Holding 12VDC relay closed for 1 second

[Powhyfo]

I have a 12VDC **broken link removed** that I need to stay closed for about 1 second after power is removed.
Can I add a capacitor and diode in parallel to the feed to accomplish this?
Any recommendations of capacitor size?
I am sorry I do not have specs on the relay, I have looked & looked and have found nothing more than what is available at the link above.

Thanks.

 

[KMoffett]

A quick Google shows that this type relay requires about 150mA at 12VDC...so the coil resistance is 12v/0.150A=80Ω. Assuming the contacts open at about 8V...about one time constant...it would require a 12,000µF/25VDC cap across the coil. And a diode between the +12V supply and the top of the parallel coil/capacitor.

You might also want to add a low value resistor (1-10Ω) in series with the diode to limit inrush current to the capacitor.

Haven't tried it, but it should be within that range.

Ken

 

[Powhyfo]

Excellent. I will collect the ingredients and give it a whirl.
Thank you very much!

 

[Powhyfo]

Update: Works like a charm! Thank you, Ken.

 

[KMoffett]

Happy to help.

Ken

 

[MikeMl]

One other consideration: So you do not weld the contacts on whatever switches it ON/OFF, you need a current limiter in the path to the capacitor.

 

[Powhyfo]

I see. Is R1 4.7 ohms?

 

[BrownOut]

12,000µF/25VDC cap

That's a hell of a capacitor.

 

[MikeMl]

I see. Is R1 4.7 ohms?

Yes. It limits the peak current required to charge the capacitor to 2.5A. Without it, the peak current would be tens of A, and could weld the switch contacts.