WANTED: Light sensitive switch (shutting OFF when dark)

[Strainhunter]

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As the title already states that's what I am looking for.

All the ones I know of and/or have come across turn ON when the lights go off but I am looking for one which does the opposite thing - turning (equipment) OFF when the light goes out.

Anyone?

 

[J.puffin]

Well I'm not sure about that switch your talking about, but is it possible to wire a relay across it to reverse the logic

 

[Strainhunter]

Well I'm not sure about that switch your talking about, but is it possible to wire a relay across it to reverse the logic

Normally light sensitive switches turn lights (or other connected stuff) ON when it gets dark, I need one that does the opposite thing meaning turning what ever is connected OFF when it gets dark.



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[renz]

You can use a light sensor (usually a current biased light sensitive diode) on the input of a comparator (cheap operational amplifier), on the other input you would have a voltage divider with some resistors and a potentiometer (knob resistor) to set the trigger level for the switch. You probably want some positive feedback for hysteresis to keep the thing from switching to much during transitional levels of light.

The output of the comparator would drive a transistor driving a mechanical relay, or possibly the emitter side of an optoisolator used to drive a triac (solid-state relay).

You would need to construct a PSU to provide power for the comparator and to bias the sensor.

 

[Strainhunter]

......

I appreciate the explanation on how to do this and I understand the basics of where you are coming from...but I don't have a degree in building electrical circuitry...

I'd rather have someone post a link to a unit I can buy...

I spent hours on Google...and couldn't find one.



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[madpenguin]

Oi.... That's a good one. I'm sure they make a Normally closed photocell somewhere.

I would probably use a SPDT relay.

http://www.grainger.com/Grainger/items/5Z542?Pid=search

While your there tell them that you want the cheapest possible enclosure to mount that relay into. I think a 4x4x4 would do it. Try to get metal. Whatever is the cheapest (if it's metal then you have to ground it out). Get a photocell from there too. Make sure the enclosure has a knockout that can be used so the photocell can mount to it. Get a length of #14 SJ cord if your working with a 15A branch circuit. Get a #12 SJ cord if your working with a 20A branch circuit. SJO, SJOTW... whatever they have. Just 300v rated flexible cord. The gauge is key tho depending on what breaker protects the circuit that you want to run your equipment off of. Get an NM connector that will fit in one of the knockouts of the enclosure to securely hold the SJ cord as well.

The use of spade/fork terminals along with a ratchet crimper is highly suggested. Terminate the incoming black wire from the cord plugged into the wall to the only screw on the relay that is by its self. On the grainger picture it's the screw that is in the upper right hand corner of the relay. By the metal strand of wire that connects the "line in" screw to the armature. Terminate the incoming hot black wire to the "line in" screw.

Then take a #14 black from that same screw and wirenut or crimp it to one of the photocell wires. Then take another piece of #12 stranded and wirenut or crimp it to the other left over photocell wire and terminate the other end to one of the center contacts of the relay.

Take the incoming white power cord wire and terminate it to the other center contact. Take a single gang bell box, which could probably be had at Grainger as well, and fasten it to the side of the enclosure via a knockout and NM connector. Take a #14 or #12 white stranded from the center contact that has the other white wire and run it into the bell box.

Take a #14 or #12 black stranded and terminate it to the relay screw that is in the lower left hand corner of the picture of that relay. That will be the contact that is normally open. So from that screw to inside the bell box with a #14 or #12 depending on the branch circuit you are working with.

Take the incoming green wire from the power cord and ground out the inside of the metal box somehow. Also fasten another #12 or #14 green insulated wire to the incoming ground and route it into the bell box. Hook up a NEMA 5-20R to the black, white and green wires that are now in the bell box. screw the receptacle down and plate it.

Now the receptacle should only be hot whenever it's dark....

Look... MY GF just rushed the shit out of me and I probably screwed that all up. When I get back home I'll proof read it to make sure it's right but there are other sparkies floating around here that can correct me in the meantime if I am wrong...

 

[madpenguin]

Umm... What Renz said would work but shit... I hope you happen to have a degree in electrical engineering.... That or you just love to tinker with electrical circuits.

And I'm not so sure your going to find something premade to buy, which is probably why your google search didn't yield anything.

My route is actually insanely easy to do, I just spewed all that crap out real quick cause I was getting barked at, thus it probably isn't worded in the most simplest of terms that I can manage.

If you have any questions, let me know and I'll make sure what I said was right when I get home.

 

[renz]

The use of spade/fork terminals along with a ratchet crimper is highly suggested.

OMG I love those things...

 

[renz]

My route is actually insanely easy to do, I just spewed all that crap out real quick cause I was getting barked at, thus it probably isn't worded in the most simplest of terms that I can manage.

Yeah I would probably have to take notes and make diagrams to figure out what you said, but the general idea is definitely sane and easy to implement.

OP: If wiring stuff up scares you, you should probably have someone experienced do it or at least help; you'll die or set fire to all your stuff if you mess up.

 

[CannabisTHC]

If you really want a nice piece of equipment you could buy a Sentinel cycle timer for around a $100. Which comes with a photocell. You can set the timer to turn on when the light comes on or when the light turns off, either way. Great thing is it checks after 30 seconds in case you walk into your grow room and shine light on the timer, it won't automatically turn on, it will take 30 seconds to make sure there is a steady dark/light.

 

[madpenguin]

Great thing is it checks after 30 seconds in case you walk into your grow room and shine light on the timer, it won't automatically turn on, it will take 30 seconds to make sure there is a steady dark/light.

Yea, all photocells do that. Especially the ones you buy to control the flood light above your garage door. It's to combat cloud cover.

 

[Mr. Stinky]

why wouldnt you just wire it up to the timer? timer off=power off... seems obvious enough

 

[madpenguin]

why wouldnt you just wire it up to the timer? timer off=power off... seems obvious enough

Because doing things the easy and obvious way are just too easy. Maybe that's a question the OP can answer. In the mean time I'm not going to let you burst my bubble and waste all the time I spent doing this mock up.... Besides, this could be for outdoor applications or any numerous things where you need to specifically rely on "when it get's dark"..... "When it get's dark" could be an unknown or changing variable. If that's the case, then you would need a photocell.

 

[Lord Humungus]

what about the CAP ART DNe?
its got the photocell action so you can have it come on during lights on, or lights off (what you wnat i believe) , or both.

i have a couple of them and i like them.

the best part is i didnt have to build them so their not all janky hehe

*i am not savvy when it comes to building things so off the shelf works great for me... if i could build it just as nice and solid i would.... i dont have building skills though. oh well.

 

[bicyclebenny]

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As the title already states that's what I am looking for.

All the ones I know of and/or have come across turn ON when the lights go off but I am looking for one which does the opposite thing - turning (equipment) OFF when the light goes out.

Anyone?

Check out this site. it has a motion sensor that turns on or off anything plugged into it. Cheap, too. I got some of their stuff on ebay that lets me know when the cat needs to come in by turning on a light by the tv. ~$15.

http://www.x10.com/products/x10_ck11a.htm

Here's the motion detector:

http://cgi.ebay.com/X10-EAGLE-EYE-M...emQQptZLH_DefaultDomain_0?hash=item1c10cae4df

 

[madpenguin]

Arggghhhh. Didn't anyone watch McGyver or the A-Team when they were young? What's with all this pre-fab junk.

 

[Mr. Stinky]

your right, it could be for outside, although i think he would have said "when the sun sets" instead of "when the lights go out". if it were outside, a digital timer would be more accurate than a photocell since cloudy/rainy evenings can get dark even before sunset, and clear evenings with cirrus clouds can be light well passed sunset.

jus sayin is all

 

[Strainhunter]

OK guys I am an idiot.

Well not in general but about this I was.


I got one of these:

http://www.hydroponics.net/i/135020

In connection with one of these:

http://www.hydroponics.net/i/133914

The whole deal about my OP was to reliably turn on/off the hood vent fan when the lights go on/off but having 240V for the hood and the fan being 120V.
I did not consider the Sentinel HID 2 Lighting Controller (1st pic) having TWO 120V outlets.
One outlet I am using for the trigger cable to run the Sentinel HPH-8...and the 2nd outlet for turning on/off the vent fan...DUH!

Now it would be nice to have a little delay in turning off the hood vent fan after the hoods got turned off (for some "aftercooling") but I guess I can't ask for too much...lol

Thanks all for your help and input!

 

[Mr. Stinky]

for running 120v fans off the 240 light circuit, just run off 1 leg of the 240.

 

[Strainhunter]

for running 120v fans off the 240 light circuit, just run off 1 leg of the 240.

That would work if they weren't all in use.

But I got a solution, see above.