I guess I'll chime in with my limited input. Why not
use simple "Inrush Current Limter thermistors ? I use
them for my 4-1000A amp and my 7.5Kv power supply.
Very simple to install and ver efficient. Purchased
from Digi-Key,Mouser or even RF Parts.
http://www.ametherm.com/Inrush_Current/welcome.html
*****************************************************
--- Ian White GM3SEK <gm3sek@ifwtech.co.uk> wrote:
> Han Higasa wrote:
> >GM all
> >
> >As Steve told whatever loop (open or closed) has
> been chosen
> >a situation where a relay contact will not close
> and inrush-current
> >limitation resistor R will never be shorten can
> happen.
> >
> >To address this a "step-start duration" timer
> should be added;
> >and to monitor this a "step start duration timer"
> timer should also be?
> >
> >Instead, robust R and an operator can do this by
> perceiving
> >"it takes too long and the step-start never lasts"
> >
> >I am using a 30-ohm 100-W resistor for the R now.
> >I think I should disconnect my step-start delay
> timer and measure
> >the voltage across R in time elapsed, to make sure
> the R will not
> >barn out.
> >
>
> A much simpler solution is a slow-blow (T) fuse in
> series with the
> current limiting resistor. This idea has been used
> by Alpha and others
> for many years.
>
> The fuse rating can be about 25% of the long-term
> short circuit current,
> eg for 230V and 30 ohms it could be a 2AT fuse. If
> the normal step time
> is less than about 1 second, this fuse will never
> blow unless the
> step-start "hangs". The step-start resistor must be
> capable of handling
> the "hang" current (the steady value when the
> resistor is tuck
> permanently between the mains and the amplifier) for
> the several seconds
> that it takes to blow the fuse, but it doesn't need
> to be rated to
> survive forever - the fuse will protect it.
>
> Incidentally, most step-starts are much longer than
> they need to be, as
> the big current pulses only occur during the first
> few cycles of the
> mains. The aim should be to make the first and
> second current surges of
> equal size, so that neither one is "worse" than the
> other. A very long
> step time doesn't really help with this - it doesn't
> affect the size of
> the first current surge, and doesn't do much to
> reduce the second
> current surge, but it puts much more stress on the
> resistor.
>
>
> --
>
> 73 from Ian GM3SEK
> http://www.ifwtech.co.uk/g3sek
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>
Mike-KK4MS
a_borg@yahoo.com
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