Every module datasheet lists two numbers that matter: maximum power per square metre and average power per square metre. On a P4 outdoor module those are around 850 W/m² and 290 W/m². The gap is not marketing — it is the difference between a screen showing full white and a screen showing normal content.
Start from the average, then add headroom
The supply has to cover the peaks without running hot at the average. Our rule is: size the supply at 1.4× the average load, and check that this is still at or below 80% of the nameplate.
A 10 m² wall of that P4 module averages 2,900 W. Multiply by 1.4 and you get 4,060 W, which is fourteen 300W supplies. At that load each unit runs at about 68% — warm, not hot.
Now the same wall sized from the peak figure: 8,500 W, or twenty-nine supplies. Twice the cost, twice the wiring, and no benefit. The peak only lasts as long as a full-white frame.
Where installers go wrong
- Sizing at 100% of nameplate. A 300W supply delivering 300W continuously inside a sealed cabinet runs its electrolytics near 90 °C. That is a three-summer part, not a ten-year part.
- Ignoring the ambient inside the cabinet. A dark cabinet in Dubai in July sits at 55 °C before the supply adds anything. Every supply derates above 45–50 °C and the curve is steeper than most people assume.
- One big supply instead of three small ones. Cheaper on the BOM, worse on reliability. Three 300W units at 45% load outlive one 900W unit at 95%.
- Forgetting the voltage. A common-cathode module rated 4.2V fed from a 5V rail will fail in weeks regardless of how well the wattage is sized.
The number we put on quotes
For each cabinet we state: module average load, supply nameplate, expected continuous load as a percentage, and the ambient the cabinet is expected to see. Four lines. It takes ten minutes and it removes the most common warranty argument in this business.
If a client wants the cheapest possible BOM, we will build it — but the quote says 92% load in writing, so nobody is surprised later.