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finishing tesla coil

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eniyuki

Sat Sept 05 2009, 09:10PM

Registered Member #2148 Joined: Tue Jun 02 2009, 02:22AM
Location:
Posts: 62

hi
i recently worked on my tesla coil mounting everything on a fabricated table.
later i will finish my sucker gap using 2 brass hose coupling 1" diameter and wiring everything up.

before i run my TC, i would like to know what i must do first/points to remember/check what i have to check etc... so damage can be reduced.

pics

eni

Sulaiman

Sat Sept 05 2009, 11:17PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Looks great !

The only helpful comments I may have are,
- Have a safety spark gap set to just fire when connected across the eht source
- Put a breakout point/rod on the toroid for early testing
- RF Earthing, how do you plan to 'earth' the bottom of the secondary?
For indoor testing about 5m of aluminum kitchen foil on the floor works.

Good luck with first-light !

Herr Zapp

Sun Sept 06 2009, 01:33AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

eniyuki -

Very, very nice construction!

Here are a few general suggestions:

PRIOR TO APLYING POWER FOR THE FIRST TIME
1. Triple-check that all your wiring actually matches the schematic;
2. Use a variac to allow you to control input power level;
3. Set the main spark gap to ~3mm for initial testing only;
4. Perform the initial power up in a semi-dark location so you can easily detect arcing or flashover at unexpected locations;
5. Have another observer present, watching the opposite side of the coil from where you are, to help detect flashover; have the observer specifically watching for any arcing in the MMC, as this is probably the single most expensive component;
6. Tape a short breakout point to the toroid, positioned against a dark background so you can easily see any dim streamers;
7. Make sure the variac is adjusted to minimum output voltage before applying power, and that the AC input circuit is protected by a fuse that is of the correct value for the variac's output current rating (i.e. 10A variac, 12A fuse).
8. Unplug and move any nearby, expensive AC-powered electronic products: LCD television, expensive stereo system, PC, etc. It's generally best to try to run the coil outdoors, in a garage, or someplace other than inside a house.
9. Make SURE that all the components in your coil that need to be connected to RF ground ARE connected, and that your RF ground is of suitable quality.

WHEN ACTUALLY APPLYING POWER FOR THE FIRST TIME:
1. Make sure that your primary tap is located at the initial position suggested by your design program;
2. Make sure that your variac is adjusted for minimum output voltage;
3. Turn on the AC POWER, and slowly crank up the variac. The spark gap should begin to fire by the time the variac is putting out 50-60 volts. The spark gap should be firing relatively smoothly and continuously.
4. Watch very carefully for any small streamers forming at the tip of the breakout point. If small streamers are detected, continue to slowly increase the input voltage, while carefully watching for any arcing or flashover at unexpected locations.
5. If all goes well, and streamer length continues to increase as input voltage is increased, continue to increase input voltage to maximum.
6. Shut everything down and remove the breakout point. Repeat steps #3-6, and see if the toroid will sustain unaided breakout. If not, replace the breakout point, and increase the spark gap spacing by 1-2mm (maximum of 6mm). Turn on AC power and again slowly crank up the variac, making sure that the spark gap again fires smoothly and continuously. Monitor streamer output.
7. Again remove the breakout point, and see if the toroid will breakout unaided. If so, set up a grounded target near the edge of the toroid, and measure the maximum streamer length (toroid to target) that the coil can achieve with regularity. Record this value.
8. Mark the initial primary tap location using a felt-tip pen, and move your primary tap point 1/8 turn further OUT from this location. See if there is any measurable change in streamer length. If not, reposition the primary tap point 1/8 turn IN from the initial location. Again, see if there is any detectable change in streamer length. If not, repeat step #8, changing the tap location by 1/4 turn, and again see if there is any detectable change in streamer length. Continue adjusting the primary tap point until you have found the "sweet spot" that gives maximum streamer length.
9. Post some photos and/or a video clip showing the coil's best performance, and let us know what the maximum measured streamer lenght is. That will tell us if the coil is attaining typical performance for your input power level, or if more tuning & tweaking is required.

Good luck with First Light!!

Regards,
Herr Zapp

eniyuki

Sun Sept 06 2009, 03:05AM

Registered Member #2148 Joined: Tue Jun 02 2009, 02:22AM
Location:
Posts: 62

@ Sulaiman
Your right, it is better to put a break out point when tuning so you can see the spark clearly.
i set the safety gap on my terry filter just when the arc breaks.(unloaded)

im a little confused how to ground these components. Searching through the net gives me different kinds of grounding tecniques and now im comfused which i should follow. Deepfriedneon gives a clear grounding schematic with drawings which is really easy to understand but some say it is not good to connect the secondary ground, terryfilter ground and center tap,strike rail on the same "EARTH GROUND ROD"

also our main outlet doesnt have a 3rd PIN which is also a GROUND right? is that what you guys called the RF GROUND?

oh lastly i woundnt fire this INDOOR :)

@ HerrZapp

Hey master HerrZapp long time no see.
have you met my fellow filipino coiler, rafft?
anyway, your input to me always helps a loooot. Thanks.

here are the things lingering in my head,

A.) I have a small variac rated at 0-250VAC 0.5KVA. Im still worrying that this might not perform well because of its rated power.
my 2 NST pulls 900watts when turned on but this variac 500watts(0.5KVA) might not pull through?a bottleneck?
ive seeing 2KVA variacs locally. might buy one of those if this 0.5KVA doesnt work.

B.)Im planning to build a control box compose of variac, switches, analog meters, power factor correction (my mother have this power saver thingy in our house which i suspect that this is a power factor correction, WILL THIS work if i add this to my control box connected in parallel to my NSTs?)

C.) I will describe how i will gonna ground this, please bear with me.

firstly, we dont have a WALL OUTLET GROUND (the 3rd pin/socket).
i will ground secondary coil and strike rail AT THE SAME EARTH GROUND ROD.
i will connect each center tap and then connect it to the safety gap(terry filter) then connect it again to ANOTHER EARTH GROUND ROD. so a total of 2 earth ground rods penetrated to the soil.

D.) in this setup, is it worth that someday i will upgrade my sucker gap into a Synchronous rotary gap?
my MMC is designed to fit both static and rotary gaps. (it has 0.015uF/40kv, static gap @ 15kv/60ma and 0.028uF/32kv. rotary gap @ 15kv/60ma). it is done by changing the position of the copper plates as you can see. something like that. hard to explain
i think that's actually for now. Will post UPDATES if something goes bad!

PS
can i see you coil?

eni

raff

Sun Sept 06 2009, 10:54AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

nice one eni!

cant wait for first light

Herr Zapp

Mon Sept 07 2009, 04:16AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

eniyuki -

As far as your concern about your 500VA rated variac and your 900VA NST load, variacs can withstand considerable overload for limited periods of time without damage. See a typical variac overload graph at:

More information about variac overloading is at:http://www.ietlabs.com/Variac/Variac.html (see the last application note "How to Get More Out of Your vaciac")

Another approach is to add power factor correction capacitors directly across your NST AC input terminals. This will reduce the apparent current being drawn by the NSTs, and reduce the overload on your variac. (First, check your NST nameplates to make sure that they are "normal" power factor units. There are "high power factor" NSTs with internal PFC capacitors, but they rather uncommon.) You don't want to add any external PFC capc to high power factor NSTs.

Your grounding problem is a bit unique, with no real AC line ground available at your AC outlets.

I'd do the following (although this might be subject to other opinions):
1. Connect BOTH of your ground rods together with the best low-impedance conductor you have. A few pieces of #12 AWG copper wire in parallel should work adequately if your ground rods are not too far apart.
2. Connect ALL the components that need to be grounded directly to one of the ground rods (bottom of secondary, NST cases, Terry filter, strike rail, etc.)
3. Position the coil as close to the ground rod as possible to keep ALL the ground line as short and direct as possible.

DON'T try to use any type of "power saving thingy" in your AC supply line. Whatever it is, it will NOT provide effective power factor correction for your NSTs.

Regards,
Herr Zapp

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