Magnets

The type and quality of the magnet in your Graham Farish locomotive plays an important part in the running characteristics of the armature. As we shall see below, there are a number of different magnets which have been produced over time by Graham Farish in Poole. The magnet will influence the current drawn by the armature – the lower the current, the better, as this will prolong the lifespan of the armature. Excessive heat is bad for an armature and is generated in the copper windings. Too much heat and the copper windings can burn out, leading to a short in the motor which often is difficult to, if not beyond, repair. The strength of the magnet can also influence the power, or speed, of the armature.

An early magnet for the 3-pole motor is not shown. This was the same size as the ones below, but was of a silver appearance. They were generally not considered to be superior magnets. You can see the different magnets produced below, see if you can identify the ones in your models. Note – the neodymium variety is not / was not produced by Graham Farish and this is something of an “after-market” adaptation, and one which works rather well.

Let us now consider the various magnets in more detail:

1) These were on earlier Farish locomotives in the late 1970’s and throughout the 1980’s. They have been found to weaken over time and if you have one of these in your locomotive today, it would be prudent to replace it with one of the later magnets. The also have been known to disintegrate / crumble over time. They are smooth on both sides without dimples, and can have a glossy appearance. A small paint blotch to denote polarity was often (but not always) applied. Continuing to utilise these magnets may induce unnecessary current draw for the motor, creating more heat and possibly leading to a situation where the motor is damaged.

2) These magnets, symbolised by their dimple on one side, were the staple magnet of Graham Farish throughout the 1990’s. They are considered to be of a good quality and have not shown themselves to weaken to the same degree over time as the earlier magnets. These magnets continue to be a viable option for “magnetising” your Graham Farish models.

3) Similar in appearance to the dimpled magnets, these are produced by/for Bachmann. Bachmann did continue to manufacture some Poole designs, thus requiring a magnet of the same dimensions as those above. This was their answer. It is slightly more sparkly, has no dimple and the corners are slightly more rounded. A good option for a magnet and what you would currently get if you bought one from Bachmann or BR Lines.

4) The neodymium variety of magnet is what I like to call “the rocket fuel option” – it certainly does pack a punch! Nominated by my good friend, Russell Hobbs, they are available in large quantities on ebay. Four lined up side by side (ACCORDING TO THE CORRECT POLARITY – IMPORTANT) will bring you low current draw in your loco operations. These have not been endorsed by Graham Farish and need to be fitted correctly to avoid damaging your armature.

Neodymium magnets are available on the internet from ebay and are 3mm x 6mm cylinders. By entering “3x6mm fridge magnet” into the ebay search function, you should find a variety of available sources. Most are shipped from China.

The below pictures and methodology for fitting the neodymium magnets are courtesy of Russell Hobbs. Russell brought to my attention the qualities of the neodymium magnet and having measured the Graham Farish magnet, found suitable neodymium magnets on the internet as replacements. An experiment he ran on a locomotive with various magnets gave the following readings (results in milliamps with the controller set to the full power setting).

Old shiny steel magnet 400mA (plus heating)
White dot magnet  270mA
Dimple magnet 200mA
Super neodymium cylinders 170mA

HOW TO FIT THE NEODYMIUM MAGNETS

Mark a dot on the chassis with a marker pen next to the magnet. The dot should be on the side of the chassis corresponding to the dot, or dimple, on the magnet. If you have a magnet without a dot or dimple, then make a dot on one side of the magnet, and the corresponding side of the chassis. Note the white dot to the top right in the picture below, it is on the same side of the chassis as the magnet white dot. Note here that when we use the term “side” for the magnet, we are not talking about different surface sides (e.g. flipping the magnet over), but rather one side of one surface. This is shown in the picture below, the dot on the magnet is to one side, not in the centre.

Next, remove the old magnet from the chassis and attach the new magnets, as per the picture below. The new magnets should naturally attract to the old magnet. Mark a dot on each of the new magnets, as per the picture below.

The last step is to insert the new magnets into the magnet housing on the chassis. Orientate them as per the picture below, with the black dots all aligned, and also aligned with the dot you placed at the side of the chassis. If the dot at the side of the chassis is not aligned to the black dots then it is no big deal, all that will happen is that you will have reversed the polarity, meaning that the locomotive will have reversed forwards / backwards commands. However, the black dots on your tiny magnets must all be aligned. This is very important. If they are not aligned then your loco will not run and power fed to the locomotive will eventually burn out the motor.

For those that prefer something more original, and something which truly is “fit and forget”, http://brlines.co.uk sell the sintered magnets which have the correct level of magnetism.

 

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