Installing Your Controller
1–13
Power Considerations
The following explains power considerations for the micro controllers.
Isolation Transformers
You may want to use an isolation transformer in the ac line to the controller. This
type of transformer provides isolation from your power distribution system and is
often used as a step down transformer to reduce line voltage. Any transformer used
with the controller must have a sufficient power rating for its load. The power
rating is expressed in volt-amperes (VA).
Power Supply Inrush
The MicroLogix power supply does not require or need a high inrush current.
However, if the power source can supply a high inrush current, the MicroLogix
power supply will accept it. There is a high level of inrush current when a large
capacitor on the input of the MicroLogix is charged up quickly.
If the power source cannot supply high inrush current, the only effect is that the
MicroLogix input capacitor charges up more slowly. The following considerations
determine whether the power source needs to supply a high inrush current:
•
power-up sequence of devices in system
•
power source sag if it cannot source inrush current
•
the effect of the voltage sag on other equipment
If the power source cannot provide high inrush current when the entire system in an
application is powered, the MicroLogix powers-up more slowly. If part of an
application’s system is already powered and operating when the MicroLogix is
powered, the source voltage may sag while the MicroLogix input capacitor is
charging. A power source voltage sag can affect other equipment connected to the
same power source. For example, a voltage sag may reset a computer connected to
the same power source.
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