I need a Relay!!!

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krikor
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I need a Relay!!!

Post by krikor » Tue Apr 19, 2005 10:28 am

Hi guys, I'm in need of a little help. I'm basically looking for a 120v relay that will switch another voltage (3,5,9,12, whatever i can change it after the relay) on when the 120 volts gets shut off. Basically heres what i want to happen, i have a light timer on some lights and i want to put the relay after the timer so when the timer turns the lights off the relay turns on another set of lights. Anyone know of a relay like that? i tried looking though digikeys catalogs but i dont understand half the stuff in there on relays. I think i need a solid state one too, but again not sure. Any ideas anyone? <p>thanks, <p>Krikor

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haklesup
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Re: I need a Relay!!!

Post by haklesup » Tue Apr 19, 2005 12:14 pm

Use any 120V relay with SPDT or DPDT switch contacts. Use the Normally Open contacts to connect your DC supply.<p>When activated the nc (normally closed) terminals will open and the no (normally open) contacts will close<p>[ April 19, 2005: Message edited by: haklesup ]</p>

k7elp60
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Re: I need a Relay!!!

Post by k7elp60 » Tue Apr 19, 2005 12:26 pm

I think what you need is a DPDT(double pole, double throw) with a 120VAC coil. This will allow you to switch on two separate voltages when the timer goes off. Each set of contacts has three terminals. The contact that physically moves is called the wiper. With the relay disconnected from any power, this wiper will make contact with the NC(normally closed) contact. When the relay coil is connected to a circuit and the power is applied this wiper will make contact with the NO(normally open) contact. Each set of three terminals works just like a toggle switch with three terminals, except that the applied power moves the contacts one way and when the power is turned off the contacts move the other way.
If you wire the voltage you want to control when the timer is off thru the NC(normally closed contacts) and wire the coil of the relay to output of the existing timer, the relay will energize when the timer is on, turning off the other lights. When the timer goes off, the voltage will turn on the other lights you want to control

L. Daniel Rosa
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Re: I need a Relay!!!

Post by L. Daniel Rosa » Tue Apr 19, 2005 12:56 pm

If you don't understand half the catalog on relays, you should steer clear of solid-state relays- they're usually designed primarily for AC and if they have any sort of thyristor output will lock-up on DC (they'll turn on just fine but won't turn off until you remove power or load).

krikor
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Re: I need a Relay!!!

Post by krikor » Tue Apr 19, 2005 8:17 pm

I think what k7elp60 knows what i need, do you know any part #'s?<p>Should I connect the relay in series or parallel with the load? Also it would be best to swich the 120v AC so I'm not losing power powering the transformer the whole time.<p>here is a pic that my buddy drew up... sorry about his art skills.
Image

Enzo
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Re: I need a Relay!!!

Post by Enzo » Tue Apr 19, 2005 8:21 pm

There is nothing special about the relay you want. You want 120VAC coil, and you also want continuous duty. That means it is OK to remain energized for extended periods. Ther are also intermittent duty relays which are designed to pulse for a brief period but mostly remain off. You don't want that.<p>As to the current handling ability of the contacts, you determine your need by the amount of current you have to control in the secondary circuit. That is the circuit that is to come on when the 120 goes away.<p>SO just wire the 120v relay so it is ON whenever the 120v is present. Get a relay with double throw such as SPDT or DPDT, and use one of the Normally CLosed contacts to control your external circuit. Normally Closed means that when the relay is NOT energized, it is closed. SInce the relay will usually be energized by the 120v, it is open most of the time, but it is still called normally closed because that is how the relay is made. Don't get confused over how the relay is made compared to how the relay is used.<p>In brief then, whenever the 120vAC goes away, the relay drops out, and when it does that, those NC contacts close, turning on your extra circuuit.<p>And a bit of a nitpick, a wiper is on a pot. The moving blade in a relay is an armature blade.

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Dave Dixon
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Re: I need a Relay!!!

Post by Dave Dixon » Wed Apr 20, 2005 6:43 am

Krikor,
Something is getting lost in the translation here. The schematics you presented show the AC line voltage being switched from one source to another. My understanding was that the second load was to be a lower/D.C. voltage.
Please be sure that you completely understand what you are doing before playing with Line AC Voltages! We don't want you to burn up yourself, or your circuits.
Thanks for the wiper comment Enzo,
Dave

krikor
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Re: I need a Relay!!!

Post by krikor » Wed Apr 20, 2005 7:21 am

Hey, i know the second scematics are differnt from my first explaination, but in the first or third drawing (theones i think would work) i would save energy and only need one plug into my power stip if i change the voltage to dc after the relay. <p>know what i mean?<p>dc transformer would be after the relay so the transformer isnt constantly using power, either way will work, ac turns off switch closes and dc goes on or load goes off my flours (the timer shuts off) and the ac switches to the led array where i will change the voltage as needed. The ac switching will be more efficent. allways good to save a little energy.

k7elp60
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Re: I need a Relay!!!

Post by k7elp60 » Wed Apr 20, 2005 6:16 pm

krikor,
This is what I recommend. A Digikey part number,PB322-ND for the relay. A digikey part number PB332-ND for the socket for the relay.
The socket has numbers on the individual connections. The numbering on the socket is different than the numbering on the bottom of the relay. DO NOT USE THE NUMBERS ON BOTTOM OF THE RELAY. The relay is a Potter & Brumfield K10 series relay, and the socket is a socket by the same manufacturer.
Connect as the socket as follows:
Pins 13, 14 go to the existing lights
Pins 9,12 go to the power source for the lights you want to turn on when the existing lights go out.
Pins 1,4 connect to the additional lights that you want to turn on when the existing lights go out.
There are other relays and sockets that will do the job, but since I have technical books for the Potter & Brumfield relays I chose this particular one as it is rated as continious duty and the contacts are rated at 15 amps.

krikor
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Re: I need a Relay!!!

Post by krikor » Wed Apr 20, 2005 9:16 pm

THANK YOU!!!!

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