Discussion in 'General Electronics Discussion' started by wjp9639, Sep 5, 2012.

1. ### wjp9639

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Sep 5, 2012
Can someone please point me in the right direction of creating a relay thet when triggered runs for a specified amount of time like 5 or 10 seconds? I am fairly new to the electronic circuit scene but learn pretty fast. Any help would be greatly appreciated and I would even be willing to compensate anyone that helps me with a small paypal payment. Thanks again!!!

2. ### amidis86

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Jul 17, 2012
describe more how you want it work..

3. ### wjp9639

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Sep 5, 2012
I want to build a relay that when it is powered on will supply power out for a determined amount of time. Say a microswitch triggers the relay to turn on and it supplies power out of the relay for a set time like 5 or 10 seconds. Thanks for your quick reply.

4. ### CocaCola

3,635
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Apr 7, 2012
555 'one-shot' aka monostable

5. ### wjp9639

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Sep 5, 2012
I would greatly appreciate it if you could show me an example circuit for this type design. I am trying to build an automatic waterer that turns on for a set amount of time once the low water sensor is triggered. Thanks!!!

25,449
2,809
Jan 21, 2010
7. ### wjp9639

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Sep 5, 2012
relay question!!!

Can someone point me in the right direction of a relay thats coil is powered by a 12v 600mw or less source and its output can handle 24v 2a current? Thanks!!!

8. ### davennModerator

13,722
1,913
Sep 5, 2009
have you googled "relay 12V with 2Amp contacts" ?

there's 1000's of hits

I presume you really mean 12V 600mA ? once you get to a few supplier sites you will get that info
the relay wont be rated at 12V 600mA it will more likely be 12V with a certain coil resistance say 12v and 270 Ohms etc
use Ohms Law to work out the current through the coil

Dave

Last edited: Sep 6, 2012
9. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,449
2,809
Jan 21, 2010
You want a relay that can be switched on by 12V 50mA (alternatively, one with a 240 ohm coil resistance or greater).

First you go to Digikey's site.

In the search box you type "relay". You will be taken here.

There are lots of things listed, but scrolling down (typically to the things with the most hits) you will find two entries, one for Power relays (over 2A), and the other for Signal Relays (up to 2A).

Let's start with the signal relays (although you may be sailing close to the wind with contacts rated only slightly above your requirement).

I simply select all the coil currents up to 50mA, coil voltage of 12VDC, contact rating of 1.5 or 2A, and all the contact voltage ratings from 24V up to 1000V (or whatever the limit is). Then I press "Apply filters". You have to do this, because I can't provide a link to the results.

Digikey tells me there are 252 relays that match this. The cheapest is \$2.66 in quantities of 1. (note that you didn't specify anything about the configuration of contacts, this one is DPDT)

If we do something similar with power relays, everything is the same except that you don't need to specify a current rating (since they're all 2A or more) then you'll find 768 relays, with the cheapest (SPDT) being \$1.15 here.

So you have more than 1000 options, follow those steps and find something suitable. Other sellers will provide similar information, although maybe not as easily searched.

10. ### amidis86

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Jul 17, 2012
something like this?

11. ### wjp9639

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Sep 5, 2012
thanks for the great reply steve, that will make it much easier to find the relay i need. as for the youtube video posted i want a circuit that does the exact opposite that when triggered it supplies power for a set amount of time and then cuts off power after the specified time. any ideas would be greatly appreciated. i think i have a circuit worjked out but the 555 only supplies 600mw i think so i am looking for a relay to match that output. thanks again for all your help!!!

12. ### CocaCola

3,635
5
Apr 7, 2012
As I stated in post #4 this is going to be the most straight forward way to do it...

You can always put a transistor on the 555 output and let the transistor drive the relay, if need be...

13. ### wjp9639

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Sep 5, 2012
can you explain a little about transistors and adding them to output of this circuit. I am not familiar with using them in circuits. thanks.

14. ### CocaCola

3,635
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Apr 7, 2012
I could, but I hate wasting my time typing what can easily be found on 1000s of websites already with a simple Google search...

http://www.kpsec.freeuk.com/trancirc.htm

Last edited: Sep 6, 2012

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Aug 9, 2012