Southern Metal Finishing

Re: Comparing Rectifier Options

This article was published in the March 06 issue of Southern Metal Finishing. If you would like register to receive our free newsletter and review our online archives please visit www.southernmetalfinishing.com

When purchasing a rectifier, it is critical to consider the unique technical requirements of the application, in order to select the proper equipment and ensure a return on the investment.

For example, when purchasing a vehicle for pulling a trailer, the preferred choice would be an SUV over a compact car. However, if the vehicle will be used for commuting to a workplace with tight parking and lower gas consumption is desired, then the compact car would be the better choice.
In the same manner, the rectifier is the driving force behind the electrochemical process. If the rectifier is not performing as expected, the investment not only isn’t generating a return, but can actually cost money in the process.

Here are some examples of bad investments:

1.  Purchasing an oversized thyristor controlled rectifier. If the application requires 50 Volts output, and the rectifier’s maximum rating is a 100 Volts, the high ripple created by reducing the output can cause unacceptable results in the finished parts, such as high roughness, dull finish and/or peeling of the plated metal. Additionally, the high power consumption caused by the harmonics generated by the oversized rectifier increases operation cost.

2.  Purchasing without regard to actual rectifier placement. Let’s say there is a good price on a used/repaired rectifier carrying a 6 month warranty. However, the unit is bulky and must be placed far away from the tank. This results in higher installation costs of running lines and extending power cables to the remote location. The resulting voltage drop due to the distance also results in higher operating costs. The better choice would have been a new system, compact enough to install right next to the tank, preferably water or oil-cooled for valuable protection from the harsh environment.

3.  Sticking with the same brand due to spare parts concerns. Remaining loyal to inferior technology simply for parts availability concerns does not make good economic sense. As designs of rectifiers change and improve, so do the controller cards, diodes and thyristors. Old parts become obsolete, new parts are more readily available than ever before.

Answering the following check list will determine the optimal solution for each application:

A. What line voltage is provided by the substation transformer?
B. How much power can the substation deliver?
C. What are the space requirements for placing the rectifier?
D. How harsh is the environment (ventilation, contamination)?
E. How much DC voltage is really required to power the process?
F.  What is the maximum DC current necessary?
G. Is the process ripple sensitive?
H. Where is the preferred location of the control – at the tank or remote (i.e. in an office)?

At one time, tailor-made solutions indicated an expensive investment. Today, as with the modern automotive industry, the larger rectifier manufacturers are utilizing their “in-house” flexibility to produce tailor-made solutions for the price of off-the-shelf rectifiers. At the same time, the delivery times are reduced by almost half compared to 10 years ago.

The Bottom Line: To ensure a pay off on investment, purchase the best available technology, and customize it for a perfect fit.

Peter VanGorp, American Plating Power  pvangorp@usplating.com

Look for Part 2 of this article in the April SMF Issue.