[SOLVED] Simple 1-2 sec power on delay relay circuit

[hafrse]

Hello,

I have a 12V low power signal delay (G6K-2F-Y), looking into a simple circuit without a 555 to delay the relay switch in 1-2 s when the +12v power is switched on from the power supply.
Thanks for any help

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[Easy peasy]

This is one of the simpler delay circuits at power on, the time taken for the base to get to ~ 1V determines the delay

for a 12V applied signal this would be in the order of ~ 0.5 sec.

 

[KlausST]

Hi,

You may use a Mosefet. It needs less gate current and has better ON voltage drop.
Maybe worse rise rate.
If you need sharp rise rate you should consider a comparator or schmitt trigger.

Klaus

 

[crutschow]

Below is the LTspice simulation of Ep's circuit (slightly modified):
The relay power is applied (yellow trace = relay current) about 1.5s after system power is applied (red trace).

 

[KlausST]

Hi,

Important: (although neither me nor Easy peasy mentioned)
* don't forget to add the free wheeling diode (D1 in crutschow's schematic)

Without it you risk to kill the transistor at switching OFF ... sooner or later

Klaus

 

[Easy peasy]

a 24 V zener across Q1, above, instead of D1, gives a relay opening speed similar to the closing speed - useful for relay contact life.

 

[hafrse]

Hello,

Thanks all for the suggestions, i tried [B]crutschow[/B] solution, but it seems that the relay fires very quickly (less that 1 sec) , how can I have longer delay using that circuit? could I adjust the R and C values in some way ?

Datasheet for the relay https://pdf1.alldatasheet.com/datasheet-pdf/view/195747/OMRON/G6K-2F.html

Many thanks in advance!

 

[crutschow]

how can I have longer delay using that circuit? could I adjust the R and C values in some way ?

Increasing the value of C should work.

 

[hafrse]

Thanks, I will increase the C vaule later today, I am using gneral perpose MPSA42 NPN transisters, not sure if they work as expected instaed of 2N3904

 

[crutschow]

I am using gneral perpose MPSA42 NPN transisters, not sure if they work as expected instaed of 2N3904

They should work similar to the 2N3904.