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Selecting The Right Rectifier

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Selecting The Right Rectifier

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    1. Selecting The Right Rectifier/Charger J. Allen Byrne Engineering, Training & Tech. Support Manager Interstate PowerCare A Division of Interstate Batteries allen.byrne@ibsa.com

    2. Overview What is a rectifier/charger? Various types. What is the intended use? Where is it going to be used? What technology? Considerations.

    3. What is a Rectifier/Charger? Rectifies ac to dc. Charges a battery. Manages a battery. Powers a load. Manages the load.

    4. What is a Rectifier/Charger? Rectifier. Rectifies AC to DC Considerations. Input voltage and Frequency, Technology. Power Factor. Efficiency

    5. What is a Rectifier/Charger Charger. Conditions the dc so that it is suitable for charging a battery and powering the load. Considerations. Voltage range. Regulation. Noise Efficiency. Control.

    6. Considerations. Technology What is available?

    7. Rectifier/Charger Types Silicon Controlled Rectifiers Use SCRs for rectification, along with conventional transformers to regulate the charger output Typical use Switchgear Industrial Motive Power

    8. Rectifier/Charger Types SCR Advantages. Easier to interface with a microprocessor. SCRs provide more precise control of output voltage. Less sensitive to line frequency changes. Disadvantages. Generate somewhat un-smoothed dc voltage which may lead to higher ripple voltage and current. Bulky and heavy. Poor power factor resulting on higher KVA power input.

    9. Rectifier/Charger Types Controlled Ferroresonant. Uses a ferroresonant transformer to regulate the charger output. A ferroresonant transformer is a three-winding transformer, having one winding in parallel with a capacitor. Silicone diodes perform rectification. Typically Used. Telecom UPS Utility

    10. Rectifier/Charger Types Controlled Ferroresonant. Advantages. The output is relatively independent of the input. The electronic controls are simple which make for reliability. Disadvantages. Lack the sophisticated control circuitry may not adequately manage batteries Can work well with flooded batteries, but may overcharge and damage VRLA batteries. Sensitive to slight changes in line frequency. Have low efficiencies since the ferroresonant transformers dissipate more heat than conventional transformers. Large and bulky, quite heavy. Make an audible humming noise while charging Typically Used. Telecom UPS Slowly being phased out

    11. Types of Rectifier/Chargers Switch Mode - Fan Cooled. An electronic rectifier that incorporates a switching regulator. Typical use. Telecom. UPS Utility Generally, this is now the rectifier of choice

    12. Types of Rectifier/Chargers Switch Mode - Convection Cooled Typical Use. Telecom Dirty locations Low temperature locations

    13. Types of Rectifier/Chargers Switch Mode - Main Advantages. Hot swappable. Should have safety features for: Auto disconnect before removal. Post-mate enable. Current walk in of load. Light weight. One person change-out. Ship overnight. Fairly efficient over wide output range.

    14. Types of Rectifier/Chargers Switch Mode Fan Cooled Main Disadvantage. Fan life. Look for: Easily replaceable fans. Fan on demand. Fan speed control. Continuous (reduced output) without fan. Redundant fans on higher power rectifiers

    15. Single Cell Charger Useful thing to have. Ensure that it is isolated from utility ac line. No external metal parts. When using on live battery, avoid sparks. Reverse polarity protection.

    16. Rectifier/Charger Types Considerations. The industrial battery charging market is dominated by SCR and Ferroresonant chargers. They have been in existence for many years. Switchmode dominate in the telecom and UPS arena. New switchmode technologies are slowly making an entry into the industrial charger marketplace. The reason is due to the higher efficiency, smaller size and lower weight that the switchmode technology offers over ferroresonant and SCR

    17. Rectifier/Charger Type Comparison

    18. Considerations. Input voltage. What is available? 120V - 208V - 240V single phase? 208V 480V three phase? Usually the higher the input the lower the power loss. -12 to + 10% normally specified. What is expected deviation from nominal voltage? Power loss at -12% can be 15% higher than at nominal line. Input frequency range? Limit inrush current.

    19. Considerations. Output voltage. What is Required? 24V - 48V - 120V other. What is the load? What is the voltage window of the load? Is the voltage window sufficient for battery? What is battery float voltage? Is equalize required? Ensure current walk-in to load.

    20. Counter EMF Cell Example: A 120Vdc system where the load is limited to 130Vdc, but the batteries can be charged at 140Vdc. During normal operation the load voltage is reduced to 10Vdc less than the charging voltage. As the batteries discharge, the CEMF device connects the load and the batteries together, directly with no voltage drop.

    21. Correct Charging Voltage Specific Gravity + 0.845 = Open Circuit Voltage (OCV) Example: 1.300 SG + 0.845 = 2.145 OCV. Charging voltage must be higher than OCV. Depends upon grid alloy type and temperature. Usually in the range of 0.10 and 0.20 V at 77F For lead-calcium, typically 0.12 V. Example: 2.145 OCV + 0.12 V = 2.265 V.

    22. Manufacturers Recommended Battery Float Charging Voltages -

    23. Considerations Temperature compensation. Adjusts output voltage to compensate for ambient temperature variations. Benefits every type of battery. This is important with VRLA batteries in order to reduce chance of thermal runaway. Typically 2.8- 3.0 mV per degree C. It is important to set at nominlal temperature.

    24. Typical Temperature / Voltage compensation for a VRLA battery

    25. Considerations Efficiency. Efficiency = Output Input What is efficiency over output loading? If charger is to be used in parallel/redundant configuration, efficiency at 50% load or less is important. Power loss at -12% can be 15% higher than at nominal line. The higher the input voltage the lower the power loss. Go for high efficiency.

    26. Efficiency and Energy Savings Battery Charger Energy Conservation Program

    27. Efficiency. Equipment is less efficient in Canada!

    28. Considerations Power Factor. PF = Cosine of phase angle that current leads or lags voltage. What is the PF over output loading? If charger is to be used in parallel/redundant configuration, PF at 50% load or less is important. PF should be as close to unity as possible. Active PF correction is good. Go for PF as close as possible to unity.

    29. Considerations Emissions testing: Input & output conducted emissions. Radiated emissions. Immunity testing: RF field RF conducted ESD Surge Voltage dips & interruptions

    30. Considerations Certifications. NRTL Testing. UL, CSA, etc. NEBS. Network Equipment Building Standards. Other Certifications. CE, IEC, Seismic, Nuclear, FCC, FAA, NEMA, etc.

    31. Some Certifications UL-1564. Standard for industrial battery chargers. UL 1012. Standard for battery chargers. CSA-C22.2 Canadian standard for battery chargers (CSA-NRTL/C to UL 1012 & UL 1564 Standards) Note. CSA is also a participant in OSHAs Cooperative Arrangement between the U.S. Occupational Safety and Health Administration (OSHA) and the Standards Council of Canada (SCC). UL 60950. Safety. Telcordia. GR-63-Core ANSI/IEEE C62.4 FCC. Part 15 for conducted noise. NEMA PE 5-1996. Specs for utility type battery chargers.

    32. Considerations Some important features

    33. Considerations Some more important features

    34. Questions? Thank you for listening

    35. J. Allen Byrne Office. 301 696 9669 Mobile. 240 344 5445 e-mail. allen.byrne@ibsa.com

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