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Registered Member #61449
Joined: Fri Jan 27 2017, 06:55PM
Location:
Posts: 2
Greetings all
I have been experimenting with high voltage generation and spark discharges for 30+ years, initially with electrostatic machines (Whimshurst and Van de Graaff (VDG)), induction coils, large transformers, capacitor discharges and Jacob's ladders and then on to Tesla coils in the early/mid 80s.
Having had some time away from the area, my interest in VDG generators has resurfaced and hence my joining this forum. I am busy putting together the parts needed to make a large device (500mm collector) and whilst I doubt if it will be as nice as (e.g.) Finn Hammer's work, I hope to enjoy the process nonetheless. I have compiled a list of hopefully useful information which is perhaps less common, gleaned from a few sources. Aspects such as collector hole diameter as a ratio of collector size, lip radius and so on which I thought might be of interest to people. This is from several sources i.e. not my own work and I can't be certain of its veracity but the people I have quoted from certainly know their stuff. . Some rules of thumb, summarised from Lloyd Ritchey's document "Hi-Perf Van de Graaff.pdf" and various posts in 4HV forum:
*An "average" machine will suffer a 20% reduction in its maximum realisable potential due to the collector entrance hole.
*A smooth collector surface is essential, but polishing to a mirror finish helps very little.
*The entrance hole should ideally be radiused,to the tune of approx. 8% to 10% of the collector's radius
*The radius of the collector entrance hole should be no larger than around 50% of the radius of the collector.
*Entrance holes with a radius smaller than approx. 33% of the radius of the collector will limit the belt size too much (a wider belt allows for more rapid charge transfer)
*50 square inches of belt per second passing over the pulleys produces 1uA of charging current
*rubber belts 3mm thick and from 25mm to 75mm wide should be approx. 75mm shorter than the distance between the pulleys. Belts up to 200mm wide should be made about 150mm shorter
*Pulleys should have a crown of between 3mm-6mm to help keep the belt centred
*A one degree taper for the outer 25% of the pulley width will help to keep the belt centred
*The distance between the collector and the base of the generator should be at least two or three times the collector's diameter
*belt width should be no wider than 80% of the column inside diameter
*brush widths should be no wider than 80% of the belt width
*pulley diameter should lie between 33% - 42% of the inside diameter of the column
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hello from a new member/VDG related