A little help please.

Discussion in 'Landscape Lighting' started by hoskm01, Dec 7, 2007.

  1. hoskm01

    hoskm01 LawnSite Fanatic
    Messages: 5,690

    The Academy of Our Lady Peace?

    Aggie Orientation Leader Program?

    Oh, you mean the Academy of Outdoor Lighting Professionals... I should have known. Hey, look at that, they are here in Phoenix. Looks good, its nice to see some organization for different trades. Until I get into lighting professionally (at this rate for me could take a while) Ill meet up with you guys and share some beers and talk lights. Maybe down the road though, I like trade shows, especially near home! When is the next show?
  2. irrig8r

    irrig8r LawnSite Platinum Member
    Messages: 4,553

    Joey, for some reason I don't think i ever got a response from you over in the Unique sponsor forum, where I asked about different methods of calculating Vd.

    James seems to be using the method I learned at Nightscaping, which Nate calls Method 4 in his book.

    I prefer the method I learned at a Vista seminar, because my tester shows it to be more accurate, and that (involves multiplying the length of the run x 2, as you say.

    Here's what I wrote about reading Chapter 5 of Nate's book back on 10-22-07

    ( http://www.lawnsite.com/showthread.php?t=203374&page=2 )

    Couldn't wait for the weekend, had to check out the book.

    So, first thing I did when I opened it was go to Chapter 5.

    Here's my take:

    Method 2 seems to come close to the results that Vista comes up with.

    Their formula is (L x W)x 2/ cable constant.

    For instance, using the example, where Method 2 comes up with 1.62 Vd, their formula comes up with 1.6 Vd. I've tried it with different wire lengths and wattage combinations.

    Their Vd numbers always come with twice the number produced by the formula I learned from Nightscaping (Method 4 in your book). Someone told me they thought the original NS formula was better applied to DC than AC, but I have no idea.

    Basically, as far as I can tell, the method I learned from Vista comes close enough for planning and estimating. A multimeter finishes the job.

    Next, I have to figure out what happens if I was using the hub system and all my lamps happen to burn out at once... what voltage would I have at the hub then, with no load? How about with just one or two lamps?

    Are you measuring the 10.8 to 11.5 volts at the hub with no load, then adding the fixtures/ lamps?

    How does that compare to NS advising greater Vd if more than half the wattage load is in the second half of the run?

    And then we get to energy consumption. We can theorize, but I think the only objective way to measure is to use the same lamps/ wattage load on your system vs. their system, both as you would normally lay them out, and measure them both with Kill-A-Watt meters.

    What do you think?​
  3. JoeyD

    JoeyD LawnSite Silver Member
    Messages: 2,933

    I am always up for a challenge!!!!

    The hub changes nothing really. The only difference with the hub is if I have 25ft of 16/2 cable on each fixture I am going to test my voltage at the hub and set it between 11.5v and 12.5v. I know I lose approx. .5v from Hub to fixture ensuring being between 11v and 12v.

    Now even if I cut some of my 25ft lead off for sake of not coiling it up, I will knoe that whatever I cut off is going to put me closer to the voltage that was set at my hub. More times the not the human eye cannot tell the difference between 11v and 12v. But nothing is better than haveing equal voltage.

    Now if lamps burn out then yeah you up the voltage to the remaining potentially causing a chain reaction. But if you are using a hub and 12ga cable as your norm then you will rarely have over 5 lights on a hub. So worst case scenario you lose the 5 lamps. But this can happen on a T and a Daisy Chain as well.

    But the Volt Meter never lies, so lets just run a test, we have done it many time, this wont be the first time.

    Joey D.
  4. hoskm01

    hoskm01 LawnSite Fanatic
    Messages: 5,690

    Im on it. .
  5. irrig8r

    irrig8r LawnSite Platinum Member
    Messages: 4,553

    So if you go back to the first message it sounds like Matt says he has 2 runs of 100 ft of 12/2. One run has 30 W, the other has 40 W. That's a total of 70 W on 200 ft of cable. (As I read it, the two runs are spliced together away from the transformer somewhere, distance not made clear)

    So, I would take each run, making sure I was using 12/2 and not 14/2 or whatever else Malibu sells these days, and attach them to the transformer separately, because otherwise it's 70 W over 200 ft.

    Instead we have 30 W over 100 ft. where you get 2.50 A x .00162 x 200 L = 0.81 Vd
    and 40 W over another 100 ft. where you get 3.34 A x .00162 R x 200 L = 1.09 Vd

    These numbers are acceptable.

    Using the same mathod, with 70 W on 200 ft of wire the calculation is something like this:

    5.84 A x .00162 R x 400 L = 3.79 Vd.

    Totally unacceptable.

    So, first thing to do, in this case, is run the two lines separately from the TF.

    Do you agree Joey?
  6. Chris J

    Chris J LawnSite Silver Member
    Messages: 2,843

    This is probably the first time I've had a problem with you, but I'm gonna speak my peace. If you're such a good friend of Matt, then you should just go ahead and do the job for him and provide him with a little knowledge. Or, you could call him directly, and tell him over the phone in 5 minutes everything you know about lighting?
    The first post of this forum is for "home owners" and/or "do it yourselfers".
    It is clearly explained that we professionals make our living from designing and installing quality lighinting systems. Please don't try to defend someone who is not a lighting pro that happens to wander upon this forum. We are not here to help people take business from our individual companies, nor should you. Even though this person might be a good person, or even a great friend, he is still not a lighting contractor. This forum is for lighting contractors!!
    No offense, but you hit a nerve.
  7. pete scalia

    pete scalia LawnSite Senior Member
    Messages: 960

    Well said Chris.
  8. Chris J

    Chris J LawnSite Silver Member
    Messages: 2,843

    I probably need to keep reading to the end of this thread before chiming in, but I couldn't resist.
    James, when using this formula you need to multply by 2. In other words, Cable length X Watts ; divided by the cable constant; then multiply by 2 (or at least 1.5) Unless the primary voltage in your area is excessively high, you should have been doing this all along. Do you check voltage at your fixtures after everything is hooked up? No insult intended, but I've seen similar senarios.
  9. Chris J

    Chris J LawnSite Silver Member
    Messages: 2,843

    No, no. This scenario dictates 2.13v of voltage drop from my calculations. Again, you are not multipying by two. Your volt meter after finalizaton will confirm your methods. You should always check the voltage at your fixtures after everything is hooked up. I'm suprised that you guys aren't doing this.
  10. irrig8r

    irrig8r LawnSite Platinum Member
    Messages: 4,553

    Well Chris, Matt is an irrigation guy. That doesn't make him the same as a DIY in my book. You see how many posts he has? He didn't just "wander in".

    I don't know him personally, just from the irrigation forum... where the guys don't take themselves quite as seriously or get into as many squabbles as seem to happen over here in lighting... I tried to explain a couple of concepts to him in terms I thought he would understand. If you have a problem with that I guess I just don't know what to say... I'm not going to apologize for it though.

    Beyond that it turned into a discussion of comparing voltage drop formulas... I found that exercise kinda useful.

    Cheers. :drinkup:

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