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Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
Hi, It’s nice to join some sort of community that deals with HV ‘cuz I love it! I’m afraid I have a few questions regarding a Spark Gap Tesla Coil I am currently building. I have downloaded a neat program called Teslamap, It does all the calculations for you, and it has made my life a whole lot easier ;)
Anyways, I’m not here to advertise… I looked around the forums and did lots of homework, but I am still not sure about Whether a conical primary is superior to a pancake (It’s a fairly small, low power coil; I have a 4’ diameter secondary and a 450W (15,000V 30mA) NST) I have gone with a 20 degree incline, is this Ok? I understand that a ‘pancake’ coil has less coupling. How do I tell if my coil is over or under coupled? What would you guys (the experts) recommend?
Thanks in advance, I realize there have been numerous threads, but none of them seem to answer my question… I hope I have searched properly or I’m going to look like a complete moron… :)
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
For what you are doing a pancake coil is the simplest configuration.
During operation, you will adjust for coupling by raising or lowering your secondary. You'll find that you will get more output by increasing coupling (lowering secondary), but this will increase liklihood of racing sparks on the secondary. So its a trade-off between racing sparks and spark length.
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
Wow, That was amazing! In all my time on forums I have never got a reply 15 mins after my post; Thank you so much! Anyways…
Thank you, That makes things a whole lot clearer… There is a slight issue; what I neglected to say was that I have almost finished my 20 degree primary. Would you suggest I continue or just build again? Thank you for your time, It means a lot and I really appreciate it.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
MF -
Your conical primary will probably be fine, but it will influence the minimum height of your secondary, or rather the minimum distance from the primary to topload. You want to have enough standoff distance (and a large enough toroid diameter) to ensure that your streamers aren't all just drawn to the primary.
I have not used Teslamap; does it calculate primary/secondary coupling factor ("K" factor)? This is an important design parameter. For typical spark-gap coils, "K" factors range from approximately 0.1 to 0.18. If Teslamap doesn't calculate "K", download JAVATC (free) from JAVATC is a fairly sophisticated design program that will help you optimize all your TC parameters, and makes it easy to change various coil characteristics and immediately see the results.
Make sure that you provide some means of adjusting the height of the secondary relative to the primary, or vice-versa. This is how you will adjust coupling during the coil tuning process. For a conical primary you may want to start with the lowest primary turn an inch or so below the first turn on the secondary; "run the numbers" in JAVATC, and see what coupling factor this relationship would yield. You will want to start out slightly undercoupled, rather than overcoupled. Overcoupling can cause arcing on the surface of the secondary that can damage the wire insulation.
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
Thanks to all who helped me! Your posts have been deleted/removed but your advice lives on! haha... I have completed the primary! 20 degree incline, 50 Ft of copper 1/4' pipe, pics:
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My First Coil; Primary Geometry help?
