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Re: [Amps] Step start resistors

To: "Peter C," <peter.chadwick@Zarlink.Com>," AMPS" <>, <>
Subject: Re: [Amps] Step start resistors
From: R.Measures <>
Date: Mon, 5 Jan 2004 05:31:52 -0800
List-post: <>
**  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.  

cheerz, Peter

>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,
>Peter G3RZP
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