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Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
Skin effect will begin to dominate at higher frequencies so surface area will be more important than DC resistance. Yes it is a matter of heat dissipation but only the outer surface of the wire will be conducting at higher frequencies so the apparent resistance of the wire will increase as frequency does.
To calculate the effective resistance of your wire at a given frequency you need to know the skin effect depth and the diameter of the wire among other things. As far as I understand, the apparent resistance will be the resistance of the portion(skin) of the conductor that the current can actually flow though.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
It's not a matter of heat dissipation, it's a matter of losses due to RF resistance limiting your output.
There seems to be a "goldilocks" region of around 1000 turns for a spark-gap coil, regardless of secondary length. What you lose in turns you make up in lower losses. While SSTCs and DRSSTC's do generally benefit from more turns to reduce the Fres to a frequency more friendly to the drive silicon, there are few reported coils with more than 3k turns.
If you use really thin wire, then it's a nightmare to wind.
This is assuming of course that you wind with the turns touching each other. You could stay with the 1000(ish) turns and reduce your wire diameter below length/1000, but then you are increasing the losses for no benefit in turns, and you would need a leadscrew winding lathe to get them uniformly spaced.
The general formula for choosing the secondary wire diameter is use the maximum you can that will get you roughly 1k turns on the former you happen to have.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Just use wire from 20AWG to 30AWG for most coils and you'll be fine. Choose the wire from you have available, and what resonant frequency you need for size of coil.
The selection of wire really isn't going to make much of a difference unless you're running a 20kW CW coil.
Plus, losses schmosses. Worrying about losses in secondary whether its the wire or coilform is not really necessary as the losses in the primary are much much more than the secondary circuit.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
You can download WinTesla, it does calculations like that for you. Based on other parameters. Took me a few tries to figure it out but someone a little more clever than myself suggested i try it out. Low and behold, i got it! Give it a shot!
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secondary wire thickness / resistance
