Transformers for low-voltage Control

Use of low-voltage systems management is becoming more widespread, as the demand for residential Air conditioning rises. This necessitates the use of a transformer to reduce the stress, usually up to 24 V. selection of the transformer is not done just by selecting the one that has the proper voltage. Volt-amps (VA) rating is equally important. To determine the VA requirements for a specific solenoid valve, see derating of the manufacturer. Not enough of transformer capacity will allow to reduce the operating capacities or reduction of the maximum operating pressure differential (MOPD) of the valve. MOPD and safe working pressure (SWP) is usually noted on the valve plate (see Fig. 6-27).

If more than one solenoid valve and/or other accessories are managed from one transformer, the transformer VA rating shall be determined by adding the individual accessories VA requirements.