Re: [TCML] Coax Capacitor

[Jim Lux <jimlux@xxxxxxxxxxxxx>]

-----Original Message-----
>From: Chris Swinson <list@xxxxxxxxxxxxxxxxxxxxxxxxx>
>Sent: Nov 23, 2007 4:48 AM
>To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
>Subject: Re: [TCML] Coax Capacitor
>
>
>----- Original Message ----- 
>From: "Ben Sneath" <bsneath@xxxxxxxxxxxxxxxx>
>To: <tesla@xxxxxxxxxx>
>Sent: Friday, November 23, 2007 11:01 AM
>Subject: [TCML] Coax Capacitor
>
>
>>a rather silly question i suppose...
>> has anyone tryed coax as a tank capacitor, i think its 10 pF
>> per foot... it'd be good up untill about 15kv would it not?
>> as for inductance, its in the 10's of uH range. you could
>> buy a roll cut it into 1' lengths, solder to a pair of end
>> plates...
>>
>

Actually, the C depends on the kind of coax.. 20-30 pF/ft might also be reasonable.  But it's a LONG way from 20pF to, say, 50 nF. (2000 ft long) and the IR losses would kill you.





>I think you will need a lot of cable to get even to 10nF value. Also coax 
>usually has air gaps which will ionise and lower the voltage to maybe just a 
>few hundred volts...


Again, depends on the coax. Solid dielectric coaxes (like the old RG-8 or RG-213) can take 10s of kV.  RG58 is probably good to several kV.  Foam dielectric low loss Cable TV coax (RG-6 types) isn't all that great from a voltage standpoint.

Mind you this is NOT the rated voltage of the coax. That's quite a bit lower (RG-213, for instance, is 5kV RMS)

Jim
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