant another magnet on the surface.
Stick one or two of these on each side of the can...
http://www.dealextreme.com/p/5964
and you'll see the difference. I've done it with other small motors and
it works quite well.
Cheap, too.
--
Skipweasel - never knowingly understood.
Man at B&Q
wrote:
> In article <2b21322b-74a6-4b2a-aaec-
> 6c6d990be...@d16g2000yqd.googlegroups.com>, robkgra...@btinternet.com
> says...
>
> > 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.
>
> Easier would be to plant another magnet on the surface.
>
> Stick one or two of these on each side of the can...
Yeah right.
Have you actually seen the motor in a 1960s model loco?
MBQ
Andrew Gabriel
Terry Casey <kt...@example.invalid> writes:
> In message <ijdmd9$hc1$1...@news.eternal-september.org> on Tue, 15 Feb 2011 11:00:36 -0000
> Graham. <m...@privicy.com> wrote:
>>
>> "robgraham" <robkg...@btinternet.com> wrote in message news:2b21322b-74a6-4b2a...@d16g2000yqd.googlegroups.com...
>> > 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
>>
>> 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.
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.
>> While clearing my garage yesterday I found my Labgear degaussing coil
>> so if you want to destroy any magnets I'm yer man :-)
>
> 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 ...
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...
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Andy Dingley
> 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 ?
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.
Andy Dingley
> Heating any iron magnet to dull red will destroy any magnetism it has.
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
24g2000yqa.googlegroups.com>, manat...@hotmail.com says...
> Have you actually seen the motor in a 1960s model loco?
>
Not for about 40 years, no.
Skipweasel
skipweas...@googlemail.com says...
> > Have you actually seen the motor in a 1960s model loco?
> >
>
> Not for about 40 years, no.
Actually - a picture might really help.
John Williamson
> In article <bd9e7392-50e1-40a1-8346-305ec4f74686@
> 24g2000yqa.googlegroups.com>, manat...@hotmail.com says...
>> Have you actually seen the motor in a 1960s model loco?
>>
>
> Not for about 40 years, no.
>
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.
John Williamson
> In article <MPG.27c48edc2...@85.214.73.210>,
> skipweas...@googlemail.com says...
>>> Have you actually seen the motor in a 1960s model loco?
>>>
>> Not for about 40 years, no.
>
> Actually - a picture might really help.
>
Or Google for Triang X04 motor.
After a bit of abuse, they looked like this:-
http://www.hornby-railway-trains.co.uk/Parts/Hornby_Motors/Brushes_for_X03_X04_Motor/RX_Motor.jpg
That's actually one from a Scalextric car, the train ones had a worm
gear, but they went the same shade of singed plastic.
Skipweasel
johnwil...@btinternet.com says...
> 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.
>
The magnets I posted a link for are only about that thick.
Skipweasel
johnwil...@btinternet.com says...
> After a bit of abuse, they looked like this:-
>
> http://www.hornby-railway-trains.co.uk/Parts/Hornby_Motors/Brushes_for_X03_X04_Motor/RX_Motor.jpg
>
> That's actually one from a Scalextric car, the train ones had a worm
> gear, but they went the same shade of singed plastic.
>
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.
John Williamson
They work fine as long as the armature bearings are perfect, but they
are sintered bronze, and never get oiled by most users, so wear a lot,
which can lead to jamming. Luckily, all spares are still available.
Man at B&Q
wrote:
> In article <8rvemjFnb...@mid.individual.net>,
> johnwilliam...@btinternet.com says...
>
> > After a bit of abuse, they looked like this:-
>
>
> > That's actually one from a Scalextric car, the train ones had a worm
> > gear, but they went the same shade of singed plastic.
>
> 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.
Why pis about? Just follow the link I posted and get the correct size.
MBQ
The Natural Philosopher
goes up, the fuse blows and everything inside is magnetized.
HOWEVER best is to replace old ferrite shite with neodymium magnets if
you can.
> Thanks
> Rob
Andy Dingley
> in general, heating a magnet to dull red heat demagnetises it
It depends on the metallurgy and the magnetic behaviour. If you heat
to the Curie point, then you _don't_ demagnetise it. Instead you
convert it temporarily from a ferromagnet to a paramagnetic material
(which doesn't behave as a magnet). However when the temperature
reduces back below the Curie point, this effect reverses and the
magnetism is restored.
If you heat the steel high enough, then you can also change its
metallurgy (any text on hardening & tempering) and these changes will
also permanently destroy any magnetism. This is _not_ the same as
Curie point behaviour. Nor (as the material is still ferromagnetic,
not paramagnetic) can you usefully magnetise it in this state by
applying a low field to it and cooling.
As to which happens first, that's a question of alloy. Part of the
unique (at the time) behaviour of Alnico was that it had a high Curie
point, the only one above a red heat. You can do what you describe to
some low-Curie alloys (and without getting to red), but not
practically to Alnico.
>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.
Yes, this is precipitation magnetisation. It's how Alnico magnets are
made in the factory.
In practice though, you're going to get spalling unless you have
something like a muffle furnace with a controlled slow heating. Alnico
is a pig mechanically, it's too brittle. No-one re-magnetises Alnico
magnets in this way. When they're first made, it's for cooling from an
initially unmachined billet and they're machined afterwards.
It's also a party trick for making impromptu magnets, but it's not
something you'd want to mix with the use of an induction magnetiser.
Nor is it easy to do - you not only have to apply a magnetic field,
but you have to apply it continuously while cooling below the Curie
point. This usually means a long bar magnet, just so that you can
apply a field to it sensibly. I know it's sometimes done for forging
horseshoe magnets, but it's a fussy process and very sensitive to the
alloy.
Andy Dingley
wrote:
> yes. a coil across the mains with a fuse is ideal. The field/current
> goes up, the fuse blows and everything inside is magnetized.
Bollocks. Capacitor banks are the usual way, to achieve a
unidirectional field.
If you have such a supply handy, or it's 1900 and capacitors aren't
usefully available, then a motor-generator set for electroplating (low
voltage, huge current) can also be used. Slightly later on (although
still quite ancient now), a minicomputer PSU (5V, 50-100A) can be used
too. It needs to be an old one (linear), because switched mode PSUs
don't enjoy this kind of abuse.
Andy Dingley
wrote:
> Take it apart and replace the sugar-lump with a modern magnet.
No, if you replace it with a similar-sized lump, then you saturate the
pole pieces and the spare flux locks the armature solid.
Harry Bloomfield
> 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 ?
That does work, but you would need to work out which way or where the
magnets poles were before you started and it MUST be DC - AC is used to
demagnetise. Another way is to stroke a strong magnet along the other
magnet, close up along the old magnet between the poles, then far away,
to return to the starting point.
Best option really is to see if modern rare earth (Neodymium) magnets
can be fitted instead, you can get them for a few pence each on ebay
for the small ones and they are extremely powerful.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
geoff
<2b21322b-74a6-4b2a...@d16g2000yqd.googlegroups.com>,
robgraham <robkg...@btinternet.com> writes
>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 ?
>
Yeah, buy a Niobium magnet
I just happen to have one for sale for �80
--
geoff
Bob Eager
If the buyer can move it....
--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org
*lightning protection* - a w_tom conductor
Dave Plowman (News)
my SD1 Rover. The original was never much good - it would stall on a dry
screen with the engine off so only 12 rather than 14 volts. In contrast,
those on my BMW are so powerful they shake the car on fast speed. A quick
glance showed the motors to be of similar size so I obtained a secondhand
BMW one - made by Valeo.
They are very similar. Roughly the same size armature, etc. But the Lucas
one has 'steel' magnets, the Valeo ceramic.
And a rough and ready bench test showed the Valeo produced 5 times the
torque off the same current limited (8 amp) bench power supply.
--
*You never really learn to swear until you learn to drive.
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
Andy Dingley
wrote:
> They are very similar. Roughly the same size armature, etc. But the Lucas
> one has 'steel' magnets, the Valeo ceramic.
I have a Volvo 960, the 2.5l straight-six. Starter failed a while
back, quite the worst starter to remove I've ever worked on. The
replacement though is one of the new permanent magnet starters, which
allows it to be a couple of inches shorter. Piece of cake to get it
back on. Works as well too.
Dave Plowman (News)
<68a7d6a5-05d4-4544...@24g2000yqa.googlegroups.com>,
Andy Dingley <din...@codesmiths.com> wrote:
> I have a Volvo 960, the 2.5l straight-six. Starter failed a while
> back, quite the worst starter to remove I've ever worked on. The
> replacement though is one of the new permanent magnet starters, which
> allows it to be a couple of inches shorter. Piece of cake to get it
> back on. Works as well too.
I have a permanent magnet replacement on the SD1 too. The actual motor is
very much smaller, but it has reduction gearing added.
--
*Why is the man who invests all your money called a broker?
Man at B&Q
Not if you replace it with the correct modern magnet, as sold for the
purpose.
MBQ
Jules Richardson
> In article
> <68a7d6a5-05d4-4544...@24g2000yqa.googlegroups.com>,
> Andy Dingley <din...@codesmiths.com> wrote:
>> I have a Volvo 960, the 2.5l straight-six. Starter failed a while
>> back, quite the worst starter to remove I've ever worked on. The
>> replacement though is one of the new permanent magnet starters, which
>> allows it to be a couple of inches shorter. Piece of cake to get it
>> back on. Works as well too.
>
> I have a permanent magnet replacement on the SD1 too. The actual motor
> is very much smaller, but it has reduction gearing added.
The one on my pickup's almost the size of a loaf of bread and weighs many
pounds. Two bolts to remove it (plus a third for power), and there's
enough space in the engine bay to do it from above rather than crawling
around underneath. Power to it comes via a big solenoid mounted up on the
inner wheel arch.
Our Toyota has one with reduction gearing though - the thing's positively
tiny, and I hope it never fails because there's absolutely masses of
stuff that would get in the way of its removal :-)
cheers
Jules
GB
> Or 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.
If the torque is greater, why would the max speed be less?
--
Murphy's ultimate law is that if something that could go wrong doesn't,
it turns out that it would have been better if it had gone wrong.
GB
> 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 ?
I have some magnets taken out of hard disk drives. When my screwdriver lost
its magnetism, a couple of strokes with one of these rare earth magnets
restored it (and more so!). Next time I'll just use one stroke. Would that
work with a Triang motor?
John Williamson
> John Williamson wrote:
>
>> Or 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.
>
> If the torque is greater, why would the max speed be less?
>
>
magnetic field, which combine to generate back EMF, which (simplified)
is the voltage the motor would generate if it were being used as a
generator. Increase the supply voltage, while keeping the same field and
it goes faster for the same torque. Increase the field while keeping the
voltage stable, and the speed decreases, as the back EMF rises relative
to the speed. The torque available (simplified)is proportional to the
current and magnetic field, and the rate of rise in current under load
is governed by the rate of change in the back EMF, which increases as
the field increases, all else being constant.
Electric traction such as trains and trams used to do this in reverse,
by having a weak field setting on the motors to increase the speed and
decrease the torque once they had reached a high enough speed. Kind of
an electrical gearbox.
Andy Dingley
> I have some magnets taken out of hard disk drives. When my screwdriver lost
> its magnetism, a couple of strokes with one of these rare earth magnets
> restored it (and more so!). Next time I'll just use one stroke. Would that
> work with a Triang motor?
No, because you can't stroke a cube. If you made a long stack of them,
you could try it.
The problem is that of remanence, the magnet's ability to remain a
magnet. Your screwdriver is intended as a screwdriver, not a magnet,
so it's made of a hard steel with a not terribly high remanence (by
the standards of deliberate magnets). However it's a hard steel
metallurgically, so it's actually fairly high (about as good as
magnets of 1900). It will act as a magnet once magnetised, but it's
'soft' enough to be re-magnetised by stroking with a more powerful and
remanent magnet.
Alnico though has a high remanence, far better than anything else of
its period. Stroking wouldn't work with any lesser magnet, however a
modern Nd magnet might be in with a chance.
John Williamson
Even so, I used to need to remagnetise motors about once a year,
especially if I was attending exhibitions with the models. I doubt any
stroking with other magnets would help in the long term.
My memories of the Triang machine are of a *large* coil, which must have
been several dozen Henrys in value on a horseshoe shaped soft iron clamp
that closed onto the magnet end of the motor, while turning on a DC
supply to the coil. The visible part of the whole thing was probably
about the size of a food mixer. The field was strong enough to reverse
the magnet's field if it was accidentally inserted upside down, with
embarassing results next time the loco was used. The operator had to
keep his watch well away even after it was turned off, too.
GB
Thanks for taking the time to explain this to me. I hadn't realised that the
train's speed was limited by the back EMF rather than the torque on the
engine - well ofc the back EMF reduces the current through the windings and
hence the torque.
Man at B&Q
>
> Thanks for taking the time to explain this to me. I hadn't realised that the
> train's speed was limited by the back EMF rather than the torque on the
> engine - well ofc the back EMF reduces the current through the windings and
> hence the torque.
The better examples of modern digital control for model railways uses
the BEMF in a closed loop feedback system to control the speed of the
loco.
MBQ
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 ?
>
> Rob
Having started this thread, and posted the link to my brother, my
thanks to all who contributed.
Brother is not the world's greatest communicator - only when he wants
something - so I don't know if he has taken on board the collective
wisdom here; I hope he has as the Collective, as always has shown the
breadth of its knowledge.
Rob