LED Strip Power Supply Sizing (25% Headroom Rule), 12V vs 24V & Parallel Wiring Guide
How to size constant-voltage 12V and 24V DC LED drivers with a 25% thermal margin, wire L-N-PE and +V/-V terminals safely, and prevent voltage drop on runs longer than 5 meters.
To prevent brightness roll-off along the strip and premature thermal failure of the driver, size a constant-voltage SELV LED power supply (12 V DC or 24 V DC, IEC / EN 61347-2-13) with at least 20%–25% power headroom and feed every 5 m section in parallel from a dedicated copper DC bus rather than daisy-chaining strips end-to-end.
> Related Category: Compare technical specifications and model options directly in the LED Strip Products, LED Power Supplies & Transformers, and Perforated Type Power Supplies categories.
Three-step LED driver sizing formula
- Total strip power: `P_load = Length (m) × Power per meter (W/m)`
- Minimum driver rating (25% headroom): `P_driver ≥ 1.25 × P_load`
- Output current: `I_DC = P_driver / U_DC`
| Strip Type | Typical Power | 5 m Reel Load | Min. Driver (with 25% Margin) | 12 V Current | 24 V Current |
|---|---|---|---|---|---|
| SMD 2835 (60 LED/m) | ~4.8 W/m | 24 W | ≥ 30–36 W | ~2.5 A | ~1.25 A |
| SMD 2835 (120 LED/m) / COB | ~10–12 W/m | 50–60 W | ≥ 65–75 W | ~5–6.3 A | ~2.5–3.1 A |
| SMD 5050 (60 LED/m) | ~14.4 W/m | 72 W | ≥ 90–100 W | ~7.5 A | ~3.75 A |
Parallel wiring rule for runs exceeding 5 meters
- AC Input (`L`, `N`, `PE`): Always bond protective earth `PE` on perforated metal-case IP20 power supplies; use sealed IP67 drivers in damp locations, kitchens, bathrooms, and outdoor facades.
- DC Output (`+V`, `-V`): Run a 1.5 mm² or 2.5 mm² flexible copper feeder alongside long coves and inject power at the start of every 5 m reel (or both ends on high-wattage 12 V strips) so PCB copper foil is never forced to carry downstream reel current.
Frequently asked questions
Should I choose 12 V or 24 V LED strips for architectural coves?
Choose 24 V DC for runs longer than a few meters: at identical wattage, 24 V draws half the current of 12 V, cutting resistive voltage drop across the flexible PCB and maintaining uniform luminance.