Solar powered switch

kansaskansas Solar Expert Posts: 97 ✭✭
My 300 watt system is at a remote cabin I use intermittently. Whenever I’m there I turn on the inverter, the ceiling fan, etc. just to challenge the batteries a bit, which are always 100%. The cabin has a 4ft tall “crawl space” where the batteries and system components are located. The humidity in this space is always higher than I would like it. I now have a heat lamp in the basement which I turn on whenever I’m there. It really helps control the humidity and never effects the battery SOC on sunny days. What would ideal is for the heat lamp to be on whenever the sun is shining brightly, whether I’m there or not. The cabin is in Eastern Kansas where we have many sunny days. What I need is a switch that would control the heat lamp; on when the sun shines brightly, off when it doesn’t. If it matters, the inverter could be on all the time. Any ideas on a “solar switch” with this capability?
Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.

Comments

  • EstragonEstragon Registered Users Posts: 1,545 ✭✭✭✭
    Many charge controllers have a load terminal that can control a relay, which in turn switches a 120v circuit. If yours has this feature, it would be the simplest solution. If not, you could add a second small fairly inexpensive controller that does.

    Another, more efficient solution would be to add a hydronic heat loop that heats from the sun directly, with a small DC pump to circulate the warm water in the crawlspace. It may even be possible to find a pump that would draw low enough current to run directly off the load terminal.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators Posts: 26,837 admin
    Possibly setting up a Schneider C40 or similar solar charge controller as a "dump" controller. Just set it below the absorb set point for the normal solar panel=>charge controller. Use the output terminals to control a resistive load bank (or heat lamp).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Raj174Raj174 Solar Expert Posts: 461 ✭✭✭✭
    Take a look at this light activated switch. It needs a 12 volt power source and can switch up to 10 amps at 120 volts.

    https://www.ebay.com/itm/NEW-Photosensitive-resistance-relay-control-module-light-operated-switch-DC-12V-/222178429023?_trksid=p2385738.m2548.l4275
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • kansaskansas Solar Expert Posts: 97 ✭✭
    Thanks for the suggestions.  The light activated switch looks like it could work, if it performs as indicated and is reliable.  At $4.13 what could go wrong?? I'll order a couple and see how well they work.  Bill
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
  • PhotowhitPhotowhit Solar Expert Posts: 4,253 ✭✭✭✭
    kansas said:
    Thanks for the suggestions.  The light activated switch looks like it could work, if it performs as indicated and is reliable.  At $4.13 what could go wrong?? I'll order a couple and see how well they work.  Bill

    I don't understand the description, it says both "normally open" and "normally closed" in it...
    Perhaps you understand it or perhaps @BB. or @Raj174 could check the specs.

    What could go wrong is ordering one that is designed to turn on loads at dusk, I believe this is more common than ones that turn on loads during the day.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • Raj174Raj174 Solar Expert Posts: 461 ✭✭✭✭
    I believe it has both N/O and N/C contacts.
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • kansaskansas Solar Expert Posts: 97 ✭✭
    My comment "what could go wrong" was facetious, referring to the cheap price,  Your point is a good one, however.  
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
  • mcgivormcgivor Registered Users Posts: 1,280 ✭✭✭✭
    The device is a photosensitive relay so the output would be 12V or 0V depending on the application via the relays NO or NC contacts, power is applied at all times, the only problem is there is no safeguard to prevent over discharge, using the load terminals of the charge controller , if applicable,  could work, but they tend to cutoff too late, when the battery is essentially dead, personally I wouldn't leave a system unattended relying on automation, things could potentially go wrong.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • kansaskansas Solar Expert Posts: 97 ✭✭
    The risk of relying on automation is a real concern.  I'm also considering using a timer to turn the heat lamp circuit on/off during daylight hours, primarily in the summer when periods of uninterrupted sun can be counted on. If the photo switch is designed to activate when the light increases (which I doubt from re-reading the specs) I may fool around with that, too.  Thanks to all. Bill
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
  • bill von novakbill von novak Solar Expert Posts: 706 ✭✭✭✭
    I'd just use a very small 12V panel and a relay.  Cheap and reliable.  Perhaps two relays - one that pulls in at 13 volts and drops out at 12, so that you never discharge the batteries too far.
  • mike95490mike95490 Solar Expert Posts: 7,284 ✭✭✭✭
    kansas said:
    ...The cabin has a 4ft tall “crawl space” where the batteries and system components are located. The humidity in this space is always higher than I would like it. I now have a heat lamp in the basement which I turn on whenever I’m there. ...
    why not do the right thing, and lay plastic vapor barrier down on the ground, and eliminate the moisture at its source?
    300w of solar, running 150w heat lamp, is not the optimal solution. $20 of plastic sheet & bricks to hold it in place is the first place to start.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • kansaskansas Solar Expert Posts: 97 ✭✭
    Bill - would you explain further?  Are there relays activated by specific voltages?  The small panel would act as the "sensor" opening or closing the relays when the voltage it is producing goes up or down?  Thanks - Bill
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
  • pdhpdh Registered Users Posts: 16 ✭✭
    Regarding use of relays that turn on or off at specific voltages -- I built a circuit like that based on the information here:

    http://www.reuk.co.uk/wordpress/electric-circuit/simple-low-voltage-disconnect-with-ne555/

    Requires some basic electronics skills to build, as you can see, but nothing too complex. The project takes a voltage source as input and turns a relay off when the voltage drops below a certain point, then turns it back on when voltage rises past another specific point. Their example circuit turns off at 11.8 V and back on at 12.8 V, but you can adjust the two voltage points by using different resistors, as they describe; or you could use a pot to provide variable setpoints.

    Or you could search for "low voltage disconnect" on Amazon -- there seem to be quite a few of them out there. (The link above is from a UK company that sells such things -- kind of nice that they also tell you how to build your own.)
  • kansaskansas Solar Expert Posts: 97 ✭✭
    It's not the moisture from below that's the issue, but, as I understand it, the differential between the moisture in the warmer air outside and the cool air inside the crawlspace. A lot is written about damp crawl spaces. They all boil down to sealing and dehumidifying the space. The crawl space is 4 ft. x 16 ft. x 24 ft., has a layer of visqueen on the ground that is lapped against the walls and covered with 4" of pea gravel. The walls are insulated with foam panels on the inside and sealed on the outside. There is a foundation drain around the footing that drains to daylight. It is imperfectly sealed to the extent that I access it occasionally. The heat lamp will lower the humidity from 80% to 70% after about 6 hrs. If I have the lamp on when I'm at the cabin for several days in a row, about 6 hrs. each day, the humidity approaches 55% and the drying effect on the overhead fiberglass insulation is noticeable. (Wish I had sprayed in foam.) If I could keep the lamp on whenever the sun shines I think it would make a significant difference. The PV components located in the crawl space are enclosed in a vented cabinet.  The heat from the inverter keeps everything dry as a bone. The batteries are enclosed in a separate battery box vented to the outside.    Bill
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
  • kansaskansas Solar Expert Posts: 97 ✭✭
    Thanks pdh.  Electronic skills are not my forte but this may inspire me. On the other hand, I'm fairly good at buying things.  
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
  • bill von novakbill von novak Solar Expert Posts: 706 ✭✭✭✭
    kansas said:
    Bill - would you explain further?  Are there relays activated by specific voltages?  The small panel would act as the "sensor" opening or closing the relays when the voltage it is producing goes up or down?  Thanks - Bill
    Sure.  Relays typically have a "pull-in" voltage and a "dropout" voltage, sometimes called a turn-on and turn-off voltage.  For example, the 12V relay PCN-112D3MHZ,000 by TE connectivity will pull in at ~8.4 volts and drop out at ~1.2 volts.  That difference is often called hysteresis, and it means that a relay won't "chatter" on and off when the light is barely enough to turn it on.  It will turn on when there's a lot of sun and turn off when there's almost no sun.  That relay needs about 10ma, which means that even a 1 watt panel will be plenty to turn it on and off.
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