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24 Vac to 12Vdc pulse

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T&E Irrigation

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Hello, I'm brand new to this site and not very cluey with electronics and wanted to ask a question. I am trying to build a circuit that, when 24Vac is applied and held, a 12Vdc pulse of .5 of second is sent to the output on 2 terminals. Then when the 24 Vac is released, a second 12Vdc pulse of .5 of a second is sent to the output terminals but in reverse polarity.
If anyone understands irrigation coils, a standard mains powered irrigation controller puts out 24 Vac to the solenoid coils while a battery operated controller puts out a latching 12 Vdc to latching solenoids. I want to build a circuit that can go in between the standard mains powered controller to operate latching solenoids. Many thanks in advance.
 

MikeMl

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Do you have a source of continuous power at the same time? 24Vac that runs the irrigation controller, for example? Another plug-in wall-wart that puts out 12Vdc?
 

alec_t

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For how long does the 24VAC persist?
How much current does a latching solenoid draw and how many solenoids?
Will all the solenoids be operated simultaneously?
 

T&E Irrigation

New Member
There will be a continuous 24 Vac supply and, if required, i will supply 12 V dc using a transformer. The solenoid will draw about 500mA. I want the solenoids to operate one at a time. A separate signal is sent from the controller , ie separate 24 vc signal, to operate the second valve and so on. I want to be able to control up-to 4 solenoids independently
 

MikeMl

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Here is a hack at it...

Input V(valve1) is 24Vac from a standard irrigation controller lasting 3s for the purpose of the simulation...

Output I(L2) is bidirectional DC current through the simulated solenoid coil lasting ~0.5sec at both onset and end of V(valve1).

Note that the negative terminal of the 12Vdc Wall-Wart is tied to the Common terminal of the irrigation controller.

Relay is DPDT 12Vdc coil with a resistance of ~500 Ohms

irrig.png

PS: are you sure you need to time the duration of the solenoid pulses? Don't the motorized valves have internal limit switches that shut off the motor when the valve reaches it's fully-open/fully-closed positions? If so, that will greatly simplify the circuit...
 
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MikeMl

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AnalogKid

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The CD4049 does not have Schmitt inputs. Try the CD40106.

Also, it might be that both 12 V pulses are the same polarity. Don't know, because all of my valves are hydraulic.

ak
 
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