Re: OLTC Thoughts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Terry,

On 11 Aug 2002, at 23:01, Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi,
> 
> There has also been discursion off list about the fact that when I turn the
> IGBTs off, the reverse diodes will still be active.  I "think" it will not
> be a problem at all.  For the energy to get back into the primary, the
> primary circuit has to be tuned to Fo.  With just the anti-parallel diodes
> in the primary circuit, the "tuning" will be devastated and the primary
> should simply not be able to re-absorb the power.  Thus, the energy will be
> trapped in the secondary.

A voltage will be induced in the primary as the secondary continues 
to oscillate. They key is whether that voltage matches the C-E 
voltage as the power supply charges the caps back up. If it doesn't 
on the first cycle of secondary oscillation after the IGBT drive has 
been shut off, it should provide a clean break. Some years ago I did 
all this with a bank of MOSFETs to investigate some of the Corum's 
claims. My primary voltage was a rather modest 30V but the secondary 
succeeded in generating thousands. The important point is that 
shutting the gate drive off seemed to work despite the body diodes in 
the FETs.
     I found no evidence to support the Corum's claims of "coherence" 
BTW ;)

Regards,
malcolm
 
> This is just a theory still.  I have nick named it the "Winston effect"
> since Winston brought it up to me ;-)
> 
> Also, if one uses the individual IGBTs to tune the coil.  The "off" cap
> will just charge negative through the anti-parallel diode and fall out of
> the circuit.
> 
> If it does not work, Dave's CEEC configuration would, but at twice the
> power loss (not a big deal) and twice the cost in IGBTs.  Hopefully, the
> single IGBT solution will work.
> 
> Cheers,
> 
> 	Terry
>  
> 
> At 11:09 PM 8/11/2002 -0500, you wrote:
> >Richard, Antonio, and all,
> >
> >I've seen Richard Hull's thyratron powered coil in operation, and as
> >Rich Wall indicated, it only began to do an energy transfer from primary
> >to secondary, firing for 1/2 cycle, and then shutting off. It used a
> >small hydrogen (H2) thyratron (type 3C45) with no reverse conduction
> >diode. So, when fired, it conducted for the first half cycle, then shut
> >off at the next current zero crossing. There were many discussions about
> >using hydrogen diodes or high current high voltage rectifiers to conduct
> >the primary's reverse current since most thyratrons don't do this very
> >gracefully or for very long. For a complete energy transfer, multiple
> >triggers would be necessary, one for each positive half cycle until the
> >primary to secondary energy transfer completed. The beauty of the H2
> >thyratron switch was that is could quench "on a dime", permitting
> >tightly controlled quenching experiments. By triggering only once, only
> >a relatively small amount of energy was actually transferred to the
> >secondary. 
> >
> >By using the MOSFETS to provide forward primary current, and then using
> >a high current diode to conduct in the reverse direction, Terry's OLTC
> >offers the capability to simply, yet tightly, control the degree of
> >quenching. 
> >
> >Best regards,
> >
> >-- Bert --
> >-- 
> >Bert Hickman
> >Stoneridge Engineering
> >"Electromagically" Shrunken Coins!
> >http://www.teslamania-dot-com
> >
> >
> >Tesla list wrote:
> >> 
> >> Original poster: "Wall Richard Wayne by way of Terry Fritz 
> ><twftesla-at-qwest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>
> >> 
> >> Antonio,
> >> 
> >> > > Richard Hull's H2
> >> > > thyratron magnifier, by necessity, quenched at the first zero crossing
> >> of
> >> > > the wave form.  So only the positive half of the energy cycle was
> >> passed to
> >> > > the primary.  While a very interesting design, it is not a spectacular
> >> > > performer, if one measures performance by spark length.  It's a
> >> phenomenal
> >> > > research device though.
> >> >
> >> > This is quite strange. A Tesla coil, or a magnifier, can't operate
> >> > correctly without at least two polarity reversals in the primary
> >> > current.
> >> > If the current is interrupted after the first half-cycle, only a small
> >> > fraction of the primary energy is transferred to the secondary.
> >> > Where is this magnifier described?
> >> 
> >> Yes, it does seem quite strange.  Even though with only one half cycle
> >> there is still some energy transfer.  The coil does spark and has a
> >> peculiar harsh audible hum.  But, overall performance is inhibited.  I
> >> posted this point because Terry's OLTC will have similar very quick
> >> quenching which may inhibit expected performance.  I have no doubt he will
> >> figure out timing problems though.  A fly back diode on each switch will
> >> get it through one complete cycle.
> >> 
> >> Richard Hull designed and built this thyratron maggey.  He has
demonstrated
> >> it at the TCBOR Teslathon.  I'm sure many on this list have seen this coil
> >> in action.  Richard is no longer on this list, but I'm sure he would
advise
> >> you where it's written up.
> >> 
> >> RWW
> >
> 
> 
>