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Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Kristian -
All of the "twin" Tesla coils I have seen have had the primaries connected in SERIES, not in parallel. I think this is the only way to guarantee that each coil is seeing the same primary current, even if the primary tap point is slightly different for each primary. The larger surge inductance provided by the "series" primary configuration may help reduce spark gap losses and maximize performance.
Brian Basura's "Mini-Twin" coil was spectacular at several of the SoCal Teslathons a few years ago. His write-up on this coil (with complete schematics) can be seen at:
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Kristian -
I wound a pair of identical 3.5" diameter secondary coils for a bipolar-twin setup several years ago, but have been too busy with other projects to finish this one. After winding, but before epoxy coating, I measured the resonant frequency of the bare coils and "adjusted" each one by adding or removing turns until the resonant frequencies were identical. The primary coils will be series-connected, just like Brian Basura's Mini-Twin was. I'm not sure where all the other suggestions for "parallel" primary connections came from, or if they were just guesses about how it should be done.
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
I did not guess. I studied the video that Kristian linked to at powerlabs, and I also found it on this site , but did not post it then as he mentions a mistake in his schematic, not to do with parallel or series primary though. That being said, it strikes me as more logical to have the mmc between the two primaries and therefore keep the configuration as "series". Although, this goes against the grain of "bipolar", where the 1/2 wave TC is driven by one primary at the middle. Coincidentally, I have found another configuration that has a spark gap on each leg of the primary and the mmc in parallel with the transformer. Any thoughts on this?
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
In a "series" primary configuration, the primary coils, tank capacitor, and spark gap can be arranged in many different "sequences", but as long as they are all in series, there will not be any difference in coil performance. The tank capacitor and spark gap can be broken down into smaller separate "pieces", and inserted in various places in the series circuit, but again performance will not be affected.
As far as component stresses, placing the spark gap across the supply transformer is generally considered to be better practiice than placing the tank capacitor across the transformer. The high frequency ringing of the tank capacitor may cause dielectric failure of the transformer secondary if a low-pass filter (Terry Fritz' design) is not used between the transformer and the tank circuit. Having the spark gap across transformer is generally thought to stress the transformer less, but a Terry filter is still recommended.
Incidentally, is there really such thing as a "bipolar" Tesla coil, or should we be calling them "dipolar" coils? In physics, "dipolar" defines a pair of electric charges or magnetic poles, of equal magnitude but of opposite sign or polarity, separated by a small distance. This sounds like the correct term for the type of Tesla coils we are describing, with the coils' output being of opposite, alternating polarity.
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bi polar primary wiring
