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Holding 12VDC relay closed for 1 second

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Powhyfo

New Member
I have a 12VDC relay 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

Well-Known Member
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
 
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KMoffett

Well-Known Member
Happy to help. :)

Ken
 

MikeMl

Well-Known Member
Most Helpful Member
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.
 

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MikeMl

Well-Known Member
Most Helpful Member
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.
 
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