Relay Delay Off

Jack Houck's picture


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


Joined: May 19, 2015

Replies: 213
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 

jaksonlee's picture


Joined: Nov 07, 2019

Replies: 122
Their purpose is to control
April 23, 2020 - 6:37pm

Their purpose is to control an event based on time. The difference between relays and time delay relays is when the output contacts open & close: on a control relay, it happens when voltage is applied and removed from the coil; on time delay relays, the contacts can open or close before or after some time delay.

Time delay is defined as the controlled period between the functioning of two events. A Time delay relay is a combination of an
electromechanical output relay and a control circuit. The control circuit is comprised of solid state components and timing circuits that
control operation of the relay and timing range. Each function is explained in the table below. Time delay relays have a broad choice of timing ranges from less than one second to many days.There are many choices of timing adjustments from calibrated external knobs, DIP switches, thumbwheel switches, or recessed
potentiometer. The output contacts on the electromechanical output relay are direct wired to the output terminals. The contact load
ratings are specified for each specific type of time delay relay.