Hallo Leo,

designing primary mains side of DC-DC converter is always critical, and you need in any case some EMI filtering, especially if electrolytic capacitor of Erik's circuit is your main storage capacitor, like in the following schematic:




When connecting all three phases together, situation becomes a bit difficult. Either use three identical EMI filter + rectifier modules and connect them all in parallel to 150µF storage capacitor or connect Erik's circuit in front of DC-DC converter, ALREADY containing such an EMI filter. But then 1nF/1kV capacitors across three diodes and 150nF X-class capacitors paralleled by S14K275 varistors across each phase, is highly recommended. Also, some current limiting resistance might be useful, like in the schematic above.

An additional word to the circuit: Schematic was drawn only for discussing purpose!

Safety class 2 is used, means, that 0V must not be touched! Also, use only absolute safe and reliable Y-class capacitors for the two 1nF capacitors!!!!!!!

When 0V of circuit can be touched, saftey class 1 should be used. Then 0V of circuit must be connected to yellow green earth cable.



If filtering measures are two high, I would suggest the idea of Oleg, if I'm right. I have drawn it here:





The use of fuses and varistors seem to me to be essential. Contacts of relais do not like heavy overvoltages, at all! Capacitors shown are optional.

Advantage of this circuit is the great easyness. Advantage of Erik's idea is, that wasting of much power can be avoided.

Good luck,
Kai