Relay Delay Off

Jack Houck's picture

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Joined: Aug 14, 2019

Replies: 0
Relay Delay Off
August 14, 2019 - 5:59am

I have a circuit that's driven through a relay that I want to stay on for about 5 seconds after the power is cut off.  I've tried using a transistor/electro cap and a 555 for the delay but can't seen to get either to give me the delay I want.  What I did find that works however is using two large elctro caps in parallel to the relay coil. But now I want to add an led circuit using the same power source and want it to shut offthat shuts off when I cut the power.  Problem is when I install a 4001 diode to prevent reverse current flow as the cap discharges I get a short (high amp) when I power up.  Not sure why that it is but I do.

So I'm wondering if anyone has any thoughts or suggestions nthat might help solve this caper. Truly would appreciate!

Jayant's picture

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Joined: May 19, 2015

Replies: 210
Use a super capacitor
August 15, 2019 - 2:42pm

Hi, I am not sure why you eant to set-up such a system. But what you are trying to do is power up the circuit through a secondary source after the primary power is actually turned off. Well bascailly the best way is to use a small coin cell. But if you just want to make the circuit stay live for 5 seconds then you can either use a powerful capacitor in parallel (like you have already done) or use super capacitor.

I am not sure where exactly you are connecting this diode in the circuit (providing a circuit diagram will help). but diodes noramally have a high coltage drop across it (0.2V) either you can try using a schottky diode instaed of a normal diode like 4001 or provide the circuit diagram here to acually check what the problem is