Increasing C2 seems to allow for lower operating voltage.
4uF looks to be right with a 40V rail voltage.
You want the relay to click on properly but also limit D5 current.
If C2 is to high the current at D5 becomes too high which could burn it, with C2 too small the relay might not turn on.
R3 and R4 should probably be adapted for the higher current but lower voltage.
It becomes a pretty neat circuit used this way. C1 and C2 becomes a voltage divider without dissipating any real power.
Really large transformers might still have problem with inrush current even when load is in series with resistors. But this will still take care of large load currents into capacitors.
4uF looks to be right with a 40V rail voltage.
You want the relay to click on properly but also limit D5 current.
If C2 is to high the current at D5 becomes too high which could burn it, with C2 too small the relay might not turn on.
R3 and R4 should probably be adapted for the higher current but lower voltage.
It becomes a pretty neat circuit used this way. C1 and C2 becomes a voltage divider without dissipating any real power.
Really large transformers might still have problem with inrush current even when load is in series with resistors. But this will still take care of large load currents into capacitors.
Yes that is correct. Direct mains connected equipment is dangerous!
My own personal viewpoint is that NO mains potential wiring or circuitry should be exposed. That is everything should be carefully insulated. This is based on my own experience as a teenager, accidentally touching on live mains connections that were not properly insulated. Lucky for me I only got some minor burns, but I could equally have wound up dead.
The problem that I have personally with this type of circuit is that components on the circuit board are at direct mains (read lethal) potential.
I think that the original rule was aimed at high current power supply's ie where say the amps rails were running off directly rectified mains, which is an even more deadly proposition.
There is some contention over the type of circuit presented (if the diode bridge is running directly off the mains) in that the diyAudio Store has a similar soft start circuit for sale. It has been the subject of quite a bit of discussion offline and there is still not a firm decision on it.
As I do not wish to present a double standard, at this stage I will say that anyone doing this should be very careful, and I would encourage them to put the soft start circuit in it's own insulated enclosure, just to remove the risk of accidental contact with lethal mains voltages. However I will not close the thread at this stage due to the above mentioned contentious item. As David_Web suggested, running the soft start off the secondaries would seem a better option. Rod elliot has a good article on soft starts on his pages --> http://sound.westhost.com/project39.htm
edit: I didn't realize that the thread had actually been closed at the request of the OP.
Tony.
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