Most of the inhabitants of this group are bonkers, so... anyone here built one? ;) Anyone happen to know how critical it is to balance the flow of water drops through the conducting rings?
For the curious:
If you are serious build a Wimshurst machine instead. There is a sporting chance of getting that to work if you are any good.
All usual safety disclaimers apply. These things bite!
Regards, Martin Brown
This might give a few clues for scale and construction ...
But where're you going to get 7 foot diameter glass discs? :-P
HV generator way back at school, but I can't remember what it's called.
IIRC, it worked like this...
You have two tanks of water, one above the other, both insulated from the environment. A shower head allows the top tank to drain into the bottom tank, with as fine a droplets as possible. You apply a high voltage to the top tank (I think we had a 5kV DC lab power supply for the purpose).
Each droplet leaves the shower head with a fixed charge, corresponding to 5kV at the self-capacitance of the droplet. When the first droplet lands in the bottom tank, it will retain its 5kV as we'll assume there are no charge losses and the capacitance of the droplet doesn't change (both false assumptions, but not badly enough to stop it working). The next droplet lands and merges with the first drop. Now the charge is doubled, but the capacitance of the combined drop only increases a little, so to preserve the charge, the voltage increases significantly. As more charged droplets are added to the lower tank, the voltage of it increases markedly, and it will arc across to ground or the top tank.
Now, the big problem with this is that by the time you've got the water part working, the bench, floor, and aparatus will be swimming in copious split water, and nothing is an insulator anymore, so it doesn't work. Somewhere near my school, Bic Biros used to be made, and we got a sack of reject brio tip balls for experimenting with. Using these instead of water was much more successful (you can clear up spillage without leaving surfaces conducting). ISTR we were easily getting 100kV sparks off the bottom tank. Biro balls don't pack as well as water droplets which reduces the voltage rising potential collecting in the bottom tank, but on the other hand, they are much smaller which means more "droplets" and hence more charge can be carried between the two tanks (I think).
Anyway, hope I remembered all that correctly...
Yes, I've seen that mentioned somewhere in the past, albeit IIRC just termed a "half kelvin generator" - perhaps it doesn't have a 'proper' name.
In message , Jules Richardson wrote
should look and sound like!
When young I had a go at vanda graph, windshurst etc static devices. Not that hard to make but lethal in action. Also prone to falling to bits, but then that was probably my fault!
Lets just say that the friction was not only in the machines, but with my Mother whose old bits and pieces I tended to press into service for making them. I'd never heard of this device before.. interesting. Brian
It would seem to be very over sized.. its the trueness of said discs and their structural integrity which would be hard to do. Brian
Aren't old records (particularly 78's) a favoured source for such things?
Old shellac records are ideal for rigidity and insulation properties.
Regards, Martin Brown
We had a commercially built one at school. The discs were about LP size
- I suspect slightly more than a 78, though I could be wrong after all this time.
I connected it once to a Leyden Jar made from a Kilner jar. I thought for a while that I had a leak somewhere, as nothing happened. It turned out to be just that it was taking a while to build up the charge... quite a nice bang.
Andy
I've never built one, but from the look of the ones on the web probably not very critical. The droplets are just a means of transferring the charge from the ring to the bucket. The secret appears to be to get a very narrow stream of water so that the charge can split it into charged droplets easily. One site suggests capping the pipes and drilling a 1.5mm hole through the cap for the flow.
aren't van-de-graf generators the easiest way to produce static charge ?
I think a lot of the modern table-top ones use acrylic sheet rather than glass, which would be a much easier material to work with. Bit pricey if it's just for giggles, though - something around 2 feet in diameter comes to about $160 here (around 100 quid?) for both wheels, assuming a 1/2" thickness.
I suppose that typically the metal sectors on the wheels only occupy the outer 50% of the disc surface - given that acrylic's normally sold in sheets there's a lot of waste in cutting discs from it, but it might be possible to build up a laminated disc (with spokes connecting to the hub), trading cost for assembly time. Of course then the question's what to use to glue everything together without sacrificing insulation :-)
*maybe* it's possible to make one out of wood too if it's very heavily varnished, but I suspect that it wouldn't perform nearly as well.cheers
Jules
I did have a quick google, 10mm thick 3mx2m sheet was over £1k
Well, it doesn't have to be 5ft.
A couple of these ought to do:
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