Motion sensor and transformer issue!

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  #1  
Old 12-05-11, 08:55 PM
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Motion sensor and transformer issue!

Try to bare with me because I'm a new at this. I'm using a motion sensor to control lights but the lights are 12v and the sensor outputs 120v. What I'm thinking is that the transformer(120v to 12v) will power the lights but 'only' if the motion sensor closes the transformers 12v output loop. Is there a powered switch for this by which the switch will only change(completing the 12v light loop) if sensor goes off and activates the switch?
To clarify, this transformer gets power(from an outlet) and has two leads coming out to power garden lights(12v, 300w max) but the sensor has to decide whether the lights get their power from the transformer. Can this type of transformer work for this? Am I on the right track?

Sorry this was wordy but I'm a beginner. Some other info is that the sensor supplies 300w max just like transformer but the volts are too high for the lights. If I connect a simple 120v/12v transformer to the sensor output will the lights still get the 300w and I can forget about the transformer I have altogether?
Thank you for your time.
 

Last edited by RealX1; 12-05-11 at 10:15 PM.
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  #2  
Old 12-06-11, 04:04 AM
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Depending on the rating of the photocell it may have to go before the transformer to make things work properly. Basically a photocell is just a switch that activates via light rather than manual input. Not sure if it would work on your situation.
 
  #3  
Old 12-06-11, 06:03 AM
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Chandler, I think the OP mentioned a motion sensor, not photocell.

I would attach the motion sensor before the 120v receptacle. So basically the motion sensor controls the receptacle. Then plug the transformer/lights in as you normally would.

This ensures the motion sensor gets 120v which it probably needs to work, and your transformer isn't on and buzzing 24/7.

The transformer is rated at 300w output, so it can run up to 300w worth of 12v lights. It doesn't care if you connect 5w or 300w worth of lights to it. But if you do away with the transformer, the bulbs will blow immediately since they can only handle 12v. Connecting them to 120v would blow them at best, and could create some fireworks.
 
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Old 12-06-11, 09:04 AM
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Awesome answers, thank you! The sensor before the transformer sounds like my best bet. The transformer plugs into standard 3 prong outlet. I just cut the cord and wire it to the sensor?
 
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Old 12-06-11, 02:06 PM
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I wouldn't cut the cord as that would void the warranty and UL listing and make it more difficult if/when the transformer needs to be tested or replaced. I would wire the motion sensor to a new receptacle that you could plug the transformer into.

Remember, the receptacle needs to be GFI protected, and the wire running to the sensor and receptacle needs to be protected, either inside the wall or inside conduit. Of course, be sure to use outdoor-type boxes too!

Once you have your plan together, I'd suggest passing it by the fine folks here just to be sure you have all your bases covered.
 
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Old 12-06-11, 02:49 PM
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Chandler, I think the OP mentioned a motion sensor, not photocell.
Well, duh, I read it more than once and still was thinking photocell. Sorry about the info, but Zorfdt got you on the right path. Funny how the brain works..........or doesn't.
 
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Old 12-06-11, 03:57 PM
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Originally Posted by chandler View Post
Well, duh, I read it more than once and still was thinking photocell.
We'll let it slide this time...
 
  #8  
Old 12-08-11, 09:03 AM
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I appreciate all the help! Things have gotten a little more complicated because I'm going to use two sensors as switches to one transformer. First of all I don't know the amps or watts input of the transformer I just know its 120v. I know the sensors put out 120v, 2.5a,300w max. Is that the same as a standard 120v outlet or will it work for a basic transformer power pack? What I'm thinking, and this is the part I need to know makes sense, is the two sensors will connect to the transformer but in such a way that only one sensor can power it at once. In other words, if either sensor activates(but not both at once) it will power the transformer.

I saw a schematic of how to connect two sensors to one load. I'm assuming the load in this case is the transformer. Can I assume that this will only allow one sensor to power it at once? This is where I get confused..
 

Last edited by RealX1; 12-08-11 at 10:14 AM.
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Old 12-09-11, 10:25 AM
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The sensors are basically like a switch. So you want to make sure your switch/sensor is rated for at least the load that will be placed on it. For example, you could use a switch/sensor rated at 300w to power a 100w light bulb, but not four 100w bulbs as it would likely burn up the switch/sensor.

You can connect the sensors in parallel so if either one triggers, the load (transformer) will go on. It's much more difficult to make it if either, but not both. You'll need some more hardware and wiring...
 
  #10  
Old 12-09-11, 10:37 AM
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This is what I read "yes, having both sensor outputs to one transformer backfeeds the second sensor which isn't an issue because it's relay is open". That's what a diagram online shows also. Somehow having both 120v outputs to one transformer isn't an issue, apparently.

Going back to what you were saying. I just need to know if the sensor can power the T yes? All I know is the sensor out is 120v, 2.5a or 300w max. The T requires 120v and puts out 12v across 300w max. Do I need to know more than that the T is 120v like how many amps it requires to know the answer? Thanks for hanging in there with me. I realize a lot of these questions are basic.
 

Last edited by RealX1; 12-09-11 at 10:56 AM.
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