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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I removed the GFCI box from the NST and this is what I found:
The GND does not appear to be connected to anything. As for the "e" (I assume this is "Earth"), when I set my DMM to diode test, put the negative probe on the Earth and positive to either of the HV terminals, I get over range reading. BUT when I swap the probes, I get around 1.8V to both of the HV terminals. On the resistance range, I get way higher reading than the expected 3kOhms (the hot-hot resistance is 6kOhms).
Now to the question: The NST is 6kV midpoint grounded. Is it possible to get 3kV (hot to midpoint) at full current from this transformer? Why do I get a reading on the diode test in just only one direction, are there any semiconductors hidden inside the potting or what?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The "e" terminal should be the midpoint of the HV winding. If your DMM is confused, it's probably because of the high inductance of the winding. Try turning off the autoranging.
You should be able to get 3kV between "e" and either HV terminal, but don't expect the "e" terminal to stand 3kV with respect to the core and primary windings.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Thanks Steve, the weird thing is that I get a "normal" 6.3k reading between the HV terminals but I don't get any reading between "e" and either of the HV terminals (in one polarity I get OL reading, in the other it's 4.5Megs), so there must be "something" inside between the terminal and the mid-point. I'm afraid to draw arcs to it because something could fry...?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The screw holes above both the Earth Ground symbol, and the letter E appear to have been partially filled in with epoxy or similar. Perhaps the transformer has been modified or even tinkered with.
I don't understand your diode function tests. Should there be any diodes in the output of what is intended to be AC supply?
Why not put a fuse in the input side, and then switch it on and measure the voltage and current available from each end of the secondary?
Make yourself a 10:1 voltage divider if you only have a 1kV DVM. It need not be wonderfully accurate to give you the gist of what is going on.
A 10M/5W HV resistor connected between the two ends of the secondary should draw about 600uA if all be well.
Make sure that there is an unmeasurably high resistance (more than, at the least, a few hundred megohms) between any of the primary inputs and any of the secondary outputs.
Is the secondary centre tap electrically continuous with the mains Earth on the input side? Product approvals for this kind of kit are quite stringent, so if it says 3000-0-3000 on the case, it should not be possible, by any miswiring by the ordinary consumer, for a voltage of 6kV to exist between either secondary terminal and Earth.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Also, if you want to measure the current, just put a 10 ohm resistor in parallel with whatever output (hv-'midpoint', or hv-hv) you want to measure. Measure the voltage across the resistor, for every volt you read there should be 100ma flowing. Or did i mess that up again.
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NST connections
