Australia & New Zealand
Uninterruptable Power Supplies or UPS are commonly used in all plants but primarily for mains voltage. These will convert mains voltage to DC for charging batteries then convert back to mains voltage for powering equipment. When the mains voltage dips, the power is sourced from the battery until the voltage returns on the mains power. Most likely this will feed a power supply to convert mains voltage to 24V DC. This not only complicates the power system design but also adds to losses in the system which must be designed in. Weidmuller can now simplify this technique with our DC UPS system. This utilises the existing 24V DC from your power supply to additionally manage a battery charging system complete with temperature based charging, visual and digital status as feedback for the control system while also managing the load. When a 24V DC input fails, the UPS will run on batteries for a pre-determined time adjustable from 0.5-45mins or when used for emergency supply till flat to hold up the 24V DC system for as long as possible.
With a UPS system, the most critical part is the batteries. For longevity from your batteries, they must be kept ideally at 22°C and less than 40°C or risk a dramatically reduced life which then adds to another maintenance task, so when the ambient temperature is high, a temperature controlled charging system increases the charging time to reduce heat in the battery and increase battery life. Weidmullers DC-UPS and battery systems combined aims for reliable long term operation when used correctly, utilising absorbed glass mat (AGM) Valve regulated lead acid (VRLA) batteries suitable for float charging systems.
When designing a backup system using a UPS , circuits must be segregated into critical (need to stay alive) and non-critical (not requiring backup ) .This must be done effectively to ensure the UPS system does not become too large or cumbersome. Critical circuits could include PLC, HMI, safety systems, solenoids, Servo control and other devices required to ensure the machine or plant is in a ready state to run when power is returned.
A DC-UPS can be inserted into any 24V DC system and will pass the supply through the unit and also charge 2 connected batteries in series. The unit is complete with 1 Digital input for Interlock normally linked, and 3 digital outputs (Relay & transistor). In normal operation output 3 would be on to indicate charging of batteries in progress.
When 24V DC supply is removed, the non-critical load will stop and the battery will instantly power the safe load or output for a pre-set time period from 0.5-45 mins or for as long as possible (deep discharge). Digital Output 2 will provide feedback that DC-UPS is buffering the load and output 1 will initiate when either the pre-set cut off time is reached, or deep discharge has caused the battery voltage too low.
WAUS Power Supplies Core Assortment Catalogue 2015 Issue #3