RE: gap breakdown voltages

["Richard Kircher" <richard.kircher-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

John, All,
	The breakdown voltage of spark gaps is very predictable and repeatable.
In the old days, this is how high voltage was most often measured.  Even
today spark gaps are accurately calibrated to protect antenna tuners and
other high voltage devices from voltages beyond their design limits.  
	
	My favorite table is in an old ITT Reference Data for Radio Engineers, 4th
edition (1954).  I compared the spark gap data in the graph of this book
with what Terry posted from the CRC and they agree out to the 3rd place if
care is taken to make the proper adjustments for barometric pressure,
temperature.  

	At first glance the two handbooks looked different, but then I noticed
that the spark gap in Terry's posting was in units of cm while the ITT
handbook used inches.  Let's face it, physics is physics and there is
nothing different about spark gaps in Tesla Coils that makes them different
when used there. 

	Residual ionization will decrease the breakdown voltage and is probably
unique to Tesla Coil use along with local temperature build-up.  That's why
so many Coilers use a fan to move air across their spark gaps.  

	Old books, the older the better, are great sources of Tesla Coil type
design information.  I was lucky enough to find my old copy for 50 cents
during a library clean-out sale.  My newer version, that I use at work was
acquired at a Garage Sale for 25 cents and it was priced appropriately
compared to the information in the older one.  :-)

Dick


At 09:32 PM 7/29/00 -0600, you wrote:
>Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>One of the most "famous" spark gap tables was published for years in the
>CRC physics handbooks.  I don't know why they stopped publishing this table
>I used often...  I scanned it below:
>
>http://1071737050/site/misc/SGapVolt.jpg
>
>Cheers,
>
>	Terry
>
>
>At 08:18 PM 7/29/00 -0700, you wrote:
>>
>>Richard -
>>
>>You are correct there are many spark tables in electrical handbooks but they
>>are not particularly consistent. Spark length is dependent on many
>>variables. The electrical handbook tables are for specific conditions and
>>not for Tesla coils. That is why I made the graphs shown in the Tesla Coil
>>Design Manual. These graphs were made from real world Tesla coil data that I
>>had collected from coiler's information. All coilers do not agree on some of
>>this information.
>>However, no one else has published similar graphs so the TCD Manual graphs
>>will have to do for the present.
>>
>>John Couture
>>
>>--------------------------------
>>
>>-----Original Message-----
>>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>>Sent: Saturday, July 29, 2000 11:12 AM
>>To: tesla-at-pupman-dot-com
>>Subject: RE: gap breakdown voltages
>>
>>
>>Original poster: "Richard Barton" <richardbarton-at-caving5.freeserve.co.uk>
>>
>>Hi Chris
>>		You'll find a spark table on page 12-2 of the
>>Tesla Design Manual, by J H Couture. I have several other
>>such tables, but none of them a particularly consistent.
>>					Richard Barton
>>
>>-----Original Message-----
>>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>>Sent: Saturday, July 29, 2000 4:32 AM
>>To: tesla-at-pupman-dot-com
>>Subject: gap breakdown voltages
>>
>>
>>Original poster: CTCDW-at-aol-dot-com
>>
>>Hello all!
>>
>>I was wondering if there exists a chart giving approximate breakdown
>>voltages
>>through air. I understand that there are many variables, such as humidity,
>>electrode radius, etc, but  ballpark figure is all I am looking for.
>>This info is of interest to me in setting my safety gaps, and knowing about
>>where they would fire.
>>
>>Thanks for any assistance!
>>
>>Chris
>>