LED Outdoor lighting question

Discussion in 'The Projects Forum' started by trader007, Jun 4, 2013.

  1. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    I have some 12v ropelights i want to install outside. I am thinking of putting them under deck railings, and under steps.

    of course, all that is easy. At very least, I want them on a photo eye to only run at night- which is simple to do.

    What I REALLY want though, is for them to be on normally at a very dim level, just so you can see it, then when you approach the area they light up full brightness.

    I am good enough with circuitry that I could wire in say a proximity sensor to bypass a dimmer or something... but i think it would be a nice touch to have a gradual dimming and brightness. Like a soft fade up and down.

    What I am asking is, is there already a device like this I could use? Or do I have to do then fun way in designing my own circuit?

    thanks in advance!!

    edit- nevermind, i see jameco sells dimmable led power supplies. it seems you can just adjust the constant current by varying the voltage at a certain point. maybe a pic controller could give this supply a 'soft' operation? http://www.jameco.com/Jameco/Products/ProdDS/2140744.pdf
     
    Last edited: Jun 4, 2013
  2. wayneh

    Expert

    Sep 9, 2010
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    Is your power supply at 12V DC? Much easier starting point.

    LED dimming is best done using pulse width modulation. You can achieve very smooth and precise control over the entire brightness range. You could use a 555 timer IC to accomplish making the PWM signal but you'll need a MOSFET to handle the on-off switching of your LED current.

    I'm sure you'll also hear about microprocessor solutions, and that might be a good choice here if you have any prior experience or desire to learn such a thing.
     
  3. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    im not into microprocessors yet. i know a good bit of electronic circuitry, but applying my knowledge into new concepts gets me lost.

    i think starting with a dimmable led power supply is the easiest route (link to pdf above). for $40, its not expensive either. 60w of led's outside for each cabin would be more then enough.

    so now, i just need to find a way to bypass the set current level and do so in a way that it slowly engages/disengages.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    That'll make things much easier.

    If I understand what you want, you just need two voltages - one for full on and the other for the dimmed state - and a way to slowly switch from one to the other?

    You could put a diode and then resistor in series between your control voltage and a capacitor on the DIM- and DIM+ pins. Choose the values of R & C that give you the slow fade you like. When your control voltage changes from one state to the other, the RC tank will slow the change.

    I think you'll need to experiment a bit to find the right component values. It'll depend on the power supply and I don't think you'll easily get the information out of the supplier.

    [edit] You may need a discharge resistor as well, and I think the cap will discharge primarily through this external resistor and not the power supply. I assume it has a fairly high impedance on DIM+. Hard to know without testing.
     
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  5. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    yeah from what the datasheet says, voltage from 0-10 at a certain input will allow you to control current on that power supply... should be easy to implement.


    you mean a capacitor and resistor, right?

    this is exactly what i was originally thinking too. because it would be very simple, easy to fix if it breaks, and the fade time isnt critical at all... i just want a soft start and fade out after a set time. the time off delay can be controlled with a 555 timer i was thinking...
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Forget what I said about the diode and discharge resistor for now. If the discharge of the cap thru the DIM+ port is slow enough, the cap discharge rate will be controlled by the same resistor it charges thru. Easy peezee.

    How long a delay do you want? Depending on what you hack together your proximity sensor may have that function built into it and you won't need to build your own.
     
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  7. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    i really dont know what i want. in my head, it goes like this-

    see dim accent lighting under deck railings... ooo thats cool. this accent is on all night.

    then walk closer to deck, maybe say 10ft away, and it quickly fades to full brightness. then, after say 10min of inactivity, the lights slowly fade back down to dim level. i would say the fade times should be about 3 seconds either way, and if its not hard to make the dim down phase slower then it would be better i think. say a 10 second fade to dim...

    i dont mind buying ready made parts if its cost effective. i think for the motion sensor ill buy a prepackaged one, since they do a good job of working only when people approach and not other environmental factors. that only signals the on/off, or high/low in my case. i need a fade controller is all i guess :D
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Should be doable. Somehow you need to make a control signal that's maybe 2V most of the time - the dim level - and switches to 10V when the motion detector is "on". I think it could be as easy as turning on a wall wart instead of a lightbulb with the motion detector, and adding the wall wart's voltage to the source of the 2V signal.
     
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  9. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    Last edited: Jun 5, 2013
  10. wayneh

    Expert

    Sep 9, 2010
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    No shortage of options. I didn't realize there were so many battery-powered options. You might be able to find one that uses the same 12VDC you already have for your lights. It's "on" state would give you the positive DC voltage to apply to your controller, no need to turn on another power supply.
     
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  11. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    well, maybe ill just use my own stuff now that i found this-

    [​IMG]
    http://www.talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#101

    if i used a computer power supply (i have a bunch of small 150w brand new ones i got on clearance), then add this circuit thats in the picture, it should work. mainly because i don't need a current limiting power supply since the resistors are built into the rope light.
     
  12. LDC3

    Active Member

    Apr 27, 2013
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    You will still need to replace the on-off switch with the motion sensor. The motion sensor will need to switch between 2 states - low and high.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    That should work fine. Depending on how the sensor switches, the switch for this circuit might be fine where it is (high side) or might need to be moved to the low side.

    Make sure you choose a darlington that can handle the current of your LEDs, and give it a heat sink. It'll get hot as it passes through the "half on" state , where it is dropping several volts under substantial current.

    I believe you could even keep a dim level by putting a power resistor in parallel to the darlington transistor. It would limit current to the entire LED strip when the transistor is off. When on, the transistor would take the current and bypass the resistor.
     
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  14. LDC3

    Active Member

    Apr 27, 2013
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    I think this is a better solution.
     
  15. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    thats sort of what i was thinking in my original idea. each bank of led's i will be using might reach 30w (12v 3a or so), depending on how big the deck is, at full brightness, but i suppose that would mean i would only need a 10w rated resistor for the low light mode that the lights will normally stay in.

    this should work great though. very simple circuit, using my own power supplies- exactly what i wanted. thanks guys! in the next couple days, ill try to get a schematic drawn up with values entered in.
     
    Last edited: Jun 5, 2013
  16. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    Specific question-

    the transistor in the drawings shows a max of 40w dissipation. That isnt really ideal for me, as i could really use double that- which would allow me to do 15ft of led strips without adding another wire run. Since I don't want to go larger then 18awg for my power runs, 15ft@75w should be a good limit to set myself at.

    so the question is, do I find a larger transistor or should I just double up a couple BD679's? If I have to look for a larger variant, is there a special kind of NPN transistor that I need or are they all generally the same?

    Edit- I believe these will work. 135w max, so thats well above what I need for still a good price- http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/WixbhOhHbn/druthM5RMK1TE=
     
    Last edited: Jul 21, 2013
  17. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Where are you going to mount your electronics. Remember being outside. The enclosure HAS to be waterproof. You don't want to burn down your deck.

    I know, because I made some home-grown LED lighting for my garden, and the power supply case was not waterproof. (I tried.) There was a fire, but it fortunately was contained to the enclosure.
     
  18. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    All of the ac-to-dc components will be inside. I plan on mounting the supply and controls in the basement with my networking gear on the wall. I will run multi-conductor 18awg out to where the led's are, and whatever voltage drop I will have by doing that will be compensated for by tweaking the power supply.

    I do plan on mounting those 135w transistors on a chunk of aluminum for heat dissipation too.

    Also, I will be using MeanWell power supplies, that I have found to be very safe when it comes to faults.
     
  19. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    :cool: Sounds like you know what you are doing. Just wanted to share my story, to warn anyone reading this thread of a possible danger. I can imagine someone deciding to try this with a computer power supply on a cinder block under their deck. Of course, I didn't mean you. ;)
     
  20. wirednuts

    New Member

    Nov 13, 2011
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    LOL! Yeah that would be hilarious to see. I love looking at hackjob installs.

    I have been an electrician for over 10 years, with extensive training in safety. I don't do anything questionable when it comes to electrical work. I always over-do it a little. Also why I am getting into LED accent lighting, as it's inherently safe as long as you use the proper power supplies and install techniques.

    The only electronics outside besides the diodes themselves would be the photo sensor and the PIR sensors.

    I am going to try these sensors from china. I would rather have something from honeywell or whatnot, but the price can't be ignored with these- http://www.ebay.com/itm/221236158512

    and the PIR sensors here- http://www.ebay.com/itm/350792365698

    I was looking on digikey and noticed I could buy the actual photo and PIR sensors themselves, but I would need to add the circuitry to go with and that's just more time consuming. These come with what they need to work, in a nice small package. The PIR sensor has a 3min timer built in too, and I figured I will probably be able to add some capacitance to extend that to about 10min.
     
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