Instruction Manual |
9
12.0 Ohm’s Law Conversions
Electrophoresis is the migration of a charged particle under the influence of an electrical field. The power
supply output parameters voltage, current, and power are related by the following two equations:
Voltage (V) = Current (I) x Resistance (R); (V = I x R)
Power (P) = Current (I) x Voltage (V); (P = I x V)
Resistance
Resistance of the assembled electrophoresis cell is dependent on the conductivity
of the gel buffer, the thickness of the gel, and the number of gels being run. Although
the resistance is determined by the gel system, the resistance can vary over the course
of an electrophoretic separation.
Voltage
The velocity with which an ion moves in an electric field will vary in proportion to the
field strength (volts per unit distance). The higher the voltage the faster an ion will
move.
Current
Current is a function of the number of ions passing a given cross-section of the circuit
at a given time. For a given gel/buffer system, at a given temperature, current will vary
in proportion to the field strength (voltage) and/or cross-sectional area (number and/or
thickness of the gels).
Power
The power in Watts, or the rate of heat generated by the system, is directly proportional
to voltage and current (P = I x V).
13.0 Common Errors Found with Electrophoresis Power Supplies
No load
The electrophoresis system is not connected to the power leads, check the power leads
The electrophoresis system has a short, the Pt wire is broken or the banana connectors
are damaged
Buffer concentration too low
Buffer volume too low
Short in power cord
Current has dropped below acceptable rating (4 mA)
Short circuit
Load exceeds 3000 mA (250V) or 500 mA (300V)
Blown fuse in the power supply
Incorrect input voltage (check input voltage switch near power inlet)
Change in load
Electrophoresis systems were added or removed during a run
Buffer leaking in a connected system
Excessive temperature increase
Excessive buffer evaporation
Loose connection in a connected system
Amperage set too low
Change in constant mode
Voltage changes to amperage
Amperage set too low. Ceiling hit and constant mode changed from voltage to amperage. Increase
amperage to 500 mA (250V) or 3000 mA (300V).
Amperage changes to voltage
Voltage set too low. Ceiling hit and constant mode changed from amperage to voltage. Increase
voltage to 500 mA (250V) or 3000 mA (300V).
The systems have automatic crossover, set voltage or amperage, and preset wattage. During the
electrophoresis process only one parameter is limiting at a time. The limiting parameter, together with
the conductivity in the electrophoresis system, and the values for the other parameters determine the
maximum output.
