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Newbie Question......Suitable power supply

Discussion in 'Power Electronics' started by Gorhad, Jul 16, 2015.

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  1. Gorhad

    Gorhad

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    Jul 16, 2015
    Would this be the same as how a smoke alarm works. When the 9v battery gets low and requires replacing it sets off an audible chirp and a red led light flashes?
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Yes, except in your case it would fire up the transmitter and send a pulse to the receiver indicating "low battery" at pre-determined time intervals. Or you could mount a water-proof button on the transmitter case that would cause the μP to test the battery and light up an LED if the battery was okay. No transmitter necessary for that, but the automatic transmit to the receiver when the battery gets low could be more convenient. The receiver may require another microprocessor to decipher the four digital signals (three float switches and low-battery) and act accordingly. Or you may choose to send valve-control signals to the receiver (instead of float switch states) and connect those to relays controlling the two valves. No μP at the receiver needed for that. You have to decide how many and what kind of "bells and whistles" to add.

    It looks like the transmitter/receiver pair you bought could work "as is" for valve control without the battery-saving microprocessor feature, but then I really cannot recommend a suitable battery because I don't know how often it would transmit, or even how you would arrange for the transmitter to "fire up" momentarily and transmit on switch change. I suppose this could be done with discrete CMOS logic at acceptably low energy consumption, but a CMOS μP (like the PIC10F206 I am currently playing with) would seem to be a less complicated path. I think if I were you I would do some investigation to see what kind of PIC (or other μP) would be most suitable. In other words, define what you want it to do, determine how many input ports (bits) you need to look at, decide whether an analog-to-digital converter or analog comparator (for measuring battery voltage under load) is necessary, determine how many output ports (bits) you need to send three, four, or five signals to the transmitter (including a "battery-low" signal), activate a "dummy load" for battery test, and activate the transmitter.

    I haven't thought this completely through, but it appears that each valve will be driven clockwise or anit-clockwise (two control lines) until a micro-switch limit is reached. Each valve needs a 24 V AC supply to energize its motor, so two relays for each valve are required: one to select direction, one to turn on the motor. Or you can wire the relays so each one selects one direction and turns on the motor. Since there are two valves, you need four control line signals coming from the transmitter to the receiver, plus maybe a fifth line for low-battery notification. All the valve-control logic, based on the states of the three float switches, would take place at the transmitter. You could add some water-proof switches there to control the mode of operation: drain the pool, fill the pool, perhaps over-ride the float switches, but you can do the same thing at the valve actuators by simply flipping the three-position toggle switch on the actuator to the appropriate position. Just remember to restore it to the "center off" position to allow automatic operation from the receiver.

    We used to have a fellow here who was quite good at taking a set of performance specifications and designing a circuit, complete with parts list and bill of materials and schematic wiring diagram, usually overnight. Unfortunately Kris died earlier this year and no one has stepped up to fill his shoes. I am sure that collectively we have the talent, but not everyone has the time available to do what Kris did. I and others here will help you learn how to use microprocessors, and we even have a forum here dedicated just for that, but you must do most of the work yourself. We will provide guidance as needed.

    Hop
     
  3. Gorhad

    Gorhad

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    Jul 16, 2015
    Is this what I would be looking for? low_voltage_battery_checker.png
     
  4. Gorhad

    Gorhad

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    Jul 16, 2015
    This is my very basic line diagram
     

    Attached Files:

  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    That's pretty close to the general idea.

    R1 and ZD1 could serve as the "dummy load" on the battery, with a comparator in the PIC performing the comparator function of IC1. Actually, many of the PIC comparators have internal references available so R1 and ZD1 aren't necessary. The two halves of VR1 can probably be calculated ahead of time (or determined by experiment) so that two fixed resistors of appropriate values can be substituted for VR1. These two resistors would then serve as the "dummy load" for the battery.

    There needs to be a way to connect the "clips" only once in while to perform the measurement, so as not to drain the battery. LED1 and R2 would be driven only intermittently by an output port on the PIC, so LED1 periodically emits a short flash when the battery is low. The buzzer BZ1 is not necessary and would drain the battery unnecessarily when it sounds. And finally, the output of IC1 goes low, turning on LED1, when the voltage presented by the wiper arm of VR1 to the non-inverting input of IC1 is less than the voltage presented by zener diode ZD1 to the inverting input. Therefore as the battery terminal voltage falls, the reduced output from VR1 eventually becomes less than the zener voltage and the comparator goes to an output "low" state. Note, however, there is no hysteresis in the circuit. At low battery voltages, close to the "trip" point of the comparator, the circuit can oscillate. A few millivolts of positive feedback from the output to the non-inverting input will prevent this from occurring.

    Have you worked out the logic of which valve position each of the two valves must be in, depending on float switch actuation? You need an option for draining the pool too, unless you want to do that manually by operating toggle switches on the valve actuators.
     
  6. hevans1944

    hevans1944 Hop - AC8NS

    4,270
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    Jun 21, 2012
    You only need to operate one valve?
     
  7. Gorhad

    Gorhad

    16
    0
    Jul 16, 2015
    Yes there is only one 3 way valve which intern is operated by one actuator. The actuator is operated by a little internal motor and 2 micro switches and cams. so it turns one way to open the valve and the other to close the valve

    Below is a breakdown of the parts of the actuator

    http://www.poolzoom.com/jandy-valve-actuator-parts.html

    So when the upper float rises and reaches its activation point it opens the valve and drains the pool and when the middle float drops to its activation point it closes the valve and the systems is normal operation

    There is a toggle switch on the valve which can be used to override the float switch ie ope or close the valve manually via the toggle switch
     
  8. Gorhad

    Gorhad

    16
    0
    Jul 16, 2015
    Hop I do apologize for my primitive explanations and drawings sorry
     
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