Signage Power Supply Load Calculator: Sizing Worksheet

The 20% headroom rule is not about future expansion. It is about keeping the driver between 60% and 80% load, which is where both the efficiency curve and the capacitor life peak. Run a driver at 30% and efficiency drops 3–5 points; run it at 95% and you cook the output capacitors. Both ends of the range are bad, and the middle is where 20% headroom puts you.

Here is the worksheet.

Step 1 — Count the Load

A typical injection-moulded signage module draws 0.72 W. Check your module datasheet — this varies from 0.24 W for small single-LED units to 1.5 W for large lensed modules, and guessing here throws off everything downstream.

Step 2 — Apply the 20% Headroom

Step 3 — Apply Ambient Derating

This is the step people skip. Take the highest temperature the air around the driver will reach, not the outdoor forecast. In a sealed sign cabinet, add 20–25°C to outside air.

Step 4 — Round Up to a Stock Size

Never round down. Round to the next available wattage.

Worked Example 1 — Shop Front Lettering

• 40 modules × 0.72 W = 28.8 W
• × 1.2 = 34.6 W
• Driver in a ventilated channel behind the fascia, ambient 40°C → ÷ 0.90 = 38.4 W
• Round up: 60 W IP67

A 36 W driver would technically cover 28.8 W at 25°C. In a 40°C channel it would be running at 80% continuously with no headroom — and the 36 W unit’s capacitors see far more ripple stress than a 60 W unit coasting at 48%.

Worked Example 2 — Mid-Size Fascia Sign

• 320 modules × 0.72 W = 230.4 W
• × 1.2 = 276.5 W
• Sealed cabinet, ambient 55°C → interpolate to 0.75 → ÷ 0.75 = 368.7 W
• Round up: 400 W IP65

Note what happened: a 230 W load became a 400 W specification. That is a 74% overspec on paper, and it is correct. Anyone quoting you 250 W for this job has not read a derating curve.

Worked Example 3 — Large Pylon Sign, 1,200 W

• 1,667 modules × 0.72 W = 1,200 W

Do not put this on one driver. Split it into four 300 W units:

Four units beat one 1,200 W unit on three counts:

1. Failure blast radius. One driver fails, you lose 25% of the sign instead of 100%. For a pylon sign visible from a highway, that difference is the difference between a service call and an emergency.
2. Cost. Four 500 W units usually cost less than one custom 2,000 W unit, because the 500 W is a stock item.
3. Serviceability. One person can swap a 500 W unit on a ladder. A 25 kg driver needs two people and a hoist.

The only argument for the single large unit is a marginally smaller enclosure footprint.

Copy-Paste Worksheet

Three Errors That Survive to Installation

1. Using the LED’s nominal wattage instead of measured draw. Measure one module with a bench supply before you multiply by 1,667.
2. Forgetting the driver’s own consumption. A 90%-efficient 500 W unit draws 556 W from the mains. Size the breaker and the cable on the input side, not the output.
3. Sizing on the first cool day. The system that boots fine in March fails in August.

Download the printable worksheet — A4, with the derating table and the voltage-drop formula pre-filled. → Get the worksheet · or send us your module count and we will size it for you: Request a quote

自检：数字锚点 28 个 · 反直觉 2 个（20% 余量不是为了扩容 / 拆成多路更便宜且故障影响小）· 主词出现 7 次（含变体 15 次）· 内链 7 条

A6 · Enclosed vs Open-Frame Drivers for LED Sign Panels

正文

The wrong question is “indoor or outdoor.” The right question is: can an end user touch it? That single answer determines the enclosure requirement under safety standards, and it cuts across the indoor/outdoor line in both directions.

An enclosed driver inside a well-ventilated indoor panel is a waste of money. An open-frame driver inside a sign cabinet that a maintenance electrician can reach is a compliance problem. Here is how to tell the difference.

What the Two Forms Actually Are

Open-frame — bare PCB, exposed transformer and capacitors, no housing. Mounts with standoffs inside another enclosure. Typical: our CPS industrial series.

Enclosed — PCB inside a metal or plastic case with terminals or a cable. Ranges from vented IP20 (N series) through sealed IP65 (CFX) to fully potted IP67 (R series).

Three-Way Comparison

Read the last row carefully. In a clean, ventilated, inaccessible panel, the open-frame driver outlives both enclosed options — it runs coolest and its capacitors see the least thermal stress. The enclosed unit’s premium buys you protection from environment and from fingers, not longevity.

The Four Install Scenarios

Scenario 1 — Back-of-house panel, locked, climate-controlled. Open-frame. An enclosed unit here runs 4–8°C hotter and costs 15–20% more for protection you do not need.

Scenario 2 — Sign cabinet, serviceable by electrician, no water exposure. Enclosed IP20 minimum. Safety standards require a barrier between a user and live parts. This is the most commonly mis-specified case: it is indoors, so someone specs open-frame, and it fails inspection.

Scenario 3 — Outdoor cabinet, drainage adequate, no pooling. IP65. See our rainproof vs waterproof field data — in a vertical installation with drainage, IP67’s 30% premium buys little.

Scenario 4 — Ground level, planter box, wash-down, or poor drainage. IP67 only. And check the IK rating too — a public-realm sign gets kicked and hit. IK08 (5 J) minimum, per IEC 62262.

The Serviceability Angle Nobody Prices

Enclosed drivers swap out in about 10 minutes regardless of rating. Open-frame takes longer only if the surrounding enclosure is cramped.

But there is a second-order cost: when an enclosed driver fails, it fails as a unit you can identify from outside. When an open-frame driver fails, the failure often takes out adjacent components or leaves carbon tracking on the panel. On a sign with twenty drivers, that difference shows up in diagnostic time.

Cost Across a Real Project

Twenty-driver sign, 200 W each:

On paper, open-frame wins. Add one service call at $180 in labour and a lift hire at $400, and the IP67 option is cheaper by year three — if the environment is genuinely hostile. In scenario 1 it never pays back. That is the whole decision.

Standards That Force the Answer

• IEC 61347-1 (lamp controlgear) and UL 8750 (LED equipment) both require barriers between accessible surfaces and live parts.
• IEC 60529 defines the ingress rating you specify once you have decided on the enclosure.
• IEC 62262 defines IK impact rating — relevant whenever the public can reach the installation.

Enclosure is a safety requirement. Ingress rating is a durability requirement. Conflating them is why so many signs end up with the wrong driver.

Tell us where the driver sits and who can reach it — we will specify the form factor, the rating and the IK level in one reply. → Request a quote · Browse by IP rating