Re: Variac blowing fuses (another newbie questin)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: m.j.watts@xxxxxxxxxxxx 

On 29 Nov 2005, at 19:55, Tesla list wrote:

> Original poster: otmaskin5@xxxxxxx
>
> Thx for all the responses.  Several of you asked for more info in
> order to diagnose.  Here's the info.
>
> - The variac is supplying power to the NST only
>
> - Original fuse was 20A - don't know whether it was fast or slow
> blow.  Replacement fuse was 15A SLOW BLOW.  When it blew, the solder
> breached the fuse's glass cylinder.
>
> - The fuse blows after I've dialed the variac up to full power from
> zero. It didn't blow immediately - rather, the coil ran for maybe
> 10-20 seconds.  I believe the variac was up to full power.  Both
> times, the fuse blew during strong continuous arc to grounded
> target.  Hasn't happened when streamers were not striking
> anything.

Interesting! That mirrors an experience I recounted where years ago
I measured the power input to one of my SG coils with a power
meter and noted that arcs caused a power cunsumption jump of
about 30% or so. I never did figure the reason for that but since it
really does happen and knowing that an attached arc reduces
primary gap dwell considerably I surmise that the breakrate
increased to the 4Fmains range. To date it is my best shot at an
explanation.

Malcolm
I
 always power up starting the variac at zero.
>
> - The variac provides 0-130 volts out.  Current rating is 20 amp.
>
> - Fuse appears to be located in the input circuit of the variac (not
> totally sure as I wasn't able to get the cover off far enough to
> thoroughly examine the wiring).
>
> - I don't know whether the NST is a high power factor type or a
> normal.  I'll check with the
> mfg to see if I can find out.  In the mean time, it's a Franceformer,
> 15000 volt, 60 ma, 890 VA, model # 15060.
>
> - My tesla coil has a static spark gap.  9 gaps made of 3/4" copper
> pipe 0.03" for each gap.  So far, its wired to use only 4 gaps (0.12"
> total) and small fan for quenching.
>
> - The value of my tank capacitor is 0.03 uF +10%, 35KV.  I'ts the
> Maxwell cap you see on eBay quite often.
>
> - The variac works (as indicated by the voltmeter) without blowing
> fuses @ no load.  Also, I run my small coil (9/30 NST powered) using
> the variac haven't blown fuses.
>
> Hope this helps in figuring it out.  Thanks.
>
>
>
>