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Secondary wire thicness

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LAN_403

Bender

Fri Dec 14 2007, 11:26PM

Registered Member #1027 Joined: Tue Sept 25 2007, 01:44PM
Location: Poland
Posts: 15

Short question:

Im building 4kW SGTC and secondary will be wound on 210mm sever pipe. I found four kilometer reel of PVC insulated wire, outer diameter 1mm, and the metal inside about 0.4mm. Is this too thin for TC use at these powers? Should i get something like 1mm pure copper wire?

J. Aaron Holmes

Sat Dec 15 2007, 07:19AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

What's more important to you? Using those parts, or using 4kW? Honesly, I'd probably say you have the ingredients of a ~1.5kVA coil there. Consider that a typical height-to-diameter ratio of 5:1 would make your secondary 1m long. Then consider that 4kW, by the Freau equation, suggests >2.5m sparks. You probably see where I'm going with this now!

Sparks 2.5x the length of the secondary are a great achievement in SGTC Land, especially on bigger coils. 1.5-2x is probably more reasonable. Even 2x would be really great! The smaller DRSSTCs blow SGTCs away on this particular benchmark (reference: Steve Conner). Anyway, I'd probably be thinking 300-400mm pipe, >1.5m length, and >=1mm (of actual copper) wire. Whatever lets you put ~1000-1200 turns on there.

Numeric wrestling matches with various rules of thumb are what make TC building fun!

Cheers,
Aaron, N7OE

Bender

Sat Dec 15 2007, 09:57AM

Registered Member #1027 Joined: Tue Sept 25 2007, 01:44PM
Location: Poland
Posts: 15

Main reason for that PVC wire is that it is quite cheap compared to pure copper wire (4-5x cheaper)

So the main problem is that sparks will start hitting coil itself at that power? And i don't need to start worrying if that 0.4mm wire cant handle the power and burns?

Steve Ward

Sat Dec 15 2007, 06:11PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

And i don't need to start worrying if that 0.4mm wire cant handle the power and burns?

That is very unlikely. Ive never actually seen a secondary run high enough current to fuse open its winding.

I still suggest magnet wire over the PVC stuff that will just waste space. Maybe you are looking at the wrong sources if the PVC coated wire is cheaper than enameled magnet wire, its almost *always* the other way around where i look.

HV Enthusiast

Sat Dec 15 2007, 06:26PM

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

Actually, i'd be kind of wary to use PVC insulated wire unless the wire was sufficiently thick not to generate too much heat. PVC has a very low melting point compared to conventional magnet wire etc... and does melt quite easily.

Bender

Sat Dec 15 2007, 10:03PM

Registered Member #1027 Joined: Tue Sept 25 2007, 01:44PM
Location: Poland
Posts: 15

So its best to give up with PVC-wire idea.

Damn.. that means that no teslacoil for me right now, im little short of money so maybe next month i get enough for good 0.9mm or 1.0mm pure magnet wire. 1km reel of that stuff costs here about 100-120e. PVC Wire would have been just 30e from flee market.

Zum Beispiel

Sat Dec 15 2007, 10:13PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

Don't give up on the idea just yet. I've seen some good TC's made with PVC wire. Sure it's not ideal, but should work. Hell, Tesla himself used some old crappy wire (think late 1800's), and still managed some great arcs.

If that is all you can get, then go for it. It might just work.

J. Aaron Holmes

Sun Dec 16 2007, 12:53AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Yes, my question about power level vs. parts on hand still stands; if he's willing to compromise on the power, he can probably use the PVC-insulated wire and the 210mm pipe and be ok. I just wouldn't expect to build a proper 4kW coil with those things, that's all.

There seem to be a couple of essential approaches to designing a coil:
1) Design for a certain performance.
2) Design around certain parts.

Approach #1 is fine, but tends to require either more money, or a lot of patience (e.g., waiting until the part that was the crux of your design shows up on eBay for 90% off the list price). So it's not for everybody. The two approaches tend not to mix very well. If you're short on $$ and have some parts, approach #2 is probably for you. That is, anchor your design to the parts you have or can get cheaply and then expand from there until you've got a complete design that obeys most of the accepted rules. This may mean you don't build a 4kW coil today, but then if you haven't already built something smaller, this is probably a good excuse

Cheers,
Aaron, N7OE

Bender

Sun Dec 16 2007, 01:05AM

Registered Member #1027 Joined: Tue Sept 25 2007, 01:44PM
Location: Poland
Posts: 15

Well i could cut the power down, but what i would be happy to see sparks about 200cm. That could be done according to 1.7 x sqrt(power) just a bit over 2kW. But will 2kW be still too much?

Kizmo

Sun Dec 16 2007, 01:14AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I think 2kW is reasonable for 8" coil.

I burned one secondary with just putting in way too much power (5kW

) and coil was wound with .50mm wire on 200mm sever pipe. It burned quite badly and output wasn't that great at all.

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