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Topics - MRMILSTAR

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1
Voltage Multipliers / CW multiplier resistor string suggestions
« on: December 07, 2019, 11:32:49 PM »
I need some suggestions on the HV current-limiting resistor string for my CW multiplier. Briefly, here is my proposed design.

* 14-stage design based on 28 TDK 1.7 nF doorknob capacitors rated at 30 KV
* Each diode string consists of three 20 KV 30 ma diodes in series
* To be powered by 1 or 2 flyback transformers in parallel driven by a ZVS circuit
* Current-limiting via HV resistor string, resistance TBD
* Everything will be under oil with the exception of the HV supply

My plan is to supply no more than 15 KV peak to the first CW stage since I have 30 KV capacitors. This should give me a theoretical output of 210 KV (15000 * 14). In order to protect the diodes I plan on having a HV resistor string attached to the final stage of the CW multiplier.

The current-limiting HV resistor string is what my question concerns. The most readily available, reasonably-priced, and compact resistor appears to be a Vishay VR68  with the following specs:

* Resistance: 470K ohms
* Voltage rating: 10 KV
* Power Rating: 1 watt

If I use 250 KV as the target resistor rating, this will require 25 resistors in series for a total resistance of 11.75M ohms. This should limit the current to more than 21 ma. I would actually like to use about half of this resistance value but the only way obvious to do that would be to place resistors in parallel which would double the number from 25 to 50 resistors. I would rather not do that for space reasons.

Does anyone have any suggestions concerning the HV resistor string?

2
Voltage Multipliers / HV resistor in oil
« on: December 01, 2019, 08:51:31 PM »
My question concerns operating HV resistors in mineral oil. As an example, if I operate a HV resistor rated for 5 KV in mineral oil does that it extend its HV stand-off capability? If I assume that mineral oil has 4 times the breakdown voltage of air, does that imply that I can safely apply 20 KV to that resistor without flash-over?

3
Voltage Multipliers / Suggestions for CW HV feed-through
« on: November 28, 2019, 06:05:46 PM »
My next project is going to be a large (300 - 400 KV) Cockroft-Walton generator. I want to house it in a 24" x 4" PVC tube. The CW generator will be operated vertically. The entire unit will be immersed in oil. My conundrum is serviceability. I am not going to assume that I will never need to repair this, therefore I will need to be able to remove the electronics from the 4" tube. I am envisioning all of the components mounted on a plastic strip or smaller PVC tube that fits inside the 4" main tube. That would enable me to withdraw the entire assembly from the 4" tube for repair if needed.

My biggest unknown right now is how to get the two HV power input leads through the bottom of the tube without leaking oil and to be able to remove the electronics assembly. I obviously won't be able to reach down into the bottom of the tube to disconnect the two HV power input leads. The best idea that I have come up with is to be able to slide the outer 4" tube off of the base. The base would probably be some kind of PVC end-cap. To make that joint oil-tight I thought about machining a groove into the 4" tube so that an O-ring could be installed between the tube and the end-cap.

Any ideas?

4
Induction launchers, coil guns and rails guns / Disc launcher attachment
« on: November 19, 2019, 05:51:39 AM »
It appears that I will be making the initial posting in this category. Hopefully, more will follow.

I finished the disc launcher attachment for my pulsed power generator today. It is designed to launch a 3.5" disk drive platter. It consists of 7.75 turns of 9 AWG double-build magnet wire wound in a spiral. It took several attempts before I figured out a way to wind the spiral accurately. The inductance is about 3.5 microhenrys. The resonant frequency with the 100 uF capacitor is about 8.5 kHz.

The coil is recessed into a 4 mm deep hole which I machined into a 0.5" thick sheet of G10. The hole is 3.5" in diameter. The coil was then immersed in 2-part epoxy and covered with a 0.03" thick sheet of G10. The G10 sheet is so thin that you can see the coil through it. A few air bubbles got trapped but that doesn't affect its strength or operation. The coupling to the disc is excellent due to the low 0.03" spacing between the coil and the disk. The final picture shows the disc launcher attachment  installed on my pulsed power generator.

The coil is recessed into the G10 and immersed in epoxy to keep it from flying apart during high-energy operation. I have watched Youtube videos of other disc launchers that mounted the coils free-standing and held in place with tie wraps but they always deform or fly apart at high power. My coil should be able to take at least 1500 Joules of energy but that is probably over-kill for a 3.5" disc. Because of the cold weather I haven't had a chance to test it yet but it should work great.

The final picture shows it installed on my pulse power generator.

5
Capacitor banks / Mysterious Chinese HV capacitors
« on: October 15, 2019, 09:12:09 PM »
Has anyone used these capacitors in any projects? I have a 20-stage Marx generator that uses these capacitors and it seems to work fine with 12" sparks. I have been able to find out that they are metallized film polystyrene construction so they should be self-healing. I have the 2000 pF capacitance model but I have also seen a 3000 pF capacitance model. They are claimed to be rated for 30 KV. I may use these for a Cockroft-Walton voltage multiplier. I was also wondering if they would be good for tesla coil duty. I suspect not. The reason that they are so attractive is the price. They sell for about $2 on E-Bay. Here is an example E-Bay link.

https://www.ebay.com/itm/2000pF-30KV-DC-high-voltage-condenser-capacitor-for-marx-generator-hv-ham-rad-DM/273846620888?epid=9020951115&hash=item3fc287d2d8&_trkparms=ispr%3D1&enc=AQAEAAADMKvsXIZtBqdkfsZsMtzFbFsbX3WcW5fmB%2Fx7ZbaZTyexrltoT9Zyh679cvGbGwMYfnOzVcfPVaNgKYixjPpdJl0YwNeaSYUyV3otBZu3ZYDcVmPybi7BFy%2FqkKQ%2FXoJE1B58Hs5Tj1CBCPGp71SDQqnJANJyGaKGkGD3UH6GRGDoKnvqrn11vwktTOQJtVmPMdK7hH3NRVucDXxtUQxGjPvsZ5qO3GrqCyr7VxPr6Cn1jSMF9v8lPvSEllYdo6Nlw6EwkJ%2BuqnA%2FdTuKIiVFv6IVwC8DkrsXVPJxbYcvly8ui%2FeG%2BGsvmsK1r%2FiNIE3zz1d9OPlyebx%2FoP6AFdqizbhKjMM2s7a9x5lLi%2FACknZn80kRUMYaLP3L%2BmS0g5bmASQgTo1pSjtNUwv4Ei1%2BJKzkd4jzUeGb0ZKtSJL9a1rtOquNz%2BIXF6Q9imwLGTYs205qB9q3YCoJTYwpEmajnUV%2B9nt5U%2FVnV3lgaGwx1PfsUWUbI%2FvZ5e3Cd39%2BVX%2Fj6fh3y4EZijZ%2F2OhD%2FD0gR9pGV530LUTAg6L7%2B4QdGO9QH%2Fbs%2BR8WKcoTzXrdtbsq0Qnaw8E4uPzo4NYURtQoDklouTLld7itmAEPYKQ%2FOvJ656oGAnEf6v4DNBseFq0PBnImyiBrXr4HJMgrTBwZxazhCsNFgw90iTYhdemeKwQ0wG48tkvQ%2F7i8CrRkURjXGs7Ok1%2B8L6yxrusXrmRtlyR1y%2F8ShVe9grRIfyYNuzRFgWyXgNsH3JCC1HLiXY9vueXFa%2FJ9KlPiBacrcv9ojNXk00Z%2FaOojrrvTfsQWk13rqLW9NI6KhDLTLspcDMu0yYay9rGlTE9Y5GnCIKoOgDeUjmHZuyS%2BbpWgzmqDXwlOiRyiMFE1SNks9udhz6kXCBAe%2FJUEGQY5I3590%2F51yEHZAhP%2FlR4MGySdxQhKiE4UYEVZrgQ9yUs9Q0CB3dSOKNJyiRyBgg%2BLvGOB3HL%2FXgsKzRk%2FpqsgSinWcJMuLieharyJZaMnh3LLQ%2FJ%2FudGbaudBhyR06Qd%2B909Sjq9wsQr062lrMSP8rdU1mr4KkM%2Fgk8kKrkOssHGoEk3xJ3h0dw%3D%3D&checksum=273846620888c8316e1b54254e779cb82cf9e547cd63

Wow! That is certainly a long link.

6
My next project is going to be a large Cockroft-Walton voltage multiplier. I want to use an AC flyback transformer as the HV power supply. Does anyone know of a method for measuring the voltage output? I would also be interested in knowing how to measure the output of a DC flyback transformer.

7
Light, lasers and optics / Power supply for gas discharge tubes
« on: September 29, 2019, 05:44:12 AM »
I bought several gas discharge tubes at a swap meet recently. They contain various gases such as krypton, helium, argon, and nitrogen. Each tube is made of glass and is about 12 inches long and 0.5 inch wide. There are leads protruding from each end. What is the best way to power these tubes to get good brightness without burning them out? What is a good voltage and current? I have on hand a NST and MOTs. I also have a variac to control the voltage if necessary. I also have various tesla coils but I wanted a power source independent of those.

8
Spark gap Tesla coils / Someone built Big TC
« on: September 24, 2019, 05:27:14 AM »
While perusing E-Bay today I found this for sale. This is the Big TC project from the July 1964 edition of Popular Electronics that someone built long ago. Its based on outdated ideas prevalent at the time such as a candlestick secondary, tightly coupled coils, glass plate capacitors, and no top load. It is built straight from the plans though. When I attempted this back in the late 1960s, I built everything but the secondary. I never finished it because I couldn't afford the acrylic tube needed for the secondary coil. Oddly enough, this one has the identical NST transformer that I used and still have which I use for a Jacob's ladder. A true classic!

https://www.ebay.com/itm/Vintage-Tesla-Coil/254367716909?hash=item3b397f562d:g:Va8AAOSwuP9diA5N

9
Here's a blast from the past. I've had this for a while. Anyone under the age of 50 may not recognize this. Before there was semiconductor RAM for memory, this is what computers used for fast working memory. This is called core storage. Each bit is stored in a tiny ferrite loop as a magnetic state. The ferrite loops are tiny, about 2 mm in diameter. These boards were assembled completely by hand!

Each loop has 3 wires passing through it for reading and writing data. The act of reading a bit actually erased it so the bit had to be re-writtten after reading! One advantage of core memory was that it was non-volatile.

This particular board contains 1600 ferrite loops thus it could store 1600 bits (200 bytes). It came from an IBM computer system. Not shown is the electronic drive and sense circuitry, made from discrete components, for reading and writing.

10
General chatting / "karma", "applause/smite" button meaning and use
« on: September 12, 2019, 05:07:24 AM »
What does the "karma" and "applause/smite" indicators under your name mean?

11
Vacuum tube Tesla coils / Interesting RF air-core transformer construction
« on: September 08, 2019, 06:09:40 AM »
My first tesla coil was a small VTTC. It used a commercially-made air core RF transformer for the primary coil, secondary coil, and feedback coil all combined into a single assembly. It is a Miller 4526 which is called "High Voltage RF Transformer".  I bought this one in 1969. They are no longer made. I am not sure what the intended use was. Possibly it was used in place of a flyback transformer in some TVs but that is only speculation. Coincidentally this part has all three of the coils that you need to construct a small VTTC.

I have attached some pictures of its construction which I find very interesting. Notice the winding method used for the various coils. All 3 coils use an overlapping zig zag pattern in their windings to reduce stray capacitance. The secondary coil uses a stack of separate winding sections with space between them to prevent the HV from arcing between turns. An arc suppression shield can be seen between the top of the secondary coil and the feedback coil. The entire coil assembly is about 6 inches high.


12
Here is a picture of the toroid top load. It is 30" x 9" made of spun aluminum. It was made by the O.W. Landergren Company.

13
Here is a picture of the secondary coil. It consists of 1410 turns of 22 AWG double-build magnet wire wound on a 8.6 inch OD section of PVC pipe.

14
Here is a picture of the safety gap. It is a horn-type gap. I have only seen it fire several times.

15
Here is a picture of the primary coil. It is tapped at turn 11.5 for a resonant frequency of 79 KHz.

16
Here are some pictures of the 10 KVA pole transformer and its mount.

17
Here are some pictures of the completed 8.6 inch pig-powered SGTC. The coil is 75 inches in height. A previous version of my capacitor bank appears. It has been improved. The coil currently is operating at 6.5 KVA with 9-foot streamers.

18
Here is the capacitor bank for my 8.6 inch pig-powered SGTC. The specs are:

1. Capacitance is 45 nF
2. Voltage rating is 70 KV
3. Configuration is 6 capacitors in series-parallel consisting of 3 banks in parallel with each bank consisting of 2 capacitors in series
4. Each capacitor is a Maxwell model 37667, 30 nF, 35 KV voltage rating, with a maximum rated rate of 500 bangs per second
5. 35 KV bleeder resistors are installed across each capacitor

Heavy copper bus bars are used to handle the 480 amp peak current per bang (240 bangs per second).

19
Spark gap Tesla coils / Components of my 8.6 inch pig-powered SGTC: SRSG
« on: August 30, 2019, 06:38:03 AM »
Here are some pictures of the SRSG (synchronous rotary spark gap) that is used on my 8.6 inch pig-powered coil. The specs are:

1. 1/2 HP induction motor modified to be synchronous
2. Rotation speed is 3600 RPM
3. Rotor diameter is 10 inches and is made of 1/2 inch G10
4. 4 flying electrodes, 2 or 4 stationary electrodes. I currently only use 2.
5. Flying electrodes are 1/8 inch tungsten, stationary electrodes are 3/16 inch tungsten
6. On-board EMI filters
7. Base is made of GP03 with steel stiffening bars underneath
8. Modular construction. It can be removed as a unit from the tesla coil base.

20
Here are some pictures of my PFC bank. Its located in the back of my control cabinet. It consists of a bank of 100 uF and 50 uF capacitors which can be individually connected via toggle switches. The maximum capacitance available is 450 uF. The pictures show an earlier version with different capacitor values.

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