Operational Modes
Introduction
The PowerEase
®
500 Power Supply is capable of operating at limiting voltage,
limiting current, and limiting power. We recommend operating the PowerEase
®
500 Power Supply at limiting voltage for most applications. See below for more
details.
Voltage Limiting
The recommended setting for operating the PowerEase
®
500 Power Supply is
voltage limited. For most electrophoresis methods, resistance increases
throughout the run. Using voltage limiting provides the following advantages:
•
Current and watts decrease throughout the run, providing a natural safety
margin.
•
The same voltage setting can be used regardless of the number or thickness
of gels being electrophoresed.
Current Limiting
Discontinuous buffer systems and, to a lesser extent continuous systems,
increase resistance during the run. If you use the current limiting setting on the
PowerEase
®
500 Power Supply, the voltage will increase as resistance increases
to satisfy Ohm’s law (V=IR, see page 20). If no voltage limit is set and a local
fault condition occurs, such as a poor connection, very high local resistance
may cause the voltage to increase to a maximum of the power supply. This will
lead to local overheating and damage to the electrophoresis cell or create unsafe
conditions.
When running under constant current conditions, set a voltage limit on the
power supply at or slightly above the maximum expected voltage.
Wattage Limiting
If power is constant, voltage will increase and current will decrease during a
run, but the total amount of heat generated by the system will remain constant
throughout the run. However, locally high resistance can cause a high
proportion of the total heat to be generated over a small distance. This can
damage the electrophoresis cell and/or gel(s).
If operating at wattage limiting, set the voltage limiting to slightly above the
maximum expected for the run.
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