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Registered Member #3904
Joined: Sat May 21 2011, 10:32AM
Location:
Posts: 28
I've soldered my capacitor bank wires together and the IKEA candle holders appear to be coating free.
Herr Zapp wrote ...
3. What are you using as an RF ground (or counterpoise) for your secondary?
The secondary is sitting on some aluminium foil which is connected via a jump lead to a radiator.
Herr Zapp wrote ...
4. What is the capacitance value of your salt-water capacitor bank?
5.05nF
Herr Zapp wrote ...
5. If your DC power supply is truly only capable of providing 5ma charging current, this coil might not operate, except possibly in a very slow "pop............pop............pop" mode. 5ma is not much current to drive even a small TC, and with lossy salt-water capacitors, you just don't have much to work with. I think you'd be MUCH better off starting with a conventional AC spark-gap coil, powered by very small NST (5 KV/25-30ma) or OBIT.
I had been running it through 2 x 2.4M resistors in "pop... pop... pop" mode. When I did this my ammeter was showing only .3 mA. Without the resistors at 5ma, I was seeing 2 inches of corona coming from the breakout point. Certainly under-powered, but no distinct pops. :)
Unfortunately my ZVS driver has now died. :( I wonder if connecting the negative terminal to RF ground wasn't such a good idea? It seems the MOSFETs have been zapped without actually overheating.
I've now swapped the DC supply for a 9kV, 50mA NST. You're right, this does make a huge difference. With the variac dialed half way up, the coil is beginning to strike the top of the capacitor bank!
magnet18 wrote ...
Do you have oil over the water in your capacitor? If not you'll probably get carona losses and take a severe cut to efficiency (& spark length)
I didn't have any oil over the water. When it was in a metal cooking pot, I didn't notice much corona or hissing.
I've since transferred it to a plastic bucket to prevent it being struck by the coil. I'm now getting quite a bit of hissing and will try adding oil as you suggest. I wonder how much is being lost in the corona?
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Herr Zapp wrote ...
Jamie -
The first thing you need to do is accurately determine the resonant frequency of your primary and secondary circuits. You can use JAVATC to calculate the approximate resonant frequencies, but since you've already got a decent o'scope, if will be more fun and instructive if you can actually measure the pri and sec resonant frequencies, and see the effects of your changes.
Do you have access to an RF signal generator? With a signal generator, its very easy to drive both pri and sec circuits with a low-power RF signal and measure their exact resonant frequencies with the o'scope.
If you can't get your hands on a signal generator, than you can quickly build the very simple & low-cost adjustable-frequency signal generator (Terry Fritz' "Tesla Coil Tuner") as shown here:
Blindly changing top load configuration in a "trial and error" effort to achieve resonance can be frustrating if you don't have a way to see how your changes are affecting the resonant frequency.
Herr Zapp
The Tesla coil Tuner That Herr is talking about is really helpful for tuning, Here is a picture of mine, however I think I am going to add an analog milliamp meter to it, Parallel tuning is kind of tricky with this. The leds dont dim much so you have to look close. Using a milliamp meter at the same time makes it a breeze. Finiding the res frequency of the secondary is extremely easy with this. Once I find it it using this then I check the frequency with the Fluke multimeter so no scope needed with this if all your doing is tuning this works really well.
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Tuning my coil
