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Re: GAMMA HIGH VOLTAGE

Posted: Sat Feb 25, 2006 3:11 am
by Wilfried Heil
No changes to the controller should be needed, at least if it can display the larger current without assuming a fault condition. The controller displays the actual amp reading, which is usually measured as a voltage drop through a resistor to ground. The voltage reading should be ok as well, it is the true output voltage reduced by a resistive divider.

You should get the schematics for this device, and understand them well, in order not to kill yourself. In my opinion this unit is just too pretty to be used as a Fusor power supply. But it would be great to have one for all kinds of other HV experiments.

Automatically tapping multiplier stages is done in capacitor charging systems, to make them charge faster at the lower voltages and then increasing the number of stages as the voltage goes up.

Re: GAMMA HIGH VOLTAGE

Posted: Mon Feb 27, 2006 8:13 pm
by DaveC
Steven -

The voltage multiplier is a capacitive equivalent to a high voltage transformer. Charge is shuttled around, rather than magnetic fields. So within the limits of the cap sizes and diodes' current
ratings, you can reconfigure, just by tapping a lower level stage.

Tapping a multiplier at a lower voltage WILL allow you to operate at more current. It's not necessary to do anything to the multiplier, other than to make the connection to the proper stage, for the voltage you want.

The divider in the HV output however will normally read from the output at the top of the multiplier. So you can get an approximate voltage reading by just taking the ratio of the voltage you tapped into, to the entire output. Example: Tapped at half the voltage, take half of what the voltmeter reads, etc.

But depending on whether the multiplier is made with larger capacitors at the lower voltage stages, you may not be able to get twice the current at half the voltage.

The ammeter should read the actual current without needing scale factors. But.... the meter circuit may need a new resistor to rescale if the meter range is exceeded.

But be careful... 200 kV is a serious voltage... and can reach and "touch" you from rather far away. With a top hat the size you have there and caps to deliver 1.5 mA, you are up about 20 to 50 times what a Van deGraaff generator of that size would deliver. So the jolt could be lethal.
A nice find... and be safe experimenting

Dave Cooper

Re: GAMMA HIGH VOLTAGE

Posted: Mon Feb 27, 2006 9:33 pm
by David Rosignoli
Richard,

Why 10J? The way I understand it, a certain amount of current is necessary to either stop the heart from beating, or cause it to beat at an unnatural rythym. This current is relatively small (on the order of 10mA I think). If you touch a capacitor with 10J of stored energy at a low voltage, little should happen. (And here when I mean "touch" I am referring to skin contact, not sticking your tongue on some terminals.) I understand the precaution of touching charged objects at a certain potential with a certain stored energy, but what is the origin of 10J?

-Dave

Re: GAMMA HIGH VOLTAGE

Posted: Mon Feb 27, 2006 10:01 pm
by Wilfried Heil
You could connect the top toroid to any lower multiplier stage, in addition to it´s connection to the top of the multiplier, thereby shorting out some of the upper stages. This would keep the HV bleeder network and the measuring resistors working as intended.

Like Dave has described, you may have to change the resistive divider for the current measurement, so that it´s output falls into the range that the controller can display.

As one can see from the image, two different colors of capacitors are used (the top ones are white). I suspect that the lower part of the multiplier has a higher capacitance, to handle the higher current needed there. Another common practice would be to put in several caps (2-3) of the same type in parallel in the lower stages.

The top toroid should have a capacitance of about 20 pF, plus that of the HV capacitor chain, maybe 100 pF in total. This thing could zap someone across a wall.

A notable omission are about 4-5 corona rings around the multiplier (see the Glassman website for similar units). The multiplier is likely to self-destruct without them, at the first arcover. If they aren´t available, you can easily make them yourself out of 16 mm copper tubing.

Re: GAMMA HIGH VOLTAGE

Posted: Mon Feb 27, 2006 11:01 pm
by Starfire
It takes about 75 ma to cause ventricular fibrillation below 50ma will cause pain but normally not fibrillation. The voltage has little bearing. The current path does - in a finger and out a finger on the same hand only jolts, but in one hand and out the other -- what sort of flowers do you like?

-- " It's the mill's that kill and the volt's that jolt "

Re: GAMMA HIGH VOLTAGE

Posted: Tue Feb 28, 2006 5:19 am
by Richard Hester
Dave - I heard the number 10J a long, long, long, long time ago, so I couldn't tell you the origin. I looked on the internet this afternoon, and a document from SLAC also listed the 10J hazardous figure and mentioned it as coming from a DOE document. Of course, the voltage level has to be above skin conduction level before the stored energy will hurt you, but anything above a couple of hundred volts is going to be really nasty at best. If nothing else, it can cause burns (I read a Lawrence livermore accident report citing burns at the 10J level), if it doesn't throw you against the wall or into something that will cause some collateral damage. As with any chaotic event, your mileage can vary widely, up to the ultimate. What I really wanted to point out is that at 200 kV, capacitances one would normally regard as "stray" can become dangerous.

Re: GAMMA HIGH VOLTAGE

Posted: Tue Feb 28, 2006 8:08 am
by DaveC
I was trying to remember the energy used for the De-Fibrillators am thinking it's something like 500 J.

But the timing of the shock in relation to the heartbeat cycle is also important. I think this is where the lower energy/current figures enter in. As I understand it, if the shock occurs in the dead time when the heart is stopped and resting, it may cause the heart to not restart.

Really nice piece of gear, so enjoy and be careful.

Dave Cooper

Re: GAMMA HIGH VOLTAGE

Posted: Fri Mar 03, 2006 2:36 am
by Wilfried Heil
Here is one currently on Ebay: Item number: 7595813165
Maybe the same one?

Re: GAMMA HIGH VOLTAGE

Posted: Fri Mar 03, 2006 5:49 am
by Richard Hester
Only 300W (200kV/1.5ma) - not much can be done with this fusor-wise. It might make the basis for a dandy little low voltage accellerator, though. Safety considerations would make it eat up a lot of floor space in a lab.

Re: GAMMA HIGH VOLTAGE

Posted: Fri Mar 03, 2006 10:36 pm
by Steven Sesselmann
It appears that the unit for sale on ebay is the same one.

http://cgi.ebay.com.au/ws/eBayISAPI.dll ... 5813165&ru

This may be a silly question, but where would the negative output be on
this unit? Is it from the top of the thoroid or would there be some kind of
massive plug at the back.

Also, I would imagine a 200 kv cable would be massive, so how would
one connect this to a feedthrough?

This would require a bit of thinking..

Steven