Powering Metal Finishing Operations

Originally titled 'A Ripple Effect'

Water-cooled switchmode power supplies offer less ripple and more efficiency.

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Most of us know that electricity and water are usually a bad combination. Your hair dryer likely has a tag on it that warns you not to use it near water. The lifeguard will order you out of the pool if there’s thunder and lightning in the vicinity.

Certain metal finishing applications, such as plating and anodizing, require use of both water and electricity, however, and over the last 25 years, Dynapower Company has come up with a series of power supply products that deliver just the right mix.

The South Burlington, Vermont, company offers a variety of solid-state switchmode power supplies in both standard and custom configurations suited for a range of applications. And because the heat generated during operation of a rectifier must be removed, these power supplies are available in both air- and water-cooled versions.

Silicon-controlled rectifiers (SCRs) often are used in plating and anodizing applications, and while SCR-based power supplies do offer some distinct control advantages over simpler rectifiers, they tend to produce higher ripple and, in most cases, lower efficiency than switchmode power supplies, says Dev Massimi, industrial sales manager for Dynapower. SCRs also tend to be significantly larger.

“Our switchmodes provide quality power in a compact, durable design that saves our customers money not only on valuable floor space, but with lower electricity bills because of their higher efficiency compared to standard SCR units. And because of their inherently low ripple, switchmodes can provide finishers greater control over their processes compared to standard SCR units,” Massimi says.

Dynapower’s water-cooled switchmode power supplies are flexible, easy-to-use rectifiers that produce less than 2 percent AC root mean square (rms) of full-scale ripple, 0.5 percent regulation over the operating range and a power factor of 0.93 throughout the operating range. DC output capabilities are as high as 150 kW in standard offerings and 690 kW in custom configurations.

Here’s how they work: Switchmode power supplies convert alternating current (AC) to direct current (DC). First, they change the AC input to an unregulated DC voltage, then this intermediate DC voltage is chopped using pulse-width modulation through an H-bridge configuration into a high-frequency transformer. Finally, the output of the transformer is rectified and filtered to provide a precisely controlled, high-current output. Switching occurs at a very high frequency (typically 50 kHz), enabling the use of transformers and filter capacitors that are much smaller, lighter and less expensive than those found in traditional SCR power supplies.

Dynapower switchmodes are regulated to keep the output voltage constant. The power supply employs a feedback controller that monitors current drawn by the load and also allows regulation of output current. The switching duty cycle increases as power output requirements increase. Voltage regulation is achieved by varying the ratio of on-to-off time of the switching circuitry. In contrast, a traditional SCR power supply regulates the output voltage by changing the turn-on time of the main AC power.

“This difference gives our switchmode power supplies a higher power factor—upwards of 5 percent greater than a standard SCR unit—a key aspect of reducing the end user’s utility bill,” Massimi says.

In this rectifying process, there is always a small amount of AC that is not converted and then distorts the DC. This “ripple” can lead to poor finishing results, including irregular, non-uniform coatings, or other surface imperfections like craters and pinholes.

According to Dynapower, it is the high switching frequency of the switchmode power supplies that enables less ripple. While less than 5 percent ripple might be expected from a standard SCR without a ripple filter, the company’s switchmode units offer less than 2 percent AC rms of full-scale ripple.

“The high switching frequency also allows the power to be supplied in a smaller package, with higher efficiency and at a faster control loop,” Massimi says.

The benefit of water-cooled switchmodes over air-cooled versions is their ability to be used in highly corrosive environments and still offer operational longevity. “With air-cooled equipment, corrosive elements can be introduced into the internals of the unit during the cooling process, which can reduce the life of the unit,” Massimi says. “Water-cooled units being sealed isolates corrosive elements from the internal mechanics, which can significantly extend the life of the unit.” And greater longevity means a greater return on investment for end users, he notes.

Featuring NEMA 4X stainless steel enclosures and optimized to be as small as possible, Dynapower water-cooled switchmode power supplies are designed to be wall-mounted where a standard remote control console is located. A touchpad interface board allows for advanced functions such as ramp, cycle, pulse and amp-hour counter, and a program mode combining any of these functions. The ability to locate the units on or next to a tank also can reduce installation costs,” Massimi says.

Four standard wall-mounted models are available: 18-volt, 1,000 and 2,000-amp versions; a 12-volt, 3,000-amp version; and a 12-volt, 6,000-amp version. All of them offer ±0.1 percent of both full-scale output voltage and full-scale output current. Operating temperature is 50-104°F (10-40°C). The smallest unit measures 20.5" × 15" × 7.5" and the largest 40.5" × 38.5" × 17".

Also available is an expandable system that allows shops to easily control multiple separate processes or a single process that requires higher electrical output. Such a modular system can include virtually any combination of power modules ranging to 10,000 amps per unit contained in a single freestanding cabinet that measures 39.5" × 39.5" × 68.5".  Multiple units can be installed in series to reach even higher power outputs.

“Our modular water-cooled expandable system is designed specifically for maximizing uptime and flexibility for our customers,” Massimi says. “You can easily swap power modules out in the event of an unforeseen issue in a module to avoid costly downtime, and easily expand by adding more modules or units to meet the growing needs of any finishing line.”