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Author Topic: Relays  (Read 485 times)

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Offline soninja8Topic starter

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Relays
« on: October 12, 2013, 11:03:26 PM »
Hello,

I am looking for a relay that turns on for about 1-5 seconds and then shuts off, and then repeats this process only when voltage is reapplied. I am setting up a relay to a starter motor and I would like it to only be on for a few seconds. If you could recommend me any relays that are capable of this I would be very pleased!

Thanks!

Offline jwatte

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Re: Relays
« Reply #1 on: October 13, 2013, 05:15:59 PM »
You will need a little bit of electronics to make that happen. Easiest would be a 555 timer circuit, perhaps. Also, if you can use a MOSFET instead of a relay, that will make it drive-able straight from the timer, which might make it simpler to build (but then it would be polarity sensitive, which relays are normally not.)

You can buy these things already integrated; do a search for "time delay relay." Typically, though, these things are built for the control industry, which runs largely on 24V, so if you don't have that available, building your own will probably be simpler.

Here's a description of various time delay functions. From your description it sounds like you want "interval on" function: http://www.macromatic.com/blog/understanding-time-delay-relay-functions/

Digi-Key has some: http://www.digikey.com/product-detail/en/DRTH24D06/CC2039-ND/3674241
But I find that more automation/control-specific distributors may have better assortment and pricing for these kinds of things.
« Last Edit: October 13, 2013, 05:18:25 PM by jwatte »

Offline bdeuell

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Re: Relays
« Reply #2 on: October 13, 2013, 07:02:14 PM »
I have seen a similar problem solved using a RC circuit to control a relay.

Perhaps someone with a stronger electrical knowledge than me could explain exactly how this is done.

It is probably less accurate than the 555 timer method tho.

Offline johnwarfin

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Re: Relays
« Reply #3 on: October 14, 2013, 08:48:47 AM »
I have seen a similar problem solved using a RC circuit to control a relay.

yes, imo this is simplest method. only 3 components: nfet, cap, and resistor. i built many for a client couple years ago to replace expensive industrial units. apply 5-12v then 4 second delay. still have 5 units left over. if op is interested i can sell for a fraction what digikey charges. however as mentioned diy would be even cheaper (and more educational to boot).

Offline soninja8Topic starter

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Re: Relays
« Reply #4 on: October 15, 2013, 08:39:31 PM »
I dont get it, there are so many time delay relays that wait a given amount of time to turn on a circuit. Why dont they make ones that wait a given amount of time to shut off a circuit? I need one thats cheap and already assembled and able to handle 12v... I know what i need is an interval on relay but I cant find a single one that fits my needs  >:(

Thanks for your recommendations you guys but its not exactly what im looking for yet  :(


Offline Pogertt

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Re: Relays
« Reply #5 on: October 15, 2013, 08:59:19 PM »
Mmmmmmmm....Cookies

Offline soninja8Topic starter

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Re: Relays
« Reply #6 on: October 15, 2013, 09:31:30 PM »
Off Delay Relay

http://www.grainger.com/Grainger/DAYTON-Time-Delay-Relay-5WML9?Pid=search


I need a relay that turns off after a given amount of time even when the trigger is still engaged, it appears that an off delay relay waits until the trigger is off to engage the timer...

Offline jwatte

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Re: Relays
« Reply #7 on: October 15, 2013, 10:40:18 PM »
You want a power trigger, interval on, relay. These are made, but they can be $50, or even $200, and may be specced for 24V or even AC mains power.

What's wrong with the relay I linked to from Digi-Key?

If you prefer Amazon, this item is $13.40 with Prime shipping available, and seems like it might work (although the specs are not 100% clear): http://www.amazon.com/gp/product/B0009WP09K/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0009WP09K&linkCode=as2&tag=enchage-20

This one will definitely work (12V coil, contacts rated for higher than that both AC and DC,) given the data sheet (note that it's DP/DT, so it can both close and delay to open, and open and delay to close): http://rcm-na.amazon-adsystem.com/e/cm?lt1=_blank&bc1=000000&IS2=1&bg1=FFFFFF&fc1=000000&lc1=0000FF&t=enchage-20&o=1&p=8&l=as4&m=amazon&f=ifr&ref=ss_til&asins=B0078RYKJA
$67, plus shipping, no Prime (and most vendors charge twice that for the same item, so buyer beware and all that)
Data sheet: www.serelays.com/library/section5/105A_TDRSRX_TDRSOX.pdf‎


Offline soninja8Topic starter

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Re: Relays
« Reply #8 on: October 16, 2013, 04:29:44 PM »
You want a power trigger, interval on, relay. These are made, but they can be $50, or even $200, and may be specced for 24V or even AC mains power.

What's wrong with the relay I linked to from Digi-Key?

If you prefer Amazon, this item is $13.40 with Prime shipping available, and seems like it might work (although the specs are not 100% clear): http://www.amazon.com/gp/product/B0009WP09K/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0009WP09K&linkCode=as2&tag=enchage-20

This one will definitely work (12V coil, contacts rated for higher than that both AC and DC,) given the data sheet (note that it's DP/DT, so it can both close and delay to open, and open and delay to close): http://rcm-na.amazon-adsystem.com/e/cm?lt1=_blank&bc1=000000&IS2=1&bg1=FFFFFF&fc1=000000&lc1=0000FF&t=enchage-20&o=1&p=8&l=as4&m=amazon&f=ifr&ref=ss_til&asins=B0078RYKJA
$67, plus shipping, no Prime (and most vendors charge twice that for the same item, so buyer beware and all that)
Data sheet: www.serelays.com/library/section5/105A_TDRSRX_TDRSOX.pdf‎


That one from Amazon looks like exactly what I need. Ill give that a try since its inexpensive and let you know how it goes. Thank you for your help!   ;D

 


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