12v/5v UPS by ‘misusing’ a Solar Panel Controller

Introduction: 12v/5v UPS by ‘misusing’ a Solar Panel Controller

About: Design, Build and hack stuff for fun!

Ever wanted a UPS for a project? Looked at the crazy prices for mains UPS and thought I only want to power something low voltage.

Well this instructable is for you then! I am going to show you have to 'misuse' a solar panel controller to create a small UPS outputting low voltage in this case 12v and 5v DC

You will need the following:


  • 12v Lead acid battery or batteries
  • Solar power controller
  • 12-24v to 12v and 5v Step down regulators (depending on your needs)
  • 24v Power supply 5-20amp (depending on what you are need)
  • Volt / Amp meter displays (optional)
  • Some stuff to power?

Step 1: Wire the Battery to the Solar Controller

Solar controllers tend to get the charging settings based on the battery, providing it is connected first. a lesson I learnt the hard way so make sure you do this first!

Connect wires from the terminals from the battery to the battery contacts on the solar panel controller. If all goes well (and the battery is not dead) the LCD display should spring to life!

Step 2: Add a Mains 24v Supply to the Solar Controller

You can use any 24v power supply with decent enough amperage to power the solar controller, remember that it needs enough to power to be able to power anything you have connected to the home-made UPS. I’d recommend using a 24v Universal Regulated Switching Power Supply commonly used for LEDs and CCTV. They are pretty cheap and they come in various amperage.

Once you have selected a power supply you need to wire it in to the solar controller’s solar panels contacts (on my controller there is solar symbol)

Step 3: Connect the Step-down Regulars:

Wire the step-down regulators

in to the output pins from the solar controller, on my controller that are a little light bulb symbol.

Step 4: (Optional) Add Amp Meters

To wire the amp meters you need to power the meters themselves from the input voltage, then the sense wire for the amp meter to goes to output of the step-down regular and the amp meter wires form the negative wire to the device.

Step 5: Test It Out!

That’s it, you should be able to turn the power off the main power the battery should take over the device. In my case I tested it with a raspberry pi and a 12v fan!

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    2 months ago

    Amazing - can I please ask how efficient these charge controllers are? One of the goals for my project is high power efficiency.


    2 years ago

    I placed 2 Amp meters, the first at the "input" (solar) side and the other at the "output" (load) side.
    I suppose you can't to the same at the battery side ? Because the current can flow 2 directions. Am I right ?


    Question 2 years ago on Step 5

    Hi, I'm very interested in this project.
    Why should you use a 24V power supply ? I suppose that a battery charger 12V should be also good. Am I right ?


    Answer 2 years ago

    Hey, from my understanding it is because the 12v battery actually charges to about 14v when full, so do you need a higher input than the battery output. I suppose you could always step up the power the make the difference. I hope this helps!


    Reply 2 years ago

    -So do you think I also can use an leadaccu charger for this ? It provides a controlled 13.8 Volts depending on the charching curve.-
    No, the voltage of the lead battery charger was not enough. Instead of that I use a 19V laptop charger now. It works now fine.