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Thread: Low voltage power transmission - AC or DC?

  1. #1
    Flashaholic* BatteryCharger's Avatar
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    Default Low voltage power transmission - AC or DC?

    I have a shop in an industrial park where it gets very dark and lonely at night. There's been a meth problem recently. My shop is in dark corner with some woods behind it, a perfect target.

    Anyway, I'm trying to add as much outdoor lighting as I can with the least watts possible. (It's already 3kw just to flip the light switch on!) In the outdoor areas I'd like to run low voltage 12v lines to power multiple lights. I have a "landscape" light setup at home with regular incan bulbs and a 12v AC transformer. I would like to use the same type of 12v AC outdoor transformer with a timer, to which I will attach some custom LED lights.

    Is there any reason landscape lighting uses 12v AC instead of DC? Is it just because it's cheaper to make an AC transformer, and incan bulbs don't care...or is there some reason it's better for running power cables?

    I'm either going to rectify the AC at the output and run 12v DC lines...or add the rectifier to the individual LEDs. Which would be better?
    I got a fever and the only prescription is more cowbell.

  2. #2
    Flashaholic* JohnR66's Avatar
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    Default Re: Low voltage power transmission - AC or DC?

    You guessed it. Incans don't care about AC. Adding rectification just adds unnecessary cost and complexity. I assume you have to run some wire a good distance to spread the light around using smaller clusters. It may be a power loss issue with a 12 volt system. It would be better to make a couple fixtures with several LEDs that are are close to the transformer.

    While rolling your own lights may be a fun project, it is often better to buy decent quality fixtures. You will find it takes quite a bit of lumens to light up an outdoor area. The office I used to work at sat on 2 acres and had eight 400 watt metal halide fixtures plus some halogen floods around the entrance to light it up.

    how much area do you need to light?

  3. #3

    Default Re: Low voltage power transmission - AC or DC?

    Less parts in the system = less crap to go wrong. I'd definitely put one single bridge rectifier on the transformer output and run the whole system on DC, instead of a whole bunch more parts and possible failure points. It'll also take very nearly the same amount of time to wire up one big bridge rectifier as it would to wire up one small bridge.........then you still have all the rest to do.

    Actually, as long as you're below the damaging reverse-voltage level, LED's will run on AC. They'll just be off half the time(and therefor half as bright, ghetto PWM), but the flicker will be so fast that in a fixed lighting situation most people won't notice.
    Got Biodiesel?

  4. #4

    Default Re: Low voltage power transmission - AC or DC?

    There's also the issue with safety, which is another reason for the preference of low voltage with landscape lighting. Moisture, dirt, bugs and damaged lines due to an errant shovel won't kill you running 12 volts. A wee bit more lethal with 120volts AC and breaker limited current.

    By default I prefer some monster metal halide outdoor fixtures for this task since nothing beats them for raw 'night-breaker' intimidation.

    However, this is one instance where LED *might* serve the task just as well. Reason being is it doesn't sound like the OP wants to efficiently illuminate an area, but act as a deterrent. Cool white Cree R2s (or higher bins) or cool white Bridgelux driven at their top current and running without optics are downright painful when viewed at night in an open area. Matter of fact, they actually seem more intense than a 250watt HID even though the HID throws more light.

  5. #5
    Flashaholic* BatteryCharger's Avatar
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    Default Re: Low voltage power transmission - AC or DC?

    Quote Originally Posted by JohnR66 View Post
    While rolling your own lights may be a fun project, it is often better to buy decent quality fixtures. You will find it takes quite a bit of lumens to light up an outdoor area. The office I used to work at sat on 2 acres and had eight 400 watt metal halide fixtures plus some halogen floods around the entrance to light it up.

    how much area do you need to light?
    Well, there's already several 250/400w metal halides in the parking lot, although my building was built after the main building as somewhat of an afterthought...so those lights don't flood my area very well.

    I've just been walking around with a 3w LED mag and pointing it where I want some light, and it seems bright enough, if I had like 10 of them. In fact I was thinking about buying some Mags and cutting the head off for a light fixture.

    I want to use the 12v system for safety and the fact that I don't have to call an electrician...in a commercial building with 3 phase power, I'm not allowed to touch the 120v for any reason without an electrician. Plus the main outdoor lights aren't on my power meter, these will be.
    Last edited by BatteryCharger; 02-02-2010 at 08:28 PM.
    I got a fever and the only prescription is more cowbell.

  6. #6

    Default Re: Low voltage power transmission - AC or DC?

    Basically that's what I did with my Light Bars I use for effect lighting. Just a bunch of 3-watt LEDs and cheap narrow optics. You don't need your mag head...unless you want to impress meth-heads with your 'spill quality'

    Plenty of cheap optics out there that have tight throw.

    I recently updated the light bar with white R2's, and the only difference from what you are trying to do is mine has smoke machines and obnoxious music blaring at a loud volume.


  7. #7
    Flashaholic* BatteryCharger's Avatar
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    Default Re: Low voltage power transmission - AC or DC?

    Quote Originally Posted by blasterman View Post
    I recently updated the light bar with white R2's, and the only difference from what you are trying to do is mine has smoke machines and obnoxious music blaring at a loud volume.
    Hmmm...maybe that would scare them away too?
    I got a fever and the only prescription is more cowbell.

  8. #8

    Default Re: Low voltage power transmission - AC or DC?

    Either Country or Techno

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