Landscape Lighting Load

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HudsonDIY

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I have a question for those in the know about landscape lighting and electrical engineering in general. I have a pool and spa which each include a 12v light. Previously they were halogen bulbs which I have replaced with LED's. They are powered from the same Intermatic control box which houses the pump timer. The transformer is a 500w unit. Obviously this is way overpowered for the new LED's in the pool and spa. Because I have some power to spare I have started adding other LED lights inside my pool enclosure. I'm no electrical genius but I can do the math. From my research I've learned that the max wattage load should be less than 80% of the total wattage or around 400 watts total. Which brings me to my question. Is there a parasitic wattage load from the wire itself?

Thanks in advance for your replies.
 

Reach4

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Presuming simple common LED lights, the wire should not affect your calculations. The effect of long wires is they would act as a series resistance, which would reduce the load on the transformer. The LEDs would glow a little less brightly.

I could imagine some kind of regulated LED lamp assembly which keeps constant brightness despite supply voltage changes (within limits). Then the power dissipated in the wires as heat would become extra loads on the transformer. I expect, even there, the effect would be small at normal wire lengths.
 

jadnashua

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An LED requires DCV to run, so whether it's supplied from a power supply external to the bulb or internally from an ACV source, it probably doesn't matter much. Internally, an individual LED is probably using something like 1.5VDC. If there's more than one, wiring them in series would allow a higher input voltage. Power = Volts * Amps, so you can use smaller supply wiring if your voltage is higher while transmitting the same amount of power. That's one reason why major power lines are hundreds of thousands of volts, to keep the wire sizes down with acceptable losses along the way. The newest performance EVs are starting to use 800V supplies, making the recharging possible with smaller cables.

As long as you maintain the recommended wire sizes and don't exceed the maximum wattage you're trying to power, it shouldn't be an issue.

The 80% rule applies to the load on the main supply line for a continuous use item (or at least not an intermittent one). You'd have to read the specs on the power supply you have to determine if it is rated for 500W continuous or not. It might support 500W continuous without overheating or shutting down. If it's a 500W peak output, then probably not and even 400W might be too much continuously. The things may require derating if it is enclosed so it cannot dissipate the heat as designed, too.
 

HudsonDIY

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Thanks for the replies. Everything I'm reading, including the specs from Intermatic state to keep max load at 80% for a magnetic (coil) type transformer. I'm no where near that at around 131w. Although I plan on adding a couple more lights in the grill area, but that shouldn't amount to more than another 24w. I just wanted to be sure there wasn't an invisible factor I had overlooked. I had to go with a 16/2 direct burial cable since the run and junction box is outside the enclosure and then run back into the enclosure wherever I needed a light.

Nights are getting longer and the days shorter, I don't want to be fumbling around in the dark.

Thanks again,
 
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