Tower of Power: The Run On Programmable Power Supplies

Date: October 13, 1997 Comparison Chart 1 , Comparison Chart2 You could be home right now. Instead, you are forced to stay at the lab to monitor that 2-D gel you're running. Think of all the things you could be doing instead. Sure, you can fill the time by doing busy work, tidying up the lab or making sense of what you scrawled in your notebook hours ago. If you run multiple gels, multiple protocols, or like the convenience of programmability, programmable power supplies were designed to meet your needs. Programmable power supplies have not only made it easier for researchers to ensure repeatability in gel runs, but they also make the electrophoresis process a little simpler. With a product as sophisticated as this, there are several items to consider prior to investing in a programmable power supply. For most electrophoresis applications, one of three electrical parameters (power, voltage, or current) will typically be held constant. All three of these variables are dependent on one another; in the course of a gel run, if one parameter is held constant, the other two parameters will change as the run proceeds. In 1827, George Simon Ohm discovered that the current in a circuit is directly proportional to the applied potential and inversely proportional to the resistance (Ohm's Law: current = voltage/resistance). This law, combined with the power formula (volts x amps = watts) defines the relationship of volts, amps, watts, and resistance. Many times, the resistance of the gel will increase as the run proceeds. In such cases, holding different parameters constant will have varying effects. For instance, by holding current constant, the velocity will be maintained, but heat will be generated. By holding voltage constant, the velocity will decrease as the gel proceeds, and heat generation will vary. Finally, holding power (wattage) at a constant level will generally result in a smaller decrease in velocity, but the generation of heat will be constant and controllable. Excessive heat, which produces a gradient across the gel, commonly results in "smiling," which can make band analysis within and between gels difficult. Cooling efficiency can reduce or eliminate anomalies in a gel run. Fluctuations in voltage, wattage, or current commonly occur during the course of a run, and in many cases, this is due to a change in conductivity of the buffer in the chamber. To obviate this problem, some power supplies allow programming of volt-hours, watt-hours, and/or amp-hours. The adjustment of volt-hours is most common since the movement of molecules through a gel is related to the applied voltage. Programmable power supplies can now handle up to four gels running under the same parameters at one time. Varying degrees of programmability are available as well. The power supplies included in this article allow users to program one or multiple electrical parameters simultaneously (voltage, amperage, wattage, volt-hours, watt-hours, amp-hours). These power supplies not only allow researchers to manipulate electrical factors, but allow storage of one or several programs. This is a convenient feature for labs constantly running complex experiments. Some "power packs" even have preprogrammed electrophoretic protocols, such as the PowerEase 500 from Novex. Automatic crossover features allow transitions from one mode of operation to another (e.g., switching from constant voltage to constant current). What happens when multiple gels are run at the same time from the same programmable power supply? Say you've got four gels running simultaneously with a constant voltage set at 200 V and upper current set at 50 mA. With constant voltage, each of the four gel chambers will receive 200 V. What happens with amperage, however, is different. As discussed previously, amperage will change during the course of a run. At any given time, however, total amperage flowing through each cell will be approximately one-fourth of the total amperage, since individual chambers may have differing current flows due to differences in resistance among the chambers. Important with any power supply are safety features. These features are designed to protect you and your equipment. Load and leak detectors ensure power supplies operate within safe limits. Ground leak detectors let the user know when some of the power is following a pathway other than that intended, while no load detectors alert users when the power supply doesn't "see" anything hooked up to it to complete the circuit. This can be indicative of a faulty apparatus. Another safety feature is auto-restart, which can restart your gel run in the event of a power failure. Short-circuit, overvoltage, and overcurrent detectors are a few more common safety features incorporated into many power supplies to ensure the reliability of your gel runs. Although several companies distribute or private label programmable power supplies, LabConsumer contacted the manufacturers to gain more information on what is available to scientists today. How do you know which power supply is the perfect match for your applications? A few items to keep in mind are output range, number of outputs, programmability, and price. Different applications require different voltages. Programmable power supplies come in a wide variety of voltage outputs-from 200 volts to 6000 volts. Accompanying this variation in voltage are contrasting power and current ranges as well. Desired ranges required by your specific applications should be kept in mind when shopping for power. Most programmable power supplies offer two to four sets of output connectors for simultaneous running. This may seem like too much if you don't run multiple gels frequently, but maybe in the future the lab will need to run three or four at a time. How much programmability do you want? There are several levels of control and memory available. Lastly, what does your budget dictate? The price range on programmable modules runs from around $500 to over $5000. Two programmable power supplies are manufactured by Bio-Rad. The PowerPac 1000 is ideal for most SDS-PAGE applications, and its programmability makes it ideal for isoelectric focusing or experiments requiring step changes in electrophoresis conditions. This unit also provides ample voltage for IEF and current for multiple PAGE gels, and its current output of 500 mA also makes it ideal for many blotting applications. The LCD display shows running conditions in large, easy-to-read numerals. Continuous, timed, or volt-hour controlled runs are purportedly easily programmed. The PowerPac 3000 is designed for isoelectric focusing, DNA sequencing, isotachophoresis, SDS-PAGE, 2-D electrophoresis, western blotting, and submarine gel nucleic acid separations. An optional temperature probe allows automatic control of temperature-between 0û and 90ûC-during electrophoresis runs without additional control modules. This is particularly useful for DNA sequencing and Single-Strand Conformation Polymorphism analysis, where constant temperature is crucial for superior gel resolution and reproducibility. Bio-Rad's power supplies have many safety features, including arc detection, a Bio-Rad innovation. A new series of programmable power supplies was recently introduced by Cole-Parmer. The Programmable Power Supply has four output terminals and provides voltage ranges from zero to 6000 volts. The unit can be programmed in increments of one volt and one milliamp. This unit allows users to program voltage, current, and time. Up to 40 sets of frequently used parameters can be stored in the nonvolatile memory for future recall. Safety features include automatic recovery after power failure, sudden load change detection, no load detection, arc detection, ground leakage detection and overload/short circuit detection. Two programmable power supplies manufactured by Atto Corporation (Tokyo, Japan) are available through Crescent Chemical Company. The AE-8450 powerStation 1000VC is designed for PAGE and SDS-PAGE in standard and mini gel sizes, as well as submerged agarose electrophoresis and semi-dry blotting. This unit can store up to ten files programmed for voltage, amperage, and time. A large, four-digit LED displays either preset or actual conditions. The AE-8750 powerStation 1000XP is similar to the AE-8450, but volt-hours can also be programmed. The AE-8750 also features stepwise programming for each of the ten independent files. Also available from Crescent Chemical Company are Serva BluePower programmable power supplies. The BluePower 200, 500, and 3000 Power Supplies allow programmable capabilities for a variety of applications. The Series-90 Programmable Power Supplies from E-C Apparatus utilize microprocessor technology, such as digital encoders to replace conventional adjustment controls and allow for precise digital control. Five different output capabilities are available from 2000 to 5000 volts. All models operate in constant voltage, current, or power modes with automatic crossover between modes. At each step in programming, the power supply presents options to the user; the user simply presses the corresponding "smart key." Three different operating modes are available-Run, Integrate, and Program. For more sophisticated techniques, Program Mode provides the option of writing and storing multiple-step electrophoresis protocols (up to 20 programs can be stored, each having up to ten steps). The PW-500V from KOH Development provides storage of up to 16 programmable files, with each program consisting of up to six steps. Voltage, current, power, and time are programmable with the PW-500V, and a dot matrix display screen displays setting parameters continuously. Standard safety features include overload detection, ground leak detection, and no load detection. Several programmable power supplies are available from LABCONCO, ranging in capacity from 1000 to 5000 volts. Programmable parameters include power, current, voltage, volt-hours, time, step, and stop. All LABCONCO programmable power supplies feature automatic stepping between programs, automatic crossover between preset values, and storage of up to five programs per output terminal. The 3000 Volt Dual Programmable Power Supply features two independently controlled sides, allowing two applications with different parameters to be run separately; this is especially useful for researchers performing isoelectric focusing or DNA sequencing. Also available are the 1000, 3000, and 5000 Volt Power Supplies. The 1000 Volt Power Supply is ideal for overnight separations, isoelectric focusing, protein electrophoresis, nucleic acid electrophoresis, 2-D gels, and preparative isoelectric focusing. The 3000 Volt Power Supply is optimal for classical DNA sequencing, analytical isoelectric focusing, and preparative flatbed isoelectric focusing. Lastly, the 5000 Volt Power Supply will come in handy to those performing ultrathin isoelectric focusing gel electrophoresis and ultrathin high-voltage DNA sequencing. Life Technologies provides the 4001P Programmable Electrophoresis Power Supply. The 4001P is designed for high voltage electrophoretic applications such as DNA sequencing and isoelectric focusing, but is suitable for use with SDS-PAGE, horizontal slabs, and tube gels. This unit can be operated in three different modes: Run mode allows constant current, constant power, or constant voltage with automatic crossover; Integrate mode allows the user to set specific volts, current, or power; and Program mode allows the user to set up unique programs for specific applications. The 4001P stores up to 12 programs with 10 steps each. The PowerEase 500, a programmable power supply designed specifically for mini-gel electrophoresis, is available from Novex. The PowerEase 500 offers eight preset and four custom methods for the user to set preferences. Preprogrammed gel types include Tris-Gly Gel, TBE Gel, IEF Gel, Tricine Gel, TBE-Urea Gel, NuPAGE Gel, NuPAGE Blot, and Western Blot. The LCD screen displays either large numerals or a graphic display, and reports can be sent to most printers via parallel port. Novex also makes available the optional GLP Assistant software package. Pharmacia Biotech provides EPS Power Supplies configured for a variety of applications. The EPS 600 allows programming of voltage, current, power, volt-hours, and time. The EPS 600 is capable of handling a broad range of low and moderate voltage electrophoresis tasks. The EPS 600 and EPS 3500 can store and recall up to three programs of power and time. The EPS 3500 XL, designed for complex 1-D and 2-D isoelectric focusing applications, offers additional regulation of amp-hours and stores up to nine programmed methods, with up to nine steps per method. The lower current limit of the 3500 XL facilitates Immobiline¨â DryStrip, IsoPrime¨, and other very low current IPG separations. Pharmacia also recently introduced the EPS 1000. Stratagene offers the new SmartPowerTM 4000 power supply for all electrophoretic applications. It has been designed for the high-voltage, low-current requirements of DNA sequencing gels as well as the low-voltage, high-current requirements for horizontal DNA gels and vertical protein gels. The temperature probe technology incorporated into the SmartPower was developed in 1991 as part of the FeatherVolt 3000 (Stratagene holds a patent on this technology). The built-in StrataTherm¨â temperature controller allows direct regulation of sequencing gel temperature. The SmartPower 4000 provides constant voltage, current, power, or temperature, with automatic crossover to allow the dominant parameter to control the power supply; it can also store up to 15 programs. Current and power on each output are monitored independently, not just total current and total power of the unit. The System 2000 Power Supply from Zaxis is a variable, programmable low-voltage power supply capable of producing up to 350 volts, 250 mA, and 87.5 watts. It is suited to automatically cross over from one mode of operation to another when a preset limit has been reached. The System 2000 Power Supply optimizes results when used in conjunction with the System 2000 EP Module. The author can be reached online at sbeck@the-scientist.com. Comparison Chart 1 , Comparison Chart2

Tower of Power: The Run On Programmable Power Supplies

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