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I want to switch the contacts of a relay after aprox 1 second. I've never done something with a relay before, so please can you check if I understand the specs correctly? This is the one I saw https://www.mouser.com/ProductDetail/TE-Connectivity-AMP/4-1393238-4?qs=EWPZcfu7wdHhD56H9BS5Bg%3D%3D

I need a 12VDC in coil but 230VAC in contacts NO/NC. I did a voltage divisor to put 12VDC at the 576 ohm coil. With a total 15576 ohms resistance (15K + R coil) and a 47uF capacitor, I calculated a time constant of 732mS. The operate voltage is 9V to change the contacts.. does this circuit looks ok? thanks in advance enter image description here

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  • \$\begingroup\$ If you are committed to this poor design. The capacitor needs to go across the relay coil for a time delay. Not the bridge. Also, this circuit isn't isolated from mains. so the whole circuit is hot even when you "divide it down" to 12V. \$\endgroup\$
    – MOSFET
    Commented Jan 24 at 21:54
  • \$\begingroup\$ sorry for the poor design.. Iḿ a newbie. How would you design a 10mS delay for the relay? \$\endgroup\$
    – jmann
    Commented Jan 25 at 11:48
  • \$\begingroup\$ That's fine. To start, for a delay on the order of 10ms, you are looking at a solid-state solution to do this reliably. Also, you are likely going to need an auxiliary supply that's already powered and stabilized prior to your start up power sequence. \$\endgroup\$
    – MOSFET
    Commented Jan 25 at 14:51

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Apart from the waste of power, this isn't a good circuit. The voltage will rise slowly and the relay won't switch cleanly. That will lead to additional arcing at the contacts, generate EMI and reduce the life of the relay.

The situation will be worse during discharge.

Buy an AC time-delay module with 230 V power and control input.

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  • \$\begingroup\$ thanks but I also wanted the delay to be as short as 10mS, so I thought I could change the capacitor to a 0.47uF and get that delay. The 10mS timer relays I've found are too expensive. How would you design a 10mS delay for the relay? \$\endgroup\$
    – jmann
    Commented Jan 25 at 11:46
  • \$\begingroup\$ The relay datasheet says, Operate/release time max. 10/8ms so just adding the relay would give you 10 ms delay. I suggest that you edit your question and explain what this is for and what constraints you are working with (budget, voltage, production quantity, isolation, etc.). \$\endgroup\$
    – Transistor
    Commented Jan 25 at 12:14
  • \$\begingroup\$ I'll ask again, sorry. I asked for the minimum operate time to the manufacturer, but they tell me they only have the maximum. My application shouldn't be less than 5ms.. that's why I ended up trying to put a RC delay circuit, but poorly :/ I'll ask again ;) \$\endgroup\$
    – jmann
    Commented Jan 25 at 12:23
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    \$\begingroup\$ You realise that you are looking for a timing function in the 5 - 10 ms range when the mains half-cycle is 10 ms? The point in the mains cycle that you switch on your circuit will be much more significant than anything else. I suspect that you may be chasing the wrong solution to whatever the real problem is. Without details of that I can't help further. \$\endgroup\$
    – Transistor
    Commented Jan 25 at 13:37

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