# Series or Parallel LED Ribbon?



## seabilliau

I have several sections of LED ribbon that I need to power. I have the appropriate transformer and dimmer, but my question is does it matter if I run the separate Ribbons in series or parallel? The sections of ribbons are at different locations and it would be advantageous to have them running from a common bus.


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## T-Man

It's about voltage. The strips are a parallel set up to a fixed voltage with samller sections in series with a resitor. SHow a picture. You cut a ribbon up to use the different section in series.


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## seabilliau

I was hoping to show this to you guys once it was all set up, but I see I'll have to give you a sneak peak now.

Each strip is about 1.5-2 feet long. Right now there are three; one under the arches of the viaduct (not visible) and two more each running across the tops of the first row of buildings. Running the wires parallel would be easier but it would not be much harder to run it in series. I just wasn't sure if it made a difference or not so I wanted to ask first before I start running wires.










The lights are not on, any appearance of light is a reflection.

_P.S. I wanted to run two more ribbons across the tops of the back row of buildings but the curves are sharp and I feel the ribbon would not lay on it properly taking away from the crisp lines it has right now._


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## T-Man

Ribbons are set up in parralel for a certain voltage. I do not think they can be wired in series. As I said they have small groups of series and that is how you can separate the tape. Each group runs off the voltage and the rest are parrallel anyway. DO you know the voltage??????


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## seabilliau

Sorry. Their voltage is 12v DC. The transformer is 12v dc, 2.5 amps, 30 watts, running through a dimmer switch.


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## gunrunnerjohn

The ribbons are set up with three series LED's and a small resistor in the 130-150 ohm range. They're designed for 12 volts at 20MA for each three LED section. The sections are actually wired in parallel if you cut longer chunks of the strip, and that's the way you should use them. If you series three of these, you'd need 36 volts to run them at 20ma. Running three of them as intended, they would be 12 volts at 60ma for full 20ma per three LED section.


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## T-Man

Along the tape there are two or three LEDs with a resistor. This cell or chain runs on 12 volts. One strip has many of these in parallel. You cannot wire them is series.


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## gunrunnerjohn

You be too slow T-Man. 

Oh, and you could run them in series, you'd have to cut each three LED strip apart and wire them in series. Why you'd want to totally escapes me.


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## T-Man

But I got your picture!

Looking carefully there are two cells each powered by 12 volts and have three LEDs and a resistor.










The only problem is running too many off the transformer and exceeding the 2.5 amps


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## seabilliau

Thanks. It makes sense now. In series my voltage would drop (like water pressure with many pipes coming off one source. But if I keep them in parallel the voltage will stay the same (one pipe coming from one source). Got it.


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## gunrunnerjohn

Also note that there's no reason to run them at the full 20ma for each segment. For one set of passenger cars I did, I used four segments, and they're all running with a total of 20ma current, that's 5ma each. They're plenty bright, when I ran them at full current, it looked like daylight inside the passenger cars!


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## T-Man

For effect keep them separate and use different resistor or diodes to drop the voltage. That way you get different shades in different buidings. The diodes are better for the longer chains. The easy way is to string them altogether. A diode will drop the voltage by .7 volts. You can insert one between your ribbon sheets and get a different results between them. The first sheet will drop by .7 volts the second by 1.4 the third by 2.1. It all depends what you want.


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