LED strip lighting power supply

[Cajonpassfan]

Some time ago, I purchased a 16' LED strip to illuminate a shallow section of my layout, and it came with an expensive 12V 6A power supply, see pics. I'd like to add another 10' section of like LED lighting strip and wonder whether the existing supply can handle that, and if not, whether one of the many wallwarts I've accumulated over the years would suffice. What kind of spec would I need? Buying another 6 amp supply seems like an overkill, but I don't want to start a fire either.
Advice would be appreciated.
Otto K.

[Smike]

Depends on the power needs of the strip of course. But I can say with confident if you connect another 5M strip to the end of strip you have now (Serial connect) with that power supply it will have a significant power/light drop off as you get farther away from the supply. Now if you wire it as parallel connection (with both getting power direct from the small power syupply)  you will have less light drop and it will be more even across the strips and it may work good enough.

[Maletrain]

I doubt that 16' of LED strip is going to draw close to 6 amps.  There should be some spec on the strip literature that says how many feet draw how many amps. There are probably sets of 3 LEDs in series with a resistor, with those sets wired in parallel between "bus" wires that run the length of the strip.  Some digging in the literature for your particular brand should give you amps per foot.  Or, if you post the brand, somebody on here may have the same thing as well as an ampmeter that can tell you what you need to know.

[peteski]

You need to find the specification for the LED strip where the current consumption (usually per 1 meter) is stated. Or measure the current if you have a multimeter handy. Then you can figure out the power supply requirements. I highly recommend to get a power supply with about 20% spare capacity (you don't want to run it at 100% load).  As far as voltage drop goes, if there is too much drop when using the strip itself as the power bus, you can split the strip into segments and use a heavy gauge zip cord directly from the power supply terminals to each segment of the strip.

[rodsup9000]

 Otto,
  Go to post 117 on my layout build and you can see my test on the LED strings, and see what I came up with on the draw of each string of LED's.
  I'm sure your PS will be able to up to two full strings.

[Cajonpassfan]

Thanks guys, much appreciated. Unfortunately I don't have the specs, or remember the brand, hence my question. @Maletrain is correct, there are groups of 3 LED's in the string, and yes, I already have a bit of a voltage drop in the second string. My intention is to wire the new, shorter 10'third string in parallel to avoid the voltage drop, and should probably rewire the existing second string as well, as suggested. At this point I don't have a way of inserting a multimeter into the modular wiring without cutting and splicing wires in hard to access places. I think I'll just buy the third string and test it on the existing power supply and see what happens. What could go wrong?

Rodney, thanks for the reference, you do everything BIG! Wow, a 30 amp LED string light supply! I read your post #117  and think I get it, but how long are your "strings"? BTW, thanks again for letting us run on your BIG WP layout last week, the gang and I had a great time, as attested by the attached photo. Running those loooong trains is an experience, sorry if we left any drool on the floor...

Thanks, Otto

[rodsup9000]

yes, I already have a bit of a voltage drop in the second string.

 I used 16 gauge lamp cord (bought a 100 ft roll from Home Depot) and soldered it on every string (5 meters or about 16 feet) so I wouldn't get any voltage drop.

Rodney, thanks for the reference, you do everything BIG! Wow, a 30 amp LED string light supply! I read your post #117  and think I get it, but how long are your "strings"? BTW, thanks again for letting us run on your BIG WP layout last week, the gang and I had a great time, as attested by the attached photo. Running those loooong trains is an experience, sorry if we left any drool on the floor...

Thanks, Otto

  Well, Kristi and I really enjoyed having you and the "the gang" out for the fun (and drool). 

[peteski]

Otto,
there is more than one way to figure out the current draw.    When the string is illuminated measure the voltage across the SMD resistor pads. Do it close to where the power is fed (to get the value at maximum voltage). Then also give me the resistor's value as shown on the resistor (it will be 3 digits - something like "151" or similar number).  That will allow us to calculatevthe current consumption for a set of 3 series-connected LEDs. I suspect I'll come up with about 20mA for each set of 3 (20mA going through the 3 LEDs).  Once we know that, you can easily figure out the total current draw.

[Cajonpassfan]

Otto,
there is more than one way to figure out the current draw.    When the string is illuminated measure the voltage across the SMD resistor pads. Do it close to where the power is fed (to get the value at maximum voltage). Then also give me the resistor's value as shown on the resistor (it will be 3 digits - something like "151" or similar number).  That will allow us to calculatevthe current consumption for a set of 3 series-connected LEDs. I suspect I'll come up with about 20mA for each set of 3 (20mA going through the 3 LEDs).  Once we know that, you can easily figure out the total current draw.

Thank you @peteski, advice and offer much appreciated. I've since remembered where I bought these, and their website indicates the current draw at 1.2A per meter. I just ordered another 5 meter string, and another 6A power supply for consistency's sake. A little more money than I wanted to spend, but not a big deal...
Thanks to everyone for your help.
Otto

[peteski]

Ah, it looks like you have things under control.   

[BAZ-man]

most strips are '15 watt' so just over 1 amp at 12 volts. So 2-3 more strings, easy.

[peteski]

most strips are '15 watt' so just over 1 amp at 12 volts. So 2-3 more strings, easy.

Well, per Otto, 1.2A * 12V = 14.4 W. That is close enough to 15W ( that's per meter).  If he has a 5 meter string, it will consume 15 * 5 = 75 W (or 6 Amps).  BTW, all those Chinese eBay sellers of the LED strips can be quite vague in the product specifications or sometimes just plain wrong.  You rally have to verify what you read.

[BAZ-man]

I'm sorry but a long list of 'white LED strips' on Amazon show 18-24 watts for more common 2835 LED package, just over the 15W I posted for the older 5050 LEDs. These are Total watts, not per-foot.

RGBW strips are 75-100 Watts total.  But a quick search will get your own answers.

I used an "LED Amplifier" (Amazon B0144NLSMW) between each RGBW string. This $13 box has a port for power for a 12V power supply (Different models have Barrel or barrier strips)

[peteski]

I'm sorry but a long list of 'white LED strips' on Amazon show 18-24 watts for more common 2835 LED package, just over the 15W I posted for the older 5050 LEDs. These are Total watts, not per-foot.

RGBW strips are 75-100 Watts total.  But a quick search will get your own answers.

I used an "LED Amplifier" (Amazon B0144NLSMW) between each RGBW string. This $13 box has a port for power for a 12V power supply (Different models have Barrel or barrier strips)

As I said, the specs in those eBay listings are notoriously incorrect or often confusing. I simply don't trust them anymore.  It would be the best to actually measure (or calculate) the current of the specific strip Otto has.  I provided couple of ways to do that.  If what you are saying is true then the strips consume less current and Otto will likely not need additional power supplies.

[Cajonpassfan]

Well, as I noted earlier, I had ordered another 16' roll and a 6A power supply. Turns out I only needed 10' to light the alcove; the scene is only 68" wide (by 9" deep by 18" high) so doubling up the LED string provides ample amount of light, burning about 43 Watts (see below). For comparison, the scene on the lower deck is only about 8" tall and a single string provides plenty of light there. Overall, I'm happy with the lighting, now I need to work on color matching and blending the scenery. The downside of good lighting is that every blemish stands out
Thanks for everyone's earlier comments.
Otto K.