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:
- There are 18 controllers being supplied by the transformer at 120
VAC.
- 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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