Single power supply for multiple 12V devices over long run; LED and swimming pool application

Question

Hi I am new to this site and have no electrical training, but I am braving the job of installing 4 5M strips of waterproof(IP68) 5050 RBG LED strips on the interior coping of our above ground pool (approximately 65 ft total length). These lights will shine down into the water but will not be submerged. (This video shows what I am attempting but is not remotely helpful in designing: https://www.youtube.com/watch?v=X6A8XivGYEk). Just jump to the middle somewhere to get the idea.

I have researched the requirements for connecting multiple strands of LEDs and understand that I need an RBG Amplifier every 1 or 2 strands to (a) use a single remote and have them all perform the same function and (b) prevent voltage drop. I have elected to use an amplifier for every additional strand beyond the first one. Each amplifier requires its own power supply.

So my wiring, which I have tested in the house with good results, looks like this (forgive the novice take on wiring diagrams):

The ends of each strip will be run under the pool coping to the exterior of the pool. Once on the exterior of the pool I will attach to the controller or amplifier as shown in diagram. As needed I will solder connections and/or use heat shrink and/or non-conductive silicon. My intent is to place the non waterproof amplifiers and the Power supplies in a lockable waterproof survival box mounted to the exterior wall of the pool. (I will have to drill some holes in the box but will make waterproof.)

Being appropriately fearful of 110V and water, I am disinclined to run 4 extension cords around my pool to my waterproof boxes to connect to my 12V power converters. While I believe I can do this with the utmost care and that I can have all connections positioned so that if failure occurs they will not go in the pool, freak accidents happen all the time.

Now to my questions: Is there a way power my amplifiers from a single power supply/converter (which I can place a comfortable distance from the pool)? My understanding is that power consumption should not exceed 80% of the supply's capacity. So if each line of lights uses 75W I need at least a 375W power supply. From that supply, which also needs to convert to 12V, I would need to make a short (~3') 12V run to my first strip of lights, then 2 longer runs (~18') to the nearest amplifiers, and finally a ~36' run to the furthest amplifier. Can this be done? Is there voltage drop to be concerned about if nothing is being powered until it reaches the amplifier? Any advice, product suggestions, etc are appreciated.

Products I am using are on Amazon: SUPERNIGHT-Waterproof-Submersible-Underwater-Controller and SUPERNIGHT-Repeater-Signal-Amplifier-Strip Sorry, as a new poster I was limited on my links.

Answer 1

The first thing you ought to do is get the local/state/national regulatory standard for electrical wiring. In the US, for example, the starting point would be NFPA 70 (the National Electric Code) which you can access electronically for free through the NFPA's website. Usually the requirements near water are different than those in dry areas, for obvious reasons you already are aware of. The standards will help you better understand the safety ramifications that you're rightfully concerned about. Note that local laws (like permitting requirements by a township) may also require you to have an electrician and/or engineer approve the design and/or perform the installation.

In particular I'd like to point out a potential misconception about using low-voltage here: even a converter to low voltage is not necessarily considered "safe" unless there is enough isolation between the high and low sides; too little and it is easy for a fault to dump line voltage on what you think is just 12V. These kinds of converters will explicitly note that they are qualified as something like "PELV" (protected extra low voltage) or "SELV" (safety extra low voltage). The use of a GFCI may or may not be sufficient to cover safety concerns, check the safety standards that apply to your location.

Also make sure the jacketing/insulation/filler in your wiring is rated for outdoor use, particularly in regard to moisture but also the potential for impact/abrasion, because anything else is is a recipe for an electrical fire (again, the relevant safety standard for your area will help you determine the exact requirements).

To get into some of the non-safety aspects of your questions:

Voltage drop: yes, this is a concern. Recall that wires aren't perfect conductors, they have some resistance per unit length, which causes a loss in voltage of I * R (per Ohm's law). You can address this with thicker wires (increased cross-sectional area results in lower resistance), or by reducing the distance to the load. It is also important to note that the power lost by I * R is lost as heat, so pay attention to the thermal rating on the insulation for the wiring you use; again, refer to the appropriate safety standard.

Power converter: most commercial/consumer power supplies are rated for indoor use, where the ambient temperature and humidity are low. They may not work as intended outdoors, particularly in warmer weather; the data sheet usually specifies permissible relative humidity and de-rating values for increased temperature. The data sheet should also specify the efficiency; no converter is 100% efficient so you'll need more power in than you get out (the rest is wasted usually as heat). If the LEDs specify an inrush current--for example, if they have a lot of capacitance on the input--this also factors into the design, as you need to check that the power converter can either supply that much current, or at the very least recover from it. These factors may or may not add up to the "80%" you suggested; check the data sheets, don't guess.