On 3/30/2011 8:07 AM, N_Cook wrote:
This 300W amp blows correct T3.15A fuses every now and then at sw on. The
owner left in the last one so I can see it is just "tired" , neat break and
2 constituent parts of fuse wire remaining.

Any issues concerning putting in an ex pc SMPS 450W, 250V land mains inrush
thermistor, unknown specs, other than 14mm diameter, 4mm wide , 1mm diam
leads, 8R cold , 1R after 20 seconds touched by soldering iron barrel. Other
than poor physical integrity of the lead "welds" to the body (like disc
ceramic cap) - will mount on small high temp board and wire into the neutral
side of the wiring, with plenty of clear air space around.

Other than zero crossing Triac sub-cicuit to delay sw off, not creating
ferrite core residual magnetism, and delayed switching on also, any other
ways around this phenomenon other than bad practise uprating of the mains
fuse? Are polyswitches used in these circumstances , ie not purely "fuse"
action or generic name for devices specific for this purpose?



Nigel,

Also keep in mind as a possibility that the main filter caps are
getting tired, and a bit leaky, so that if the amp has not been switched
on for a week or 2, it might have abnormally high inrush current as the
caps charge/form back up.

Lastly, the older 'spring wire' fuses seemed more tolerant of the
inrush current compared to the modern chemically treated wire ones.
Maybe use an old style fuse, if you can find one.

It would be helpful if you would mention the make and model of the
product in your posts.

Regards,
Tim Schwartz
Bristol Electronics