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Re: [TCML] Calculating transformer output at lower voltages

On 6/8/12 3:54 PM, mddeming@xxxxxxx wrote:

Hi Gary, Jim, All,

I ran a test like that about 7-10 years ago using a pair of Triplett 630-A meters on the HV side (they have a top 6KV AC scale), and a Radio Shack 22-147B on the low voltage side to measure the respose in the "forward diection". I ran 0 to 48 V input using one 630-A then 45V to 95V input using a 630-A on each side of ground. These two plots were very colinear. I then tested it "backwards" using two of the RS 22-147Bs from 140V down to 0 V on the secondary and got a second plot which was fairly linear, but NOT Co-linear with the first two.
The 147Bs were calibrated before and after against a Fluke 77 series II and showed less than 1% deviation over the 0-140 V range.
I suspect that putting low voltages on the secondary may not create the same magnetizing effect as a low voltage on the primary due to the physical layout of coils and core especially with current limiting gaps. But if one is looking for only a "ballpark number", the reverse method should be OK.(~10-15%).

and in reality, they only make NSTs in certain turns ratios..

120V:15kV	1:125
120V:12kV	1:100
120V:9kV	1:75	
120V:6kV	1:50

So a pretty rough measurement will tell you which one you've got AND whether one of the secondary windings is shot.

Where this all becomes more interesting is when you get the mystery HV transformer at the surplus place.
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