Rockwell Automation 2080-LC50 Micro830 and Micro850 Programmable Controllers User Manual - Manual (Page 29)

Rockwell Automation Publication 2080-UM002F-EN-E - December 2013 15
About Your Controller Chapter 2
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
to reduce the electrical noise that enters the controller 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
During power-up, the Micro800 power supply allows a brief inrush current to
charge internal capacitors. Many power lines and control transformers can supply
inrush current for a brief time. If the power source cannot supply this inrush
current, the source voltage may sag momentarily.
The only effect of limited inrush current and voltage sag on the Micro800 is that
the power supply capacitors charge more slowly. However, the effect of a voltage
sag on other equipment should be considered. For example, a deep voltage sag
may reset a computer connected to the same power source. The following
considerations determine whether the power source must be required to supply
high inrush current:
• The power-up sequence of devices in a system.
• The amount of the power source voltage sag if the inrush current cannot
be supplied.
• The effect of voltage sag on other equipment in the system.
If the entire system is powered-up at the same time, a brief sag in the power source
voltage typically will not affect any equipment.
Loss of Power Source
The optional Micro800 AC power supply is designed to withstand brief power
losses without affecting the operation of the system. The time the system is
operational during power loss is called program scan hold-up time after loss of
power. The duration of the power supply hold-up time depends on power
consumption of controller system, but is typically between 10 milliseconds and
3 seconds.