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--- project:sprinklers [2024-04-17 Wed wk16 13:21] – [Sprinkler Solenoid 24VAC Woes] baumkp
+++ project:sprinklers [2024-04-30 Tue wk18 17:22] (current) – [Sprinkler Solenoid 24VAC Woes] baumkp
@@ Line 17: / Line 17: @@
 I would consider normal supply voltage tolerance to be minimum +/-10% this aligns with the IEC standard for electrical power distribution. So a 24VAC system should be able to absolutely reliably operate between 21.6 to 26.4 VAC.  As the solenoid operation voltage was typically between 25 - 26VAC this condition is meet.  The stand-by voltage was not a concern for the solenoid operation and the controller clear had no problems with this. Checking the controller circuit I would expect it would reliably operate with 24VAC ± 20% or 19.2 to 28.8 VAC.  The controller solid state outputs had 40V snubbers which could start snubbing the sinusoidal peak voltage over 28.2 VAC RMS.
-Next I measured the DC resistance of a new solenoid at 33.1 Ω.  Based upon the specification printed on the Solenoid 24 VAC, 50/60 Hz, Holding 0.25 Amp and inrush 0.43 Amp maximum I calculated the solenoid impedance to be 96.0 Ω.  This means the solenoid holding reactance calculates as 90.1 Ω.  The solenoid apparent power is 6.0 VA and real power 2.07 W.  With 25.2 VAC supply at the solenoid this becomes 0.264 A current, 6.68VA apparent power and 2.3 W real power.  Reactance has the following relationship with Inductance and frequency, X<fs xx-small>L</fs> = 2π F L, where X<fs xx-small>L</fs> is impedance (Ω), F is frequency in Hz, L is inductance in Henry.  So the with 60Hz the solenoid effective impedance increase from 90.1 Ω at 50 Hz to 108.2 Ω.  At 24VAC 60Hz the solenoid current then drops to 0.21 Amp (was 0.25 Amp at 50Hz) with apparent and real power dropping to 4.87 VA and 1.49W.  On my system with 25.2 VAC at the solenoid calculations show that adding a 12 Ω resistor into the solenoid circuit reduces the solenoid voltage to 23.9 VAC and current to 0.249 Amp.  The voltage drop across the resistor is 3.2V and power drop 0.79 W.  The resistor was rate at 1 W operation.
+Next I measured the DC resistance of a new solenoid at 33.1 Ω.  Based upon the specification printed on the Solenoid 24 VAC, 50/60 Hz, Holding 0.25 Amp and inrush 0.43 Amp maximum I calculated the solenoid impedance to be 96.0 Ω.  This means the solenoid holding reactance calculates as 90.1 Ω.  The solenoid apparent power is 6.0 VA and real power 2.07 W.  With 25.2 VAC supply at the solenoid this becomes 0.264 A current, 6.68VA apparent power and 2.3 W real power.  Reactance has the following relationship with Inductance and frequency, X<fs xx-small>L</fs> = 2π F L, where X<fs xx-small>L</fs> is impedance (Ω), F is frequency in Hz, L is inductance in Henry.  So the with 60Hz the solenoid effective impedance increase from 90.1 Ω at 50 Hz to 108.2 Ω.  At 24VAC 60Hz the solenoid current then drops to 0.21 Amp (was 0.25 Amp at 50Hz) with apparent and real power dropping to 4.87 VA and 1.49W.  On my system with 25.2 VAC at the solenoid calculations show that adding a 12 Ω resistor into the solenoid circuit reduces the solenoid voltage to 23.9 VAC and current to 0.249 Amp.  The voltage drop across the resistor is 3.2V and power drop 0.79 W.  The resistor was rated for up to 1 W operation.
 A USA based brochure for the K-Rain Valve KR7101 gives the following specification for the valve: Voltage: 24VAC 60 cycles, 0.4 amps in rush, 0.2 amps holding. Pressure 20 psi minimum to 150 psi.  This aligns well with the calculation showing 0.21 Amp at 24 VAC 60 Hz.