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Re: NST Variations
Original poster: "Dale Nassar by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dnassar-at-i-55-dot-com>
I have found the same type of variation on dozens of NST's. I don't have
an instrument to directly measure the high voltage 60Hz output (I plan to
build a HV rectifier and filter and get it from the peak DC with a HV
probe, however.) BUT...I have found that this variation has, in no way
(for my units at least), had any adverse effect in phasing and paralleling
units for increased output current--in fact, they 'act' like the voltages
exactly match--every time--maybe I just got real lucky so far??
BTW, I have found that when removing shunts for increasing output secondary
current, that the NST's tend to sometimes hum really loud at 60Hz.
THE SOLUTION: I pot the (de-tarred) NST's in paraffin and the problems all
...thought some NST coilers might find this helpful.
At 03:19 PM 5/17/02 -0600, you wrote:
>Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> While doing preliminary resistance testing on a set of 15/60 NSTs of
>different origins, I noticed a couple of anomalies that might or might not
>have some significance. I expected to find some variation in coil resistance
>among different manufacturers, but a variation in secondary DC resistance of
>up to 32% seemed unusual:
>Franceformer: 4696 Ohms, Transco: 5897 Ohms, and Allanson 6612 Ohms.
> More puzzling perhaps, was the consistent variation between left and
>right halves of the same secondary. For consistency, I defined the "right
>side" as the one with the primary terminals. In France and Allanson cases,
>the right side had 3% higher resistance than the left side. In the Transco
>case right was 5.5% higher than left. Readings were checked at two different
>times with three different meters: Radio Shack 22-174B, Fluke 8000A, Fluke
>8275A with filtering. Repeatability variation was <0.4%. I realize that with
>only 3 transformers there is still a 1 in 8 chance of the left/right
>variation being simple random error.
> I am wondering if these simple tests could indicate compatibility for
>use in an NST "farm". If so, it could save people time and money (and
>strain). Has anyone else encountered this phenomenon? I will be running AC
>tests this weekend.