Announcement

Collapse
No announcement yet.

Electronic circuit question

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Electronic circuit question

    Hi

    No machining content but this group is probably the best one I know for getting an answer to this...

    I have a small, 12v, fan used to ventilate a composting toilet. The fan runs off of a small photovoltaic panel. When the sun is reasonably direct on the panel, all is good. If no direct sun, the output voltage drops to 8-9-10v and the fan stops turning and just buzzes...

    Sooo does anyone have, or know of, a circuit that will switch on the power to the fan only when the input is up over 11 or 12vdc AND will run off of the panel's variable output?

    Iirc, the panel produces (Max) 10-15w so I'd have an amp, or so, to play with. Sorry I don't have more detailed specs handy.

    Thanks in advance
    Frank

  • #2
    A simple comparitor such as a LM311 with a Mosfet on the output to switch the fan on when the threshold is over 11v, settable by a small trim pot.
    If running off the same supply, you would want to drop and regulate the LM311 circuit supply with a 9v zener.
    I use strip (Vero) board for small proto-types such as these.
    Half way down the page
    http://www.futurlec.com/Protoboards.shtml
    There are dedicated Electronic forums such as All About Electronics.
    Max.

    Comment


    • #3
      I am sure that such a circuit could be invented,(see above ) that would cause greater complication, and consume some amount of power itself, requiring more photovoltaic panels to maintain the same level of operation.

      So my suggestion is to just skip the circuit and go directly to add another panel of a size that would supply enough power to operate the fan more reliably during daylight hours.

      This would allow you to orient additional panel(s) to better advantage when the existing panel is not in direct sunlight.

      Dave
      Last edited by becksmachine; 08-14-2017, 11:02 AM.

      Comment


      • #4
        Originally posted by becksmachine View Post
        I am sure that such a circuit could be invented,(see above ) that would cause greater complication, and consume some amount of power itself,

        Dave
        The circuit I described would be in the low Ma range, apart from the Fan itself of course.
        Max.

        Comment


        • #5
          PV panel output is very "squishy", so quite probably there will be problem with oscillation since when the fan gets turned on it'll pull the panel voltage lower which will turn the fan off again... which allows the unloaded panel voltage to go up again which turns the fan on which pulls the panel... you get the idea. The solution to that is some positive feedback hysteresis... which adds some more componets, but isn't difficult if you understand how a comparator works.

          A possible simple solution would be to turn on a small double pole relay with the TL431 (basically a 3 pin comparator that acts like an adjustable voltage zener diode that conducts current (from cathode to anode) when the voltage reference pin is above 2.5V ) and make it so the relay "self energizes" it's own coil (one set of contacts in parallel with the TL431), the other set of contacts controls power to the fan. The relay would turn on when the TL431 triggers it (reference pin above 2.5V), then would stay on until the panel voltage fell too low to keep the coil energized, usually about 1/3 of rated coil voltage. This "should" work would take only a couple parts: Small 12V double pole relay, a TL431 and either 2 resistors or a potentiometer. If oscillation is still a problem, use a DPDT relay and have the normally closed contact turn on a dummy load (resistor) to load down the panel a bit when it's not powering the fan.

          (the resistor divider or potentiomenter is set or adjusted so that the wiper or middle node is 2.5V when the panel voltage is high enough to run the fan)

          Comment


          • #6
            Largish electrolytic capacitor connected parallel with the fan motor could be enough to quiet it down in some cases. 10000 uF or something like that.

            Comment


            • #7
              Is the goal to run the fan? Or to stop it trying to run when there is not enough power?

              Running the fan requires power, and on a cloudy day, there may not be enough, so it's not going to happen, at least not continuous running.

              The fan will likely not be damaged by trying to run without sufficient current, so you could just ignore it.

              A third option is to combine some others... Put in BOTH the large capacitor AND the on/off circuit.

              The idea there is to store up charge on the large capacitor, and when the voltage reaches the fan voltage, run the fan long enough to do some ventilation. When it drops too low, the on/off circuit turns it off, starting the cycle again. That way you get both results at once, both ventilation, and no buzzing motor. And it will work at any time the panel produces more power than the tinty amount the circuit uses.

              You will want the on/off circuit to have hysteresis, so that it will turn the fan on when the voltage is at the fan's maximum rating, and does not turn off until the voltage has dropped near the turn-off point of the fan.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                Add an inverter and a battery to store the PV power when the fan isn't on. Then you should have plenty when the fan is on.

                metalmagpie

                Comment


                • #9
                  Originally posted by metalmagpie View Post
                  Add an inverter and a battery to store the PV power when the fan isn't on. Then you should have plenty when the fan is on.

                  metalmagpie
                  That also... and you could do it the simple way, by having the same low voltage cutoff, and just using the panel to charge directly..... use a timer circuit, so the fan is on part time and off the rest, and cuts off if voltage is too low. With the right time ratio of on vs off, set with a 555 type circuit, you can have the fan run 24/7 intermittently, unless you have a lot of cloudy days.
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #10
                    Hysteresis can be easily achieved with a positive feedback resistor on the comparitor circuit.
                    If there was a demand, it would be a nice project for a 8pin micro with added features.
                    Max.

                    Comment


                    • #11
                      Originally posted by MaxHeadRoom View Post
                      Hysteresis can be easily achieved with a positive feedback resistor on the comparitor circuit.
                      ....
                      Yes indeed. And it can be large value resistors for a low power circuit.

                      That IS a possible product idea.... A friend of mine who is off-grid has a C-T also and he has the same sort of exhaust fan.... which I can see the point of.... I suspect I'd want to have a 24/7 fan operating, because those things can be just about as stinky as a chamber pot, if they do not have a fan.

                      His runs off the main system batteries, and draws way under an amp, so he does not need any extra stuff. But as a "stand-alone" unit, there might be a niche market.
                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment


                      • #12
                        Originally posted by J Tiers View Post
                        ... those things can be just about as stinky as a chamber pot, if they do not have a fan.
                        Adding a fan to a chamber pot will probably make it more stinky. Adding a lid to the chamber pot would probably be more effective.
                        Location: Long Island, N.Y.

                        Comment


                        • #13
                          Originally posted by RichR View Post
                          Adding a fan to a chamber pot will probably make it more stinky. Adding a lid to the chamber pot would probably be more effective.
                          Ummmmmm.....

                          The fan vents OUTSIDE!

                          You did not think it vented inside, did you?
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            Originally posted by RichR View Post
                            Quote Originally Posted by J Tiers
                            ... those things can be just about as stinky as a chamber pot, if they do not have a fan.
                            end quote

                            Adding a fan to a chamber pot will probably make it more stinky. Adding a lid to the chamber pot would probably be more effective.
                            Nice play on the sentence structure.

                            Dan
                            At the end of the project, there is a profound difference between spare parts and extra parts.

                            Comment


                            • #15
                              Ignoring all the bull****, adding a 12V relay with the coil across the solar panel and the normally-open contacts switching the panel's output to the fan motor might do the trick. It'll positively power the fan when there is enough voltage and drop out when there isn't.
                              Location- Rugby, Warwickshire. UK

                              Comment

                              Working...
                              X