Feedback on HVDC schematic

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Brendan_Murphy
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Feedback on HVDC schematic

Post by Brendan_Murphy »

I'm really looking for feedback on this HVDC schematic that I've created so far. Sorry that it's not very clean and just drawn on a whiteboard, I've just been changing things recently. Though so far this is what I've come up with using the XRT, Components, and parts that I currently have.

https://imgur.com/KZDfUXX.jpg
So the parts step by step:

A) This is my induction power supply that I built about a year ago. Basically how it works is there are inductors of various values that are individually controlled by contactors in series (with the hot line) that I can toggle on and off. This way, depending on the combination of inductors that I select in series I can have any desired output I want. I have 6 different inductors inside the supply and if all of them are toggled on it can output a maximum of 3Kva. It runs off Single phase 120v, 30 amps on a dedicated outlet.

B) Standard variac, rated for 3kva used to take the voltage up slowly of course.

C) XRT that I got off eBay. verified working by the seller, has been out of oil for a few months. Allegedly it's rated for 100KV (@120v on the primary) and max current 20miliamps. I would like to make an enclosure for this XRT similar to my favorite EE on YouTube “photonicinduction” if you've heard of him. I do have access to the tools to create an enclosure similar to it. As far as getting the air out of the coils I'm going do the method that he recommends (https://youtu.be/oYFU03XWUxk?t=380)

D) Because I didn't want to deal with creating my own high voltage meter I decided it would be easier and safer just to spend the money on a proper high voltage probe meter. I have swapped the polarity within the meter so that the dangerous DC negative is on the insulated end of the probe.

E) This is the only part of the circuit that I have not built at all or have really looked into what parts I'll want exactly. However I have read through Richards's FAQ on “metering a fuser for voltage and current”.
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Dennis P Brown
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Re: Feedback on HVDC schematic

Post by Dennis P Brown »

What commercial high voltage probe measures above 40/50 kV?

For your question "E", I'm not clear what part of the circuit you have not built yet? Is it the HV output section?

If so, one thing that you would need to do is place the diodes and ballast resistor are under oil as well. Also, all solder points (aim for ball shape) or wire joints need to be as smooth as possible and either under oil or sealed in silicone. Richard has an FAQ on this subject but it doesn't consider systems over 30 or so KV. That is a very special level that few here use.

Also, you might want to be very careful measuring those high voltages, above 50 kV the discharges and conductive paths tend to get unpredictable/flaky and these voltages for a real fusor supply are extremely dangerous. Certainly, never hold a probe for those voltage levels.

Richard warns that adding an amp meter between ground and the power supply requires great caution to prevent the fusor body from being isolated from its ground and becoming hot; read the FAQ on that subject carefully to design that part of the circuit (something I too need to take note of.)

In the vid, they replace the oil as soon as they removed the old oil. Not experienced with pre-soaked x-formers and how long they can stay out before there are issues. Others here might have experience/info. I assume it hasn't dried out yet. If your x-former has been out of oil for a while, I'm guessing that at the least, might be a good idea to get it back under oil to give it time to re-soak again. There are threads on this topic where people preheat the oil, and tap the system to help dislodge bubbles. You might want to search for those threads or ask for advice. Don't risk a good x-former.

I have a 70 kV x-former and I have an old metal case (with a sealing lid) that I converted to be a vacuum chamber specificly to enable me to place the x-former under vacuum and then back add oil (still under full vacuum.) Mine is new so it hasn't had oil previously so I need to add oil and decided the vacuum method is the best course. My metal case was an old container that held dendrite powder and someone threw it out complete.
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Re: Feedback on HVDC schematic

Post by John Futter »

Brendan
When I had to service my HV tank on my SEM Phillips had several pages in the manual on how to do this
The tank itself was not strong enough to take a vacuum so a purpose built one was constructed out of line pipe to take the entire hv tank.
Phillips said to use a two stage rotary pump and maintain a vacuum of better than 1 x 10^-1 millibar for 24 hours
the reason given for the vacuum depth and time was to expel water vapour from the windings.
The manual said the 24 hours was a minimum and extra time under vacuum was always better
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Brendan_Murphy
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Re: Feedback on HVDC schematic

Post by Brendan_Murphy »

So yes, my probe is only rated up to a maximum of 40 KV. But I’m not trying to surpass that. At the moment I’m just using a voltage multiplier set up just so I can have voltage, but of course it’s pathetically weak as expected. So now I’m trying to build a new power supply that is capable of supplying more current.

As for E, I should’ve circled, i’m talking about the current shunt circuit between the fuser ground and the DC positive. I don’t have the parts for this yet so I haven’t been able to test it and see if that’s somewhat of the correct schematic. Also thanks, I did not think about the possibility that the shunt could isolate the fuser from ground.

As for protecting the transformer from internal arcing. I want to do it the right way, not the cheap or easy way. I’m not sure if preheating the oil, then letting it pull a vacuum as it cools down back to room temperature will be strong enough to get the air out though. Of course I do have a vacuum pump but I have absolutely no idea how I would pull a vacuum inside of the transformer housing and pour the oil in at the same time.

As far as the rest of the circuit goes, please anyone let me know if it looks correct or if I have the right or wrong idea for what I need to build. I have course don’t want to blow anything up that I don’t have to
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Brendan_Murphy
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Re: Feedback on HVDC schematic

Post by Brendan_Murphy »

John,
Sorry, you must’ve posted this while I was typing my response to Dennis. I do have the intentions of building a purpose built steel enclosure for the XRT that is able to withstand a decent vacuum. I have plenty of TIG and enough manufacturing experience to know how to create this. However, for actually pulling the vacuum and filling the oil into it while under vacuum, I have no idea what the procedure is. And wow 24 hours under vacuum is quite a while. Do you have any estimate on how many cubic feet you were trying to pull?
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Dennis P Brown
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Re: Feedback on HVDC schematic

Post by Dennis P Brown »

Sorry that my post wasn't clear; I meant that one pulls a vacuum then adds the oil (need not be warm.) The idea behind warm oil was for a preivous wet transformer getting oil after being out for a while. But certainly, warm oil having a lower viscosity will work better for a x-former already under vacuum.

A x-former that still is somewhat wet from oil but has been out for a long time, as John says, humdity will likely have caused water to now be present in the windings/oil and be a major issue to get out (thanks to the existing oil.) Warming the x-former and then pulling a vacuum might also be a good approch; however, warm is relative and over heating a x-former isn't good for the windings. Any two stage vacuum pump can easily get below 0.1 millibar (75 microns) and 5 to 10 microns would be the norm. Of course, out gassing by water and old oil will likely prevent getting that low. So, I guess once that level is achieved and done for 24 hours, one is good.

Testing a 40 kV voltage probe is easy; just build a small voltage multiplier (VM.) The current is irrelavent - its voltage that matters not current. Best to build a safe one for high voltage testing.

Extending a commercil voltage probe to higher voltages is a bad idea. It is designed for a max voltage and adding another resistor isn't a good idea - the higher voltage might run along the probe and short to ground. Measuring voltages above 45 kV that have lethal currents is a difficult and dangerous procedure (I built a 120 kV VM that carried alot of power and never measured its voltage because I realized it was far too dangerous.) People do measure these types of supplies and there are youtube guidence that I've viewed in the past. The idea is use a series of resistors under oil in a long glass tube. However, no one holds these when they are used. They are mounted and used from a safe distence (an idea I intend to use once I set my old VM back up with better shielding.)
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Re: Feedback on HVDC schematic

Post by John Futter »

Brendan the sem tank was approx 1.5 cu feet the transformers about 4" cubed high frequency ferrite
the rest of the tank was made up of 6 transformers in series for the filament and the 20 stage full wave multiplier caps and diodes
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Re: Feedback on HVDC schematic

Post by Richard Hull »

I have manufactured special 40 kV and above voltage and current metering systems for some years under a contractual basis for amateur fusor operators here. 30 kV is a break-over point where special concerns arise over the casual voltmeter implementation at increased voltages. Super efforts are required over 60-70 kV. Oil bath or special potted dividers are the order of the day as one approached 100 kV.

I once advertised custom built voltage and current metering systems on trading post store. Blessedly, I no longer do this as there was no real money in it to recompense the labor and hassle. It turns out there was a break-over point in my pricing, beyond which the average fusioneer would not dare venture.

High voltage metering is not a dabble for the non-hacker in that area of electronics. Still, as most folks never go much over 30 kV until just recently, the issue is usually handled by more skilled hands doing such work and not a lot is found in the FAQs about such metering in the rarified operational range at or above 40 kilovolts. I attach a couple of my higher voltage efforts that went to a fusioneer willing to pay.

Richard Hull
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This system was done for a fellow who wanted 80kv, but never went beyond 40kv
This system was done for a fellow who wanted 80kv, but never went beyond 40kv
Custom made 50 kilovolt, 50ma metering system, circa 2010
Custom made 50 kilovolt, 50ma metering system, circa 2010
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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