Freaking me out a little / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Freaking me out a little

1 2 next

Move Thread

LAN_403

EvilTesla-RG

Mon Dec 22 2008, 06:35PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

I am having a few problems with my new SGTC.

And givin the insane voltage in these things, it is scaring me a little.

First off, What fire danger is thier with these things? Does the high frequency sparks cause fire as easily as lot frequency sparks?

Allright, down to my problem(s)

My capaciter is a plate capacitor. It is made out of polyethaline storage bags. It is a stack of forty, compressed, of these bags, every tenth one has a plate in it. Such that thier is at least an inch and a quarter between the plate and the edge of the bag.

The NST is a 15 kv, 30 MA Franceformer.

The largest sparks the NST can throw by itself are about an inch.

So my cap is good right? NO!!!

So, I fix my cap (replacing the burnt storage bags with new once)

AND I set my spark gap to about three quarters of an inch, so, instead of shorting across the capacitor, it shorts across the gap like it is supposed to.

Well...It works....sort of.

I unpluged the thing to quickly to get a good look at the capacitor, but from what I could see, it was good.

What scared me, was that the spark gap was going a little crazy, it was sparking to some nearby bolts (which I suspected might happen, so they were safe to get shocked)

But, also, thier were two sparks on my Primary Coil. One going to the secondary, and one really long one going to my Strike Rail.

The one to the secondary makes sence, I haven't adjusted the coupling yet.

The other one is the reason I really posted this. From my understanding, the primary circuit isn't very high voltage (relitivly speaking) It can only throw sparks around three inches long. I later measered the length of the spark going to the Strike Rail, it was between five and six inches. MUCH longer than it should be.

Also, the strike Rail is wired to the secondaries ground.

Well, My thought on this are that it is simply a coupling problem. Since the coupling isn't set right, thier is a VAST potential between the primary and the secondary, making very large sparks between the two. So, once I set the coupling, this problem will go away.

But, I want to know what YOUR thoughts are, I will wait for an intelligent reply before awakening my monster again.

Arcstarter

Mon Dec 22 2008, 07:40PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well, the strike rail should be split with about 4 inches or so so it is not a shorted turn if you havent already done this, but this will probably not solve anything. But anyway, the strike rail should be connected to a stake pounded as deep into the ground as possible, cement, dirt, clay or what ever. After you put a spike in, if it is dirt or clay or anything like that, wet it down to improve continuity.

The coupling will indeed fix the sparks up the secondary from the primary, AKA racing sparks. Could we get a pic perhaps? That would help alot. How high up the secondary is the primary and what sort of primary do you have(flat spiral, etc.)?

Also, your caps are indeed somewhat 'not good' for tesla coils, or at least from the sound of it. Do you know the capacitance? You would want 7.4nf cap rated for probably about 40kv. I say that because the nameplate rating is dc, so you divide by 2 to get the ac rating(not necessarily the actual ac rating, but what us coilers use

). Then you want a few kv safety margin for a truly good cap/mmc.

Hehe, i just found out that if you used the .15uf cde caps you would want 20 in series for 7.5nf, and that would be exactly 40kvdc rating :).

What scared me, was that the spark gap was going a little crazy, it was sparking to some nearby bolts (which I suspected might happen, so they were safe to get shocked)

How far away were these bolts? If they were farther that the gap of the spark gap, you might have a problem and a very dead nst(remember, nst's die if they are killed :P). Sounds to me that the tank voltage is way to high, but i wouldn't know unless i saw the pics of the bolts it was arcing to.

Also, leave the primary alone, only connected to the tank circuit(i think, that is what i have always done). The bottom of the secondary must be grounded very good. You should connect it to a LONG( a few feet, as much as possible) stake pounded DEEP into the ground, with the ground wet for improved conduction as stated above. The bottom of the secondary should be attached to the spike with fairly thick wire, and the wire should be as short as possible, to reduce any resistance. This might be causing it, because it happened to me before. Or, it could help with the racing sparks at least.

That is all i got right now. :P

Have fun and good luck

EvilTesla-RG

Mon Dec 22 2008, 08:45PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Thank you for the reply

The Strike rail is seperated so it is not a short.

I have noticed that actully, the ground need not be directly through the earth. If ran through a filter, it can be connected to the house ground. I have seen this done on a few coils, one of which was factory produced.

The cap was desined for this coil. It an handle approx 40 KV, and 8.3 nf. That is what I desined it for.

HOWEVER! that doesn't take into acount arcing around the insulation, which is what it was doing.

The primary is a flat spiral, the coupling was horrible. The Secondary was a few inches lower than the primary.
Which explains the racing sparks.

The bolts were about the same distence away as the size of the gap.
I have a safty gap, and a capacitive low pass filter protecting my NST, so it is fairly safe.

The two biggist things I am worried about is
1) fire, what are the chances of a stray spark catching something on fire?

2) The sparks between the primary and strike rail are over five inches long, this strikes me as a little long for a primary circuit to be making.

Anouther quesiton, does changing the coupling change the potential between the Primary and secondary?
If so, that would explain getting five inch sparks.

Mads Barnkob

Mon Dec 22 2008, 09:34PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

just to add something about the fire chances...

Do not apply alcohol to your tesla coil while its runnijng, neither should you try to intake it along with tequila shots. If your tesla coil was to catch fire its more likely to come from you smoking or trying to cool it with what you thought was a reverse flamethrower.

most devestating sparks in a tesla coil would be sparks running in a cabonized trail of the secondary form, it might not be easy to spot, but the fire slash explosion hazard is relative low due to you should see the coil not performing well and thous turning it off to investigate the problems.

and now, the bed.

Arcstarter

Mon Dec 22 2008, 09:57PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

About the fire hazard. It is not non-existent, but if you are smart, it is doubtful that you would have that problem., and from what i have heard you are smart.

But, if a carbon track appears, it might catch on fire. It is less likely with a sgtc, due to the lower current, but a vttc or sstc will probably catch fire after too long(almost did for me last night with my vttc even though i only had it on for maybe a second at a time).

Well, the large arc from the primary to strike rail is puzzling. But the strike rail should be grounded with rf ground, as should the secondary. The strike rail and primary should not be connected in any way i believe. That still does not explain the huge 5 inch spark though :/.

For coupling you should have the bottom turn of the secondary, and the top turn of the primary level. Then change it from there.

If you can take a video, do that so we can see what is going on.

EvilTesla-RG

Mon Dec 22 2008, 10:09PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Awsome, alright, thanks

That is what I wanted to hear.

I will mess around with it. If I don't fix it quickly, I'll post a short movie. Though I really don't want to leave it on very long. I'm scared of the evil thing

I know my name is EvilTesla, But I think I've been out-eviled by my own creation. I sware it is trying to tell me "Turn me on, I dare you, I'll kill you."

No I'm not high, just an extremly overactive imagination.

EvilTesla-RG

Mon Dec 22 2008, 10:50PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Alright, fixed the wierd five inch sparkes. I raised the secondary so it was an inch above the primary

Now I have to fix my capacitor. It is still arcing around the edges. I know of two ways to fix this.

First, I could go crazy with hotglue, and hot glue it so it will not arc over the edges.

I don't like this idea, becouse i really don't like the idea of taking a hot glue gun out on light polyethaline.

Other idea is to put the capacitor in oil, which is what I orgininaly intended to do, but thier are no containers the right size. They are too small, or so big that it would be very expensive to fill them with oil.

again, what are your thoughts?

Arcstarter

Tue Dec 23 2008, 05:24AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I know my name is EvilTesla, But I think I've been out-eviled by my own creation. I sware it is trying to tell me "Turn me on, I dare you, I'll kill you."

No I'm not high, just an extremly overactive imagination.

I think that is the first thing that made me laugh out loud today :D XD.

Well, for the caps mineral oil or transformer oil would be good, but expensive. There are cheaper oils out there though. You can just use plain old vegetable oil though. Sunflower seed oil is good though, and i know Ultra7 has had a good experience with it, and he said that it did not start to smell for him.

Buy some good caps if this one doesn't work well. CDE caps are great.

EvilTesla-RG

Tue Dec 23 2008, 04:51PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Thanks. Still not sure what I am going to do....

Coronafix

Tue Dec 23 2008, 11:57PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Vegetable oil is cheap.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob