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Re: [TCML] Low Frequency AC



Frank,

Can't help you directly, but I saw a potential solution in a different application a while back.

I have an in-floor heating system that uses three pumps to mix and balance the circulating water temperature. The metering pump has a nameplate rating for 120 VAC, 60 Hz, and no brushes. Still it runs at a ride range of speeds depending on the heat demand.

Intrigued, I put a small filament transformer for isolation, and a scope across the controller feed to the pump motor. I found a very interesting wave form being generated apparently by selectively triggering a triac. The character of the pulse train varies over a wide range of values depending on the intended pump sped. The voltage impressed on the pump motor was a series of amplitude and phase modulated 60 Hz pulses. The net result was the synthesis of a sinusoidal waveform at much less than 60 Hz. I wonder if such an arrangement applied to a small iron core NST would work for you.
I'll try ASCII art, view in fixed font for best results:


      |                             |
    | | |                         | | |
  | | | | |                     | | | | |                     |
  | | | | |                     | | | | |                     |
| | | | | | |                 | | | | | | |                 | |
| | | | | | | | | | | | | | | | -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              | | | | | | | |                 | | | | | | |
              | | | | | | |                   | | | | | | |
                | | | | |                       | | | | |
                | | | | |                       | | | | |
                  | | |                           | | |
                    |                               |


Each column of "|" characters represents one half of a 60 Hz cycle, whose amplitude and polarity are determined by the firing timing of a triac.

If you could design a similar controller, it might work for your application.

Dave



Frank wrote:
Hi all,
I have a really strange question that is not really Tesla related but will all the HV expertise out there, someone might have a suggestion.

I need a high voltage, say around 6KV @ 30 ma +- AC source at 15 hz.

I was thinking of rectifying the AC to 110, no filters, and then building a mechanical chopper to drive a NST, kind of like an old vibrator car tube radio circuit.

I know the low frequency for the transformer is not very efficient but I am also not looking to run the system for more than a couple minutes.

I have picked up an a custom made Holtz tube in the form of a full wave bridge rectifier and I need to drive it at a low frequency so you can see each leg of the bridge conduct.

A Holtz tube was a unique type of Geissler tube where a large dia tube has a series of glass funnels inside and then it is pumped down. The shape allows current to pass in only one direction. The forerunner of the cold cathode rectifier!

The tube is currently still in Germany but I have some pix of it in operation if anyone is interested. It is powering a Geissler tube and you can see the tube is operating on DC by the lack of glow on one electrode of the Geissler.

Thanks, Frank  _______________________________________________
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