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Re: Fw: Input frequency (fwd)
---------- Forwarded message ----------
Date: Mon, 03 Aug 1998 12:24:50 -0700
From: Jim Lux <James.P.Lux-at-jpl.nasa.gov>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Fw: Input frequency (fwd)
Tesla List wrote:
>
> ---------- Forwarded message ----------
> Date: Sun, 2 Aug 1998 12:50:09 +0100
> From: "chris.swinson" <chris.swinson-at-zetnet.co.uk>
> To: tesla list <tesla-at-pupman-dot-com>
> Subject: Fw: Input frequency
>
> -----Original Message-----
> From: chris.swinson <chris.swinson-at-zetnet.co.uk>
> To: tesla list <tesla-at-pupman-dot-com>
> Date: 01 August 1998 22:09
> Subject: Input frequency
>
> Hi All,
>
> Say if you had a Neon say, 10Kv at 50ma running on the usual 230V 50Hz
> mains. As far as I can gather if you use 230V input but at 100Hz you would
> actually get 20Kv at 50ma, thus more wattage input. Has anyone tried this.
> It may stress the Neon transformer but would this work ?
Actually, no, you'd get 10 kV at half the current, 25 mA. The unloaded
output voltage is determined by the turns ratio and the input voltage,
which didn't change in your example, so the output voltage would remain
unchanged. The output current for a neon transformer is limited by the
equivalent of a large series inductor. The impedance of that inductor is
proportional to frequency, i.e. twice the impedance at twice the
frequency. Since it is in series, with the same voltage, the current
will be halved.
>
> Also does any one know of a 230V adustable frequency circuit ? I treid to
> think up one, It would entale half wave recitfier on the mains with a cap to
> give about 230 V DC. Then switch it using power mosfets using a 555 timer
> to alter the frequency. It would be nice if some one had such a design
> before I try my idea ( I'm not very bright in mosfet designs, essp power
> circuits :-( )
What you describe is known as an inverter. For higher power uses they
are popular as motor speed controls to generate variable frequency (and
voltage) 3 phase power to drive an induction motor. Inverter circuits
are simple in theory, but hard to make work reliably and efficiently in
practice, although getting one to work at a single frequency/load
combination is somewhat easier. This is particularly so, when you drive
inductive loads (as you are contemplating) or in a high EMI environment
(which anywhere near a tesla coil is).