100 foot separation of LEDs from Supply from PV array?

Discussion in 'The Projects Forum' started by roboPuppy, Oct 19, 2011.

  1. roboPuppy

    Thread Starter New Member

    Oct 17, 2011

    I have this project going where LED floodlights are going to be separated from the power supply (in the garage or in the house). The solar arrays are going to be mounted on the garage's roof.

    Obviously, I live close to a neighborhood where everything that is not hidden - disappears. I also live on a postage-stamp lot, which in this case is actually beneficial!

    The distance could be a maximum of a hundred feet between the three.

    The floodlights are not always on, they will be flashed only, just as a photo-flash, maybe a bit longer.

    My approach is to send a high-voltage DC pulse, or a train of pulses, to the LEDs, but I do not want the voltage to be too high. A kid might want to yank at one of the LED arrays at the wrong time and could be electrocuted.

    Here is what I have in mind so far, and if you just write "good idea" or "bad idea" I would appreciate that.

    For the LEDs:
    - Distance from source will be 100 feet at most.
    - Power: about 30-40VDC for an array that consumes 80 mA, for about 500ms or less.

    Oh, these are cheap white LEDs, free to take if you need them so much, I really do not care. I have hundreds of them and there is more where they come from. They are rated at 80mA for pulsing at long intervals, and most of them work as expected.

    - Conductor: I am planning to use Cat-5 as it rolls off the spool - no modifications. I will use two leads and leave the rest for "future use". I have plenty of this.

    For the solar array:
    - Distance from power supply either 10 feet, or about 50.
    - Configuration: I was thinking of a high-voltage array of 100 VDC or higher at no load, assuming no kid will be stupid enough to climb a garage roof and yank on the panel. Then, I remembered when I was a kid - nixed. There is more on this in power supply.

    For the power supply:
    - I picked up nearly a thousand of 1F memory backup caps on Ebay at $10 for a hundred. I will be using these, but I would not discuss this here because it is off-topic. I will post on this as soon as I have presentable ideas. What matters is that I will be using these in parallel, so stepping down high DC voltage to 5VDC is a real challenge. As of now I have no idea how to configure the solar cells or what conductor to use.

    I am leaning toward higher voltage because the panels will still be producing at dawn, or in overcloud. This is important because the caps are the most leaky type of all electrolytic. Trickle-charging them until the last moment is crucial when sizing the bank I will be needing.

    I prefer to use the same CAT-5, which is good for high voltage, and bad for high current - I assume. I really want to use those CAT-5 cables, you can probably tell. I have spools of them, and these days they worth only what copper they hold.

    If you have a VERY good idea about how to use them please post a thread and direct me to it. Just don't ask me to sell them to you. Those spools are tombstones of better times when I bought them at full price because I needed them. I really abhor the idea of selling out of good memories.

    I am also so full of assumptions about this project I cannot even think of a good noun to give Google to work with.

    Cheers, and thanks for reading.
    Last edited: Oct 19, 2011
  2. wayneh


    Sep 9, 2010
    So, let me follow: You want to infrequently? pulse an array of LEDs, something like 40? of them, for up to about 1/2 second (possibly repeating a few? times). The power for this will come from a solar panel and be stored in super caps (only?, no battery?). All portions of the system should be reasonably safe in case a neighborhood n'er-do-well is in the act when a pulse comes through or when the sun is shining on the panel. You want to use cat-5 cable for long interconnects.

    Is that all right?

    A few thoughts and questions: I think you need a battery. Leakage from the caps at night will probably neuter your system. What triggers the flashes, and how often must they trigger?

    Offhand I don't see anything to stop your plan but you need to think about how much power from your panel -after all the losses along the way - can really be stored (and for how long) and compare that to how much power you'll need under worst-case (cloudy January).
  3. roboPuppy

    Thread Starter New Member

    Oct 17, 2011

    The number of LEDs in the series array will depend on the voltage, I probably won't know that until I measured it with a voltmeter.

    Supercaps only, and about as many as needed. I will keep adding them until I have voltage left over by the morning. Then I add more until I have a enough voltage to make a flash or two.

    I really do not know because the capacity of each of those caps is different, even if they are rated the same.

    This is just and experimenty, something I am curious about. Maybe later, if it works, I will triger the flashes by motion sensors, trip wires, whatewer. For now I will just use a push-button.

    I am just not sure about a few things - especially the CAT 5 thing, and would like to know some opinios about that before I start dragging hundreds of feet of it all over the yard.
  4. wayneh


    Sep 9, 2010
    If you just need your cat-5 cable to sustain 80mA, I don't think that's a problem even for 100% duty. I don't have the specs in front of me, but I can't believe 80mA would fry it. And you can parallel the unused conductors until you find another use for them. The insulation of cat-5 is plenty for DC voltages no higher than the range you mentioned. Again, I don't know the voltage specs but I'm sure it's fine.