stay on relay

Thread Starter


Joined Aug 20, 2009
hi can anyone help i need a 12v relay that comes on with signal as normal relay dose, but after signal drops the relay remains closed for approx 10 seconds ?


Joined Jan 8, 2009
2 ways -

The hard way - Get a 555 timer, wire it in monostable mode to get very accurate timing.

The easier way, if you dont need it to be precise, add a 4700uF (or maybe more) capacitor across the relay terminals. Sometimes you can make it work with a 1000uF and a transistor. Timing will need to be experimented with to make it accurate.


Joined Aug 6, 2009
Here's a possibility. The cap is charged quickly when the input trigger is applied, and so the relay operates very fast, but C1 cannot discharge quickly because of the diode so the relay should stay closed for a few seconds. I have guessed at part values, R1 would probably need to be adjusted to get the right timing.


Steve C

Joined Nov 29, 2008
How much innacuracy can you stand to have in the circuit? Do you need BASICALLY 10 seconds, and it's cool if you are off by a ton? 10 is the ballpark?

bam, easy.

Thread Starter


Joined Aug 20, 2009
thancks steve will give that a go, the 10 seconds is a ballpark figer but any were from 8 to 20 seconds would be good , is the part number for the trasistor a comon numer did a search on maplins did not find it!
thancks again