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Testing salt water cap with spark gap

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HM_Murdock

Fri Sept 03 2010, 02:26PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

I have built a saltwater cap, and I want to make certain I am testing it correctly...

Using a 9kV/30mA NST, and I plan on wiring it as such with 10AWG stranded (600V) wire and two bolts for a temp spark gap.

Two questions:

1- is this ok to test with (have I got this right?)?
2- where should I set the initial gap?

radiotech

Fri Sept 03 2010, 03:28PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

What are you testing the electrolytic gap for?

HM_Murdock

Fri Sept 03 2010, 03:35PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Not 100% sure I have the right terminology here...

I basically want to test out my spark gap to make sure my cap is working and get an idea of the max width I can go on the gap to still get a spark. I have read this is how you are supposed to test the gap before hooking it to your primary on the TC?

radiotech

Fri Sept 03 2010, 06:43PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Spark gaps can be used to check voltage and somtimes are calibrated with a voltage scale. This oil gap is adjusted to see if the oil can prevent arc-over of a particular voiltage, to see if the oil is good.

HM_Murdock

Fri Sept 03 2010, 07:25PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

I am building a SGTC cap bank.

I want to be able to set up the safety gap (which I just realized I left out of my drawing) and the main spark gap.

I have read conflicting information on how to go about this, so I am trying to find out the 'right' way to do it.

Best I can tell, I should wire up JUST the NST and safty gap, and set the safety gap wide enough to where it just quits arcing.

then, I hook up the circuit as shown below, and set the spark gap so that it is just close enough to keep a constant arc, at which point it should be quite loud (and the safety gap is not firing)

Am I on the right track here, or what?

Muttyfutty!

Sat Sept 04 2010, 01:28AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

First disconnect the cap, you don't need it to set the safety.
Next, increase the safety gap size in small increments until it no longer fires and
increase it very slightly more. so when the main gap fires the safety gap doesn't.
The idea it that if the main gap fails, the safety gap fires before the voltage spike fries a Cap/NST etc...

This is a very good site to get you started, I recommend reading it thoroughly :)

Good luck, and don't forget to exercise caution when working with HV (or any) Capacitors...

HM_Murdock

Sat Sept 04 2010, 02:22AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Thanks Muttyfutty!

I have read (and re-read, and re-read) that site (and used the Teslamap program), as well as all the other ones I can find. In fact, that site is where I got my spark gap settings procedure from. I just wanted to make sure I had the wiring right, and was going about it the right way before I actually did it.

Got my new cap made tonight (used wine bottles this time, and all saltwater - no foil). Must have done something right, as it is LOUD!!

Got my safety gap all set, then connected the cap and spark gap. I could possibly go a tad wider on the spark gap, but I'm not looking to push it. As-is, the safety is just a hair away from firing with nothing but the NST connected with it, and it doesn't fire at all with the cap bank hooked up. Getting a solid 10.41nF with this cap.

Here's some pics, and a video...and man, the video doesn't do the volume justice...sounds like firecrackers going off like a machine gun! Me like!

]spark_gap_test.wmv[/file]

Xplorer

Sat Sept 04 2010, 04:01AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

Nice work. 10nf is on par with what you need. I think 13nF is an LTR static gap for a 9/30. Once you want to upgrade to a real capacitor, 11 CDEs in series will do it.
If you thought the SG was noisy, just wait till you get your first streamers. Even small ones (~6in) are defining.

-Tony

Muttyfutty!

Sat Sept 04 2010, 04:45AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

WOW, looks good!
When I first connected my 8nF cap to my NST I jumped about 2 feet in the air in shock, Never before had I heard such a loud bang!
Now I know what to expect when I (finally) finish my SGTC...

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