Using timers to disconnect certain loads at night?

Hey. Everyone,

I had a though today (Oh No!) that sounds like a good idea to me. Then it occurred to me that if it was such a good idea then how come I have never seen anyone else do it??

My though was to try and find a VERY low draw timer that would disconnect certain loads at night. The timers power consumption would have to be tiny or I could see eating up my power savings running the timer.

What got me started on this was seeing some folks who run their refrigerator from their solar/battery/inverter. They manually unplug the refrigerator in the evening and plug it back in when the panels start making power in the morning.

I like the idea but would like to automate it.

What do you all think? Anyone done this? Good idea? Bad idea?

I look forward to your replies.



  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited March 2018 #2
    Have used these programmable timers in the past, powered by an AA cell/battery they are motor rated, FWIW

    Edit It looks like this particular timer is line powered with a lithium backup battery to keep clock running during outages, the ones I used were entirely powered by an AA
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
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  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    I use a common line powered timer, 3 watts burned, to cycle my deep freeze off winter nights
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  • PhotowhitPhotowhit Solar Expert Posts: 5,998 ✭✭✭✭✭
    I regularly used a wall plug in grounded timer to turn on and off my air conditioner during the afternoon. I worked noon until 9 and often left before my battery reached float stage and I used it to turn on and off my window air conditioner. First so it would cool down the place in the afternoon once I reach roughly float and then to come on a half hour before I expected to be home, so I could come home to a cool home. Worked very well.

    Depending on your needs, they also make spring loaded timers to shut things off. I think up to 2 hours.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
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  • fratermusfratermus Registered Users Posts: 48 ✭✭
    I do it by running those items on a low voltage disconnect set rather high, like 12.7v.  That way discretionary items are automagically turned off when charging stops.

    LVD --> relay --> opportunity circuit *

    It was surprising to see how little power I use at night in my campervan with discretionary loads turned off that way.  

    If you aren't using the LOAD output of your solar charge controller you can use the LVD on it to do this without buying any other gear.
    This timerless approach has an additional benefit of not needing adjustment as the seasons or daylight savings change;  it takes its cue from the sun.

    * ok, it's actually LVD --> delay --> relay --> opportunity circuit.  In my setup Vlvr == Vfloat;  adding a delay allows the charging system to
    climb past Vfloat to Vabs in the morning before engaging the opportunity loads.

  • DanS26DanS26 Solar Expert Posts: 261 ✭✭✭
    Intermatic makes 2, 4, 6, and 12 hour spring loaded load while operating.  Check out the amp ratings for your application.

    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with
  • NANOcontrolNANOcontrol Registered Users Posts: 254 ✭✭✭
    I have a load I WANT TO TURN OFF at first daylight. I use a relay connected directly to the solar panel.  Relays will typically close at nearly half their rated voltage and open at almost 20%.  To the relay I add a zener of about 1/3 the relays coil voltage in series.  I actually use a TL431 adjustable zener to set the exact voltage, but a zener will work well enough.  This is simple, cheap and would  also work for day loads.  Opportunity loads are best left to voltage sensing.  I use a micro and some loads don't turn on till 13.9V on the battery. The selection of pre-made boards is slim with a dropout in the 12.7 range and time delay which I consider a must. I haven't found any.
  • PNW_StevePNW_Steve Registered Users Posts: 79 ✭✭
    Thanks Everyone for the input.

    I got a little distracted from the project but will be diving back in shortly and putting to good use the above info.

    Thanks again.

  • mike_smike_s Registered Users Posts: 155 ✭✭
    Note that if you want DC load control, many solar controllers (most Chinese ones, even some better ones like the Midnight Kid) do low-side control - the switching occurs in the negative rail. That presents a problem in any negative ground system like an RV because the battery and loads are all connected together with ground, so the controller's can't control loads. It makes the load control useless. Morningstar Prostars have high-side control and should be able to be set as desired - "after sunrise, on" and "after sunset, off". I'm sure there are others.
  • MrM1MrM1 Registered Users Posts: 487 ✭✭✭✭
    I use a wall plug timer for my fans on the CC and battery bank.  The whole setup draws less than .2 AC amps. 

    Dont know if this would work for you and dont know what charge controller you use,  but if your CC has a low voltage opportunity output for diversion,  then you can program the CC to handle loads when the sun is out and the batteries are mostly charged to divert the remaining solar power to loads.  I set one up on AC post inverter with an SSR

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