Wimshurst Machine Tips and help

The Wimshurst Machine

Wimshurst Machine

The Wimshurst Machine is a classic Victorian Machine, it was invented by James Wimshurst in 1883 and is a considerable advance on earlier machines. It works by having a very small electric charge that it then effectively amplifies by induction across the discs and then storing the charge in Leydon jars until the charge is large enough to break the air between the electrodes and cause a spark. The twin discs move in opposite directions so one will induce an opposite charge on the other and then move the charge away from the one that induced it and induce some more. The charge is collected by charge collectors that can be combs or points or sprays of wire that do not touch the disc. There are also neutraliser bars that are across the discs from bottom left to top right. These as the name suggests neutralises the charge across the disc. Wimshursts will only work when the handle is turned in one direction, if you want to reverse the direction that your machine works you must reverse the orientation of the neutraliser bars. The brushes on these bars are normally in contact with the discs. Due to the potential charge that can accumulate in the Leydon jars Wimshurst machines are considered more dangerous than a VDG. Care must be taken with using one and that people do not place their fingers too near the jars. Some schools consider them so dangerous that they will not use them. While the commonest reason for schools not to use them is their machine does not work. The speed the handle is turned affects the rate of charging. Most have metal segments on the discs called sectors. The discs were originally made of glass but mostly now made of perspex or other plastics.



The picture above is of my favorite machine, I have another but it is not nearly as pretty.







Why bother?

Wimshurst Machines are elegant and beautiful in how they work and the sight of one working in near darkness and lighting up like a Christmas tree as the charge is accumulated and flows is to use a much over used word, awesome. They are also much less prone to failing due to high humidity than other generators.

Pretty arcs

wimshurstarc doodlemar2012



Trouble shooting

Wimshurst Machines vary a lot in size and quality of manufacture, I have one, some fifty years old made by a now defunct Scottish maker that is tiny, with discs only 23 cm or 8 inches across that is real well made and is extremely reliable and has only ever let me down after being in a room where successions of teenagers had sat after being made to remove their shoes on a very rainy day. Personally the smell of all those socks was enough for me too. I also have a larger machine made by a very reputable and well known lab kit maker that is flimsy, rickety and very unreliable. Just as a digital multimeter can be connected across a Van de Graaff you can do the same with a wimshurst, take care, the leydon jars can bite. When it is working properly, there is a discharge from the neutraliser bars and from the pick up combs. They look wonderful in a darkened room, but you can test and see what is happening, or not, by testing it in the dark.



Dirt

The machine should be clean. Wiping with a lint free cloth, such as a well used and well washed tea towel works well. Rough spots can cause a problem as well as charge will leak away.



Obvious Things

The discs should move in opposite directions, the neutraliser bars should form a cross when seen from the front, their brushes should make good contact with the discs but not so much as to cause a lot of friction. The charge collectors should not touch the disc but should come close. A common problem is that the metal sectors have fallen off. These can be replaced with new sectors made from self adhesive aluminium tape that is used for repairing printed circuit boards and is available from electronics suppliers.



Not Charging

Wimshurst Machines are normally self starting, once the handle is turned they will start to charge. Sector less machines need to be started however and the same technique can be used to try to get a misbehaving machine to go. The method is to charge a perspex , glass or ebonite rod by rubbing it with an appropriate material. The rod is touched to a neutralising bar and so transfer its charge. This then can get the machine going. With all Wimshurst charging problems it is a good idea to see how it goes in the dark, you might find that only one of the charge collectors is lighting up or only one neutraliser bar is glowing.

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