Waterproof LEDs on AC circuit

Discussion in 'The Projects Forum' started by ansi, Apr 4, 2011.

  1. ansi

    Thread Starter New Member

    Apr 4, 2011
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    Alright here's the project I have, We have a new ( to us ) waterfall that the previous owner has hooked up some 12v automotive sized lights in. It's old and all of the bulbs are broken and wires are not in the best of shape. What I want to do is replace this lighting with my own. Drilling new holes and putting them in different locations behind the falling water and in the front pointing at the face of it. Was thinking of using LEDs ( maybe 5 or 6 of them ) on a circuit but I would like to have it use a 110v power source so I can plug it into an outlet and not have to change batteries every few months or whatever. The LEDs I'm sure would have to be waterproof and I'd most likely need a transformer ( waterproof as well, since it is outside ) to convert the AC current to a DC one (is that right?) so that I can plug it in. Basically looking for a parts list and some guidance.

    Thanks in advance,
    Travis Ballard
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    You will need a step down transformer for certain. 12 volts is about as much as you would want around and in water.

    LED's have different requirements. Different colors have different forward voltages, and the operating currents can be quite different.

    Can you give an idea as to the actual LED's? With part numbers, we can make suggestions.
     
  3. Wendy

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    Mar 24, 2008
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  4. ansi

    Thread Starter New Member

    Apr 4, 2011
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    I have yet to purchase any LEDs or anything as I'm not entirely sure what it is that I would need so I was maybe hoping for a little guidance on that as well. Saw some nice 10mm ( I think ) ones at Radio Shack earlier that were nice. As for color, think I'm just going to stick with cool white and maybe a couple green ones. Or all cool white. I think the cool white would probably look the best behind the streams of water acting like a back light. Just an idea but I'll definitely take any advice I can get.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just put them behind a plexiglass/lexan/acrylic shield
     
  6. ansi

    Thread Starter New Member

    Apr 4, 2011
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    Not really sure that would be a possibility because of the face of the waterfall. It's pretty rough and looks like actual rock.
     
  7. russpatterson

    Member

    Feb 1, 2010
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    The liquidator houses are good for finding LED's

    http://www.allelectronics.com/make-a-store/category/340/LEDs/1.html

    http://www.goldmine-elec-products.com/products.asp?dept=1093

    I would get a 12V switching supply (or use a PC ATX supply if you can keep it out of the elements enough).

    All Electronics has some enclosed 12V 3-5A supplies that would work well.

    If you want to use the super bright, don't look straight at it or you'll have a headache for 24 hours, you could go with the stuff they sell at http://www.ledsupply.com/

    That's a much more expensive route but you can light up the side of a 3 story building with some of those.

    Pick your LED's then you can calculate the voltage, power and if you can just add some resistors or need to go with a constant current driver (for the high power LED's).
     
  8. ansi

    Thread Starter New Member

    Apr 4, 2011
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    Hey Russ, Thanks for the reply. After browsing the links you sent me, I think I'm going to purchase 5 of these http://www.allelectronics.com/make-a-store/item/LED-77/AQUA-HIGH-BRIGHTNESS-LED-5MM//1.html and then 5 of these http://www.allelectronics.com/make-a-store/item/LED-127/ULTRABRIGHT-WHITE-LED-5MM-15-DEG/1.html

    I think that would look nice, putting the white ones behind the water as a backlight and the aqua ones in front as accent lights. out of the 10 I'll probably use 3 of the white ones and all 5 of the aqua ones. Maybe put the other 2 white ones on it too. Would that matter? Would we need to know exactly how many we want to do before we start? or can I add 1 or 2 more as needed if it comes to it?
     
  9. wayneh

    Expert

    Sep 9, 2010
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    I'd suggest a full survey of what's commercially available before building your own. There are all sorts of LED strips, tapes and whatnot, even xmas tree strings that use LEDs. (A good source of weatherproof LEDs). Something in all of that might be what you like or will give you ideas.

    You do NOT need DC for LEDs, since they are diodes. However the strobing of the LEDs at 60Hz is detectable to most folks and can be annoying, not soothing. As noted it is probably a good idea to have lower voltage anywhere near water. Still better is to design so that water contact is not possible, since any contact of conductors with water - even moisture - will eventually cause problems at any voltage.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    One major flaw with that statement, modern LEDs have a PIV rating that is equivalent to their Vf. You MUST have a LED or diode that conducts the other way to prevent them from exceeding their Peak Inverse Voltage, or they will blow. If you have a choice, DC is usually the best way to go. If you want to use low voltage AC then you must plan for it, and have diodes/LEDs facing the other way across each LED.
     
  11. ansi

    Thread Starter New Member

    Apr 4, 2011
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    Alright so assuming that those 10 LEDs are what I have to work with, What transformer do I need? How would you build this. I'm not very sound in the world of electronics, I'm a web developer by trade and the only electronics work that I have done is limited to re-capping the main board in one of my monitors. So If one of you is up for it I could use a hand to hold through this. I'll even toss you a few bucks for your help. I don't have much, but at least it's something.
     
  12. russpatterson

    Member

    Feb 1, 2010
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    So if you want the easiest solution then buying a commercial setup is a good idea. If you want to build it yourself then buying the LED's, resistors and power supply is a pretty straightforward project. Read the articles Bill Mardsen posted above about calculating forward voltage drop (Vf) for all your LED's and the ballast resistor(s) you'll need. Basically you want to think of it like this: You start with 12V, you want to use that up with LED's and at least one resistor. So if your LED's Vf is 3.0V then you could use four in a row to make up your 12V ( 3V x 4 LED's = 12V). Only I've read that you should add at least one ballast resistor so you need to go with 3 LED's then add a resistor that would use up the remaining 3V.

    For waterproofing: be sure to keep the power supply in a place where it won't get wet. The LED's themselves are ok to get a little wet but the wiring will corrode. I tin all the exposed copper on the wires then use wirenuts with silicone.

    Are you going to put a timer on it or just switch it on when you want to? I have a water feature with all kinds of LED's, both above and below water, that runs on a 12V battery I charge with a solar panel. It comes on at dusk and runs until the battery's depleted. That's adding considerable complexity but if you're interested the whole project is open source and I can provide you with the details.
     
  13. ansi

    Thread Starter New Member

    Apr 4, 2011
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    Here's a photo of the waterfall to show you guys what I want to do. I've marked off the 5 aqua LEDs and the 5 white LEDs. the aqua LEDs have arrows to also show the direction they'll be pointed for more of a visual reference.
     
  14. russpatterson

    Member

    Feb 1, 2010
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    Look in the datasheets for the LED's you want. You'll find the Vf (forward voltage) and it will say how much current the LED uses at that voltage. For example Vf = 3.0 at 10mA (10 milliamps or 0.010 Amps). You need to add up figure how much power all your LED's and resistors will pull and then get a power supply that is rated for double that capacity. Here's some power supplies: http://www.allelectronics.com/make-a-store/category/480/Power-Supplies/1.html

    All the electronics info you need is on this site. In that link that Bill posted or on the Vol. 1 DC ebook section on this site.
     
  15. debjit625

    Well-Known Member

    Apr 17, 2010
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    Why dont you use a power adapter 5 VDC and for the current their are 10 LEDs now max these can have 20mA so the total amount of current needed is (20mA * 10 = 200mA) so get a power adapter that can source 5 VDC and 200mA or more.

    Now for connecting the LEDs if you are using white color LED then they have approximate 3.5 Vf and we want it to operate at 20mA so we need 75 ohms current limiting resistor for each LED .

    If your LED's Vf rating is something different then the current limiting resistor have to be recalculated.

    Good luck
     
  16. ansi

    Thread Starter New Member

    Apr 4, 2011
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    I just don't want to change batteries often so that's why I was thinking of plugging it in. I would love the solar method you're talking about that turns on at dusk. That would be awesome and I wouldn't have to do anything. I like a challenge so why not.
     
  17. wayneh

    Expert

    Sep 9, 2010
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    We're going off topic, but that's simply not true. The xmas tree LED strings you see everywhere are just a string of LEDs and a single resistor. They flash at 60Hz, with a low duty cycle. I believe they're off below about 70v and they only come on during one half of the cycle. They apparently are able to withstand the peak ~170v reverse voltage during the other half of the AC cycle.

    Given that the OP is working with moving water, the strobing of an AC source might be quite unpleasant. So we're in agreement that a nice dry transformer somewhere is the way to go.

    I'd probably build this using a 12v transformer or laptop power supply, or maybe a 24v transformer that you can get in the hardware store if you can't find the right wall wart. I think I'd wire this with all the same-color LEDs in series, if not in one string then in however many are required. This way, the resistor on each string can be chosen to give the desired brightness (current) for each color. You could just put a resistor on each LED but that would be marginally less efficient, but would prevent a failure of one from affecting any of the others.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    Have you opened them up? Bet you will find a small diode in there. What is true is the typical PIV of a 3.6Vf LED is around 5V. Try looking at their datasheets.

    They may be depending on the cumulative PIV adding, which is poor engineering. Sounds like Chinese crap though.
     
    Last edited: Apr 5, 2011
  19. russpatterson

    Member

    Feb 1, 2010
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    Ansi, why don't you get a 12V supply from All Electronics, get your system working. Then you can add the automatic solar part later just by swapping out that power supply with the battery and solar controller. The 12V supply isn't much money and you can use it for something else later.

    Do you understand about adding up the Vf's and how to calculate the voltage drop across a resistor?
     
  20. ansi

    Thread Starter New Member

    Apr 4, 2011
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