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project:sprinklers [2024-06-08 Sat wk23 12:02] – [Sprinkler Solenoid 24VAC Woes] baumkpproject:sprinklers [2024-08-24 Sat wk34 16:27] (current) – [References] baumkp
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 To fully resolve this issue I purchase a single channel digital oscilloscope and tested the voltage at the controller out and the node boxes closer to the solenoid valves.  The operating measured voltage was between 25.8 and 25.2 VAC RMS.  The wave form was very sinusoidal and the offset was negligible, about 0.2 V.  On this basis the whole DC issue was closed out as not applicable in my case.  The 24VAC supply voltage with no outputs operating, just the controller powered was 27.2VAC.  To fully resolve this issue I purchase a single channel digital oscilloscope and tested the voltage at the controller out and the node boxes closer to the solenoid valves.  The operating measured voltage was between 25.8 and 25.2 VAC RMS.  The wave form was very sinusoidal and the offset was negligible, about 0.2 V.  On this basis the whole DC issue was closed out as not applicable in my case.  The 24VAC supply voltage with no outputs operating, just the controller powered was 27.2VAC. 
  
-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.+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 (as they are not powered) and the controller clearly had no problems with this having operated reliably for 10 years. 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 rated for up to 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. 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.
  
-I measures the voltage across the resistor with the Oscilloscope at between 2.81 to 2.88 VAC RMS and resistor was measured with a multimeter as 12.1 Ω, so circuit current is 0.232 to 0.238Amp.  This places the solenoid operation back into name plate specification range.+I measures the voltage across the resistor with the Oscilloscope at between 2.81 to 2.88 VAC RMS and resistor was measured with a multimeter as 12.1 Ω, so circuit current is 0.232 to 0.238Amp.  This places the solenoid operation below name plate specification.
  
 I measure the voltage across the resistor when operating an old solenoid valve and it was 3.03 VAC RMS, with calculated current of 0.25 Amp.  Interestingly the waveform across the resistor on the new solenoids looked distorted, more triangular, whereas the old solenoid valves waveform was much more sinusoidal.  I wonder if the new solenoid coils were saturating leading to the distorted current wave form, I don't know for sure, nor what the impact on the solenoid actual power draw would be. I measure the voltage across the resistor when operating an old solenoid valve and it was 3.03 VAC RMS, with calculated current of 0.25 Amp.  Interestingly the waveform across the resistor on the new solenoids looked distorted, more triangular, whereas the old solenoid valves waveform was much more sinusoidal.  I wonder if the new solenoid coils were saturating leading to the distorted current wave form, I don't know for sure, nor what the impact on the solenoid actual power draw would be.
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 **Summary** **Summary**
 +
 After 12 weeks of reliable operation with no further solenoid failure the use of a 12 Ω resistor to limit solenoid current and power draw has rectified the solenoid failure problem.  It appears the use of valve solenoids specified for dual 50/60 Hz use on 24 VAC are prone to failure with use on 50Hz supplies with voltage at solenoids greater than 24.0 VAC. After 12 weeks of reliable operation with no further solenoid failure the use of a 12 Ω resistor to limit solenoid current and power draw has rectified the solenoid failure problem.  It appears the use of valve solenoids specified for dual 50/60 Hz use on 24 VAC are prone to failure with use on 50Hz supplies with voltage at solenoids greater than 24.0 VAC.
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 ====References==== ====References====
   *[[https://www.electronics-tutorials.ws/accircuits/power-triangle.html|Power Triangle and Power Factor]]   *[[https://www.electronics-tutorials.ws/accircuits/power-triangle.html|Power Triangle and Power Factor]]
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