Re: OLTC Thoughts

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

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.

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
>