** I use a minimum value of R that - when added to the transformer
primary R - does not exceed the mains circuit-breaker (or fuse) ampere
rating. For example, a Heath SB-220 has 10A breakers and c. 2-ohms of
primary R when wired for 240V. Thus, to limit inrush-I to 10A, the
stepstart R needs be at least 22-ohms total.. More R adds step time.
As stepstart-R keeps increasing, at some point, the HV will stop rising
before it reaches the desired 60% level which closes the stepstart relay.
In other words, mo' is not always mo' betta.
- The typical delay time for a stepstart using a value of R that limits
inrush-I to the circuit-breaker rating is a bit under 1-second -- which
is about the same time it takes for a thoriated-tungsten filament/cathode
to reach full emission.
>Any ideas on what values to use for step start resistors? In the past, I've
>tended to choose a value from the available stock - something like 50 ohms,
>100 watts, which limits the surge current to just over 4 amps. I expect
>that a value such that the current won't exceed the full load primary
>current of the transformer is probably best, but any suggestions?
>(I'll probably still use what's available in my stock of vitreous enamelled
>wirewound resistors about 10 inches long and an 1 inch in diameter,
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