On 15 Jul, 09:23, "N Cook" wrote:

Toroidal , not E-I lamination transformer
I'm coming around to thinking 5 amp anti-surge in the mains fuse-holder and

whatever fuse the toroidal gets needs to be antisurge. Toroids are
known for their sometimes heavy inrush.

This will give no protection to the output devices of course, it
really will be nothing more than basic fire protection.


a 5 amp fuse shunted in the + and - rail traces from the DC side of the
bridge rectifier before the reservoir caps, but undecided whether quick-blow
or anti-surge ones there.

You'd get much better fuse response if you put them after the
reservoirs, because they dont then need to handle high peak cap
charging currents.


I'm just trying to engineer a more respectable equivalent of fuses for trace
rupture.
Eventually one DC rail ruptured as a fuse. I've now decided to do some
calculation to determine what the rupture current for that trace was.

Then as the common return almost fused and is the same dimension but in the
even worse case then carries twice the current

worst case is 1x not 2x. The common psu rail carries near zero if
similar fault currents flow in both + and - rails.


, halving this trace rupture
current to use as the fuse rupture current and reduce that for current
carying capacity , by half again ?

If all output trannies fused short circuit all round so loading both DC
rails the combined common return would have ruptured at whatever that
rupture current is for the trace that did burn up.

then there would be near zero current in the common rail.

Anyone know the term for laying double traces of solder along copper traces
to increase current carrying , so I can research it ?
I'm intrigued how you lay quite accurate molten solder runs and parallel
over and with existing traces.

I dont think I've ever seen any attempt to do it to accurate
dimensions. Neither flow soldering nor hand soldering work like that.


Copper fusing current of the trace = 12 amps
Lead+Tin elipse then 6 amps (not as much as I would have intuitively
thought)
Total 18 amps

No, because cu and slobber blow at very different temps. 18A probably
wont even be close.


I'm left wondering precisely what youre trying to achieve. If youre
trying to protect output devices, none of the above will do it. If
youre trying to protect speakers, the above are not whats wanted. If
all you want is to prevent charring of pcb due to repeated blowing,
its going to be cheaper in the end to prevent the repeat blowing.
Really whats propsed so far doesnt seem to solve any real world issue.
The amp sounds roughly designed, intended for a limited service life,
and to change that you'd need to add a full set of current and safe
area protection for the output devices, almost none of which can be
achieved with fuses.

What are you really looking to achieve?


NT