# RE: Cap question (was H bridge RSG)

```Original poster: "David Dean by way of Terry Fritz <twftesla-at-qwest-dot-net>" <deano-at-corridor-dot-net>

Hi Ray,

The storage cap sees the full tank current while the gap is firing. Also the
storage cap must appear as a short to the RF of the tank so as not to be
included in, or affect the tuning. Thus the requirement for a very low ESR
in the storage cap.

Also in your example, "If Cs is 100 times larger than Ct (1uf/.01uF) each Ct
(tank cap) charging will only drain Cs (main storage cap) 1% of it's
charge." is true for the first presentation when the initial charge in the
tank cap is 0, however at the end when the gap quenches due to the
equalization of the voltages on the tank cap and the storage cap, the
voltage on the tank cap is equal and opposite in polarity to that of the
storage cap upon the next presentation. That makes the voltage to be
processed twice as much, and the energy transferred from the storage cap to
the tank cap four times as much.

later

deano

>
> Original poster: "Ray Haynes by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <ray.haynes-at-home-dot-com>
>
> I don't understand LR's comment about needing a "largish storage
> capacitor,
> also rated for RF; and the huge voltage reversals, probably +2V
> to -2V (I'm
> assuming he meant +/-2KV)". I agree with the largish part but not
> the rest.
>
> Here's my thinking. First I make a fullwave rectified HV supply using a
> large storage cap (Cs). My tank cap (Ct) is .01uF and RSG with a rate of
> let's say 600BPS (hoping). If Cs is 100 times larger than Ct (1uf/.01uF)
> each Ct (tank cap) charging will only drain Cs (main storage cap)
> 1% of it's
> charge. And at 600BPS that Cs gets fully charged (ideally) once for every
> five Ct charge cycles; the fullwave rectifier doubles the mains
> frequency to
> 120Hz and 600BPS/120Hz = 5. That seems to be roughly 5% ripple on the main
> supply cap which doesn't seem to indicate a need for any RF
> requirements for
> the large storage cap. Actually my simulations show more like 2%
> ripple due
> to the fact some Ct charge cycles are provided directly by the rectifiers
> (SG closes while mains are at a peak)
>
> Is there a flaw in my thinking?
>
> > -----Original Message-----
> > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > Sent: Saturday, May 19, 2001 8:02 PM
> > To: tesla-at-pupman-dot-com
> > Subject: Re: H bridge RSG
> >
> >
> > Original poster: "LWRobertson by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <LWRobertson-at-email.msn-dot-com>
> >
> > Hi Ray and Steve
> >
> > A classic coil discharges at some voltage, then
> > the RF oscillates around zero, approximately. The
> > H-bridge never stops at zero, but goes straight
> > from +V to -V, and oscillates there, adding the
> > RF amplitude to the DC voltage.
> >
> > Advantages are very reliable firing, it will never
> > power arc, and the primary voltage is doubled,
> > adding some oomph. I would think it should work
> > well for MOT power supplies. It can be run at any
> > speed.
> >
> > The disadvantages are the necessity for a largish
> > storage capacitor, also rated for RF; and the huge
> > voltage reversals, probably +2V to -2V almost.
> >
> > At the moment its running on a 8 inch rotary with
> > a maximum of 240 BPS. I'm (slowly) getting parts together
> > for a 12 inch which should be good for 360 BPS,
> > and ultimately hope to make a 22 inch with 24
> > electrodes. Expensive, though.
> >
> > Its a simple enough circuit - I'll be glad to send a
> > schematic if you want.
> >
> > LR
>
> snip.....

```