The SoftStart is a simple compact mains current inrush limiter. It's purpose is to restrict the initial huge current surge through the transformer that occurs in the first 100mS or so after switch on.  
 
In operation it places a pair of 5W power resistors into the mains-transformer primary circuit for a few hundred milliseconds until the surge current has mostly subsided. As this is charging the power supply from which it derives it's power, the circuit senses the charging of the capacitors and switches a 10A relay to bypass the power resistors for normal operation, once partially charged.
 
The unit has an LED added which will fade as the relay drops and can be used as a remote LED if needed.

 

softstart.jpg
Voltage 240V/ 120V AC mains (to order)
Rated up to 500VA with +/-23,500uF 63V tested
Delay typ 500mS
Supply 30 -75V DC (single only needed)
Dimensions 35mmW x 50mmD x 25mmH