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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Has anybody else thought about the large static charges that build up in a polythene bag full of expanded polystyrene chips? Small fragments stick all over your hands, fly around and adhere to the plastic bag, creating lively and varied electrostatic fields.
If I half filled a sphere of the right sort of plastic with the polystyrene foam chips, and drove it with a little motor, I would expect large charges to be developed.
If the sphere were hermetically sealed, the interior could be kept anydrous with silica gel, and so avoid the great curse of influence machines, atmospheric moisture.
But how best to extract the charges from the generator and store them away in a modern Leyden jar? I could imagine that fixed brushes inside the sphere could collect charges from the polystyrene as it moved past, but where would the other electrode be? I know that there must be an easy solution, but I just can't visualize it.
I imagine that if aerofoils were fitted to the plastic sphere, the wind could drive it and produce a small high voltage current.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
This would be an electrostatic friction machine. The Wimshurst machine is based on electrostatic induction. A problem with friction machines is that if you take charge from one of the frictioned elements, you must replenish the charge on the other element, or the machine stops working. In a classical friction machine, glass is frictioned against leather. The glass takes away positive charge, and the partially conductive leather friction pads receive more positive charge from the ground, or from the negative terminal of the machine. In this way the machine can work as long as it is turned. A machine using plastic foam chips and a plastic panel (maybe a tube) would have to replenish the surface charge on the panel. Maybe by periodically sweeping a grounded brush over it, at both sides.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Thank you Antonio. Do you think that electrostatic charge will be a function of the triboelectric series difference between the plastic bag and the polystyrene foam particles moving inside?
Registered Member #350
Joined: Mon Mar 27 2006, 05:14PM
Location:
Posts: 106
A friction machine is always very inefficient. So it's better to use a wimshurst machine instead. You could take a normal wimshurst machine and enclose it in an airtight box. You get much better performance if you fill the box with CO2 at several atmosphere pressure. Or even better SF6 gas but that is difficult to get.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
You could use a vacuum cleaner motor to blow the chips through the correct material sphere, then through a tube 'toroid' with a grounded tinsel brush in it to replenish the charge.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
About Wimshurst machines, this is a machine that I built recently, insulating the sectors behind adhesive plastic foil, leaving just small buttons for contact: The same machine with conventional disks works almost in the same way.
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Wimshurt's Machine Revisited
