RE: [TCML] NST Measurements

[G Hunter <dogbrain_39560@xxxxxxxxx>]

--- On Mon, 1/19/09, Jeremy <jeremy_runescape@xxxxxxxxxxx> wrote:

> From: Jeremy <jeremy_runescape@xxxxxxxxxxx>
> Subject: RE: [TCML] NST Measurements
> To: "TCML" <tesla@xxxxxxxxxx>
> Date: Monday, January 19, 2009, 12:20 AM
> measuring the output amperage is looking to
> be a pain. will a normal ammeter do the job or will the hV
> fry it's circuitry?

Most ammeters have very low internal resistance.  Therefore, it is reasonably safe to use them check the output current of an NST.  The ammeter will present a near short-circuit to the NST.  The NST will self-limit the current to no more than 30 or 60mA.  Ohm's Law prevents the ammeter from feeling more than a few mV.  I've tested many 30 & 60mA NSTs using a regular DMM set to the AC Amps function.  Every NST has measured within 2mA of it's data plate rating.

If you plan to try this, I suggest you connect the ammeter to the de-energized NST HV terminals securely, so the leads can't fall off.  Use alligator clip test leads or something.  Next, plug in the NST and observe your ammeter reading without touching or handling the meter or NST.  Unplug the NST before disconnecting the ammeter.

Never probe the bushings of an energized NST.  The HV will arc to the probe tips as soon as they are in range, instantly ruining your ammeter!  For testing purposes, unplug the NST to turn it off.  Do not rely on any switch, breaker, or pull chain.

Forgive me if I'm preaching the obvious, but we can't know who else might be reading along.

Cheers,

Greg


      
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