High Voltage Multiplier Issue

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Dennis P Brown
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Re: High Voltage Multiplier Issue

Post by Dennis P Brown »

I reworked/reduced the voltage multiplier (VM: returned it to 8 stages again, all door-knob caps; and I added a far higher current tolerant diode to the first stage.) This has created a dramatic increase in the overall performance of the VM.

The current performance (directly from the VM output) looks fairly good thru a 1.00 G-ohm resistor; with the variac at 18% load, the voltage is 50 kV and the current is about 48 micro-amps (read by a 50 micro-amp meter; I think the curent would increase much further if the voltage is further increased - that measurement will require another meter.) I've noticed that both the current and voltage is fairly linear under this light load (not likely to remain linear above 50 kV or so) on the VM.

Aside: I think this pretty much shows my HV probe is based on a 50 micro-amp meter (good to know. Might build a 0 - 5 kV meter now that I know some performance data for 60 Hz systems.) Also, ignoring RMS, this means each stage in the VM is giving slightly more (2.3) than a doubling of voltage: obviously, if the RMS voltage is used, that value is not really more than twice; so it appears, to first order calculation, my stages are operating close to theoretical values. For no real loss/load on the VM, this result isn't exactly surprising but is reassuring that the circuit performance is close to idealized values.

Using no resistor and exciting the globe of my accelerator with the VM, the current from the VM appears too great (the VM can handle it but it is at a dangerous level for me): that is, at just 5-10 kV, the VM is outputting a full 1 milliamp! (measured)

So, I hooked up a 5 G-ohm resistor to the accelerator metal globe (the current meter is at ground and a wire leads from that to the other side of the 5 G-ohm resistor that is attached to the globe), and at about 140 kV (about 45% load on the variac), I am drawing somewhere around 30 - 50 micro-amps thru the resistor (hard to accuracy read on the milli-amp meter I used for this test.) However, the sphere is being highly charged (and carrying a possibly lethal charge, apparently (the caps in the VM are not being fully discharged by that minor loss thru the resistor and static discharge by the globe (which is really charging the area nearby.)))

So, it appears I will need to feed the VM's output thru a high resistance resistor (Value?) so the current from the VM is tightly limited (needs to be non-lethal); all that remains is to determine a resistance to yield 100 - 150 micro-amps for the max voltage (say 50 - 60% load on the variac); the VM's voltage and current are extremely high for my application - apparently, the VM can deliver a number of milliamps in the 50 kV range with no load.

This VM is working too well. I am guessing that a resistor in the 750 to 1000 M-ohm mounted as an output source for the VM will supply all the current I need regardless of corona losses by the sphere (apparently, just need to match my voltage probe resistance since that appears to yield my required current ... . ) So for the globe to be elevated to the range of 135 kV (I have weak confidence in that number since it can't be measured) adding an output resistor of a Giga-ohm should do it - my only concern is making certain the VM will operate in a safe, current limited, range for the 120+kV that will be obtained on the exposed accelerator sphere. I will try some values and test with a current meter on that device to be certain of the final performance.

So much for my worrying that 60 Hz wouldn't cut it for supplying enough current from that VM to excite my accelerator ... my only real worry, it turns out, is preventing it from supplying a lethal current to the operator (my accelerator's main sphere (contains deuterium supply/ion gun and its power supply) is rather large and exposed to an operator.)

Aside: if memory serves, low milli-amps is the cross over for kV systems to be lethal (60 Hz); if others have more exact figures, do weigh in.
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Dennis P Brown
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Re: High Voltage Multiplier Issue

Post by Dennis P Brown »

Well, for proper operation/testing of the voltage multiplier system for the accelerator it looks like I need to locate a 1 G-ohm extra long (4-5 inches) HV resistor. Until then, I can't really do much. Still, made a lot of good progress (90% of which simply consists of getting a better understanding VM's.)

If I can procure the resistor, I will put the deuterium accelerator back into running condition: that is, fill the small secondary deuterium tank; repair the sphere's internal mounts; check the operation of the deuterium ionization gun in the sphere, and retest the vacuum system's performance (might have to bake out the main system again.) Also, I will place silver on the target holder (for a final proof of operation test via Ag activation.) Finally, re-install the anti-electron back streaming device in the target head to suppress x-ray generation (which can, in this device, be significant.)

So, now that I feel that I have achieved the operational VM I need to excite my deuterium accelerator, and unless someone wants to ask questions or address issues relative to the VM system, this thread is done. I will, once I get the affore mentioned issues properly addressed (locate and install the required resistor), re-start my "Ion gun" thread for this accelerator project as, and hopefully, it then moves forward again after its long hiatus.
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Bob Reite
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Re: High Voltage Multiplier Issue

Post by Bob Reite »

Get 10 100 M HV rated resistors and put them in series for your 1 Gigohm resistor.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
Silviu Tamasdan
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Re: High Voltage Multiplier Issue

Post by Silviu Tamasdan »

I recently bought a couple of 1.5G resistors on ebay. They're supposedly rated for 35kV. They come from a Russian seller but unfortunately those were the last pieces he had. I don't have them yet but from the pictures they're about 5 inches long each. Nice feature is that they have threaded terminal ends so you can screw them together in series.

Keep looking, you'll find what you need.
There _is_ madness to my method.
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Dennis P Brown
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Re: High Voltage Multiplier Issue

Post by Dennis P Brown »

Thanks for the comments: A longer string of resistors (in air) is always a good idea but mine would be under oil and are fairly long so not too worried on that score.
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