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Re: [TCML] Voltage/power dissapation drop across HV DC current limiting resistors.

Matt,
OK, I see that with a NST, the center tap of the HV winding is grounded internally to the case.
You could monitor your corona current by putting the neon transformer case on insulated supports and inserting your DMM in current mode between the case and earth ground. I would make sure beforehand that there is high isolation (very high resistance) between the NST ground terminal and the 120 VAC line input terminals.
What is the purpose of the resistors that you mention? If there is any appreciable corona current, then there will be a significant voltage drop across the resistors, wasting energy as heat, and reducing the voltage available at the corona electrode.
As I see it, the object of the corona is to spray as many electrons as possible (or remove as many as possible, depending on the polarity) on to the VDG belt. The energy with which you blast them onto the belt should have no impact on the ultimate potential of the VDG output. The main thing is to have as high a corona current as possible without getting arcing.
It would be simpler to use a Variac in the NST primary circuit to set the HV output to the optimum level that doesn't produce frank arcing. Then, you wouldn't need any resistors at all in the HV output circuit. Adjusting the spacing of the corona electrode relative to the belt may help get maximum current without arcing. 

What sort of corona electrode are you using?

(Or am I missing something?)

Dave

On 9/25/2015 11:30 PM, msweeney23@xxxxxxxxx wrote:

Im using a 15KV AC 30ma NST mid-tap grounded NST rectified via two potted 12KV 350ma dioides on either side (4 total to be safe). I have 100 10Mohm 3.7KV 500mw resistors i intend to setup in chains of 5 potted for 50Mohm at approx 17KV each.

Im using both sides of the NST to drive two pumped VDG one positive and one negative (5ft tall). Im expecting approx 350KV minumum each and want to study the interaction of the two polarities.

Thus far ive only used triboelectric driven VDG so very low amperage in the single microamp range. Im concerned about static behaviour allowing the collector to ground to the lower brush down the inside of the VDG and thus need to ensure current flow is highly restricted.

My current 5ft VDG (14 inch diameter collector) has thrown repeated 30inch perpendicular discharges to ground which is totally counter to my expectations. These HV static machines are not at all behaving as expected and others on this list have mentioned strange behaviour to be expected along insulators. However these 30 inch discharges are perpendicular to the VDG through air.. i dont understand this it doesnt match expected potentials from the collector size. Its all a mystery to me and id like to study it while remaining safe (i dont intend to touch these pumped VDGs).


My very first VDG doubled the expected discharge length and ive actually witnessed over 40 inch repeated discharges on the 5 foot during very dry conditions (minnesota winter). In some instances ive recieved non visible shocks from 6 feet away. During ideal conditions the VDG constantly popped 12 inch discharges out into thin air exactly 90 degrees apart but ive yet to reproduce this (maybe too humid now).


Currently i dropped to a 3.5ft VDG but get lots of leakage from the underside and in the dark i see streamers up from the drive motor.


Its all new to me and very mysterious :)

----- Reply message -----
From: "David Speck" <Dave@xxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Subject: [TCML] Voltage/power dissapation drop across HV DC current limiting resistors.
Date: Fri, Sep 25, 2015 8:02 PM

Matt,

what kind of HV source are you using to power the corona generator?

There must be some place where the low potential end of the HV circuit
connects to ground.  You could safely insert your DMM running in current
mode between the low end of the HV supply and ground to monitor the
corona current.

More risky, but technically possible for a  one time measurement, would
be to insert the DMM in series with the high potential end of the
circuit -- between the supply and the corona electrode.  You would just
have to float the DMM and its leads away from any grounds, and be
certain not to touch it during operation.  A quick and dirty platform
made of 4 clean Styrofoam hot cups with a top surface of corrugated
cardboard could support the meter and leads on a temporary basis.

Dave

On 9/25/2015 12:19 PM, msweeney23@xxxxxxxxx wrote:

Im facing this problem and i dont know enough to figure it out.

If i have a HV source used to produce only corona (bottom brushes on a VDG) what voltage drop would occur across a resistor in series? Without this i cant determine expected power dissapation.

I cant assume the corona source shorts directly to ground (the roller is grounded) there must be some specific resistance (impedence?) Of the plasma between the brushes and grounded roller but i really dont know what that would be without directly measuring it, and i cant do that with my digital Meter. I could use an analog meter to measure total current flow but at these voltages im concerned even that could pose problems (approx +/-10KV DC).

Any help would be greatly appreciated!

Thanks,

Matt Sweeney

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