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UV Curing

(November 2000) posted on Tue Nov 14, 2000

Bron Wolff discusses how you can assess and improve your UV-dryer performance by learning from his company's experience.

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By Bron Wolff

But wait. We also had to figure in a power factor, a number that is typically absent from spec sheets and represents the actual power delivered to the curing system. In our case, the factor was 0.92 (your local power company can tell you the power factor for your facility). When we multiplied this value against the actual wattage and divide by the lamp length, we found that the corrected theoretical output of the lamp was 21,600 watts x 0.92 ÷ 72 in. = 276 watts/in.

We wanted to check theory against reality, so we went back and measured the actual voltage being delivered to our system. We discovered that the 72-in. lamp was supplied with 2166 volts, but was only pulling 7.9 amps.

Going back to our formula, we calculated the actual power rating of our lamp as 2166 volts x 7.9 amps x 0.92 = 15,742 watts. Dividing this number by the arc length, we got 215 watts/in. as the lamp's real-world output--more than 22% lower than the projected output and more than 28% below the 300 watt/in. at which the lamp was rated!

The ballast dictates the current that reaches the lamp, and we couldn't change the 7.9 amps available unless we modified the whole power supply from the ground up. This option was too expensive, so instead we decided to increase voltage available to the lamp and the efficiency with which our lamps were converting current into curing energy.

We contacted our lamp manufacturer and explained our need for lamp that could handle increased voltage. We explained that the ballast spec sheet listed a maximum "open circuit voltage" of 2840, and that we wanted to bring our current voltage level from 2166 volts to about 2600 volts (leaving a margin of safety with the maximum open-circuit voltage). This would give us total lamp power of 2600 volts x 7.9 amps x 0.92 ÷ 72 in. = 262 watts/in., a bit shy of the theoretical 276 watts/in. but much better than the 215 watts/in. we originally started with.

Naturally, the lamp manufacturer thought we were smoking dope. But the real fun began when we explained our additional requests.

Optimizing Output


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