Planning of an electrical control of the irrigation system …
Plan electrical control
Control garden irrigation via smart home
24 V alternating current
Convert 24 VAC to 12 VDC
Calculation power supply unit
Top hat rail transformer power consumption
Plug-in power supply power consumption
Plan electrical control …
We continue with the planning of the electrical control of an automatic garden irrigation system.
Control garden irrigation via smart home …
We have changed the products of the garden planner, as mentioned on the previous page, again a little and also expanded with a switch actuator so that the irrigation system can be integrated into our Smarthome. In order to have no 230VAC voltage outdoors and especially no 230V in the valve box, we have decided to install a 24V AC power supply indoors and for safety reasons lead only 24V to the valve box!
24 V alternating current …
Some may wonder why we decided to use an AC power supply and not simply a ready-made 12V DC power supply with direct current, which you can use for the Homematic HM-LC-Sw4-PCB switching actuator (by the way, the Homematic 4-channel switching actuator has an operating voltage range of 7 V to 15 V DC). The problem here, however, is that you absolutely have to apply alternating current, i.e. AC, for these solenoid valves so that the coil in the solenoid valve does not burn out. Alternatively, you could select other DC magnetic valves with direct current.
Convert 24 VAC to 12 VDC …
In order to obtain the correct supply voltage for the DC switching actuator and for the AC solenoid valves, we have developed a AC-DC Buck Converter, AC 24V to DC12V 3A *Ad ordered. Thus, we now have a circuit AC 24V from the transformer for the solenoid valves and another DC 12V for the Homematic 4-channel switching actuator in the Gardena valve box. How we have wired it exactly, we show then in the further course of this tutorial with Practical testing.
Calculation power supply unit …
Now we need to calculate what the approximate power rating of the AC power supply should be. The 24 VAC solenoid from our wasted Hunter PGV-101-GB solenoid valve requires an inrush current of 370 mA and a holding current of 210 mA at 50Hz. So one solenoid valve requires up to 8.89 watts for a short time. Thus, with three solenoid valves, a maximum of 26.67 watts of power is required for a short time and a maximum of 15.12 watts of power is required during simultaneous irrigation across all three valves. Since it is not possible to avoid 100% that all solenoid valves have to be switched together, the calculation of the necessary power supply should be based on the highest possible short-time load to be on the safe side. By the way, without current the valve is closed and no water flows, so you only need the current when you activate the irrigation.
Here are again all important values for a Hunter PGV-101-GB solenoid valve:
– Inrush current 370 mA (at 24V approx. 8.89 watts)
– Holding current 210 mA (at 24V approx. 5,04 Watt)
– Voltage 24 VAC
But not only the maximum power of the power supply is important, but from an ecological point of view of course also the power consumption.
Current consumption measurement values with top-hat rail transformer …
Own measurements with a Vemer vn319000 transformer TMC 30/24 top hat rail transformer resulted in the following values:
– No load without transducer approx. 1 Watt
– No load with AC-DC Buck Converter, AC 24V to DC12V 3A without consumer also approx. 1 Watt
– With a Hunter solenoid valve PGV-101-GB approx. 6.2 Watt
– Idle with AC-DC Buck Converter, AC 24V to DC12V 3A and Homematic HM-LC-Sw4-PCB approx. 2.4 Watt
– With Homematic HM-LC-Sw4-PCB and 1x Hunter solenoid valve PGV-101-GB approx. 7.2 Watt
– With Homematic HM-LC-Sw4-PCB and 2x Hunter solenoid valve PGV-101-GB approx. 12.0 Watt
– With Homematic HM-LC-Sw4-PCB and 3x Hunter solenoid valve PGV-101-GB approx. 16.8 Watt
Since one may not tinker of course simply even at the distribution box – Attention, danger to life!!! – and an electrician naturally additional costs for the professional installation causes, we would like to test therefore still another solution completely without DIN rail transformer, but with plug power supply, as one knows it from light chains for the external area (IP44).
Current consumption Measured values with plug-in power supply unit …
Own measurements with a TDCPower power supply 24VAC 21VA resulted in the following values:
– No-load operation without consumer approx. 3.3 watts
– With a Hunter solenoid valve PGV-101-GB approx. 6.2 Watt
– Idle with AC-DC Buck Converter, AC 24V to DC12V 3A and Homematic HM-LC-Sw4-PCB approx. 3,6 Watt
– With Homematic HM-LC-Sw4-PCB and 1x Hunter solenoid valve PGV-101-GB approx. 8.3 Watt
– With Homematic HM-LC-Sw4-PCB and 2x Hunter solenoid valve PGV-101-GB approx. 12.1 Watt
– With Homematic HM-LC-Sw4-PCB and 3x Hunter solenoid valve PGV-101-GB approx. 16.9 Watt
Price of automatic irrigation system including integration into the smart home …