Inrush/softstart

[Dennis Brady]

The simplest softstart IMHO is a DC relay with high impedance coil,
in series with a resistor, then series that with the diode ( 400 PIV ) and
connect an electrolytic capacitor across the relay coil. Connect this
across AC line of whatever you want soft started.

The relay only needs to be a SPST,( normally  open ) as minimum useable
relay.

Put the relay point(s) in series with the AC line of the filaments xfmr, for
example. The last part is a resistor or bulb across the relay points.

The delay time is a function of the combination of values of the parts
you use. For filaments, you only need to delay "a couple" of seconds.
I usually try for 2-to-5 seconds. The value of the resistor across the
relay points adjusts how high the startup voltage is.

This 'lashup' is obtainable from junk-box parts and has a very wide range
of  delay time. I had to resort to this for my transmitters because the
RF was getting into the solid state modular control blocks I used at first,
causing the filaments to bright/dim while I was sending.

73 de W5FRS
Dennis

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