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Do magnets go off? I have a couple of older cars with the black magnets that dont seam to be very strong, also I have a couple that have button magnets that are a bit weak that I am thinking of changing to bar magnets.
 

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Russell Sheldon
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Hi Rich,

Magnets are easily demagnetised if not handled with care. Special care should be taken to ensure that the magnets are not subjected to adverse repelling fields, since this could partially demagnetise the magnets. Cars should be stored in such a way as to reduce the possibility of partial demagnetisation. The worst possible scenario is a metal toolbox for carrying your cars in.

Also, bear in mind that magnetic flux density (field strength) is affected by many external forces. Heat is not as serious as one might expect. Typically, a ferrite magnet will lose 3-5% of its strength by being elevated from room temperature to 100 decrees Celsius, the boiling point of water. When it cools, the strength returns to very near normal, so this is a reversible effect. There is a point where a magnet will lose all of its strength, never to return until re-magnetised. This is called the "Curie temperature." For a ferrite magnet, this is somewhere around 450 degrees C, about 850 degrees Fahrenheit. Cobalt curies at about 800 degrees C.

The silent killer of magnets is called "contact demagnetisation." Every time you allow a magnet to stick to something, the magnet loses energy! The effect is not as serious on the poles as it is on the sides or ends. The worst possible way to package magnets is in a poly bag, stapled to a card where they are allowed to contact everything and stick together. Impact has an effect on the flux strength, but it really isn't significant.

I hope this helps!

With kind regards,

Russell
 

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How old are your older cars? Magnet material has got better over the years, so what seemed like quite good magnets at one time are quite weak by modern standards.

As Russell says, magnets can loose their strength. If they do they can be remagnetised up to the maximum the magnetic material can sustain. So old weak magnet material can only produce fairly weak magnets however hard you try to remagnetise it.

With cheaper magnets it can be cheaper to buy new ones than get the old ones remagnetised.
 

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Nobby Berkshire
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Having just bought a few old 1960s Scalextric cars I can assure you that the motor magnets are exactly the same as they were back then. Unless you are thinking of living until you are 150 years old you will not notice any loss of magnetism.

What you are probably experiencing is that modern magnets are relatively more powerful that your older ones appear to be weaker through time, while your tyres are getting so old and slippy that you are not as stuck down as before.

But if you just want to fit massive magnets, then go ahead!
 

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The earlier Scaley magnets were a waste of time if you want a real magnetic effect. I would imagine you are referring to the cars with the magnet in a pocket on the outside of the chassis rather than being seated internally. Those magnets can be replaced with the standard bar magnet or the stepped bar magnet - not something that I have a great deal of faith in - or as I have done using a magnet as supplied on line by several companies in the UK, take care to get the dimensions right.
The same applies to button magnets to an extent as they are available in various thicknesses, but I don't really like them in Scaley cars as they have such a narrow field of attraction. I have replaced the button magnet in certain Scaley cars by dremelling out the pocket and gluing in a bar magnet, best example is the Cadillac Northstar LMP which then becomes competitive with the MG Lola.
My other policy is to always replace the stepped bar magnet in F1's with a full standard mag' because these cars are mega quick and the stepped magnet just can't hold them.
I really enjoy tinkering with magnets, I know this is not the view of everyone, but it's an individual choice, don't forget either that SCX have an adjustable magnet sysytem, on cars which can't take a bar magnet I have devised various ways to lower the button mag' as it is the distance from the rails that detemines magnetic downforce, and in doing so it just give me that little bit extra grip without the car being a bore to drive. Certain Fly Classics come under this banner.
As has been said it is still important to have decent sanded & lubed tyres, otherwise the magnet alone is not enough.
I am fortunate that I can run mag's on my 15' garage track and can then drive non-mag at my club - NERCS, near Newcastle - so I get to drive in both disciplines.

Hope that helps,

Dave
 

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QUOTE (Screwneck @ 13 Sep 2011, 05:32) <{POST_SNAPBACK}>Having just bought a few old 1960s Scalextric cars I can assure you that the motor magnets are exactly the same as they were back then. Unless you are thinking of living until you are 150 years old you will not notice any loss of magnetism.

What you are probably experiencing is that modern magnets are relatively more powerful that your older ones appear to be weaker through time, while your tyres are getting so old and slippy that you are not as stuck down as before.

But if you just want to fit massive magnets, then go ahead!
I'm a little curious to know how accurately you've measured the magnetic fields in the 60s and now to know they are exactly the same as they were back then.

How much magnets deteriorate depends on how they have been used / abused. In some cases a loss of magnetism is very noticeable in quite a short period, Russell has already explained some reasons why. If magnets haven't suffered from these sort of things, they may well still be usable after 40 years.
 
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