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I wanted to ask that is it good to giving 12v to 12v operated relay from 230v to 12v transformer+ rectifier + 1000uf 50 v capacitor , I am taking 12 v and ground from capacitors legs !

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    \$\begingroup\$ Carefully measure the actual voltage across the capacitor with a multimeter (in DC voltage mode). You will almost certainly find it higher (perhaps much higher) than 12V, and therefore perhaps exceeding the maximum coil voltage for whatever relay you are using - check its datasheet for that maximum value. \$\endgroup\$
    – SamGibson
    Mar 10, 2016 at 17:03
  • \$\begingroup\$ How much current does the relay coil take? Or better, yet, can you edit your question and add a data sheet or at leas a link? \$\endgroup\$
    – EM Fields
    Mar 10, 2016 at 17:20
  • \$\begingroup\$ @SamGibson. The rectified voltage across the cap will rise to 1.414 times the transformer's RMS output voltage and decay at a rate depending on the capacitance, the load current, and the period of the charging waveform . \$\endgroup\$
    – EM Fields
    Mar 10, 2016 at 17:35
  • \$\begingroup\$ @EMFields - agreed, I know I could have mentioned sqrt 2 etc. Due to the lack of specific data from the OP, I thought a quick way to answer his stated question (i.e. is [that setup] good) was to measure the voltage, assuming that the OP was already using this circuit (I now see its ambiguous whether this is a theoretical question or already in use, as I interpreted it). The unknown load on the output, relative to the unknown transformer rating, means we don't know what the actual transformer output voltage will be (do we?) - hence measure it :-) Yours is a more complete approach :-) \$\endgroup\$
    – SamGibson
    Mar 10, 2016 at 18:29
  • \$\begingroup\$ Please provide a schematic and clarify your question. \$\endgroup\$
    – Voltage Spike
    Mar 10, 2016 at 18:46

2 Answers 2

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Under normal conditions you can do exactly that if the relay has a coil rated 12V DC. You may not even need the capacitor but it could reduce humm and/or buzzing in some cases.

If the relay coil is 12V AC then you can leave out the rectifier and capacitor and drive it directly.

The two types of relay have some minor differences so it is best to follow the manufacturers ratings. Some relays are rated for either AC or DC. Typically a DC rated relay will not pick up with the same AC voltage while a AC rated relay may hold the contacts closed for a bit longer or sometimes until it is bumped as the armature may have become excessively magnetised.

Transformers usually supply a bit more than the rated voltage when not loaded but under some load they should droop to close to the rated voltage and this should match what your relay needs.

Your relay's datasheet, model number or supplier link would help confirm your use case.

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Full-wave rectify the 12VAC and you can run the relay directly from that rectified DC without using a capacitor.

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