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Registered Member #2677
Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64
In Dan McCauley's book DRSSTC: Building the Modern Day Tesla Coil, he has several sections discussing frequency splitting in a DRSSTC system and goes on to say that in operation, two coupled coils with the same natural Fres will have an upper and lower frequency pole defined as Fnatural/1-k and Fnatural/1+k, respectively. He also says that if the primary is tuned to a natural resonant frequency that is far enough below the secondary's, the lower frequency pole will almost completely eliminate any harmonics at the upper pole, thereby eliminating notching of the primary current waveform caused by the higher harmonics. How do I best tune the primary to eliminate the upper harmonics and current notching? I have tuned my primary coil to what would be the lower pole of the system if the primary and secondary were tuned to the same natural Fres but ScanTesla still shows severe notching of the primary current. The system will run on primary current feedback.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Actually, some of your terminology is a bit off. If you're primary circuit is tuned well below the natural fres of the uncoupled secondary, you will get the majority of excitation at the lower frequency pole and just a slight excitation at the upper frequency pole. It doesn't "eliminate" them.
This type of tuning doesn't eliminate frequency splitting. Its basically just ensuring that the frequency content of the sampled current waveform is primarily made up of a single excitation frequency, not multiple. In the latter case, where multiple excitation frequencies occur (i.e. upper and lower pole), you can get what is commonly referred to as "frequency or mode hopping" where the feedback can lock onto either lower or upper frequency and potentially (in theory at least) cause problems.
Perhaps you are concerned that you are seeing notching occur during a single interrupter burst? If thats the case, decreasing the coupling between secondary and primary will increase the time between notchings. Increasing coupling on the other hand will move the notches closer together (transfers energy more efficiently)
Richie Burnett has probably the best source on the net as far as frequency splitting and all that fun stuff goes. His website link is as follows:
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DRSSTC Frequency Splitting
