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Dr. Slack

Tue Nov 13 2007, 07:44PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

As far as I can see, a Dirod is essentially half a Wimshurst.

Now if you take a Dirod, and drive the induction electrodes directly from an HV source instead of relying on self-excitation, you end up with what is essentially a bipolar Peletron using a disc instead of a belt.

Replace the conductors and belt of a Peletron with a rubber belt and spray charging, and it's a VDG.

All induction machines work the same way - charge two electrodes when they are close together, do work separating them which raises the voltage, then collect the charge on the inside of a terminal. All else is detail.

If you had a small industrial robot, or some meccano or Lego gears, you could automate an electrophorous!

Spedy

Wed Nov 14 2007, 12:54AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

DrZoidberg, smallish "film-can" Leiden jars are perfectly safe, and my little sis loves to take discharges from a approx 3/4-cup Tupperware Leiden. If you do choose to make a Leiden jar, be sure to make it Small, like no bigger than a 5cup container. You could make some BIG jars from big plastic buckets, but be INSANELY careful with these when charged, big ones will kill yah given the chance.

Hope yer electrostatics project works out.

Coyote Wilde

Wed Nov 14 2007, 02:17AM

Registered Member #175 Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111

A bit more research, and I think I've finalized my design to a 30cm Wimshurst machine, using old LPs for the plates (as in Bauerb2 'quick and dirty' setup) and layden jars from small mason jars (as jam-makers use). Possibly motorized; haven't yet decided that. Depends if I have a motor that will strap on without hassle or not... anyone think it would be worth it?
I'll post when I get time to start assembly, but due to schooling, that likely won't be until near the end of the month, and then I'm into exams...
I'm aiming to have the display piece ready by Christmas, regardless.

Spedy

Wed Nov 14 2007, 03:57AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Good to hear. Wimshurst machines are good, but I've never had the patience to get all those delicate foil pads just right.
Glass's surface leakage is HORRIBLE (the mason jars), I recommend you use something else.
Be sure to get those pictures, I cant wait to see it.

Dr. Slack

Wed Nov 14 2007, 01:13PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

As a contribution to polyprojectitus, I'm brewing up a Pele-disc generator. A 12" vinyl LP, Wimshurst style pads stuck on, spray charge on one side, collect between a pair of Ikea bowls on the other side.

What is the voltage limiting mechanism with this type of arrangement? Presumably it's the HV terminal sparking to the discharged segments exiting its field-free space on the way down?

Maybe an even simpler Disc-De-Graff is possible without the pads, and with friction charging at the bottom. I've never had any problem accumulating a dust-attracting charge on LPs.

Coyote Wilde

Thu Nov 15 2007, 02:04AM

Registered Member #175 Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111

Niel, isn't the Disk-De-Graff you're thinking of the same sort of device Bauerb2 describes earlier on? Performance sounds quite decreased compared to a more advanced impulse machine.

As to the surface losses of glass, the jars I have on hand are over large, and so I've room for 4cm clearance at the top, to further separate the conductors. Will that be enough? I don't have to hold onto charge for very long, after all...

Antonio

Thu Nov 15 2007, 02:07AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

You can spray directly at the disk surface, with a grounded plate at the other side of the disk, or just charge a plate at one side of the disk and place a grounded comb at the other side. Something as was done in the old CarrÃ© machine, that used the disk of a friction machine as inductor plate.

Pellat67

Dr. Slack

Thu Nov 15 2007, 02:28PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Niel, isn't the Disk-De-Graff you're thinking of the same sort of device Bauerb2 describes earlier on? Performance sounds quite decreased compared to a more advanced impulse machine.

Yes, it looks like it. I wasn't claiming that I thought of the idea first, though I will claim priority for the name I gave it. Simple construction mitigates poor performance somewhat.

As soon as you get any more complex than that, it's probably worth going all the way to a Wimshurst.

BTW, one thing I haven't yet bothered to either work out or find out, does it matter which way the discs on a Wimshurst turn, and if so, which way? Should a segment travel collector - 135arc - inducer - 45arc - collector, or the other way round?

Antonio

Thu Nov 15 2007, 04:09PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

If the machine is turned in the wrong direction, high voltage appears at the upper and lower quadrants instead of at the lateral quadrants.
The correct direction makes the disks move from the charge collectors to the nearest neutralizers.

Wimsch

Spedy

Thu Nov 15 2007, 04:29PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Coyote Wilde wrote ...

Niel, isn't the Disk-De-Graff you're thinking of the same sort of device Bauerb2 describes earlier on? Performance sounds quite decreased compared to a more advanced impulse machine.

As to the surface losses of glass, the jars I have on hand are over large, and so I've room for 4cm clearance at the top, to further separate the conductors. Will that be enough? I don't have to hold onto charge for very long, after all...

Probably not. You'd have to treat the glass, otherwise just breathing on it could short out the Leiden jar.
Here's a treatment from A.D. Moore's Electrostatics : dissolve a few slivers of paraffin in some lighter fluid on the glass, and rub it till only a thin film is left. (be sure to wait for the fumes to go away lol) Then, charge the capacitor, and breath on the space in between the outer plating and top terminal. If you can't draw a spark after that, the capacitor is still to leaky and should be treated again.

You could also do the breath-test w/ the untreated leiden, to see if you don;t need the paraffin/lighter fluid treatment.

Hope this helps.

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