Irrigation & Lighting Division

Selecting Power Conditioning Transformers:

In a perfect world, Power Conditioning Transformers should be operated between 40% and 100% of their Volt-Ampere rating.  The life of the transformer is maximized when it operates at 100% of its rating because it runs coolest under this condition. 

In order to select the proper size transformer, it is necessary to know the total load for the worst case scenario.  Then choose the next larger available size, in Volt-Amperes.

Example:
On a golf course with a single power source, the following information is collected:

  1. There are 18 controllers being supplied by the transformer at 120 VAC.
  2. From the controller manufacturer’s catalog, we find that each controller has a current draw of 0.19 amperes when it is at rest (no load.)  “At rest” means that the controller is not activating any of the solenoid valve(s).

The power required by the controller electronics (at stand by) is:

Controllers’ Power Needed = Volts X Amps X Number of controllers
Controllers’ Requirement = 120 X 0.19 X 18 = 410.4 VA

 

It is known that each controller will simultaneously activate up to 3 solenoid valves when the irrigation cycle begins.  This means that 54 solenoid valves (3 valves per controller X 18 controllers) will be activated at the same time, as a worst case scenario.  We learn from the valve manufacturer’s catalog that the valves operate at 24 VAC with an inrush current of 0.40 amps.

The power required to operate the solenoids is:

Power needed by solenoids = Volts X Amps X Number of solenoids
Solenoids’ Requirement = 24 X 0.40 X 54 = 518.4 VA

 

The total power supplied by the transformer, at maximum load, is:

Transformer Supplied Power = Controller Requirement + Solenoid Requirement
Transformer Supplied Power = 410.4 + 518.4 = 928.8 VA

 

From the table below, choose the size transformer just larger than 928.8 VA, which is Paige Electric part number 250040, rated at 1000 Volt-Ampere.

Paige
Part No.
SOLA
Part No.
Voltage Output Capacity
(Volt-Amperes)
Output Input
250000 63-23-112-4 120 120, 208, 240 120
250010 63-23-125-4 120 120, 208, 240 250
250020 63-23-150-8 120, 208, 240 120, 208, 240 500
250030 63-23-175-8 120, 208, 240 120, 208, 240 750
250040 63-23-210-8 120, 208, 240 120, 208, 240 1000
250050 63-23-215-8 120, 208, 240 120, 208, 240 1500
250060 63-23-220-8 120, 208, 240 120, 208, 240 2000
250070 63-23-230-8 120, 208, 240 120, 208, 240 3000
250080 63-23-250-8 120, 208, 240 120, 208, 240 5000

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