Hey @Robinlawrie! Sounds like these are 5V pixels in a 60 LED / m strip.
I would recommend you run a long 12 AWG bonded pair behind the entire length, and connect it to the strips at 3 points: middle, as you suggested, as well as at both ends. I think you can power it from the middle (best) or probably either end. If you need to keep the big wire aligned with the strip, you can zip tie every foot or so, or use silicone RTV adhesive to hold it in place.
I agree with timster: turn down the max power and you can use smaller supplementary power wires. 50% power looks 75% bright.
Here’s a recent real world datapoint.
I did a project last year that involved running 60/m 5V LEDs up to 270 in a line before power could be re-injected. I chose to run 10AWG behind each strip. This was actually because some of these fixtures were chained, so these rails could be used to delivering power to the next fixture in the chain, up to 500 total LEDs across three fixtures. It worked really well, all the way up to 2 MHz clock, and 100% power. We ultimately chose to run them at 70% max. That’s 30% less heat, 30% less load, some unknown percentage longer lifespan, and yet subjectively it looked only 10% less bright.
This is absolutely true! Let’s assume full white, the worst case scenario. At your injection point, 5 V may have dropped to 3 V from the thin copper traces in the strip, but the same current through your 12 AWG will have only dropped to 4.5V or so. Then when you connect it to the strip, that 3 V is buoyed back up to 4.5 V. Current actually flows backwards into the positive copper trace in the strip from the far injection point. The center between injection points in the strip may still be down at 4 V, but now that’s the lowest instead of having some trying to operate at 3 V. In this example, for simplicity in the explanation, I’m ignoring the mirrored voltage rise happening on the GND conductors.
Right! Instead, you want to make short pigtail leads that reduce your big wire down to something manageable like 18AWG within a few inches of the strip. In open air, 18AWG can actually safely handle 16A (and in my experience, that chart includes some pretty nice safety margins, especially for short connections). For the connection topology I recommended, note that it is only conducting half the max current, so 9A of your 18 per strip.
The quality of this 12 AWG → 18 AWG connection is kind of inversely proportional to how easy it is to make it. You can look up these techniques on YouTube, listed here from highest quality to lowest.
- Inline twist-and-solder, or window strip and solder, with heat shrink or electrical tape covering.
- Band splice (this is a specialized press that many contract manufacturers have)
- Dissimilar gauge butt-splice connectors using a proper crimper
- Terminal blocks with crimped ring terminals
- Wago 221-412 lever nuts can handle 12-24 AWG wire
- Low-temp “Heat shrink solder seal” connectors
I don’t recommend the vampire press-to-piece taps.