[kipman725]

I am building a power supply for a monster quadrophonic sub amp that has 60mF of rail capacitance a 640VA toroidal transformer. Can I get away with just using an NTC current limiter to limit the inrush and use a slow blow fuse or would something more elaborate be recomended?

 

[amb]

Your choice of the NTC thermister is crucial. It must be rated high enough in current and low enough in resistance after warmup not to become a bottleneck (and cause voltage fluctuations as current demand changes).

I tend to prefer using a large, fixed power resistor (say, 5-10 ohms) in series with the hot AC line into the transformer primary. Then, I use a time delay circuit to drive a relay (with high current contacts) to short out that resistor after a few seconds. This accomplishes the current limiting but gives you very low resistance afterwards, and does not heat up like a thermister would. The downside is more complexity.

 

[kipman725]

Probobly the best idea to use a timer of some sort as it's a sub amp so sometimes it will just sit there drawing minimal power and if the amp is turned on and off suddenly the thermistor is not usefull. I was planning on having a microcontroller in there anyway for volume controll.

 

[peranders]

Out there you have many softstarts and the best solution for you is a resistor in series which will be shorted after 0.5-2 seconds. My solution gets it's power from the mains but you can solve this in a number of different ways. I have also used a time relay, Elesta, together with a resistor. Since you have a toroid transformer the reset time is important.