LED light strips amp load

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Old 01-12-17, 09:21 AM
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LED light strips amp load

Through the help of another thread, I am ready to wire up some LED light strips in my basement. I am running two separate runs, each off of their own 200 watt magnetic dimming transformer. (The two images in my pic below are not of the two runs, but two different wiring examples of one of the runs) Each transformer is going to be wired off the same dimmer switch. I'm going to run the strips in parallel, so they each have their own direct connection to the transformer, but my question is about my wiring method. I'm thinking of two different methods, one of which saves me some wire, but not sure if it's the best way to do it. Depending on the strips I get, each one could be pulling up to 6amps, so I'm wondering if the #18/2 thermostat wire I bought is going to cause a voltage drop or have any other problems. Here is a crude MS paint mockup of the two wiring options I was considering:
[ATTACH=CONFIG]75702[/ATTACH]

Question I have is that in the first one, it seems that the first part of the wire will be handling the amps of two of the light strips. Where in the second image, each pair of wires will only be handling the amperage of one light strip. Can I do it the first method without any issues? Or should I break them out with a splitter at the beginning like in the second example? I will be using the 5 meter light strips, so the length of the longest run of #18 wire would be a bit more than 30 feet.

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Old 01-12-17, 09:40 AM
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In both your examples the two wires coming off your transformer will be carrying the full load of all your lights. That should be kept to as short a run as possible and since it may see 18 amps I would use 12 ga wire.

In your first drawing you are correct that the beginning of the wire feeding the second lights will be carrying the current for two lights, up to 12 amps so I'd go for 14ga wire. Since the wire feeding the first string only feeds one string and carries 6 amps I would use 14ga since you will already have it on hand for the other run though you could go smaller if you want to buy a third gauge.

In your second drawing you have separate wires going to each light from the buss bar so they can be lighter gauge. You could get away with 18ga especially since you allude that the load may be less than 6 amps but if you'll be pulling a solid 6 amps then I'd go up to 16ga to be safe and minimize the voltage drop especially if your runs are longer.
 
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Old 01-12-17, 09:48 AM
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Most 5 meter lights strips draw less than 24 watts (2amps)
 
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Old 01-12-17, 10:00 AM
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That's good info. PJmax, you might be right, but just not sure and want to error on the side of caution. These are some that I am considering buying, which have 600 lights per strip instead of 300. The details say that it needs 12v/5A power supply, but some of the comments are stating that 5A isn't enough. Definitely would be if I were to buy the 300 light strand.

Pilot Dane, thanks, it's good to know I'm thinking things through correctly. I can easily get some of the heavier wire. Makes me wonder what gauge the leads coming off the transformer are. However, now that I look closer at it (this is the one I was going to buy), it states that 15.6 amps is the max output current. so maybe I ought to just stick with the 300 light strips. I don't want to fork out for a beefier transformer.
 
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Old 01-12-17, 10:30 AM
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From what I can see a strip of that length and using 600 LED's is just over 4A of load. Some power supplies may not start up with the load that close to the max which is why they want you to use a robust 5A supply or a larger one.

No need to run the supply near max either as that will cause it to run hot and shorten its life.
 
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Old 01-12-17, 10:43 AM
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Originally Posted by PJmax
From what I can see a strip of that length and using 600 LED's is just over 4A of load. Some power supplies may not start up with the load that close to the max which is why they want you to use a robust 5A supply or a larger one.

No need to run the supply near max either as that will cause it to run hot and shorten its life.
Yeah these strips are supposed to use around 48 watts each, so three strips would be around 150 watts, so a 200 watt supply should be enough overage right? I am thinking of just going with the 300 light strips, which use half the wattage, and going with the 150 watt supply. Then I'm only using a bit over half of the power of the supply.
 
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Old 01-12-17, 10:58 AM
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Originally Posted by Pilot Dane
In both your examples the two wires coming off your transformer will be carrying the full load of all your lights. That should be kept to as short a run as possible and since it may see 18 amps I would use 12 ga wire.
Weird question, the electrical circuit I'm running this all off of is 120VAC, 15Amp circuit. So it is all run with 14 ga wire. So would it be doing me any good at all to run 12 ga wire out of the transformer? Not that it matters, I can run 12 ga, just curious.

Also I'm curious how the math works on this. If three light strips will be pushing close to 15 amps, and I'm running two of these banks on the same circuit, that would be a combined load of 30 amps. But that is out of the 12 volt DC transformer. So this will run fine on my 120V AC 15 amp circuit right? So say I'm running 300 watts total for all 6 light strips, would the math work out as: 300W/120VAC = 2.5A load on my home circuit?

Edit: I may be way off base here. Not an electrician as you can tell.
 
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Old 01-12-17, 11:02 AM
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300W/120VAC = 2.5A load on my home circuit
That is correct.

#14 wiring on a 15A breaker is fine for this circuit.
Dane recommended increasing the size of the low voltage wiring. As the voltage goes down the current goes up. As the distance increases the loss increases.
 
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Old 01-12-17, 11:09 AM
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Originally Posted by PJmax
That is correct.

#14 wiring on a 15A breaker is fine for this circuit.
Dane recommended increasing the size of the low voltage wiring. As the voltage goes down the current goes up. As the distance increases the loss increases.
Ah of course. Tried to do maths. failed at electronics. Thanks!

Edit: is there a nice clean method for splitting the wires if I wanted to do it like option #2 in my drawing? Some sort of little bus thing or something? So I don't have a splice mess on my hands?
 
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Old 01-12-17, 04:29 PM
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For the runs that are just going in my crown molding, not behind walls, is it ok to just use 14 gauge lamp cord? I'd just rather not run romex up there.

Edit: doesn't even look like they make #14 lamp cord. What do you recommend using for these longer runs in the crown molding? I am probably just going to do 300 light strips, the 3528 model, so probably only around 2 amps for a 5m strip. So maybe I could use the #18 thermostat wire? Then do I need to worry about voltage drop my longest run was like 35 feet? Sorry, I really feel clueless about this.
 
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Old 01-12-17, 04:51 PM
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A direct run of #18 thermostat cable is perfectly ok.
With each strip on its on feed there will be minimal voltage drop.
 
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