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Alternative high voltage coupling - sparkgap to solid state.

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Ash Small

Mon Feb 21 2011, 06:44AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

3l3ctrici7y wrote ...

Sometimes it was an occasional spark here or there and other times it would spark/arc too rapidly to distinguish one from the next, but usually nothing at all.

With the apparent similarity between yours, mine, and the one I was basing mine on, and my failure to accomplish the goal; I think there must be some subtle but critical thing I was doing wrong.

As a perhaps interesting aside, here is a page about getting huge voltages out of an HEI coil by removing the iron E-core and treating it as a Tesla coil.

There is a definite mystique about simple traditional designs (spark gap TC), but I think if I ever revisit this HF arc starter, I will try to make it out of a ZVS and see if I can get favorable results. Maybe weld aluminum foil using the HF alone. That would be so awesome, but totally impossible.
uzzors2k said that with his ZVS the wires start to glow, so perhaps welding with the HF isn't so far fetched ;)

After I built mine I was looking into constructing a Non-Transferred Arc Inert Gas Plasma Torch (Micro-Torch). These work on a similar principle, but the arc is struck in the torch and the plasma is blown out to the workpiece by the gas. They run at very low currents and are used for welding thin foils, etc. The most significant difference is that the welding current is at 220 volts, as this gives a more stable arc at low currents. The same principle could probably be used for TIG welding.

The other method for welding thin fiols is Electron Beam Welding, but that requires a vacuum chamber.

I don't see why a Mazilli/ZVS circuit wouldn't work, you wouldn't require a very high voltage to get an arc under argon so you would have even more current available for welding. I might try this myself.

(My present circuit just uses the single transistor flyback driver, you can't get much simpler than a 2N3055, two resistors and an old TV flyback to charge the tank circuit.)

3l3ctrici7y

Mon Feb 21 2011, 07:51AM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

Wah-hoo! My thread made it to two pages :)

The Micro-Torch sounds interesting; maybe a lot like the non-transfered version of plasma arc welding.
The biggest thing I see about home-brewing a torch is the water cooled nozzle. Staring off with an existing tig or pac torch seems like a good thing.. then "just" build the nozzle. I supposed it might be fairly straight forward if one had a lathe.

220v.. Good thing it's inside the torch. I have seen "designs" for cheap DIY plasma cutters that used rectified mains voltages. The electrical safety people chime in loudly after such things are posted. I like the non-transfered mode of operation, because then the weldment does not need to be grounded, or fight with a ground clamp. Sadly, I don't think it's practical at higher currents. I have seen some plasma cutters that have HF internal to the torch.. so you can push the button and it will spray plasma out the nozzle even without having a work piece under it.

I couldn't quite work it out in my head and convince myself that a ZVS would work with such a small number of turns on the secondary. There are complexities related to the total number of turns and the core material that I do not understand. I guess that with an FBT, it has a large number of turns and will produce a long arc in air.. but we only really need a 6-10mm under argon.

Newton Brawn

Wed Feb 23 2011, 08:41PM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi 3L3 and Ash :
I just posted some mater on the Forum under " HV CAPACITOR dV/dt CAPABILITY estimation (or design)"

I hope it could be of your interest

Regards

Newton Brawn

Thu Feb 24 2011, 11:15AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi 3l3 and Ash!

here is the schematic diagram:
]arc_starter_and_stabilizer.pdf[/file]

I made Copy and Past from previous post in order to put the information togheter:
The caps that shunt the buzzboz output high current terminals are normally paper-foil 400-600V. Polyester or polypropylrene METALIZED caps are not suitable. Some manufacturers use of 0.02uF. Other (Miller, Esab, etc) use caps up to 10uF.
0.02uF is enough to avoid the hv enter in the secondary coil or buzzbox diodes .
Also 2uF in series with 10 ohm 2w CARBON resistor bridges the hi current work terminal to the ground. This is the way to rf grounding the buzzbox secondary, avoiding the secondary 55V winding get the RF voltage.

Other interesting point is that for proper arc start, just one pulse of 10 kV 0.5 microsecond is required. this pulse tobe at each 8.333ms, for a 60Hz buzbox. Using only one pulse close the zero voltage passage a lot of energy is saved, reducing the size and ratings of conponents.

The ignition coil may be replaced for homemade pulse tranformer. 24turns in primary 400 turns at secondary, ferrite core from flyback. insulation 0.2mm polyester between layers. No more 20 turns per layer.

Glass capacitors 1000uuF, 10kV proper handymade are reliable.

Any comment??

Regards

Newton

3l3ctrici7y

Thu Feb 24 2011, 10:27PM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

That's cool stuff, thanks for posting Newton :)

It had not occurred to me that running directly off of the line will cause it to run synchronously with an AC output buzzboz and that this would cause it to relight the arc at just the right time :)

Newton Brawn

Fri Feb 25 2011, 04:29AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

3L3, Ash:

Yes this is the big diference! just one pulse at right time. Save energy and a lot of component ratings.

There is a old patent 2880373 , Tajbl. It describes the art and technique how a pulse shall to start a arc. It is realy hi tech concept. Carefull revise how the pulse acts on the ignition.
However, do not consider the saturable transformer, it is something superseed, old tech...

look also

, general note 11, circuit show at figure E9.17. This circuit starts the sodium bulbs up to 1000W. I think I have some test sheet with documentation of the test results.

Regards

Newton

If u found a microwave in the street, just crrier it to home !

3l3ctrici7y

Sat Feb 26 2011, 11:24PM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

Newton, thanks for the link.
I really like the clever circuits that get put in datasheets.
Using the sidac in place of a spark gap is a really nice simplification.
Though, it would probably take a hefty sidac to handle 20kV+ and 1kA+ that a gap would.
Going back up a few figured, E9.11 is pretty cool too :)

Some time ago when I was hunting down info about HF igniters I found a scan of a manual that showed the use of an autotransformer for the HF igniter portion. I have attached it to this post.

Newton Brawn

Fri Mar 04 2011, 02:01AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Nice schematic !
Simple arrangement. It can work as a wellding arc starter or high pressure lamp starter. The transformer to have a magnetic shunt to limit the secondary short circuit current. Secondary to deliver more tham 5kV in order to trigger 1,0mm air gap. It may be a furnace ignition transformer @ old style version. It may produce 30~100 pulses at each 8.33ms, so the air gap shall have a heath sink.
Remenber that a sidac schema fig E9.11, prduces only 3 pulses each 8.33ms, saving a lot of energy.
The circuit "arc_starter_and_stabilizer.pdf" attached to thre thread Fri Feb 25 2011, 01:29AM produces only 1 pulse each 8.33ms, the air gap is always cool. This mean a LONG, LONG life for the spark gap tungsteniun electrodes. ( I use tungstenium carbite inserts from scraped cuting tools from the lathe... )

The "arc_starter_and_stabilizer.pdf" characteristics are:
Vtrigger=3600V, Cap = 700uuF.
The energy delivered in one pulse is in the range of:
0.5 x 3600^2 x 700 x 10^(-12) = 0.0045J
Triggering one pulse at each 8.33ms or 120 pulses per second...
0.0045J x 120 = 0.544J/s
Since 1watt is 1joule/second the power dissipated by the air spark gap power is 0.544watt. (it is less than 1W resistor)

If the cap is 1000uuF and the spark gap fire 30 pulses at each 8,33ms, the power dissipated by the spark gap is +- 23W (hot spark gap). It is the case of Miller HF 15 arc starter.

The characteristics of the air spark gap are really good. But is difficult to trigger at voltages lower than 3000V.
One single Sidac can fire at 120V up to 240V . Sidacs, have high "short circuit resistence" that sometimes reduces the efficience of tesla ckt. I have fired up to 6 sidacs in series (1380V) using the configuration E9.11, the caps capacitance are reduced to keep the energy and dv/dt lower.

Let me know the voltage delivered from the welding machine to the lamp. Also if it is DC or AC, and frequency.

Regards

Newton

3l3ctrici7y

Sun Mar 06 2011, 10:28AM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

Hi Newton,

I do not understand..

"Let me know the voltage delivered from the welding machine to the lamp. Also if it is DC or AC, and frequency."

What lamp??

Newton Brawn

Mon Mar 07 2011, 09:57PM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi 3L3 !
Sorry for the question. I was thinking that you are designing a starter for a xenon arc lamp.
Now I read again all the posts and I conclude that your project is for a welder machine. Can you confirm ??

As I said before, the ignition pulse of 0,006 joules is enough to start the arc. The pulses reaches 15000 volts during 0.5 to 1 microseconds at the welding torche / electrode. This pulse produces a spark of 3-4 mm in the open air or 12mm in argon/welding atmosphere (cool electrode, cool atmosphere ). Also you can touche the electrode, see the sparks going to yours fingers and you do not fill any electrical shock.

Also read the concepts of a arc starter written @ Google Patents, patent 2880376, by Franz Tajbl. It is the bible for construction of arc starters. The main concepts and technics for arc starter are spelled out. Of course, the saturated core tranformer used in that patent is something superseed.

Regards

Newton

EDIT: Please see the next post with the video clip "10kV in the hands"

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