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Encapsulated spark gap

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Art

Thu Apr 14 2016, 10:27AM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
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Posts: 66

Hi Guys,
I have experimented with a spark gap enclosed in PVC tube with a stop at each end.
Compared to the same spark gap in open air, I didnâ€™t notice much, if any difference,
until enough carbon formed to conduct and ruin the spark gap.
The open gap was never quenched with fans or magnets.

What could be expected different if a gap was encapsulated with a glass tube such as borosilicate?
My gut feeling was that the air would all be converted to byproduct, and it would stop working,
but that doesnâ€™t appear to be the case so far.

The reason is Iâ€™ve been able to increase power greatly for the same noise from the spark gap with it enclosed.
Cheers, Art.

Toasty

Thu Apr 14 2016, 11:18AM

Registered Member #56785 Joined: Fri Aug 28 2015, 02:54PM
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Posts: 20

My guess would be that it will be filled with byproduct and it will start firing
Irreguraly maybe even continuess. With encapsulating your spark gap you do the exact opposite of quenching it. Thats why you never see people use that kind of spark gap.

jpsmith123

Thu Apr 14 2016, 12:44PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

What are you using for electrodes? Many commercial spark gaps use a copper-tungsten alloy that erodes quite slowly. Graphite is supposed to be good too.

Proud Mary

Fri Apr 15 2016, 12:53AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

What is the origin of the "carbon formed to conduct and ruin the spark gap" in your experiment? If carbon it was, it must have come from somewhere.

Have you thought of using automotive sparking plugs set into a die-cast metal box? You can buy them with gaskets or "O" ring rabetting round the lid seal.

Sulaiman

Fri Apr 15 2016, 06:35AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Self quenching multi plate sealed spark gap

Art

Fri Apr 15 2016, 12:13PM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

Hi, The carbon to ruin the spark gap might not actually be correct.
It could just as easily be whatever new gas formed in the tube as Toasty suggested.
Itâ€™s not possible to see inside while working, but the inside of the tube has uniformly darkened (not any solid black track).
The gap is pure tungsten rod held with large copper terminals,
and the copper also has a uniform oxidisation to make it look made of bronze since being inside the tube.

Without other information, I think it would take the gap being
enclosed in another material at least on my own to determine where the residue is from.
The PVC does get hot of course,
and there also will be a small leak where the rod comes out to be adjusted.

Automotive spark plug is an interesting idea, I could see it working if the box was common to one terminal,
but I donâ€™t see it being easy to adjust.

Blackcurrant

Fri Apr 15 2016, 03:57PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

You could try filling it with argon.

I have seen my rotary spark gap make NO2
Maybe it could be carbon from CO2 or your electrodes melting?

Proud Mary

Fri Apr 15 2016, 04:47PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Art wrote ...

Automotive spark plug is an interesting idea, I could see it working if the box was common to one terminal,
but I donâ€™t see it being easy to adjust.

Life is easier, neater, and safer, if you hold the die-cast metal box at Earth potential with a stout metal strap, braid, or length of fat arc welder cable.

You can fit gas in and out ports to your box using screw up type bicycle inner tubes valves. If you are careful with your gasket seal, you can operate your ignition chamber at increased or reduced gas pressure - so long as you don't overdo it!

A similar valve fitting could also be used to view or irradiate the spark gap, introduce sensors and so on.

Finally, sparking plug adjustment tools and gauges are most inexpensive, and while the range of gap size is rather limited, you can set the gap quite accurately across the range of, typically, 0.5-2.55 mm in ten increments.

Art

Sat Apr 16 2016, 12:59PM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

The maximum of 2.55mm sounds very small compared to where I have best performance, though I havenâ€™t measured it.
I take it the Earth is the chassis ground on the supply side rather than the Earth shared with the secondary coil.

I wonder, now that might require good clearance.
I canâ€™t remember now if a flyback transformer is isolated,
or an arc might favour the grounded metal box,
but a cage around the spark gap sounds like a good idea.
Maybe some copper rod can be fed through a ceramic standoff like in a spark plug.

Sulaiman

Sun Apr 17 2016, 11:01AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Enclosing a spark gap is an EXCELLENT idea,
The noise is literally deafening !

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