Essjay
04.06.2021 9:18:13
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* [Note: 1]
(My secondary frequency is 81 kHz with the primary about 73/74 kHz = -9%) here
Tuning a tesla coil can be done in various ways depending on what equipment you have access to. The most accurate is with an oscilloscope and signal generator. Another method is to use JavaTC the software design program, which will give a good estimate of the resonant frequency and where you need to tap the primary coil.
In both cases you can get the best final tuning point by testing different tap points close to the estimated point, to get the best result.
It is also always a good idea to initially run at a low power, as if the coil is badly out of tune and ran at full power, you could cause damage, either to the secondary coil or the capacitors. more
If you have not used JavaTC then now is a good time to get it and use on the coil you have already built, otherwise assuming you do not have an oscilloscope, you could calculate the resonant frequency yourself. See Here or Here for the necessary formulas. here
The instruments are connected as shown above. On the secondary's example, the wire simulating a streamer is optional, and the probe must not be allowed to swing or move around, otherwise it will upset the reading.
Set the signal generator to an initial frequency around 20 to 30 kHz below the expected frequency. Then gradually increase the frequency and watch the oscilloscope display for a peak.
At some point the voltage that the oscilloscope is measuring will sharply increase, then abruptly decrease. Just how suddenly this occurs is affected by the coarseness of the tuning and the coils own characteristics. I modified my own generator so that I had quite fine tuning in the range of 50 to 150 kHz (suited for my coils).
Strictly speaking the primary frequency should match the secondary frequency, but when a streamer forms on the toroid it adds capacitance to the circuit and this loading causes the secondary's resonant frequency to drop slightly, something that is often overlooked. The amount that it drops will vary depending on how long the streamer is, and where, or indeed if, the streamer strikes anything.
But by making the primary a bit lower, it means when the secondary frequency drops, it will then hopefully match the primary one.
An approximation of the amount of frequency drop can be obtained by trailing thin pieces of wire from the toroid to nearby objects, and then remeasuring the resonant frequency of the secondary circuit again. These simulated streamers should only be the length that you know the tesla coil is capable of. Streamers less than three foot, probably won't affect things much, so with a small coil it is usually best to tune the primary the same as the secondary frequency.
By trying different lengths and horizontal and angled positions you can then come up with an average frequency drop to aim for. You then tune the primary to this new frequency. I aim for up to 10% on my 8 inch * [Note: 1], and less than 3-5% on smaller coils, but trial and error is the only way to find out.
It will mean of course with this method that the primary is initially slightly out of tune before a streamer forms, but it then comes fully into tune when a streamer is present.
This initial out of tune period does not seem to affect things, but the fact that it comes into tune when a streamer forms, makes for longer streamers or sparks overall. Unfortunately you can only use this method to make allowance for the effect of streamers if you are using an oscilloscope and a signal generator to tune your coil though. more
eg. 0.5 x 1ms x 0.08 A x 792v
The following equipment and procedure provides very repeatable results and is perfect for an �apples with apples� approach for comparing different inductive ignition coil designs in regards to their storage ability.
Coil primary current control is vital for good ignition systems as stored coil energy is related to coil current by a square rule (1/2 x primary winding inductance x primary current �). It is important to ensure your testing is done with a well controlled primary current i.e. use the same ignition module or current regulated power supply to drive the coils for comparative testing. [links]
Simply join enough of the zeners up to achieve a rating of approximately 800V. Record the voltage for your later calculations. You could actually measure the total voltage under use but adding up the individual ratings will usually be fine eg 11 diodes used x 75V rating each = 825V. more
The overall design is up to you, we mounted the diode string on an old plastic sheet, just make sure its an insulator material (wood is fine). [links]
Zener diodes are diodes that will conduct in the reverse direction when the voltage gets above their rating, sort of like a pressure relief valve. You can string them together to raise the voltage as it�s often hard to find individual high wattage ones with high zener voltage ratings. Using multiple diodes also helps them dissipate the heat better if only low wattage ones are available. more
First we’ll measure something nice and simple: A battery volt drop measurement. more
As I mentioned earlier, voltage is not the only thing you can measure with your ‘scope. With the introduction of transducers, you can measure current, pressure, temperature, vibration, noise and so on..
Once again, we’re going to leave the trigger function out of play. When you’re ready, start the engine and look at the screen. You should now be looking at the ignition primary pattern. (See figure 2.2) here
Note: that where I state voltage or time per division, I am basing that on the ‘scope set-up. You may want to convert that to total screen voltage and total screen time. more