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Tuning the mini-coil kit from Teslastuff

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Steve Hobley

Thu Oct 07 2010, 04:49AM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

I recently assembled the Mini-coil that Alan used to sell through his Teslastuff ebay store. The coil is a standard NST + Static spark gap coil. I'm using 5 440pF 40kV doorknob caps in parallel for the tank.

2096

It's "functional" but out of tune - does anyone have any tips on tuning such a small Tesla coil?
All my regular equipment is for much larger / lower frequency coils.

Thanks in advance,
Steve

quicksilver

Thu Oct 07 2010, 04:09PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

It's really a beautifully made coil Steve. but much more information is needed. Have you tried running all the specs through JAVATC?

Steve Hobley

Thu Oct 07 2010, 08:12PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

Actually the picture is of Alan's coil - mine is a little bit rougher (pic attached)

6000V NST - 30ma
5 x 440pF 40Kv caps in parallel
SSG
Primary - 4 turns of 1/4" tubing 45 degree angle (approx)
Topload - 1.5" diameter brass sphere
Secondary - 30 AWG wire, 3/4" former about 7" coil height - (15 ohms resistance)

I did run some numbers through TeslaMap and I seem to recall getting a secondary resonance of 2Mhz - but I could be mistaken - will check later.

Alan responded to me saying that he tuned his by attaching about 6' of wire from the spark gap to one side of the primary, and then removing 12" at a time till it was operating correctly.

Steve Hobley

Fri Oct 08 2010, 01:21AM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

I fed some measurements into Teslamap and got this:

Mini coil
10/7/2010

---------- Power Supply ----------
NST V Out 6 kV
NST I Out 30 mA
NST Input V 120 V
NST Input F 60 Hz
NST VA 180.0
NST Watts 188.0 W
NST Impedance 200 Kohms
Max Arc Length 23.3 in
NST PFC Cap 33.2 uF

---------- Primary Capacitor ----------
Your Cap 2.2 nF
Resonate Cap 13.3 nF
LTR Static Cap 18.6 nF
LTR Sync Cap 25.2 nF

---------- Secondary Coil ----------
Single build magnet wire
30 AWG
Wire Length 143.9 ft
Wire Weight 0.04 lbs
Wire Resistance 14.9 ohms
Coil Height 6 in
Coil Diameter 1 in
Coil H/W Ratio 6.0 : 1
Coil Turns 549.9
Inductance 1.11 mH
Capacitance 2.23 pF

---------- Top Load ----------
Overall Diameter (1) unknown
Ring Diameter (1) unknown
Overall Diameter (2) (optional) in
Ring Diameter (2) (optional) in
Sphere Diameter 2 in
Top Load Adjustment 95 %
Top Load Capacitance 2.70 pF

---------- Top Load + Secondary ----------
Resonate F 2,149.80 kHz

---------- Primary ----------
Wire Diameter 0.25 in
Wire Spacing 0.25 in
Hole Diameter 1.5 in
Coil Angle 45 degrees
Coil Adjust 95 %

Needed primary inductance with:
Your Cap 1.57 uH
Resonate Cap 0.26 uH
LTR Static Cap 0.19 uH
LTR Sync Cap 0.14 uH

Turn 1 0.1 uH
Turn 2 0.3 uH
Turn 3 0.6 uH
Turn 4 1.2 uH
Turn 5 1.9 uH
Turn 6 2.9 uH
Turn 7 4.2 uH
Turn 8 5.8 uH
Turn 9 7.7 uH
Turn 10 10.0 uH
Turn 11 12.8 uH
Turn 12 16.0 uH
Turn 13 19.7 uH
Turn 14 23.9 uH
Turn 15 28.6 uH
Turn 16 34.0 uH
Turn 17 40.0 uH
Turn 18 46.6 uH
Turn 19 53.9 uH
Turn 20 62.0 uH
Turn 21 70.8 uH
Turn 22 80.4 uH
Turn 23 90.8 uH
Turn 24 102.1 uH
Turn 25 114.3 uH

one more question - I keep tripping the GFI socket when I get up to about 50% on the variac - the NST is under 200W - anyone know why this is happening?

[Edit: Double post]

HV Enthusiast

Fri Oct 08 2010, 11:41AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Tesla coils create lots of noise which tend to interfere with GFI sockets.

I would find an alternative socket to plug your coil into.

Steve Hobley

Fri Oct 08 2010, 12:22PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

Thanks - when I moved it to another outlet it seemed to be OK.

I managed to get some improvements in performance last night - here's a quick video:

HV Enthusiast

Fri Oct 08 2010, 02:19PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Looks good.
You might be able to try a larger topload, with modified tuning of course, to get longer arcs. I think you should be able to get at least 10" arcs from a 6kV/30mA.

Also, if youre 6kV/30mA is an open frame type transformer (which are common with 4kV and 6kV transformers), you can remove the shunts for additional current output.

Steve Hobley

Fri Oct 08 2010, 02:53PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

I do have a slightly larger sphere, but it has no mounting - I will experiment. Thanks for your help.

BTW - I keep gazing longingly at your MiniBrute kits - do I have to buy the book on top of the 399 kit, or does the kit have basic instructions?

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