Would a power supply included with an LED strip lights support multiple cuts if the overall length doesn't change?

Question

Hobbyist question, not a professional (that'll become very clear shortly).

GOAL:
I have some multi-floored Lego buildings that I'd like to light up the inside. Buildings are on 3 shelves laid out side by side with a potential of 10 per shelf (shelves are 10' wide).

LAYOUT:

• The LED strip lights (16.4') includes a power supply (I only know it's 12V and have contacted the seller for more details of the PS).
• I'd run the power from the PS to a main terminal block.
• The main terminal block would connect to a pair of subsequent terminal blocks (a pair located on each shelf - 1 for the positive leads and 1 for the negative leads - 6 total).
  • Each terminal block has 8 terminals (not enough for 10 buildings per shelf but it's what I have on hand for now)
• I would be using 22AWG to connect the shelf terminal block to the building. There would be JST plug between the building and the shelf terminal block so the building could be easily disconnected for repairs/updates/etc.
• The connecting wire would enter the back of the building to the lower level
  • If the building had additional levels, connecting wires would be attached to cut LED strips in series.
  • Each level within a building would have a 3" section of LED strip.
• Am I missing anything?

PLAN
I'm looking at buying an LED strip of lights (16.4' or 196.8"), cutting pieces off, and attaching them to the inside of the Lego buildings. Each strip would be connected using 22 AWG wiring. There would be JST connectors between the terminal blocks so the building could easily be removed for whatever reason. Terminal blocks are being used for tidiness primarily.

QUESTION
There are 23 buildings and around 65 levels in total but no more than 3 levels per building. I'd only need 3" sections for lighting for each level building (for a building with 3 levels, I'd be using a total of 9" of LED strip lights). I expect to use the entire LED strip.

Would my introducing of the multiple terminal blocks and JST plugs add too much resistance to the circuit that I would need to rethinking my layout and/or power supply?

What are some things I should consider (for safety) or am I overcomplicating this project?

Answer 1

The short answer is: length doesn't matter, resistance does.

LED strips are made of flexible printed circuit (FPC) material that uses copper tracks to connect the LED segments together. Such tracks vary in width and thickness depending on the manufacturer. I generally regard these as a poorer conductor than just about any wire except perhaps ≥24 AWG.*

If you were merely cutting segments apart and inserting 22 AWG (or any gauge) wire, you're effectively adding resistance, which would be increasing the load, and might eventually exceed the power supply rating.

However, it sounds like you are creating a star topology, in which various shelves or buildings (or whatever) are each connected to a wire terminal. This effectively shortens the overall length and reduces resistance by connecting loads in parallel.

I'll try to explain with the below schematic examples.

^{simulate this circuit – Schematic created using CircuitLab}

1. In the first example, meant to represent an unmodified LED strip, there is an existing resistance of the strip itself. This resistance is represented by R_D1, R_D2, etc. Without cutting the strip, this inherent resistance is additive because the entire strip is in series. (Technically, a 12V strip might have 3-LED segments connected in parallel, but I'm only addressing the resistance of the strip itself.)

2. In the second example, I've inserted R_wire to represent the additional wire that you've added, regardless of gauge, it will add some resistance. (The thicker the wire, the less resistance per linear distance, but it's still adding something.)

3. In the third example, I've again added R_wire to represent the wire, but now the strip has been cut into segments and (presumably) the wire is connecting them to the terminals you described. It's my hope that you can see the two illustrated segments are in parallel, which presents a lower resistance than they would in series.

Obviously, you can't conclude from this alone whether you are adding too much resistance. If you were adding several meters of 22 AWG wire everywhere, then that could still present a problem despite connecting things in parallel. My goal here was to illustrate how you can model and measure your project to determine whether things are being improved or not.

TL;DR: In general, as long as you're connecting various segments in parallel instead of in series; and as long as you're ensuring that +12 V doesn't come into direct contact with GND (a short), you should be OK.

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* I have some LED strips that vary in width, but I wanted to do some calculations just to compare them to various wire gauges. For a strip with a 4 mm wide track using 1 ounce (36 µm) copper, the cross-sectional area is about 0.15 mm². If the strip is using 2 ounce (72 µm) copper, the cross-sectional area is 0.30 mm². Here are the cross-sectional areas of wire gauges from 26 to 20:

• 26: 0.13 mm²
• 24: 0.21 mm²
• 22: 0.33 mm²
• 20: 0.52 mm²

As you can see, even with 22 AWG wire it has a greater cross-sectional area than a moderately robust LED strip. You can refer to wire gauge charts to find this information as well as resistance-per-length figures.