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Re: [TCML] Primary short



I was in the middle of a test after adjusting spark gap, when the sparking suddenly ceased. I disconnected the primary wiring, and the secondary wiring, and measured secondary to gnd as 8 ohms either side, and total of 17 across entire secondary. Then I hooked up primary with series ac ammeter, an when raising input with a variac, the current started to rise to 3 amps with variac at about 3, and no ac voltage at secondary. Obviously, increasing input beyond would blow breaker. I understand secondary damage, but primary short does'nt make sense to me. Thanks Dave ----- Original Message ----- From: "David Rieben" <drieben@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, January 19, 2010 5:34 AM
Subject: Re: [TCML] Primary short


Hi Dan,

I assume you're referring to the measured DC resistance of the
primary side of your NST? Actually, the .7 ohms sounds about
right, as the operational AC "resistance" is a function of the induc-
tive reactance of the primary coil and the frquency of the AC in-
troduced (assuming 60 hz in this case). Have you actually hooked
the NST up to 120 volts AC or whatever its rated input is? Unless
it immediately trips the service circuit breaker (or blows the fuse)
then I would say that your NST is fine.

David Rieben


----- Original Message ----- From: <ag2z@xxxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, January 18, 2010 9:42 PM
Subject: [TCML] Primary short


Has anyone out there ever had a 15kv/30ma NST suddenly develop a shorted primary during a short test? Less than one minute. The resistance of the primary became .7 ohms. Secondary is intact on both sides. This is an old Gardiner NST with spot welded bottom plate. Primary connections are along the lower part of case making access very difficult. Thanks. Dan
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