relays and contactors?

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  #1  
Old 11-04-04, 02:28 PM
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relays and contactors?

can someone give me a quick rundown here?i need to control two loads with two contactors.there is a heating load that will be on for a certain amount of time then a cooling load which will be the same but they can never be on at the same time.i was originally going to use a mechanical timer with no/nc contacts(double throw),but that timer is unavailable here.how could i use a sp 120v relay to operate these two coils on the desired timing schedule i need?
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Old 11-04-04, 05:39 PM
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What voltage are the loads? What is the control {contactor coils} voltage? If each load is to be on when the other is off I would use contactors that are mechanically interlocked {if you're not already}.Or you could use delay on break/delay on make timer switches for each load.Each timers setting can be adjusted to make or break its respective contactor coil.A schematic will need to be drawn. I hope this helps
 
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Old 11-04-04, 07:09 PM
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the voltage for the load would be 120v.the contactors are not mechanically interlocked.how do you do this?are they a special type or is there an application for doing this?

i was thinking there must be a timing relay with n/o,n/c contacts along with n/o delay on make,n/c on delay settings to control the mags.i was looking thru the idec website and was unsure which would work
 
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Old 11-05-04, 07:33 PM
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How much are you willing to spend on this project? I would guess that 2 120v.contacts {mechanically interlocked} are not cheap,if they are even made. Will one load be on at all times or will they both be off for different periods of time?
 
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Old 11-05-04, 08:02 PM
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What exactly are you trying to acomplish.

Is this to be able to operate an a/c and a heater off of the same breaker?
 
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Old 11-05-04, 08:07 PM
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I don't think so Greg. It sound as though O.P want to control 2 loads on the same piece of equipment. It could be a home-made low-temp freezer with electric defrost
 
  #7  
Old 11-06-04, 03:59 AM
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Ya, could be.

A Precision brand commercial defrost timer would work for this and a relay would not be necessary.

Click image:
<img src="http://precisionmulticontrols.com/images/defrost/tnl6040.jpg">
Image credit: precisionmulticontrols.com

Or, if cost is a concern, this timer for a household refrigerator will allow a 20 min defrost cycle every eight hours:

Click image:
<img src="http://www.partselect.com/assets/partimages/451059_1_s.jpg">
Image credit: partselect.com


Maybe sparxx347 will fill in the details.
 
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Old 11-06-04, 06:26 AM
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If an interlock is of concern, you don't need to do it mechanically. Select a couple of contactors with auxilliary contacts. Use the aux contacts as permissions for the timing circuits that control the contactor coils. Maybe the whole problem has been solved and the equipment is already available off the shelf if the application was known, like the other guys are guessing.
 
  #9  
Old 11-06-04, 07:24 AM
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Use one contactor and use the normaly open for one device and the normally closed for the other device. Only one will be on at a time.
 
  #10  
Old 11-06-04, 11:22 AM
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this is to run heaters and fans off of the same power source.basically when one is off the other is on for a set piece of time.i could go with an integrated timer relay to automate it for what i need but that gets expensive also.i guess i could use a mechanical timer(intermatic t101)to time a relay with no/nc contacts to switch the loads on the contactors
the loads are 30a,120v,and will cycle back and forth,when one is on,the other is off.
 
  #11  
Old 11-07-04, 11:29 PM
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Thumbs up idec timer

k thanks guys i got it....used a timer/recycler to switch the loads back and forth...cheers
 
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