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Re: MOT Voltage Doubler
Tesla List wrote:
>
> Original Poster: "Gregory R. Hunter" <ghunter-at-enterprise-dot-net>
>
> > The point I was trying to make about the voltage doubler circuit is
that if
> > it only raises the voltage to 2.8 x RMS, then there's little point in
> > including it in a TC power supply. Consider the case of two identical
> > 2200VAC MOTs with their cores shorted together and grounded, their
> > secondaries in series, and primaries reverse-phased. The two MOTs will
> > develop 4400VAC as measured across the two HV output terminals. 4400VAC x
> > 2.8 = 12320V peak-to-peak. Now, if we include tho two voltage
doublers, we
> > get roughly 12320VDC pulsed (2200 x 2.8) + (2200 x 2.8). If a TC is being
> > fired by 12320V, does it matter that much if it's AC or pulsed DC?
>
> But, oops, the AC case is 12kV peak to peak, but the voltage across the
> output is only half that at a maximum, or 6 kV. The doubler
> configuration allows you to work the maximum positive voltage against
> the maximum negative, whereas the AC configuration gets only to the peak
> voltage (1.4 *Erms), albeit with opposite sign each time.
>
> Are you saying that peak-to-peak does not = RMS x 2.8? You've lost me.
No... the peak to peak voltage is 2.8Erms. However, in the usual TC
circuit (i.e. no diodes as a doubler) the voltage your caps will get
charged to is only 1.4 Erms. Peak to peak measurements are sort of
fictitious, because the maximum instantaneous voltage between the
terminals is only Epk, not Epk to pk. A peak to peak measurement
compares the voltage at the peak of one half cycle to the peak at the
next, some 8.3 mSec (or 10 mSec, as the case may be) later.
If you want to charge a capacitor (or any circuit) to the actual peak to
peak voltage, you have to store energy for that half cycle (done with a
pair of diodes and a pair of capacitors in a peak to peak voltmeter). A
voltage doubler does the same. A doubler will allow you to charge the
caps to 2.8Erms, for 4 times the energy per bang.
Just to confuse things more, there are actually two configurations for a
doubler, called, confusingly fullwave and halfwave. The first has the
two output caps in series, and essentially two half wave rectifiers, one
which charges one cap to +Epk, the other which charges to -Epk. The
other kind, which can be extended to many stages in the Cockroft-Walton
scheme, has one cap in series with the transformer output, and the other
across the output, so that on one half cycle, the series cap charges,
and on the other, the output cap charges.
The full wave scheme has better "regulation" under load (i.e. the
voltage doesn't drop as much) and the ripple is less. However, the half
wave scheme can have one output grounded, whereas in the full wave
scheme, the centertap of the output caps is grounded.
Thoroughly confused now?