Updated for 2010, this guide covers how to estimate, warranties and quantity discounts, an estimate form, design and engineering fees, service and installation hourly rates, a letter footage chart, and ...
Going electronic
In the past five years, energy-saving electronic ballasts have proliferated. Today, it‘s hard to obtain a magnetic ballast, even for replacements.
The ubiquitous electronic units’ properties and installation requirements differ from the magnetic units. Therefore, the sign installer must carefully select the proper ballast type and model for each purpose to avoid failures.
Regardless of ballast type, a fluorescent lamp ballast must fulfill three, main tasks:
1. Prior to lamp start, it must preheat the electrodes by running enough current through the filament wires. Once the lamp operates, the heating current must be reduced or switched off to avoid overheating the electrodes.
2. The ballast must provide high voltage across the lamp to start the gas discharge between the electrodes once the electrodes have been heated.
3. It must provide a high-enough voltage across the lamp, once the lamp has started, to sustain the gas discharge and, simultaneously, limit the operating current to a proper value for each lamp size.
Electronic ballasts, which were first introduced in the late 1980s, use electronic components to convert 60Hz voltage and current to high frequency to operate a fluorescent lamp. Besides all electronics, one part remains the same: The magnetic choke still limits the current (see ST, October 2008, page 58), but the choke can be much smaller if the frequency is high enough (keep in mind that an inductor’s inductive resistance [impedance] depends on the frequency of the alternating current [AC]). Thus, at twice the frequency, you need only half the inductance to achieve the same, current-limiting action.
In modern electronic ballasts, the frequency is roughly 60 to 100kHz, or more than 1,000 times the main frequency. Thus, the inductance can be 1/1,000 or less to achieve the same purpose. Besides the advantage of less electrical loss, electronic ballasts also enjoy smaller sizes and less weight.
Modern semiconductors allow the ballast to convert direct current (DC), or generate DC by rectifying AC line voltage, into 60 to 100kHz high frequency with losses of only 1 to 2%, compared to magnetic ballasts’ 4 to 8% power loss.