Low voltage sensing switch

Discussion in 'General Electronics Chat' started by shezza, Aug 4, 2014.

  1. shezza

    Thread Starter Member

    Mar 19, 2014
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    So to better explain what Im after, I have a 12v solar panel circuit. So the panel, controller, battery and light.
    I wanted to expand this lighting system, but expect on cloudier days, the battery wont get the necessary charge. So I was wondering how Id go about getting a sensor to pick up the voltage dropping past a certain point and then I will have either a backup charger (that I guess could preferably turn off at a certain voltage as well) turn on to charge the battery up or the power source is changed from the battery to direct from the 240-12v transformer.
    Or any suggestions would also be appreciated.

    Thanks
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The simplest solution to select one of two power sources is to use two diodes into the load.
    The source with the higher voltage takes over automatically.

    Similarly, the solar panel charging a battery via a diode will charge the battery when ever the voltage of the solar panel exceeds that of the battery.
     
  3. shezza

    Thread Starter Member

    Mar 19, 2014
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    So I suppose a 1n4007 diode would be suitable? You are saying to place two of them... Could you possibly explain where and also explain in somewhat simple terms how the effect takes place?
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    If the AC power is off, and the lights are running only on battery, then you should also provide an automatic low-voltage load disconnect. You should never discharge Pb batteries to less than 1.9V per cell (~11V for a 12V SLA), so an auto-shutoff is usually used.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    [​IMG]


    When the voltage on the anode of the diode exceeds the voltage on the cathode by the diode forward voltage, the diode will conduct. For a 1N4001-1N4007 diode the forward voltage is about 0.6V. For a 1N5817 Schottky diode the forward voltage is about 0.3V.

    The LM317 voltage regulator prevents over charging the battery.
     
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  6. shezza

    Thread Starter Member

    Mar 19, 2014
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    Well diodes are pretty handy things then! So are you recommending I use the 1n5817 then as I will lose less voltage?
    Also, what are the resistors and capacitor for?

    The Solar panel controller protects the battery from over charge and also from being sucked dry, so I wont need the voltage reg.

    I drew up a rough schematic of my project and would love some input. Its a bit rough, but Ive never drawn up a circuit with all the symbols before.
    Couple of questions... do I need a diode on the "out" side of the PIR switch to stop reverse voltage? Also, all the earth symbols... is that rather than drawing up two sets of wires everywhere?

    While Im here, does anyone know if a linear actuator can be manually pulled and pushed? Im considering installing one on the front gate and having its operated on a third full time PIR switch which opens it, as well as the RFID scanner and the electric door strike button from inside.
    [​IMG]
     
    Last edited: Aug 5, 2014
  7. shezza

    Thread Starter Member

    Mar 19, 2014
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    Bit of a bump as I really want to get into the wiring tomorrow. Its the only thing that keeps me sane (keeping busy).
     
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    What is the third wire/connection between the lamps? Lamps need two connections; power and ground in a simplistic view.

    Without that connection, the lamps are powered when the photoelectric switch closes AND it's corresponding motion sensor turns on (PIR switch).

    Is that what you want?
     
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  9. AlphaDesign888

    New Member

    Jul 27, 2014
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    Talk to us about your sanity.

    Tell us what is sanity, can you define it for us?
     
  10. shezza

    Thread Starter Member

    Mar 19, 2014
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    I am having two wire running everywhere.

    So basically, the dusk arrives, the photoelectric sensor acts on it and allows power to pass it to both PIR sensors. A person walks by one and switches the lights on. The PIR timer runs out and the PIR waits to be set off again.

    The wire between the two lamps is simply for my understanding. Going from the inside of the garage roof, then stepping down to go under the bottom rung of the fence.

    I can define it according to the dictionary, but surely you can google easier than you can send the message you have. So ill give the answer I think you are looking for. If you are even truly after an answer :p

    What sanity is to me is what counts in this case. Not having a low mood through boredom would be the appropriate definition for this situation :)
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Ok, as long as you realize that there should not be an electrical wire there as drawn. The rest of your diagram makes sense to me as a block diagram, interpreting the PIR switches and photoelectric switch as building blocks. The actual devices are a bit more complex.
     
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  12. AlphaDesign888

    New Member

    Jul 27, 2014
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    It is true. I am bored out of my brain (or what's left of it)

    But technically speaking, from an legal point of view, sanity is knowing
    what you are doing.
     
  13. shezza

    Thread Starter Member

    Mar 19, 2014
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    There shouldnt be a wire between the two globes? How is power meant to get to the second set of globes? Cant wait for the second PIR to be set off...

    Also, do I need a diode after the PIR sensor to stop voltage from entering the PIR switch backwards?

    And If the 1N5817 diode uses 0.3v and the 1N4007 uses 0.6v, when would I want to use the diode that uses up more voltage? Purely when I need it to handle more Amps? My lights could be using anywhere up to 10A (Not sure how much Ill end up dimming them if at all). Do I need to have higher than 12v powering the circuit to make up for the voltage loss being the LEDs run off 12v roughly... or is this loss only beyond each diode? Does every diode drop voltage? Or only the ones blocking the voltage? If someone could simplify it a bit, would really appreciate it!

    Legal shmegal ;)
     
    Last edited: Aug 9, 2014
  14. shezza

    Thread Starter Member

    Mar 19, 2014
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    Sorry... need to bump this!
     
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