Solar UPS controller functional diagram

Below is a functional diagram of all components which usually fit in a small box – except of cause the solar panel.

The ups controller is a small box that connects all components

UNplug is a small device that connects all components: inverter, battery, charge controller and solar panels

The “heart” is UNplug which is monitoring all connected devices:

  1. Battery
  2. Solar charger
  3. Inverter
  4. Solar panel
  5. Utility power (wall plug)

The assembly is very easy and should not take more than 15 minutes. Once all components are connected you will start making your own energy!

There are only three states the system is operating in:

During the day solar power is fed to your appliances and battery, and at night grid power takes over



During a blackout, the controller automatically switches to battery to keep your appliances powered


  • During day the solar panel delivers power to the inverter and the excess energy charges the battery. The 120V outlet is powered by the inverter. When the energy consumption is higher than the energy from the solar panel then the battery is discharged. The discharge level can be adjusted between 10-80%. It is best to set discharge to 10% to maximize battery life.
  • During the night the inverter is turned off and the utility power from the wall outlet is just passed through. If there is a black out at night then the controller immediately starts the inverter to power the 120V outlet (there will be a short warmup delay before the inverter is operational).
  • You’re Protected! If there’s an outage, and you can’t switch back to the grid, this is when the batteries take over. Unplug provides automatic uninterruptible power (UPS) with built-in surge protection.

Recommended also:Latest project milestoneProject videoTechnical Specs

15 comments for “Solar UPS controller functional diagram

  1. Pingback: ray bann
    • Markus Loeffler
      September 17, 2013 at 8:55 am

      Hi ray-bann – I am not sure I understand your comment. Maybe someone can help translating it?

  2. Markus Loeffler
    September 18, 2013 at 7:24 am

    I have not installed RSS but I will do that today. Thanks for the comment!

  3. a
    June 20, 2014 at 3:24 pm

    Way cool! Some very valid points! I appreciate you penning this post plus the rest
    of the site is very good.

  4. dleec45
    February 22, 2015 at 10:19 pm

    Love this project…..only think I would chance is add wind as a source because where I live there is a lot most of the year and I’ve thought for years how awesome it would be if I could capture just a small part of what slips by my house…..thanks

  5. beee
    May 26, 2015 at 4:36 pm

    Lead acid batteries can be problematic, even dangerous. Why not use Lithium batteries? Just so I understand correctly, is this UNplug system grid-connected? A so-called “expert” friend of mine had a look and said it was not grid-connected, so myself not being an expert, I must ask. Thanks.

    • Markus Loeffler
      May 26, 2015 at 4:47 pm

      You can use Lithuim batteries – they are just not that common. You also need to pick a charger that wants to work with that type of battery. UNplug is NOT grid connected in the sense that you feed energy back into the gird. At night energy is taken from the grid to save battery life and when there is sunshine UNplug disconnects from the grid again.

  6. Luis Delgadillo
    August 3, 2016 at 10:27 pm

    Where I can buy this controller?

    • Markus Loeffler
      August 4, 2016 at 10:00 am

      There are currently some pre-production units available, please contact me directly:

  7. Raffy
    October 9, 2016 at 4:58 pm

    How is the swtching done? by magnetic contactors, scrs, etc. what is the time lag between switching? is the transfer noticeable? do we need to put a power-on-delay module for high inductive loads such as refrigerators, ac systems, etc.


    • Markus Loeffler
      October 9, 2016 at 9:17 pm

      The switching is done by relay, the delay is about 15ms. The systems is designed to work with inductive loads especially a refrigerator. All kind of loads like computer, TV, radio, charger have been tested and none of those show any effects of the switching. Only incandescent light bulbs show a switching flicker.

  8. Stephen G Dingman
    August 7, 2018 at 8:44 am

    I have built a similar system and have been using it for about a year now. I have used my setup to run a refrigerator and a deep freeze together. I switch a DPDT relay that has 30 Amp contacts. It works great. I only run these two devices because they are inductive loads, and are merciful to switching. I haven’t built the system into an all inclusive enclosure because I have 4 -12 volt deep cycle glass Mat batteries wired in parallel, so it would be too heavy, so the batteries set on a shelf. I use an Arduino UNO and use it to monitor battery % of charge. When the batteries get to my set, turn on point, a pin goes high to turn on my 3000 Watt pure sine wave inverter. I have a 5 volt wall wort plugged into the inverter output. The 5 volt from the wall wort is sent back to the UNO, triggering another output pin to go high that triggers the DPDT relay to switch to inverter power. When the batteries deplete down to 90 %, the relay is de-energized, switching back to grid power. I’m happy with it, but I’d like to wi-fi my power particulars to a page where I can evaluate. I don’t quite have it completely the way I want it yet. I still have work to do.

    • April 26, 2019 at 12:01 pm

      care to share some more details?

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