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maximum secondary turns

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sparky

Mon Jun 11 2007, 07:06AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I'm going with a VERY tall secondary, and I am trying to get as much inductance as I possibly can without going too extreme. My secondary is a 6.25" PVC sewer pipe - and about 46" tall. With end caps in place I have about 43" of winding length. I will be winding with 27AWG to kick up the inductance.

I'm going to have 2440 turns when I'm finished. My primary is made of 1/2" copper tubing....
Is there a threshold number of turns in Tesla Coiling? Can this induce racing arcs? Any thoughts...opinions?

I'm curious....

uzzors2k

Mon Jun 11 2007, 07:51AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I think the only limit is how much current the wire can carry. To thin and it might melt, destroying your secondary. Otherwise I can't see any ill effects from too many turns, besides increased resistance.

Marko

Mon Jun 11 2007, 08:10AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi sparky

I would say, that you really can't have ''too much turns'' on a SGTC.
It's just about winding with thinnest possible wire, and thinner wire is better since you can get more inductance in smaller volume.

First you construct the capacitor to meet requirements of your power supply, and then you use largest number of primary turns with lowest possible resoant frequency for the secondary.

But there's a simple thing you have to consider, what is the power you really have available? The huge secondary like that would look really funny if you powered it with a small NST and got 50cm or so sparks from it, and would be a waste of resources.

Sparks can generally exceed 3x the length of secondary so unless you have a big pig I would radically reduce the length of that secondary.

Sulaiman

Mon Jun 11 2007, 11:23AM

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

Although I generally go with 'bigger is better' for an SGTC secondary,
mainly due to lower frequency / higher primary impedance / lower SG losses,
(also higher 'Q' and easier pri-sec coupling)
I did find a limit to this;

As Firkragg said, the primary capacitor is chosen to match the NST or OBIT or whatever,
With an optimal one spark per half-cycle of mains frequency (60Hz=120bps, 50Hz=100bps)
the energy stored in the capacitor for each spark is fixed/limited.
The energy stored in the primary capacitor is transfered to the secondary capacitance,
higher secondary capacitance causes lower secondary voltage, hence shorter arcs.

This effect was evident with my 6.25" dia sewer pipe with 28.5" 27awg 1800 turn winding,

with a 5-0-5 kV 20mA OBIT and single static un-blown SG. (18" arcs)
As above, 18" arcs with a 3ft secondary does look 'wimpy'

I would use the 6.25" pipe but use H/D <=3.5,
(H/D=PI sounds 'cool' to me), (my next coil will be H/D=PI/sqrt(2))

With the pipe and wire you have, I would cut the pipe in half and make two identical coils;
Then you can try
'TWIN' SGTC
'Wireless Power Transmission'
or you could stack them to have one double height/turns secondary to compare.

A low H/D coil will also be better for SSTC/DRSSTC/OLTC etc. experiments

That's my thinking anyway.

P.S. a 'Twin' is a good idea since roughly speaking
each secondary receives half the energy hence 0.707 the voltage - 1.414 times the voltage between the twins.

P.P.S. your planned coil would have a resonant frequency of about 60 kHz with suitable topload
which would require a VERY large primary coil = very expensive with current copper prices.
I'd consider 8mm 'micro bore' copper tubing for cost and size and ease of construction, with negligible efficiency loss.
I think that you could make two 8mm primaries for the cost of one large 1/2" primary.

P.P.P.S. The OBIT mentioned above no longer works, I tried too large a spacing for the spark gap and 'killed' it
don't be dumb like me, use a safety spark gap OR don't open the main spark gap too far.

sparky

Mon Jun 11 2007, 02:21PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

No SSTCs here....I'm going with a traditional coil setup.

I'm powering the 6.25" diameter BY 43" tall secondary with a pretty decent power supply. Either I will run this coil with a dual PT in parallel for 7 kVA or a 15kVA PIG. My cap will be around the 0.08 uF level....so I am preparing for some serious output especially since I've gone with a 1/2" copper tubing primary.

I got quoted the other day - $250 Canadian for each PT (1.5kVA - 14.4KV) or $500 for a 15kVA PIG (15kVA 14.4 kV) hummm.... oh the madness :) Muhahahahhaah.... I think the PIGGY will be a nice addition.

Sulaiman

Mon Jun 11 2007, 02:29PM

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

Aaaah, much higher power level than I was considering - so ignore everything I wrote

Steve Conner

Mon Jun 11 2007, 02:29PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If you're going to spend that much, why not go the whole way and get some larger diameter pipe so you can have a secondary with a decent aspect ratio. Very tall, thin secondaries can cause problems with the coupling being too low.

Marko

Mon Jun 11 2007, 05:46PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Huh, for 15kVA, your secondary may actually be too small!

You would have possibillity for 200inch arcs so you could go up to 70 inch secondary length, maybe a little less but not for much!

You may also consider using fatter secondary, but I don't know!

Or you may leave this one as is, get on a big topload and have more spectacular sparks..

sparky

Mon Jun 11 2007, 11:03PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I'm not going to run all 15kVA - I'm going to try a simple 8KVA to start and see where the performance goes. 6.25" PVC X 43" tall secondary is all I'm after for now. 8" diameter PVC is rather expensive.... I am trying to make my Tesla Coil portable as much as possible. I maybe changing the design of my coil too --- I might go with PTs instead of a PIG unit. Yet again, if I find a 10 kVA PIG I might just go with it instead. Then I have to find ballasting materials too... humm.... this project is going to be a lot of work, but it sure is going to be fun!!

I calculated that my inductance on my secondary to be 140 mH and my primary to be around 15 uH. My Cap will be 0.08 uF 48 kVDC rated...
I think thats plenty of inductance for 6.25" secondary.... really :)

UPDATE

I ran out of wire at 31" .... still it was a lot of work and it appears to have payed off. I guessing 1700 turns - 145 ohms measured. The primary is literally no resistence and it is 1/2 copper tubing. I'll be doing a test with the NSTs (12kV 120mA) using a 32 nF cap just for a test. I'm expecting intense streamers... even off a static gap!

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