new guy simple question

new guy simple question about timers

Hi guys. I'm new here so a little back'ground. I'm an automotive mechanic with a background in automotive electronics. that being said I'm working on a project and while I do work on automotive components this goes a little deeper than I ever need to go. I need a component that I can momentarily trigger to energize a relay for 5 seconds. I have been looking all over and I'm not sure if this would best be done with a capacitor, an inductor or possibly a common 555 timer. Please excuse my lack of knowledge on some of the common theories, quite frankly in a lot of automotive applications anything solid state is almost considered a magic box and no info is ever given on the internal workings. thanks in advance guys this could really help me out in a big life changing kinda way.

Matt

hi,
please specify your detail applications,so we can design circuit for u.

matthai,
Sigmatt labz.

G'day Mate,

Bit tricky using passive components only! but depending on how accurate you need the 5 seconds a 555 timer should give reasonable results... remember to use an extended temp range part for automotive use...

Follow the design of the mono-stable configuration as shown here... https://en.wikipedia.org/wiki/555_timer_IC#Monostable

you may also need to put a relay driver on the output depending on the current required by your relay coil something like this should work...

**broken link removed**

A good starting point for Resistor and Capacitor values that would give reasonable accuracy over the automotive temp range would be 470k and 10uF, this will give you close to 5 sec.

Let us know how it goes.

thanks for the ideas. I will give it a try. I have done research but never worked with a 555 timer so this could be interesting. i am currently using a relay (12v 30/40 A) to open said circuit. my problem is the circuit must be held open for aprox 5 seconds for the device I am trying to turn off to power down completely (Not overly sure how this is happening in the module, like I said automotive electronics can be very veg) . I need to make sure the end user does not need to hold the trigger for said 5 seconds. Now that I am typing this out I realized I have not attempted to remove the ground from said component. if said component has only one ground and it was only removed for a short period would that get around any normal components that would be keeping it alive? I understand that that is a very broad question but its hard for me to give details of the internal working of the module I am trying to shut down. thanks again for the help.

I don't quite understand your asking in your last post... whats the issue surrounding the ground? A monostable 555 circuit can also be thought of as a pulse extender.... give it a small pulse... get a bigger one out.... this will intern switch your relay for this time... the relay and 555 timer circuit can be totally isolated from your other circuit... i.e. no common ground. as the relay is an isolation device.

Matt if you have knowledge about relays then the best choice for you is the timer relay. No additional circuit is required just power the relay and you can set time whatever you like also they are not very expensive. Note that theses relays are used in industrial motor control.Hope it will help you.

here you can find some simple circuits for time relay:
http://www.bowdenshobbycircuits.info/page2.htm
I think that the one titled: Power-Off Time Delay Relay will suit your need.

If you use a 555 or other active device to drive the relay, be sure to include a diode across the relay coil with polarity as shown in some of the posted links. It prevents the inductive "kick" that occurs when the relay releases from damaging your circuit. A garden variety rectifier like a 1N4001 is fine.

Den