Catalogs > Automation Systems Catalog > Programmable Controllers > MicroLogix 1500 System > Power Supplies
Power Supplies
Power Requirements and Transformer Sizing
Each AC -input power supply generates a shutdown signal on the backplane whenever the AC line voltage drops below its lower voltage limit. It removes the shutdown signal when the line voltage comes back up to the lower voltage limit. This shutdown is necessary to help ensure that only valid data is stored in memory.
The external transformer rating (in VA) of each power supply is greater than its real input power (in Watts) because a capacitor-input AC /DC supply draws power only from the peak of the AC voltage wave form. If the transformer is too small, it clips the peak of the sine wave; when the voltage is still above the lower voltage limit, the power supply will sense this clipped wave form as low voltage and could prematurely shut down modules in the chassis.
In the following graphs, we display the backplane power load on the vertical axis. Since these supplies have multiple outputs, the backplane power load is given in watts.
For the dc-input power supply, we display the input real power in watts. For each AC -input power supply, we display the input real power in watts, apparent power in VA, and the transformer load in VA, each in a separate graph.
- Use the real power value in watts for determining the amount of heat dissipation you will have inside the enclosure.
- Use the apparent power value in VA for estimating power cost.
- Use the transformer load value in VA of each power supply plus all other loads on a transformer to determine the required transformer size.
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