Simple Mains Rectifier Failed (Is it ESR?)

[Psi]

Also note that 240 * sqrt(2) = 340 so any capacitors across the supply should be rated for at least 340 V.

Keep in mind though, that X rated or mains filter caps often give the voltage in AC already.
It's pretty normal to see 275VAC written on mains filter caps.
Some caps even show both AC and DC ratings, like 275VAC / 600VDC

The DC voltage for a mains filter cap is often significantly larger than Vmain * sqrt(2) in order to deal with spikes and surges.

[IanB]

Keep in mind though, that X rated or mains filter caps often give the voltage in AC already.
It's pretty normal to see 275VAC written on mains filter caps.
Some caps even show both AC and DC ratings, like 275VAC / 600VDC

The DC voltage for a mains filter cap is often significantly larger than Vmain * sqrt(2) in order to deal with spikes and surges.

Thanks. I may have seen something similar written on the large unpolarized capacitors found in old style fluorescent tube ballasts. Back then a mains rated 8 uF capacitor was as big as my hand with two nice big screw terminals spaced well apart.

[Mechatrommer]

Watch the voltage rating of all the resistors

if i violated this rule, what could happened? i believe those resistors will die. correct? but not in this case.

You can minimize fireworks if you use a low energy supply for testing. Put two small transformers back to back to make an isolation transformer. Then even if you have an accidental short there won't be enough power available to make flashes or bangs.

thats is certainly a good idea. but my point is the reasom why the bang occured. if i used your method, then everything will be ok until the project completed, every parts are in the board get ready... but then if the root cause is not solved, when the whole circuit is being put in real mains supply, the whole may go bang wasting everything. i dont mind the bangs i kind of used to that its just small wire. i'm trying to figure out this mystery why? but i guess some have already given the possiblities for that.

Now if the components are all OK, the cap will charge up _slowly_.

i havent checked if the cap is charging up properly since i didnt put series resistor. but i did check if it can hold charges, yes it was 330V and slowly discharging.

[IanB]

thats is certainly a good idea. but my point is the reasom why the bang occured. if i used your method, then everything will be ok until the project completed

Everything will probably not be OK. If there is a circuit fault it will likely show up as a failure to operate properly. You will be able to measure incorrect voltages and take corrective action before the leakage or short circuit current becomes catastrophic.

Testing on a low energy supply won't necessarily help to catch poor construction quality, but it will catch many instances of circuit design faults, wiring errors, bad connections or faulty components.

[SeanB]

Add the nice big 4R7 ceramic surge current limiter you find in power supplies to the input. that will at least limit inrush current and will help.

[saturation]

This is a simplest and safer way and better than just a current limiting resistor.  You can use a function generator to test your design then scale everything up ... or to save time, you can build a working prototype from the transformerless design thread based on the Microchip app note:

https://www.eevblog.com/forum/beginners/ltspice-help-transformerless-power-supply-simulation/msg33779/#msg33779

The reference to the above is TB008 is no longer available on Microchip's site [ you can read complaints about its safety] nevertheless is quoted everywhere and copies elsewhere:

http://ftpserver.org.ru/fileecho/51_EMBED/91008A.PDF

thats is certainly a good idea. but my point is the reasom why the bang occured. if i used your method, then everything will be ok until the project completed

Everything will probably not be OK. If there is a circuit fault it will likely show up as a failure to operate properly. You will be able to measure incorrect voltages and take corrective action before the leakage or short circuit current becomes catastrophic.

Testing on a low energy supply won't necessarily help to catch poor construction quality, but it will catch many instances of circuit design faults, wiring errors, bad connections or faulty components.