Layout Lighting and DCC

[Scottl]

Wire is all about the amps. 

[peteski]

The low resistance (or heavier gauge) for the expected current load is even more important for low voltage circuits.

If there is a 2V drop over a length of wire when carrying 20A of current (this drop is independent of the voltage being used), in a 120V circuit that is 1.6% of the 120V (the voltage arriving at the load side will be 118V). But the same 2V drop @20A (over the same length of wire) will result in 16.6% drop in the 12V supply voltage, with only 10V arriving at the load side.

[daniel_leavitt2000]

I really hope I can get away with 14AWG wire as it is already in my ceiling. All the data I have been using is based on the 8' tape of LEDs being equipped with a 5W power supply. If the draw is less than I can revise my numbers.

How do I determine what the draw would be on one of these strings? I have not touched a multi-meter in years.

[Scottl]

There is a rated current per LED, and you can multiply that and add a safety factor.  For example, my 600 string of 5050 LEDs is rated at about 144W @12V total.  I am going to supply it with a 120W supply and use 14ga house wire (which is overkill).

[peteski]

I really hope I can get away with 14AWG wire as it is already in my ceiling. All the data I have been using is based on the 8' tape of LEDs being equipped with a 5W power supply. If the draw is less than I can revise my numbers.

How do I determine what the draw would be on one of these strings? I have not touched a multi-meter in years.

The place where you bought the strips should have provided you with the specs of some sort. Once you have thenm you can do all the calculations needed.  No multimeter needed (but I'm sure you will have to dust it of in the next couple if years for all sorts of layout troubleshooting). 

[daniel_leavitt2000]

Ok Pete...

http://www.amazon.com/gp/product/B00JQV6Q4I/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Cool white: 16.4' @ 14.4 watts


http://www.amazon.com/gp/product/B00JQV6NNC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Warm white: 16.4' unknown watts. same company as the cool white above, so I am guessing it will be about the same.

http://www.amazon.com/gp/product/B00HSF64E6/ref=od_aui_detailpages00?ie=UTF8&psc=1
Blue: 16.4' @ 4.8 watts according to sears:
http://www.sears.com/lighting-ever-le-lampux-12v-flexible-led-strip/p-SPM8261879902?sid=IDx20140425xECNMPHM12&srccode=cii_20121666&cpncode=38-22298741-2&redirectType=SRDT

http://www.amazon.com/gp/product/B00EPZNXNC/ref=od_aui_detailpages00?ie=UTF8&psc=1
Amber: 16.4' unknown wattage, though It should be similar to the blue above which has the same size/count LEDs.

So now we have the whites at .88W per foot and .29W per foot on the two colors.

31W for each color over the 105' run. 2.6 amps.

92.2W for each white over the 105' run. 7.7 amps.

That sounds a lot more practical than before.

Now this has me confused:
http://en.wikipedia.org/wiki/American_wire_gauge
This says that with the proper insulation, even 14AWG would be more than enough, though the voltage drop would be bad.

[peteski]

Ok Pete...

http://www.amazon.com/gp/product/B00JQV6Q4I/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Cool white: 16.4' @ 14.4 watts


http://www.amazon.com/gp/product/B00JQV6NNC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Warm white: 16.4' unknown watts. same company as the cool white above, so I am guessing it will be about the same.

http://www.amazon.com/gp/product/B00HSF64E6/ref=od_aui_detailpages00?ie=UTF8&psc=1
Blue: 16.4' @ 4.8 watts according to sears:
http://www.sears.com/lighting-ever-le-lampux-12v-flexible-led-strip/p-SPM8261879902?sid=IDx20140425xECNMPHM12&srccode=cii_20121666&cpncode=38-22298741-2&redirectType=SRDT

http://www.amazon.com/gp/product/B00EPZNXNC/ref=od_aui_detailpages00?ie=UTF8&psc=1
Amber: 16.4' unknown wattage, though It should be similar to the blue above which has the same size/count LEDs.

So now we have the whites at .88W per foot and .29W per foot on the two colors.

31W for each color over the 105' run. 2.6 amps.

92.2W for each white over the 105' run. 7.7 amps.

That sounds a lot more practical than before.

Now this has me confused:
http://en.wikipedia.org/wiki/American_wire_gauge
This says that with the proper insulation, even 14AWG would be more than enough, though the voltage drop would be bad.

Geez, these things are worse at having accurate specs than the MRC DC throttles.  Looking at the review of the daylight white strip:

They are 5050 SMD LEDs and are non-waterproof. There are 300 LEDs on a 5 meter strip. These are some of the most efficient and cool running LEDs I have tested. The product description says they use less than 14.4 watts per meter. Well actually they use much less. In my testing, a 1 meter long piece (39.4 inches) uses 8.76 watts. When they are powered to 12.0 volts they use .73 amps (12.0 volts X .73 amps = 8.76 watts). I am currently using them as counter lights (undercabinet lights) in my kitchen. During the day I run them at 12 volts and at night I run them at 8.2 volts, which makes a very nice night light for the kitchen. When run at 8.2 volts the whole 5 meter strip only uses 3.3 watts. Great product.

Anyway, forget the insulation thing - that is a voltage (not current rating). The material used for insulation and its thickness is what gives the ROMEX cable the 600V rating. But you are dealing with current.

According to the chart, 14 AWG wire has 2.525 ohms per 1000 ft. That is 0.2525 ohms per 100 ft.

If you just hooked up the full 5m LED strip to the end of the wire (so the full current would run through the full length of the wire) the voltage drop (of a 100 ft run) would be (two lengths of the wire) times (the total current consumption of the LED strip)
(2 x 0.2525 ohms ) X (0.73 Amps/meter X 5 meters) = 1.8 Volt drop.   That assumes the specs provided by the reviewer are correct. The parenthesis are there for clarity.

But since you will have the wire paralleling your LED strip and have a feeder ever foot or two, the full current will not be going through the 14 AWG wire.  Plus since the trace on the strip is also in parallel with the wire, some current will be passing through it.  To do a calculation of the exact voltage drop of this configuration would get much more complicated, but it is safe to say that the total voltage drop from the beginning to the end of the 5 meter daylight LED strip paralleled by a pair of 14 AWG wires will be less than 1.8V on the end of the strip.  I guess probably less than 1V.

[daniel_leavitt2000]

Pete, you sure you don't want to come over and help wire? You have been a great help here. Electricity is still sorcery to me so this has been a huge learning curve.

[basementcalling]

Daniel, I am just going to let you keep asking the questions. So far you are doing a great job getting answers I need for my layout as well.  Keep on going. I keep being the dummy in the room who doesn't want to open his mouth and reveal how ignorant I am on electronics.

[John]

I'm also puzzled with John's setup. First of all, it seems to be a waste to have a pulsing DCC signal from an expensive booster "wasted" for powering LED lights. Why not just use a cheap dedicated DC supply?  DCC signal is not buying anything (not like the brightness can be controlled through DCC).  Plus (since LEDs need DC 12V) they are running at roughly half brightness: The DCC signal flips polarity (at about 50% duty cycle) and the LEDs will only illuminate on one of the cycles (so they are off half the time).

I have a 12VDC line that runs all around the layout, powered by an old laptop PS (2 amp I think -- I'll check later) .. I use that to drive all my SE8s, and other devices .. I have some of the LED lights running off them as well .  in some places, it was just easier to run them off the main DCC bus (for now) .. I need to have the electrician come in to run another 15 amp ckt into the layout room to get rid of some of the power strip nightmare, so for now, I don't want to add more plugs to overload sockets

[peteski]

I have a 12VDC line that runs all around the layout, powered by an old laptop PS (2 amp I think -- I'll check later) .. I use that to drive all my SE8s, and other devices .. I have some of the LED lights running off them as well .  in some places, it was just easier to run them off the main DCC bus (for now) .. I need to have the electrician come in to run another 15 amp ckt into the layout room to get rid of some of the power strip nightmare, so for now, I don't want to add more plugs to overload sockets

That makes a lot more sense!  The way I understood your statement was that you were running the lights from the output of the DCC booster.   That's what is usually called a DCC bus.    You were using the 12V DC supply power which feeds the booster to also feed the LED lights.  I suspect that it is more than 2A supply, or you don't have very many LEDs (or trains running at the same time).

[daniel_leavitt2000]

Just a little update. I have purchased 5 spools additional of each color plus mounting clips, automotive molding tape, and two 15amp 12V power supplies.

I talked with my electrician and we will be running additional circuits to the power supplies.  I plan on using jacketed 4 circuit 14AWG cable (used for household wiring) as feeder wires. These will double as a mount for a cloth valence (think shower curtain). This will really keep costs down and avoid any drilling into the ceiling.