[Prev][Next][Index][Thread]
Re: Ballast Transformers.
Hi Harvey,
Just following your argument through there seems to be
a problem:
> Original Poster: "Harvey D Norris" <Tesla4-at-excite-dot-com>
>
> On Thu, 09 Mar 2000 13:48:59 -0700, Tesla List wrote:
>
> > Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
> >
> > Hi Mark,
> >
> > > Original Poster: "Mark Broker" <broker-at-uwplatt.edu>
> > > A ballast is a small step-up transformer. But, the power-handling is
> > >very low. I think on a standard 4' light ballast, the voltage is only
> > >a couple kV.
> > >The current is also quite low (a 4' flourescent bulb is rated ~50W).
> > >I was told that a ballast also modifies the frequency, or rectifies it,
> > >but I have seen slow-motion pictures that show the lights flickering
> > >at about 60Hz.....
> >
> > A few corrections to the above post ;o))
> >
> > A ballast is NOT a transformer (although one can use an xformer as
> > a ballast). A ballast has only ONE winding. In a fluorescent lamp a
> > ballast does two things: First of all, it limits the maximum current
> > that can flow (an "ac resistor") and second of all, it provides a
> > starting "kick" for the lamp (they need HV to ionize the gas/mercury
> > vapor inside the lamp). However, this HV "kick" is NOT due to
> > "transformer" action, but rather that the inductor stores energy in
> > the form J=0.5*L*I^2. In other words, the inductor tries to keep
> > the same current flowing as you open the windings. It does this by
> > raising the voltage (Ohm´s Law). Also, a ballast will do NOTHING
> > to the frequency or towards rectifying the AC voltage. At a certain
> > frequency, the ballast will appear to have zero ohms (not including
> > the resistance, the copper wire has). This is called the resonance
> > frequency, but it cannot change the applied frequency. It can´t
> > rectify the AC, because it basically is nothing more than a coil of
> > long wire.
> >
> >
> > Coiler greets from Germany,
> > Reinhard
> If the ballast contains a ferromagnetic core, it is doubtful that the
> inductive reactance will go to zero at resonance.
The inductive reactance never goes to zero at resonance for any
coil. A coil doesn't suddenly lose its properties because it is
included in a resonant circuit does it?
Resonance of ferromagnetic
> coils seems to be a misnomer. The only coils I could get to truly resonate
> at 60 hz showing full ohms law conduction value were air coils of
> commercially sold 14 gauge wire spools of 500 ft lengths.
> By placing many of these in series I could contain enough resistance to
> safely resonate them from wall voltage conditions.
?? Not sure what you mean. You don't want resistance in a
resonant circuit anyway (unless its designed to have some losses)?
By then placing iron
> cylinders in the cores I could derive a higher inductive reactance value,
> but when this new reactive value was balanced with a new capacitive
> reactance value, it did not then conduct the full ohms law value at its
> designated new parameter of resonance, as was the case with an air core. To
> give another example of the nonattainability
> of ferromagnetic resonance take the typical 1.5 KVA power 440 volt
> transformer. I measure 0.2 ohms on the primary, 2 ohms on the 440 secondary.
> If I attempted to resonate the primary with the secondary open, by ohms law
> conduction that would mean 120/0.2= 600 Amps, a situation that is easily
> seen as impossible.
The impedance of the winding is Xl, not Rdc.
Likewise if we attempted a series resonance of a typical
> ferromagmetic fan motor, and not the more familiar tank or parallel resonant
> circuit known as "power factor correction", we would find the motor burning
> up because the wires could not hold the amperage, if it were to even
> approach its ohms law
> conduction values supposedly always attained at resonance. Ferromagnetic
> coils cannot fully resonate because of the time lag of causitive voltage and
> amperage produced and limited by the rotation of the inertial iron domains,
> which then become less effective low loss reluctance paths at frequencies
> past 400 hz. For ferromagnetic transformers that might function efficiently
> these higher freq, and the superiority of a 4 phase system using a low
> hysteresis loss transformer see 4 phase vs 3 phase/transformer without
> hysteresis
> at my messageboard under Searl machine HDN
OK - so hysteresis losses become greater as frequency increases.
No great surprise there I think. So too do eddy current losses. All
can be lumped together and modelled as an effective series
resistance or transformed to an effective parallel resistance.
Regards,
Malcolm