[Prev][Next][Index][Thread]
Re: Top Toroid
Tesla List wrote:
>
> Subscriber: FutureT-at-aol-dot-com Sun Feb 2 17:42:40 1997
> Date: Sun, 2 Feb 1997 12:34:58 -0500 (EST)
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: Top Toroid
>
> << << Hi Malcolm and all
>
> > I have been following with great interest the various posts on gap
> > losses but not always accepting the conclusions put forth. I assume from
> > your answer above that as the surge impedance goes down then the surge
> > current increases. Are you then saying that gap losses go up due to this
> > increased current? Doesn't this assume that the "resistance of the gap
> > while it fires remains constant?
>
> > My experience with synchronous gaps leads me to a different conclusion.
> >I feel quite sure that the current in a firing gap is a function of the
> > voltage in the cap as well as other factors. I note that the contacts in
> > my gaps run much cooler when the gap is firing near the peak of the
> > mains voltage. When firing ahead of the peak (by adjusting the gap
> > position with respect to the motor shaft) I notice that the gap pins get
> > much hotter. I attribute this increase in gap heating to increased
> > resistance in the gap due to a lower current/voltage. I believe that the
> > gap resistance is dynasmic and definitely increases at lower currents
> > which can definitely be controlled when using a synchronous gap. My
> > primaries usually are 3 to 7 turns and I think on the low impedance side
> > and therefore have low surge impedance. Still at 1800va input I have no
> > trouble using .25" brass contacts in the rotary and they give very long
> > life.
>
> > Flames and comments will be appreciated
>
> > Skip
> >>
>
> >Skip,
>
> >In the normal situation where the gap fires at full capacitor charge, the
> >input voltage has already passed its peak due to the shift in phase that
> >occurs when a cap is charging. The result is that the firing gap "shorts"
> > the power supply when it's at a low power point, and less transformer
> energy
> >is dissipated (and wasted) in the gap.
>
> >In contrast, when the gap fires "early", before the cap is fully charged,
> > the intantaneous transformer voltage may actually at its peak AC voltage
> > point. Shorting the transformer at the AC peak will burn up a lot of
> power.
> > This happens normally and occasionally in a NON-synchronous gap and is a
> > disadvantage. Perhaps this effect is what is heating your gaps, when your
> >sync-gap fires "early".
>
> >In a related matter, the longer the dwell time, the more power will be
> wasted
> > in shorting the transformer. In one non-synchronous experiment, I reduced
> my
> >dwell "distance" from 3/4" (considering the "overlap" of electrodes) to zero
> >dwell, by "offsetting" the gaps. My input power was reduced from 16 amps,
> to
> > 13 amps and spark length stayed the same. This is probably one of the
> >easiest ways to improve TC efficiency, BTW (in a non-sync system).
> >Ballasting, and resonant charging effects, and external series gaps, will
> >also determine how much power is wasted during this "power arcing". I
> >suspect that many of the ballasting difficulties in non-sync systems can be
> > traced to this "shorting at the AC peak" effect. This effect may create
> >the need for using a combination of inductive and resistive ballasting in
> > some high powered TCs to reduce tranformer saturation and possible
> >"thumping".
>
> >Taking this further, it would seem that a non-sync gap with a lower break
> > rate should be more efficient than one with a high break rate, since more
> >"full power shortings" will occur during each half cycle when using the
> high
> > break rate.
>
> > Regarding the gap resistance, it seems to me that a gap with low current
> that
> > fails to vaporize much metal would have a higher resistance.
>
> >Coiling for today and tomorrow, comments welcome.
>
> >John Freau
> >>
> After I posted, I thought about this some more, and wonder also if you may be
> seeing what Robert Jameson spoke about at an ITS Symposium: If your dwell
> time is relatively long, and your gaps are close, with no external series
> gaps, the gap may "refire" while the gap is still "presenting". The gap fires
> BEFORE the electrodes line up (due to close spacing), the cap discharges, but
> starts recharging, The gaps are becoming even closer as they whiz past each
> other, allowing the gap to "refire" at a lower voltage than normal. Since in
> the "early firing set up" of the sync gap, the voltage is rapidly rising,
> this could make the scenario more likely to occur. Robert found that when
> this undesireable "multiple firing" occurs, it causes heavy current and rapid
> gap heating. They heat due to this scenario: The cap can charge up, and fire
> the gap, charge and fire the gap, many times during one presentation. Each
> of these firings is at such a low energy level that very little energy is
> transfered to the secondary. Since the cap never charges very much during
> each "refire", the transformer is basically constantly forced to charge a
> mostly uncharged cap. The mostly uncharged cap draws terrific current during
> each multiple firing and rapidly heats the gaps.
>
> John Freau
John and all
I use only neons. The charge current is absolutely limited by the neon
to either 60 or 120ma(depends on neon being used). It would be
interesting if someone out there can calculate the time it actually
takes to charge a cap from a current limited neon. I have been unable to
come up with a formula which satisfies me. The formula would have to
assume a rated neon voltage and current and incorporate those parameters
in a formula which includes the cap value. With the timing determined ,
it would be easy to determine if multiple firings are even possible.
By the way , in some testing I have done, it appears that the neon will
put out its max current only when the input voltage is at maximum. At
say 60 volts input you can only get 30 ma from a 60ma neon. This must be
taken into account in any formula and has been a stumbling point for me.
Help anyone!!!!
Skip