Manual Power Supplies
Frequently Asked Questions
What are the relations between Voltage, Current, Power and Resistance?
Power (W) = Voltage (V) x Current (A)
Resistance (
W
) = Voltage (V) / Current (A)
How does a power supply react after pressing RUN?
The internal generator will start building up the high voltage at the output terminals while voltage and
current are constantly measured and power calculated. When one of the pre-set parameters is
exceeded, the generator stops and will keep that parameter constant.
How important is the resistance of an electrophoresis unit?
The resistance of an electrophoresis unit depends on its size, gel thickness, amount of buffer, buffer
conductivity and temperature. This resistance will normally decrease in time due to a slowly increasing
temperature. Electrophoresis units which have a resistance below the minimum load resistance of a
power supply will trigger an alarm! Read the output voltage and current during a run to measure the
resistance and use above formula to calculate the value.
How to keep a constant voltage during a run?
Program the desired voltage and a higher current and power then the maximum expected values:
Current > Voltage / Resistance
Power > Voltage x Current
How to keep a constant current during a run?
Program the desired current and a higher voltage and power then the maximum expected values:
Voltage > Current x Resistance
Power > Voltage x Current
How to keep a constant power during a run?
Program the desired power and a higher voltage and current then the maximum expected values:
Voltage > Current x Resistance
Current > Voltage / Resistance
Why are my output values different from those of a similar experiment?
Either your programmed parameters are not equal to those described or the resistance of your
electrophoresis unit is different (see above). It cannot be due to e.g. an other model of power supply as
the relations between Voltage, Current, Power and Resistance are monitored in the same way by any
instrument (the electrical laws cannot be disregarded!).
What about connecting more than one unit to the same power supply?
The outlets being in parallel each electrophoresis unit will be supplied with exactly the same voltage.
However, current and power may differ due to differences between them even when exactly the same
model, gel, buffers, etc... are used. Therefore, it is recommended to run several electrophoresis units
only in the constant voltage mode on the same power supply.
Mind also that adding tanks will increase the current and the power. These parameters may be limited
by the power supply and cause it to switch over to constant current or constant power.
Rev. 1605
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