Recent Posts

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1
Very nice control panel / cabinet.

How much PF do you gain from engaging that large choke?

The big choke is to provide current limiting for the pole transformer, currently set at 26 amps. The PF correction is accomplished with a bank of capacitors contained within the black box in the back of the cabinet shown in the video. I haven't tried to compute the PF but when I engage the PFC capacitors, the current draw from the wall reduces by about 4 amps.
2
An update on the secondary. I have been doing some fiddling with the coil and it is behaving like a real DRSSTC.
Yesterday I was getting 23 inch strikes to a grounded rod at about 150 Vbuss. Raising the voltage to 200 volts was
a non-starter as the unit was steady OCD at 500 amps.

After some thought I decided to raise the coupling. I have a nice method of doing this, the whole secondary is
on a plastic screw thread made from a plumbing drain pipe. I just disconnect the secondary ground and spin
the secondary up or down to change the coupling. The range is about 5 cm which should be more than enough.

Lowering the secondary by about a centimeter turned the coil into a new creature. The OCD is staying off (until
there are ground strikes on my garage door). The strikes are at 30 inches (76 cm) and the whole thing is just
nasty (in a good way).

I'm getting some sort of low frequency ringing in the current waveform that I don't understand. I'll do some searching
but may have to ask for a more experienced eye to explain what is happening. The collector voltage wave forms are
wonderful, very little overshoot and I am miles away from the 1200 volt limit of the IGBJTs.

Cheers.
3
Spark Gap Tesla Coils (SGTC) / Re: SGTC tesla coil:Why is it so dangerous ?
« Last post by Mads Barnkob on May 17, 2021, 11:13:57 PM »
SGTC do have a very high peak current, compared to the sparks from a SSTC or VTTC (there are many videos showing you can touch this, without feeling pain, but no-one knows about long term damage). Same goes for a DRSSTC, these hurt as well due to a higher peak current.

It could also be the higher Joule energy in each bang, you are getting into defibrillator territory with Joule levels above 1 Joule. 300 Joule is maximum of common defibrillators.

A SGTC is a lot more dangerous to touch, than a inverter type Tesla coil. A SGTC can in a fault condition carry mains current straight through to you, due to the high voltage transformer.

The bullshit claims of 1 million Volt always nags me, its more in the ballpark of 250-500kV and it seems to run very unstable.

I guess they could have seen the same results on Nico if they was zapping him with a stungun. I hope for Nico that he went to the hospital and had his heart checked with a cardiogram.   
4
Very nice control panel / cabinet.

How much PF do you gain from engaging that large choke?
5
Voltage Multipliers / Re: My 14-stage Cockroft-Walton voltage multiplier
« Last post by MRMILSTAR on May 17, 2021, 10:29:06 PM »
Very impressive build , looks really good ^^ .

When you calculate the output resistance needed , is this simply the expected output voltage divided by the target current you need ?

Cheers

Thanks DashApple. You must have a load resistance or you will probably burn out the diodes. Its a combination of Ohms's law, what sort of HV power resistors that you can buy for a reasonable price, and the diode current rating. Its also a function of what you are trying to accomplish. I just wanted to generate streamers. Its a trade-off.

The design can supply 750 ua at about 400 KV. Using those specs yields a desired load resistance of about 500M ohms rated for about 300 watts and 400 KV. This would have yielded an uninterrupted streamer of about 30 cm. I couldn't find any resistors for a reasonable price that would yield that combination.

What I could find for a reasonable price is the resistor combination that I have. The 6.3M ohms loads down the generator more than 750 ua so the streamer is constantly interrupted and is re-established as the voltage drops below that needed to bridge the 30 cm. This causes the crackling sound even though it looks continuous. A continuous DC streamer would make very little noise. Moving the toroids closer together makes the streamer more continuous and quieter because a lower voltage is needed to bridge the toroids.

The 6.3M ohms load draws about 60 ma which is actually beyond the steady-state 30 ma rating of my diodes. They have a surge rating of 1 amp however. So far the diodes have held up. If I blow any I will replace them with fast 100 ma diodes.
6
General Chat / Re: Safe source for High Voltage Wire?
« Last post by johnf on May 17, 2021, 08:52:28 PM »
Dave
that is DC voltage as used in our ion implanters for terminal acceleration voltage
7
Voltage Multipliers / Re: My 14-stage Cockroft-Walton voltage multiplier
« Last post by DashApple on May 17, 2021, 08:50:26 PM »
Very impressive build , looks really good ^^ .

I like how the multiplier joins as the base with the flat plates to provide the connection .

When you calculate the output resistance needed , is this simply the expected output voltage divided by the target current you need ?

Cheers
8
General Chat / Re: Safe source for High Voltage Wire?
« Last post by davekni on May 17, 2021, 08:36:30 PM »
John,

Is 70kV for RG213 or RG8 DC voltage?  I presume so.  If AC, how do you handle corona degradation?
9
General Chat / Re: Safe source for High Voltage Wire?
« Last post by johnf on May 17, 2021, 09:12:41 AM »
We use RG8/ RG213 coax at work up to 70kV
this comes with a caveat we test cable to handle this before use, except for Huber Suhner coax which is good to go out of the box.
We generally use it with the earth braid intact ie that is earthed for safety but each end the inner is extended by 250-300mm past the outer braid but inside respective cabinets at this point.
I also use the inner conductors on their own up to 50kV these I protect with Polyethylene pipe or similar to provide a hint of double insulation
10
General Chat / Re: Safe source for High Voltage Wire?
« Last post by johnnyzoo on May 17, 2021, 08:58:05 AM »
Car ignition cable is OK for moderately high voltages and low...moderate currents. Note that many ignition cables are made with carbon composite conductor which has relatively high resistance and you probably don't want to use such cable. Buy copper cable instead. It can be found in some car parts shops.

And as said above, trusting your life on cable insulation is usually not a good idea in these hobby projects. Many things can go wrong. Maintain distance and use a non-conductive stick for adjustments and drawing arcs. Make sure that the stick is really non-conductive.
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