Southern Metal Finishing

Re: Comparing Rectifier Options - Part 2

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A Check list for Buyers - Part 2
By: Peter VanGorp,  American Plating Power

At one time, buying a rectifier was simple – make the purchase and hook it up to the tank. However, the process has become more daunting today for those who want to make a sound decision with regard to a capital investment expected to last for the next 10 years. Considerations are numerous: control method, ripple specification, open vs. sealed enclosure, PVC vs. steel enclosure, insulation amplifiers, field bus system – more than enough to confuse even the most savvy decision maker.

The developments in both the PC industry and power engineering over the past 20 years not only generated new fields of activities for the plating industry, but also triggered new ways of producing the DC power supply to power the process. SMPS rectifiers (switch mode power supplies) are about 10 times smaller and lighter in weight than standard SCR systems, and at the same time they provide a better DC quality. To the plater who considers the total concept (control, installation, and cooling), this is one example of how the power supply can provide a number of advantages.

The new technologies such as SMPS, current and voltage control, field bus communication, and compact design do offer a number of advantages, along with some challenges.

The following 2 examples highlight issues that may be encountered when following the advice of a sales person who has a major in marketing instead of engineering:

A. Bigger is Better  Overrating an SCR controlled rectifier will create more problems than one can imagine. The higher output voltage creates harmonics in the mains supply, which will require a larger substation transformer with a higher K-factor to cope with the extra (unutilized) power. At the same time, the DC quality is reduced, which could result in a lower performance of the tank, particularly if the parts are used for decorative applications.  It is advisable to check how high the existing line’s DC voltage is, to ensure a proper operation. It is also advisable to consult with the chemical supplier, to find out more about their latest developments with regards to higher ASF values and shorter process times. The rectifier supplier can then provide a system which is rated for the application, while not using an electronic limitation to achieve it.

B. Smaller is Better  A compact design can cause problems if the downside of that kind of engineering is not considered. A compact design requires a more efficient cooling, similar to PC's, where the latest processors require an additional fan for cooling in order to achieve the high computing speed the PC is capable of. Similarly, the compact air cooled rectifier should feature an air guiding system or even better - a stepless fan speed control to reduce the amount of cooling air, and therefore dirt, inside the unit. Today’s SMPS designs are utilizing the internal heat sink as a mounting plate for the power components and the electronic parts. The cooling air is guided through the heat sink, which acts like a channel for the cooling air and separates the cooling air from the rest. Additionally, the 19'' rack design allows those systems to be enclosed into a cabinet for even better cooling.
After the fresh air is guided through the cabinet, the warm exhaust air can be redirected through a duct pipe and re-used, for example, to warm up the loading area during winter time.

A downside to the water-cooled compact SMPS is the moisture created inside the rectifier due to low water temperatures. Those wishing to use this powerful technology can consider adding a temperature booster that will eliminate the possibility of condensation. It can then be integrated into a cabinet to offer a multiple output rectifier system and allow the control of each plating cell individually.

Overcoming the challenges of compact design allows for the advantage of achieving more power from the same foot print, while also providing a better control of the plating process.

A suitable supplier should offer the full range of rectifiers to produce the best available solution for each application. In addition to the standard SCR control systems, they should carry a full range of powerstat systems (100 - 10000 A), and SMPS rectifiers. They should offer open or sealed cabinets, convection air or forced air cooling, oil cooled systems, and water cooled solutions with temperature boosters.

A true expert will offer the best technology to meet a specific application, and will appreciate the unique environment of the plating shop as well.

This article was provided by Peter VanGorp of American Plating Power, Ft. Meyers, FL.  You can contact him via email at