Re: [TCML] Low Frequency AC

[David Speck <dave@xxxxxxxxxxxxxxxx>]

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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