How to Size a Corona Treater Power Supply (Watt Density, Width, Speed, Material)

Every buyer of a corona treater meets the same wall: suppliers quote 3 kW, 5 kW, 8 kW — and nobody shows the math. Buy too small and treatment falls short at speed. Buy too big and you pay for headroom you'll never use, on a supply that runs detuned. Here is the calculation, step by step.

The core formula

The industry-standard sizing relationship is:

> Power (kW) = Treat width × Line speed × Number of sides × Watt density

• Treat width — the actual width of the web at the treater (not the nominal roll width), in feet or meters — keep units consistent.
• Line speed — the maximum production speed, not the everyday speed. Sizing at average speed guarantees under-treatment the day you speed up.
• Number of sides — 1 for single-sided, 2 for double-sided treatment.
• Watt density — the power density needed to reach your target dyne level on your substrate. Most converting systems are sized for roughly 4.0 kW·min/ft² or less; the exact figure depends on material and additives and is best determined by testing your actual film.

Worked example

Film width 1.0 m (3.28 ft), max line speed 80 m/min (262 ft/min), single side, required watt density 2.0 kW·min/ft² (measured on your film):

> 3.28 ft × 262 ft/min × 1 × 2.0 kW·min/ft² ≈ 1,720 W ≈ 1.7 kW

Add 10–20% margin → spec a 2.0–2.2 kW supply. Run the same math at 110 m/min and the requirement jumps past 2.3 kW — which is exactly why two converters running "the same film" can need different supplies.

Three mistakes that ruin the calculation

1. Sizing at average speed. The day you speed up, watt density drops and dyne levels fall with it. Speed upgrades are the #1 cause of "treatment suddenly insufficient."
2. Ignoring additives. High-slip films need measurably more watt density for the same dyne level — copying a competitor's kW rating is not data.
3. No margin. A supply running at 100% output has no life left and no stability left. 10–20% headroom is standard practice.

Where does the watt density requirement come from?

Three sources, in increasing reliability: industry experience for similar films → supplier estimate → measured on your actual film. For a critical substrate, a bench test that steps power and records surface energy per step turns the whole calculation from guesswork into a curve.

Don't forget the rest of the system

Power sizing is only one layer. The supply must be electrically matched to the electrode station (mismatched pairings misbehave no matter how correct the kW figure), and electrode length must match the web width — an over-wide electrode wastes power and burns the roll covering; an under-wide one leaves untreated edges.