Holding 12VDC relay closed for 1 second

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Powhyfo

New Member

• Jul 11, 2009

• #1

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.

 

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KMoffett

Well-Known Member

• Jul 11, 2009

• #2

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

 

Last edited: Jul 11, 2009

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Powhyfo

New Member

• Jul 11, 2009

• #3

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

 

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Powhyfo

New Member

• Jul 14, 2009

• #4

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

 

K

KMoffett

Well-Known Member

• Jul 14, 2009

• #5

Happy to help.

Ken

 

MikeMl

Well-Known Member

Most Helpful Member

• Jul 14, 2009

• #6

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.

 

Attachments

• DelayLimiter.png

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Powhyfo

New Member

• Jul 21, 2009

• #7

I see. Is R1 4.7 ohms?

 

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BrownOut

Banned

• Jul 21, 2009

• #8

12,000µF/25VDC cap

Click to expand...

That's a hell of a capacitor.

 

MikeMl

Well-Known Member

Most Helpful Member

• Jul 21, 2009

• #9

Powhyfo said:

I see. Is R1 4.7 ohms?

Click to expand...

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.

 

Last edited: Jul 21, 2009