Comparison of APC LINE-INTERACTIVE with Franek DOUBLE-CONVERSION
Both units have been technically classified as an Uninterruptible Power System (UPS), unfortunately for the average consumer; they are not made aware of the different types of UPS available and their specific applications. The purpose of this document is to clarify the different types of UPS and their specific design applications.
- Per the International Electrotechnical Commission (IEC) 62040-3 standard, there are three defined types of UPS:
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Passive Standby
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Line-Interactive
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Double-Conversion
These terms define how the UPS operates with the utility power. Without getting too detailed, the level of performance and protection improves depending on the topology with passive standby being the lowest form and double-conversion providing the maximum protection. Because the APC LINE-INTERACTIVE represents a line-interactive model and the DOUBLE-CONVERSION is double-conversion, this discussion will compare only their specific advantages and disadvantages.
A line-interactive device consists of a protected (filtered) bypass line, a standby, idling inverter and a very fast detector-switch. The load, which should be a computer because that is primarily what these units were designed to protect, is directly connected to the output of this system.
This computer load is then connected indirectly to the utility source through the bypass line, AVR circuitry and appropriate noise filters. As the utility line fluctuates, droops or sags, the line-interactive will attempt to correct and compensate through its filter and AVR circuitry.
If the power disturbances become too hostile, as in the case of brownouts, blackouts or frequency deviations to name a few, the detector circuit will “quickly” switch or transfer the load to the idling inverter circuit which is driven entirely by the internal battery. Once the problem is corrected, this same detector will acknowledge by “quickly” transferring the load back onto the bypass line.
This is ideal for computers because of their internal capacitance, they do not see these “quick” transfers and they are not vulnerable to minor voltage fluctuations. The computer load represents a very stable, constant load with a power factor of about 0.67 to 0.70. Line-interactive devices offer a very economical advantage for computer protection and will protect against most (80%) of all defined problems. The downside of the line-interactive is that the inverter is not high quality because it is not necessary for it to operate continuously. It utilizes the battery when it is necessary to operate the inverter regardless of the problem. Because of more frequent exercising of the internal battery, these systems typically require new batteries within 2.5 to 3 years max. Because of its detection circuitry, its performance is not conducive to erratic load profiles, like scientific equipment. Most research lab instruments consist of motors, solenoids, heaters, and lasers.
Only double –conversion technology should be used to protect critical lab instruments. Double-conversion is usually as much as twice as expensive because it contains an inverter that drives the load 100% of the time. The inverter is a high-quality device that outputs a stable, low harmonic, perfect sinewave. Regardless of what happens to the utility line, there is no switchover or transfer reflected on the output. The inverter has a dual input, a battery, and the utility. The only time the battery is used is when the utility decreases beyond 20% of nominal, which is when the battery takes over. The inverter output remains unchanged because one of the two sources is always present. This system has also been tested and is used in hundreds of applications with the Model 310.
Applied Biosystems specifically recommends Franek Technologies’ product for their applications because of the continuous inverter operation. Their field service representatives have actually had to remove APC devices in harsh environments because the continuous switching and fatiguing output caused the laser to fail. Double-conversion is designed to protect against all (100%) power disturbances.
Scientific instruments cost hundreds of thousands of dollars. Reagents and calibration costs are astronomical. The data that is generated is, in many cases, priceless and cannot be corrupted. The scientist’s time, if the test has to be redone, is not free. With all this costly investment, why settle for 80%, at best, protection, particularly when the instrument manufacturer recommends a specific, proven solution?
When comparing power protection solutions, it must first be decided what level of protection is desired and makes sense for the application. The higher the risk, the more secure protection is needed.
Examples: Line-interactive for personal and medium-to-low risk computer applications, double-conversion for mission-critical or high-cost applications, then redundant double-conversion for extremely high risk or life-support. Once the topology is determined, comparisons should be drawn against like systems. It is not logical to compare the line-interactive topology with double-conversion because they serve different purposes. Comparisons should only be drawn between like topologies.
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