Re: Where can I find...

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "Matt Woody Meyer by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <meyerml-at-stolaf.edu>
> 
> Does anybody know where I might be able to find a reliable but still
> inexpensive motor for a SRSG?  1800rpm should be fine.

Others will answer this in gory detail, but what about a small bench
grinder. I've seen them on sale for $30...

You might want to try a triggered spark gap... At this sort of power level,
it might work just as well as a SRSG, and has the overwhelming advantage of
no moving parts, whirling blades of death, etc.  Lots of possible designs,
but they tend to be based on a cheap auto ignition coil (doesn't need to be
HEI or special... whatever you get at the junkyard for a dollar), a light
dimmer ($4), and a small motor run capacitor (a few uF).  Check the archives.


> 
> Also, does anybody know a good place to get capacitor oil?

First choice: a local "oil jobber"... look in the yellow pages... you can
get dielectric oil from all the major oil companies (i.e. Shell,
ExxonMobil, Unocal, etc.)  What you want is called "transformer oil" (there
are specialized capacitor oils, too., but regular old transformer oil is
easier to come by.  Univolt 60 is one tradename, Diala AX is another).  A 5
gallon pail should set you back about $25-30.

Second choice: a feed store, where you can buy mineral oil (used as a
laxative for farm animals) by the gallon

Other alternatives (less desirable to my mind, but others may differ):
Cooking oil (turns rancid with time), drugstore (mineral oil in
tiny/expensive bottles), motor oil (choose a "single weight" with minimal
additives... probably the cheapest thing they've got), hydraulic fluid, etc.

Note that some commercial capacitors use Castor Oil as a dielectric, which
has some benefits (twice the capacitance compared to mineral oil).

What ever kind of oil you use, keep it dry! (this is the real problem with
cooking oil.. nobody cares if it is 0.1% water for cooking, but it makes a
huge difference in electrical breakdown strength)

> 
> Just out of curiosity, how does the TC designer program go about calculating
> arc length?  9.7 feet seems a bit much from the coil I'm working on :)


Probably applying the empirical equation: spark length (inches) = 1.7 *
sqrt( input power in watts)...  Works fairly well, but bear in mind that
it's an idealized number.. 

you've got something like 120 mA -at- 12 kV or 1440 watts, which works out to
64 inches...  9.7 feet does seem like a bit much..... 4 or 5 feet is
certainly within reason, and 3 feet is almost a certainty...