Re: Vacuum jar rotary spark gap / thyratron (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 16 Aug 2007 17:20:23 -0700
From: huil888 <huil888@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Vacuum jar rotary spark gap / thyratron (fwd)

Gary -

I'm not sure if this is entirely true ....

I have watched a dry-pig-powered coil in operation that utilized a single 
vacuum-contactor (mechanically operated, high-voltage, high current switch) 
as a "sealed" static spark gap. In their intended use as a switch for very 
large AC motors, the vacuum extinguishes the arc at the zero-crossing of the 
AC current as the contacts are separated. Normally the contacts are pulled 
apart rapidly to open the circuit, but in the Tesla coil application the 
contacts were mechanically held at some small fixed distance to function as 
single static gap. One end of the ceramic vacuum bottle is sealed with a 
metal bellows to allow one contact to be moved. Typical ratings are 400-800A 
at 7.5KV, with a flashover voltage of 40-60 KV. Currently, there are a 
number of 3-phase vacuum-contactors listed on eBay,  and also several sets 
of the vacuum-bottles themselves (search "vacuum contactor").

In my desktop mini-coil I use a series of Victoreen 2.5KV vacuum 
surge-supressor spark gaps (at least I think they are evacuated) as a 
multi-segment static gap, and the coil runs very well. The small (~1/2" dia 
X ~2" long) ceramic-cased gaps heat up fairly quickly, but seem to quench 
quite well.

Regards,
Scott Hanson

----- Original Message ----- 
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, August 16, 2007 3:08 PM
Subject: RE: Vacuum jar rotary spark gap / thyratron (fwd)


>
> ---------- Forwarded message ----------
> Date: Thu, 16 Aug 2007 16:07:35 -0400
> From: "Lau, Gary" <Gary.Lau@xxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: RE: Vacuum jar rotary spark gap / thyratron (fwd)
>
> The biggest problem with a gap in a vacuum is that air is a necessary
> component of a spark gap.  It's the plasma between the electrodes that
> conducts the current through the gap.  No air, no plasma, and no
> current.
>
> If your spark gap is louder than the sparks coming off your top load,
> then something is seriously wrong.  There's no such thing as a quiet
> coil.
>
> Regards, Gary Lau
> MA, USA
>
>> From: Timka <tomasdoc2002@xxxxxxxxx>
>> To: tesla@xxxxxxxxxx
>> Subject: Vacuum jar rotary spark gap / thyratron
>>
>>
>> Anyone tried before to make a vacuum jar rotary spark gap?
>>
>>   I have a nice deep vacuum pump and I'm thinking to make a rotary
> spark gap
>> using 10,000 rpm hard drive motor with attached tungsten electrodes.
> Everything
>> will be assembled and placed under a thick and large plastic jar from
> which I would
>> pump all the air away.
>>
>>   Since that motor is DC I can change RPM with voltage and it also has
> a nice Hall
>> sensor build in, which I can use to monitor RPM with external meter.
>>
>>   I'm doing it because I'm tired of spark gap noise, so I think that
> if I create above
>> mentioned enclosure it would help to ease stress to my ears.
>>
>>   Any suggestions and constructive criticism would be extremely
> appreciated.
>>
>>   Also,
>>
>>   As a part of tube exercise I also decided to give it a try with
> thyratrons instead of
>> spark gap. It seems that thyratron tubes are relatively easy to set up
> as spark gaps
>> using proper drivers. I have a nice thyratron driver (NanoFast 204-7
> Trigger 3.5KV).
>> Does anyone know if there any limitations on tubes to be used?
>>
>>   Again, suggestions and constructive criticism would be extremely
> appreciated.
>>
>>   Many thanks,
>>
>>
>>   Tim
>>
>>
>>
>>
>>
>>
>> Tesla list <tesla@xxxxxxxxxx> wrote:
>> ---------- Forwarded message ----------
>> Date: Thu, 16 Aug 2007 17:00:06 +0100
>> From: Chris Swinson
>>
>> To: Tesla list
>> Subject: safe capacitor discharge times ?
>>
>> Hi all,
>>
>> Was thinking today, Electrolytic capacitor and current ratings. Of
> course if
>> you wack a screw driver across it, will discharge faster than
> capacitor
>> rating (10amps is about as good as I have seen, maybe 1amp for smaller
>> values), capacitor will be damaged in anycase trying to give a large
> high
>> peak amp pulse, could heat up or even explode...
>>
>> so onto my question, if I have a pulse of 100amps, but the rise time
> is only
>> 1amp per uS, instead of a 100amp rated capacitor, could a 1amp one be
> used
>> instead ? It would in effect draw 1amp for 100uS for example but has
> passed
>> 100amps in total.
>>
>> Cheers,
>> Chris
>>
>>
>>
>>
>>
>>
>>
>>
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