Rectifiers: Nearly Everything You Need to Know

What is a Rectifier?

A rectifier is an electrical device used to convert alternating current (AC) into direct current (DC) by allowing a current to flow through the device in one direction only. Diodes work like one-way valves within the rectifier to maintain this flow of current. This process is generally known as &#;rectification.&#;

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While rectifiers have many uses, they are most often used as the primary components of DC power supplies and high-voltage direct current transmission systems. In an industrial setting, rectifiers are typically spec&#;d based on voltage applied, current needed in the process, quality of the power, and how the control will be arranged.

Ripple is an important measurement for determining the efficiency and quality of a rectifier. Ripple is the clarity of the power (how clean it is) expressed in a percentage. AC divided by DC equals the percent of ripple.

Since our founding in , Dynapower has been at the forefront of the development of custom and standard rectifier solutions for metal finishing, mining, steel, chemical, defense, and hydrogen production industries worldwide.

Types of Rectifiers

There are a wide variety of industrial rectifiers, including SCR, powerstat, tapswitch, switch mode, IGBT chopper, and thyristor rectifiers. Tapswitch and powerstat rectifiers offer little to no control for operators. They have a very low ripple reading, low amperage, and low cost, yet they are typically very expensive to repair.

Alternatively, SCR, SMPS, and IGBT chopper rectifiers offer seemingly infinite control for operators; they can easily control voltage from top to bottom between zero and 100 percent.

SCR Rectifiers

An SCR rectifier is a semiconductor power supply that meters electricity by opening electrical &#;valves&#; that work together to rectify electricity. The longer the &#;valve&#; is open, the higher the voltage leaving the rectifier will be.

Dynapower RapidX Series SCR Rectifier

SCR rectifiers are variable voltage DC power supplies that are low frequency, high ripple systems. These systems are rugged and have a history of durability in the market&#; a number of our customers have systems still running after 40 or 50 years. They regulate and react steadily, carry a lot of power in large copper windings, and are fairly easy to troubleshoot with large, easy-to-identify components.

Switch Mode Power Supplies

A switch mode power supply (SMPS) is an electronic power supply that uses a switch from AC to DC, back to AC, then once again back to DC. This is all done at high frequency allowing for the internal parts to be smaller. They utilize a high primary voltage&#;where 480VAC input units typically see 700VDC&#;switching voltages inside the transformer.

With smaller parts, tighter windings, smaller footprints, and an even tinier tolerance, these precision pieces of equipment offer good space efficiency per watt, modern computer interfaces, and intuitive controls.

Switch mode power supplies have been around for roughly 40 years. Traditionally, these were used in smaller current applications and only in the last 10 years or so have large-scale switch modes been successfully deployed.

Dynapower Water-Cooled Switch Mode Power Supply

High Power IGBT Chopper and Thyristor Rectifiers

Dynapower also designs and manufactures high power IGBT chopper and thyristor rectifiers for large applications like green hydrogen production, electrowinning, chlor-alkali production, electro-refining, and other specialized applications.

Our design capabilities include the complete High Power Transformer Rectifier System&#;inclusive of fully integrated operator interfaces and control systems for a single unit or entire multi-unit SCADA network.

Our IGBT chopper and thyristor rectifiers may also be provided with auxiliary equipment as required by the specification&#;including switchgear, power factor correction, harmonic filters, heat exchangers and free-standing cooling systems. The chopper rectifier designs consist of high-frequency switching technology in a modular design package that converts the transformer secondary AC voltage to a regulated output DC voltage. Larger power systems are constructed of multiple chopper modules to obtain the specified current requirements.

Dynapower IGBT Chopper Rectifier Dynapower Thyristor Rectifier

Rectifier Cooling Options

Rectifiers can be air cooled, water cooled, oil cooled or hybrid cooled. Traditionally, most rectifier manufacturers offer air or water cooled rectifiers. Air cooled units are typically larger per watt of power because they need more surface area to dissipate the heat, while water cooled units are typically smaller because surface area is not a factor in cooling these units.

Rectifier Maintenance

Although extremely durable and long-lasting, rectifiers do occasionally need repairs. The majority of rectifier issues are caused by the overheating of electrical components, like a circuit board. The root cause of overheating could be corrosion, bad cooling lines, a wrong component put in during a repair, breakdown of organic varnish in the transformer, or poor bussing connections.

Good heat management is important for long-term rectifier maintenance. The general rule of thumb to minimize heat is: clean, flat, and tight:

1. Keep all contacts clean.
2. Ensure all electrical surfaces are mounted flat to one another.
3. All electrical surfaces must be tight.

Why choose a Dynapower rectifier?

Dynapower is your one-stop shop for everything rectifiers, from our expansive lines of pre-engineered and custom rectifiers to our comprehensive aftermarket services&#; including field service, training programs, spare parts, and controls upgrades.

When considering the purchase of a new rectifier, taking the time to pick the right equipment and maintenance plan can help maximize your uptime while saving your business money while improving safety and performance. Dynapower offers a full range of service and support to keep you powered up and confident in the life of your product.

Rectifier Engineering Upgrades

Dynapower works with our customers to identify areas of their processes that can be improved through engineering upgrades. These include items like safety improvements to ensure that the unit is in compliance and that maintenance work can be performed properly on it.

When implementing our engineering upgrades, we harness our 50+ years in the power supply business to bring our customers the best possible upgrades for your systems. These include improvements like extra thermal sensors, water pressure check valves, fan sensors, flow sensors, chemical contamination sensors, and more.

Rectifier Controls Upgrades

Dynapower offers Touchpad, Touchscreen, and Multi-Unit Controllers for our rectifier units. Our Touchpad Controller can be easily integrated into both SCR rectifiers and switch mode power supplies. These controllers give our customers the ability to make precise voltage adjustments, pulse duration, cycle time, and dwell time.

Rectifier Spare Parts, Preventative Maintenance Plans & Field Service

Dynapower stocks a wide variety of rectifier spare parts for rectifiers, like control boards, thermal switches, all types of fuses, and various rectifier diodes. If you don&#;t see the part you&#;re looking for, we have a Spare Parts Hotline at (802) 860- to help you locate it.

Dynapower also offers field service and preventative maintenance services for Dynapower and Rapid Power Technologies equipment and most other rectifier brands. Our field service includes commissioning, repairs, routine maintenance, and equipment evaluation.

Dynapower&#;s preventive maintenance programs are designed to ensure that your equipment is inspected and adjusted on a regular basis, extending the reliable operating life of the equipment. Our goal is to prevent unnecessary equipment failures, ensure proper operation, and minimize your repair and operating costs.

Rectifier Refurbishment

It&#;s important to stay on top of your rectifier&#;s performance and maintenance to prevent issues such as loss of efficiency, system failure, injury, or extended down time. Our rectifier refurbishment program includes a full cleaning and reassembly of your Dynapower or Rapid Power rectifier. We also offer the convenience of a complete in-house refurbishment using our state-of-the-art, industry-leading test equipment.

Whether buying new or looking for service and support for an existing rectifier, contact Dynapower today for all your rectifier needs.

Fundamentals of Rectifier Operation, Monitoring, and Maintenance

Sustainability seems to be the latest catch-phrase, and cathodic protection (CP) is an important component for the sustainability of many metal structures. What better way to preserve and maintain infrastructure than to mitigate corrosion? Some CP systems are comprised of sacrificial anodes that naturally corrode to protect less active metals such as steel. Others require power sources to drive protective current in the right direction. The most common impressed current voltage sources are rectifiers, which can break down. Well-maintained rectifiers can provide uninterrupted CP, which reduces repair costs and labor/technician time. This article discusses the fundamentals of rectifier operation and maintenance along with basic recommendations.

Sustainability is the capacity to endure. The root purpose of any cathodic protection (CP) system is to mitigate corrosion. Preserving a pipe or other metallic structure by preventing corrosion damage allows it to endure. Therefore, corrosion mitigation leads to sustainability.

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CP is most commonly achieved by means of a galvanic (sacrificial) or impressed current system. A galvanic CP system is comprised of sacrificial anodes typically made of active metals (aluminum, magnesium, or zinc) that corrode in order to provide protective currents for a less active metal, such as pipeline steel. An impressed current CP (ICCP) system utilizes external power in the form of a rectifier or other voltage source that drives impressed current anodes (e.g., cast iron, graphite, and mixed metal oxide) to corrode in order to distribute protective current to the structure (cathode).

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. It is imperative that a rectifier remain in a state of constant operation. Because a rectifier is an electrical device, it is vulnerable to power surges. A nearby lightning strike can cause the circuit breaker to trip or a diode to short. Therefore, routine inspections and monitoring are necessary to maintain a properly functioning, long-lasting rectifier.

Safety is the most important aspect of all inspections. The goal of any task related to rectifier operation is to perform the work safely, which includes wearing the proper protective equipment.

Operation

There are three major components in a rectifier: transformer, stack, and cabinet. The purpose of the transformer is to safely separate the incoming AC voltage (primary side) from the secondary side, which is adjusted to control the output voltage of the rectifier. Typically, these adjustments are made with tap bars connected to the secondary side windings at intervals that offer several setting options. The stack is the actual rectifier and is comprised of a set of silicon diodes or selenium plates that function as unidirectional current valves. The diodes or plates are configured so that cycling AC flows in one direction and is blocked in the other, resulting in both directions of the AC wave flowing in the same direction. The cabinet, which includes the test panel, safely houses these components, and allows for monitoring and other advanced operations.

Additional items that may be found in a typical rectifier include a circuit breaker, voltage and current output meters, lightning arrestors, surge suppressors, transformer tap bars, and fuses.

Table 1 lists general rectifier do&#;s and don&#;ts.1 This information helps to ensure personnel safety and reliable, long-term operation of the rectifier.
 

Monitoring

Routine monitoring is recommended for all rectifier installations. The main purpose of monitoring is to ensure the rectifier is still operating and that a power surge hasn&#;t tripped the breaker. Some facilities require certain inspections at particular intervals. For example, natural gas and petroleum pipeline operators are required to inspect their rectifiers six times per year in intervals that don&#;t exceed 21 months. Also, company policy may dictate an even stricter inspection interval.

Monitoring is typically comprised of both a visual inspection and electrical testing. The visual inspection might include looking for physical damage of the installation/ cabinet/components, evidence of overheating, and signs of insect/rodent nests, along with recording the specifics of the rectifier unit and meter readings/tap settings. Testing often includes taking manual measurements of the rectifier output voltage and current to verify meter accuracy and structure-to-electrolyte potentials. Equipment to remotely monitor rectifiers that are difficult to access is also available; however, these devices are best used as an adjunct to on-site monitoring rather than a replacement of it.

Prior to performing visual inspection and testing, it is important to put on the appropriate personal protective equipment (PPE). As a minimum, safety glasses, leather work boots (with moisture barriers where appropriate), and leather or rubber gloves should be used. Company policy may identify additional PPE requirements.

When first approaching the rectifier, be aware of its surroundings, such as uneven footing, poisonous plants, or standing water. Use all senses to detect evidence of malfunction, including visual (e.g., scorching) and audible (e.g., crackling). Test the cabinet for the presence of AC with an approved AC detector. The old-fashioned way of determining whether the cabinet is electrified (or hot) was to brush it with the back of the hand. With the advent of the AC detector, this is no longer necessary or advisable. Knock on the cabinet to notify any inhabitants (wasps, mice, spiders, and even snakes) that you are coming in. Be sure to have insect spray handy.

Maintenance

The major causes of rectifier failure are neglect, age, and lightning. Before performing any troubleshooting of a non-functioning rectifier, be sure to turn it off, both at the circuit breaker and at the panel disconnect. The most common rectifier problems include faulty meters, loose terminals, blown fuses, open structure/groundbed leads, and lightning damage (even where lightning arresters are present). The purpose of troubleshooting is to systematically isolate the rectifier components until the defective part is found, and following the rectifier manufacturer&#;s recommendations for maintenance and troubleshooting is recommended.

Test the circuit breaker, transformer, rectifier stack, meters, fuses, choke, capacitors, and lightning arrestors separately. Keep an eye out for loose connections, signs of arcing, and strange odors. Additional testing may be required to verify the integrity of the structure and groundbed lead wires.

Table 2 contains a troubleshooting chart2 designed to help diagnose rectifier problems quickly.
 

Common Scenarios and Tricks of the Trade

Often a rectifier is found with voltage output and no current output. Since output voltage suggests that the rectification circuits are intact, one or both of the output cables might be broken, or the anode groundbed might be completely depleted. To begin troubleshooting, identify a suitable temporary ground that is electrically isolated, such as a culvert, fence, power pole guy wire anchor, or street sign. Turn the rectifier off, then disconnect the structure lead wire, and connect the temporary ground to the negative lug. Adjust the tap bars to one of the lowest settings, and energize the rectifier. If the rectifier now produces both volts and amps, then the structure lead wire is broken. If there are still no amps, then turn the rectifier off, return the structure lead wire to the negative lug, disconnect the anode lead wire, and connect the temporary ground to the positive lug. Energize the rectifier. If the rectifier now produces both volts and amps, then the anode lead wire is broken or the existing groundbed is depleted. If there are still no amps, then additional testing is required to evaluate the effectiveness of the structure and anode lead wires to determine if the problem involves both wires.

Another common occurrence is to find the rectifier with a blown fuse. This may be the result of a power surge and simply requires the installation of a replacement fuse. However, rectifier fuses can be quite expensive. Temporarily installing a circuit breaker across the fuse clips permits testing the rectifier&#;s operation without consuming several fuses. A typical home-style circuit breaker, appropriately sized for the application, may be used for this test. Simply attach test lead wires to each end of the circuit breaker, and attach the lead wires to each of the fuse&#;s existing mounting clips. Be sure to prevent the circuit breaker and lead wires from contacting the rectifier cabinet or any other metallic object. Energize the rectifier. If the breaker doesn&#;t trip, then simply replace the fuse. If the circuit breaker trips, then other problems exist and additional troubleshooting should be performed.

Sometimes a rectifier can be found with a tripped circuit breaker. This might be the result of a power surge and simply requires the circuit breaker to be reset. However, surges are not desirable as the rectifier might remain off for long durations. Be sure to test the effectiveness of the rectifier&#;s electrical grounding and follow the National Electric Code (NEC) guidelines. Install supplemental grounding as required. In addition, there are available surge suppressors that may be installed to help mitigate power surges. Be sure to follow the manufacturer&#;s sizing recommendations.

Rectifier housekeeping is also very important to prevent insects, rodents, and other animals from building nests. Insect and rodent nests can be dangerous inside a rectifier cabinet. Insect stings or even snake bites are definitely not desirable. However, the nests themselves can cause problems too. Apart from being a possible fire hazard, a nest can impede air flow through the rectifier cabinet and lead to overheating (and eventual failure) of the components. Ensure that insects and rodents do not move into a rectifier. Some of the ways to keep pests out are to seal all penetrations into the cabinet other than those intended for ventilation, or use a chemical pesticide to dissuade their interest in moving in. For sealing the penetrations and conduits, a duct seal or a viscous-elastic amorphous apolar polyolefin (e.g., VISCOTAQ&#;) may be used to close any of the cabinet openings. A simple and effective chemical pesticide that is ideal for use within a rectifier is a small, open cup of mothballs. They are easy to acquire and work very well.

Summary

A key to the sustainability of structures is effective CP as a means of corrosion control/mitigation. Rectifiers are great tools that help to provide effective ICCP. They require routine monitoring and, at times, minor repair. Rectifier monitoring and maintenance is a necessity, but it can be performed safely, which helps ensure reliable, long-term rectifier operation.

 

How to avoid voltage drop when using full bridge rectifier as reverse polarity protection

 

I found a couple of old bridge rectifiers. After reading some docs and tutorials about reverse polarity protection decided to give them a try. The problem is nobody offered a solution against the voltage drop (and the power loss) after the rectifier, which is usually mounted at the load side not at the supply side.

What is the way to avoid this drop - using higher voltage as input or additional circuit to overcome this at the load side?

Note that I chose this way of protection so the protected device will continue to work

Switchmode Cathodic Protection Rectifiers

GSM Module (For GSM module add G after your switchmode ordering code)

Optional GSM Modem using RS232 for telementry. Modem can send instantaneous values of output voltage, current and reference potential measurement, 24 Hour period logged values, 8 bit user defined alarms including phase failure , circuit breaker and fuse rupture. Modem can also relay present control mode and has the ability to change control mode, set up parameters and boundary values. This requires a registered sim card.

Manual Control (For manual control add M after your switchmode ordering code)

This is a feature where the user can switch over from automatic control to manual output voltage using a potentiometer style knob accessible from the inner door.

*For other options please contact us, these include and are not limited to:

Current sharing

Switchmodes can be arranged in parallel in current sharing mode for special high power applications up to W

Replacement parts

Lightning equipment, fuses, LEDs, metering equipment, electronic PC boards, electrical components etc.

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