inrush-current
I have a transformer with several secondaries, and this is how I'm planing to control the inrush current:
simulate this circuit – Schematic created using CircuitLab
I'm using a resistor to limit the inrush current and MCU will energize the relays after a few seconds to bypass the resistors.
Can I use a single resistor and relay on the primary to limit the inrush current instead of using a relay for each secondary?
How can I activate the relays without an MCU, using only analog circuitry?
No, that will not affect inrush current and in fact it's just a neon lamp + resistor to indicate power on.
For inrush current limiting you can use an NTC thermistor or one like this in series with the primary. It's imperfect though- the resistance drops when it gets hot so if the user flips the switch back and forth with it hot, you can get the fuse blowing if it's not an appropriate slow-blow fuse type.
Another approach is to put a power resistor in series with the primary and short it after a second or two with a relay contact. You must use a fusible resistor so if (when) the relay fails, the resistor will burn out without causing undue excitement, sirens, etc.
Edit: BTW, it's also possible that the problem is not the inrush current (especially if this is not a toroidal transformer) but sparking when the power is removed or the switch bounces. In that case, an MOV across the input 230V at the transformer (after the switch) and/or a surge protector on the devices that are affected may help.
As rioraxe says, D2 and D4 are backwards, and you're trying to charge the bottom bank of capacitors with the wrong polarity. They don't like this, and they're passing a lot of current. The voltage you measure before the relay closes is the result of the voltage-divider action of the 47Ω resistance and the leakage through the capacitors. This voltage drops as the capacitors heat up and the leakage current increases.
Then, when you throw the relay, there is nothing to limit the current. Fortunately, the diodes burn up before the capacitors explode in your face.
Best Answer
Putting inrush protection on a transformer primary is a pretty standard way of doing things because it also handles primary magnetization current inrush problems too.
Avoiding an MCU means having a small timer circuit that, when timed out (having been initially triggered by the instance of power being applied), activates the relay as you show in your diagram.
Or, you could avoid all the complication and use a negative temperature coefficient varistor/thermistor in series with your primary winding. This is a pretty standard solution in many power supplies.