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add big delay to AC line

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alexxx

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Hello all.

Below you can see a simple circuit, where DB2 is a manual switch. When it is not pressed (NC) the LED is on. When it is pressed, then the LED is off and L goes to Lout through the push switch. L and N are the two wires of the AC mains line 230V/50Hz.

switch_230V.png

What I want to do is add a simple circuit if possible to delay this Lout. So when DB2 is pressed, then L will reach Lout after 10-15 seconds. Can this be done simply with passive components? It would be great if no MCU is added.

Thanks.
 

Are you really intending to put 230 milliamps through that LED?

You certainly don't need an MCU to give you a 15 second delay, but I don't think you can do it with just passives. You can use a time-delay relay (easy, but expensive) or you could design a circuit using something like a 555 timer and a TRIAC.
 
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    alexxx

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Hi Barry. Why are you saying 230mA? There is a transformerless power supply with the capacitor, so there will be voltage drop and a current limit from the capacitor itself. It is a cheap and simple circuit to drive the LED from mains.

So this is what I suspected as well, that this cannot be done with simple passives. Thanks. I will use a 555 as sugested, or a small MCU like ATTiny13.
 

Hi Barry. Why are you saying 230mA? There is a transformerless power supply with the capacitor, so there will be voltage drop and a current limit from the capacitor itself. It is a cheap and simple circuit to drive the LED from mains.

So this is what I suspected as well, that this cannot be done with simple passives. Thanks. I will use a 555 as sugested, or a small MCU like ATTiny13.

I am saying 230 mA because you've got 230volts across the LED and a 1K resistor. 230/1K=230 mA. What kind of current limit are you expecting from a capacitor? The reactance of that cap is about 14 ohms.
 

Hi,

but there´s additionally a capacitor in series. With an Xc of 14469 Ohms.
Making a total Z of about 14503 Ohms.

Limiting the total current to 15.86mA RMS.
With the single side rectifier it makes 7.14mA LED average current.

Klaus
 
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    alexxx

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Klaus can you thing of a way to do it with just passives? I mean there is a way if I add a bridge rectifier after the capacitor and then use an RC circuit with big time constant to activate a TRIAC.

But what I mean is if I can use a passive cicuit directly on the AC line to introduce a 15-20 seconds delay?

Thanks.
 

Hi,

but there´s additionally a capacitor in series. With an Xc of 14469 Ohms.
Making a total Z of about 14503 Ohms.

Limiting the total current to 15.86mA RMS.
With the single side rectifier it makes 7.14mA LED average current.

Klaus

Ah. I thought that was 220 MICROFarad. Now I see it's nF.
 

Hi,

Half wave rectifier, RC, diac, triac...

I don't know if this works reliably.

Klaus
 

Maybe a stupid question, but why don't you put the rectifier in series instead of parallel, increase the 1K to limit the LED current, and put the cap across the LED? I'm not sure why you're using a cap to limit current rather than a resistor.
 

Hi,
I'm not sure why you're using a cap to limit current rather than a resistor.
Because a resistor generates more than 3W of heat.....and thus additionally increases the bill for electrical energy.
3W can easily melt a plastic case.

Klaus
 

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