10 Things to Consider When Buying air cooled rectifier

Rectifiers - electrical devices that convert alternating current (AC) power to direct current (DC) - are used to provide power for a number of finishing applications. There are many reasons that a coater may wish to purchase a used rectifier, including lower cost, an immediate need or the desire to have a spare unit. Although the initial advantages may make this approach attractive, it is important to use the same care in purchasing a used rectifier as with a new one. Key considerations include the manufacturer, control type, size, input and output amperage and voltage, cooling method, efficiency, ripple, age and condition, warranty, and price.

1. Manufacturer.Is the manufacturer still in business? Is the manufacturer located conveniently so that replacement parts and schematics are easily available? Is the brand of rectifier the same as other units you have in your shop so that parts and circuit boards are compatible? What is the reputation of the manufacturer within the industry?

2. Control.What type of control does the used rectifier have? Is it tapswitch, powerstat, saturable core or SCR? Do you need to have either constant current or constant voltage for your process? If so, will you be able to use a rectifier that cannot provide this capability? Do you control your rectifiers with a PLC? If so, you might not be able to control your rectifier unless it has the proper type of control for the voltage and amperage output.

3. Size.What kind of footprint does the rectifier have? Will it fit in the space you have available, or will you have to locate it farther from the line? If it has to be relocated, will the existing buswork fit or will new bussing be required? Will there be a voltage drop if the bussing is extended, and will that affect the process?

4. Input Voltage and Amperage.Does the used rectifier have the same voltage requirements as those available in your facility? If not, are you willing to install a step-up or step-down transformer to provide the proper voltage? Will it draw more amperage than your wiring will accommodate? If so, are you willing to add larger feed lines, fuses, and disconnects to accommodate the used rectifier?

5. Output Voltage and Amperage.Does the unit have sufficient voltage for the process? If you are using it as a spare, can it operate in different applications? If the maximum output voltage is too high, will it operate efficiently or without excessive ripple at lower voltages? Does the used rectifier have sufficient amperage for your application? Can it operate at full output without overheating? If the used unit puts out more amperage, can the existing buswork accommodate it?

6. Cooling.Do you prefer air-cooled or water-cooled in your shop? Can you accommodate the heated water generated in a water-cooled rectifier in your process, or will you have to send it to a sewer and pay waste treatment fees? Using an air-cooled rectifier in a location with high humidity and a chemical atmosphere can compromise its reliability.

7. Efficiency.Is the used rectifier as efficient as the unit it is replacing? If not, it might draw more amperage to do the same amount of work and might overload your existing wiring.

8. Ripple.Does the used rectifier have higher ripple than your process can accommodate? If so, are you willing to buy a choke? How will the additional price of a choke affect what the rectifier is worth to you?

9. Age and Condition.Although age and condition are intertwined, you are primarily interested in the condition of the rectifier. A unit that has been kept in a clean environment and well maintained might be in better condition than one that is not as old but has not been well taken care of. Pay particular attention to the major components, including the main transformer, SCR stacks, diode stacks, tapswitches, powerstats and contactors. The ancillary components, including meters, relays, pots, stepdown transformers, and even firing boards, can be replaced or repaired. If the wiring is in a tangle, troubleshooting can be time-consuming and expensive. If possible, examine the unit in person. If that isn't possible, have the dealer send digital photos and nameplate data so you can confirm its age and condition.

10. Warranty.What sort of warranty is provided for the used rectifier? Does it include both parts and labor? Will the unit have to be sent back to the provider for warranty service, or will the provider send a technician to perform the work? Will you be responsible for travel costs? Is the unit completely rebuilt, which involves more removal and replacement of components than if it is reconditioned? Or is the unit merely sold in 'as-is' condition, which means that you will assume more of the risk if the unit fails? Is the dealer someone you have done business with before, and is he or she reputable?

11. Price.What you are really looking for is value. Are you paying too much for the type, make and condition of the rectifier you are buying? If you are buying for bottom dollar, you may be willing to take a unit that will require some work to recondition it if the major components are in good condition. If you need a unit that works perfectly as soon as you apply power and hit the 'start' button, you might need to pay a little extra.

Some coaters buy used rectifiers without due consideration and wind up with more grief than relief if they need them to replace a line unit that fails. Just as with the purchase of any other major piece of hardware in your operation, some initial foresight and effort can save you a lot of headaches in the long run.


For more information about rectifiers, contact JP Tech, Inc. at 262.642. or , or visit www.drrectifier.com.

Q. Our shop is looking to purchase a new rectifier, and I was curious as to what environmental issues we should consider before making a purchase.

With competitive price and timely delivery, Kehong sincerely hope to be your supplier and partner.

A. Understanding your environment is crucial when selecting a rectifier. Exposure to the vapors and particulates in a metal finishing facility can cause premature failure of the rectifier. Understanding this will aid in determining the type of protection needed and should help to decrease downtime. 

Several environmental factors should be taken into consideration when considering the purchase and installation of a rectifier: They are the available space and location, temperature, and humidity. Understanding these factors and the types of available cooling methods will help to increase the longevity of the rectifier and your return on investment.

Many ask why they should worry about the degree of protection for a rectifier. The two primary reasons are: 1) the decision made can extend the life of the rectifier, and 2) the return on investment can be improved. Downtime and repair expenses also can be significantly reduced with proper protection.

Understanding the various types of cooling methods will help you determine the degree of protection required for the rectifier in your specific environment. That degree of protection can be defined by internationally recognized standards such as NEMA, IP or IEC. 

Air-Cooled Rectifiers

Air-cooled rectifiers generally require a clean environment or air supply, as the components that are cooled by the surrounding air will be susceptible to any corrosive particles or fumes that may be in the general vicinity of the equipment. Air quality, air flow, available space (to prevent air flow restriction), ambient temperature and humidity should all be reviewed for compliance with the manufacturer's specifications. This will help in determining the correct air cooling design (convection-cooled, forced-air-cooled, air-to-water heat exchanger or ducted air) to suit your needs and environment. 

For more air cooled rectifierinformation, please contact us. We will provide professional answers.

Many modern designs incorporate variable-speed, thermostatically controlled cooling fans, which can greatly minimize the amount of air being drawn into the rectifier. In addition, a rectifier with direct air flow should be considered. With these types of rectifiers, air is directed through the heat sinks, only cooling the power components. The sensitive electronics are also isolated from the cooling air to improve the rectifier's longevity. Conformal-coated circuit boards will also greatly improve the rectifier's resistance to corrosive environments and improve life expectancy.

Preventative maintenance of an air-cooled rectifier is based on the air cooling design and should be scheduled according to the surrounding environment and manufacturer's specifications. This may include cleaning air inlet filters, and visual inspection of cooling fans and heat sinks on a weekly to monthly basis. 

Water-Cooled Rectifiers

Unlike an air-cooled rectifiers, water-cooled rectifiers can be installed into a harsh environment with minimal susceptibility to corrosive particles. The rectifier enclosure is mostly sealed to completely sealed, depending on how it is specified, and adds a protective barrier from the environment. The choice between an open-loop or closed-loop water cooling system would be based on meeting the manufacturer's water-cooling specifications for optimal performance and longevity. If the quality of your cooling water does not meet the specifications required by the manufacturer, then a closed-loop system or an external water source will need to be considered. It is also strongly recommended to maintain the water temperature above dew point, as this will help prevent condensation inside the rectifier and resulting potential hazards. 

Preventative maintenance of a water-cooled rectifier can be kept to a minimum, provided the water quality and temperature is within specification. Visual inspection for leaks of the internal and external water-cooling circuit will provide optimal performance and prevent any downtime, potential hazards and/or loss of water flow.

Oil-Cooled Rectifiers

Oil-cooled rectifiers are typically the largest of the mechanical packages offered, but the downside of this technology can be offset by its reliability. Unlike like air- and water-cooled designs, this type of rectifier can be installed in the most aggressive environments, because its power components are submersed into nonconductive oil. Heat is dissipated through fins that are external to the main rectifier enclosure, which is completely sealed from the environment and provides exceptional protection from any contaminants. Preventative maintenance is almost nonexistent on oil-cooled rectifiers because they are completely sealed from the environment. The extent of this benefit varies based on the rectifier technology (thyristor or variable transformer) used for the power section. The manufacturer will specify the oil level, oil-change interval and/or other components that may need to be replaced, based on operation. It is recommended that any maintenance work be scheduled for during a plant shutdown so as to not disrupt production.

Rectifiers can be a substantial capital expense for any company and, depending on the process, can cost hundreds of thousands of dollars. Factors such as process control, ripple percentage, rectifier technology and any other options required for your process will also need to be considered in evaluating the return on investment. By taking into consideration the degree of protection required for the rectifier, you will help to minimize any disruption in production, and maintenance and repair expenses, as well as the hazards that are associated with the environment. This in turn will help increase your overall return on investment, improve your process results and achieve smoother running and lower cost of production.

If you are looking for more details, kindly visit water cooled rectifiers.