[ARC5] NC-270 Success

[Kenneth G. Gordon]

On 10 Dec 2016 at 7:02, Scott Robinson wrote:

> If your power transformer gets hotter at 122V than at 110V, as in the 
> example below, the iron in it is probably saturating at the higher 
> voltage, considerably raising the primary current.  Feeding it 100V is a 
> good idea.

There were several articles in Electric Radio Magazine concerning both the NC-270 and the 
NC-190 which uses, as I remember it, the same power transformer.

It was discovered that the power transformer was "marginal" at even 110 VAC. The authors 
of those articles used several methods to reduce the load on the transformers, but the final 
solution was to operate them at reduced input voltages, and at least no more than 110 VAC.

I prefer a bucking transformer when I need to reduce our line voltage here. I have several 
Variacs, including one HUGE one, weighing well over 100 lbs, which was used to control 
the input voltage to a large X-ray machine. The Variac is capable of well over 5KW.

However, it is easy to forget where one has the control set with a Variac, while the bucking 
transformer is fixed at one "setting". This reduces the chance for "operator error".

In addition, larger Variacs must use some form of "step-start" to prevent tripping line 
breakers almost every time they are turned on. I have a larger Variac which I use on my 
bench, and I had to add TD relay and a large resistor to that one to prevent having to reset 
the breaker which fed the bench every time I attempted to use it.

I MUCH prefer bucking transformers for this use.

Ken W7EKB

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