UPS for Wifi Routers V3

Introduction: UPS for Wifi Routers V3

Last year, I successfully made a router UPS v2 for my router and fibre convertor. It was able to provide two outputs at 9V and 5V with a backup time for 5 hrs.. I made this for a friend, who was facing frequent electricity cuts

He needed UPS that could support 12V 2A, in this instructables I will share how I modified my previous circuit to work as single output...

In this project i am using inexpensive, standard modules that are easily available and relatively simple to build the whole UPS

Update : After 1 month of usage, my MT3608 modules burned out. We need to replace it with better module that can handle 12V and 2A....

Alternately : Use 3S config and remove the MT3608 entirely


I have been making and using DC Lithium ion battery UPS for few years now. Based on requests from friends and family, I have been modifying these circuits to support different setup and I think after 3 years, I have all the combinations as below, depending on your power requirement you can choose which version you want to make...

  • Version 1 :Link (5W)
    • Single Output 9V and 0.5A
    • Can be modified to set output to 5V, but not 12V
  • Version 2:Link (15W)
    • Dual Output 9V/0.5A and 5V/1.5A
    • Can be modified to supply two 5V outputs
  • Version 3: This Page (24W)
    • Single output 12V/2A
    • Can be modified to step-down to 5 or 9V
  • Version 4 : Link (36W)
    • Dual Output 12V and 5V
    • Output can be modified to both 5V or 9V
    • Or Single output at 12V

Step 1: What Do We Need ?


  • SMPS 12V 3A ( Amazon )
  • Step UP converter MT3608 (Aliexpress)
  • CC CV Step Down Lithium chargers XL4015 Aliexpress
  • 2S Li-ion battery protection WH-2s80A ( Aliexpress)
  • 18650 Li-ion batteries ( I extracted them from old laptop)
  • Switch
  • Wires
  • 2 pin AC plug
  • MDF wood for box ( I made my custom box)


  • Hand Saw
  • PVA glue ( Fevicol)
  • Drill
  • Hot Glue gun
  • Soldering Iron
  • Sandpaper
  • Black Acrylic paint

Step 2: Circuit Diagram

We do not have any 2s lithium ion battery charging boards, like TP4056 that can supply constant voltage, current and provide battery protection on single module.

So have to break it into two

WH 2S80A: 2S 18650 battery protection, capable to divide voltage across two batteries, overcharge protection, short circuit protection etc. Battery once charged does not draw current and this module will prevent overcharging. This is key for this circuit to work as UPS

XL4015 : Is used as Li-ion charger and for 2S config we need it to provide 3A constant current and 8.4 constant voltage


Green light : When Battery is completely charged and / or no current drawn from SMPS

Blue light : Current is being pulled by XL4015 to supply CC of 3A or has a load connected at the output

Step 3: Testing SMPS

Tip : It is easy to configure and troubleshoot each module separately. This prevent unwanted overload or short circuits

  • Connect the SMPS to AC mains and make sure that the SMPS is supplying 12V DC
  • Using Ammeter check that the SUpply is capable to provide 3A

Step 4: Config XL4015

  • Connect the output from SMPS to XL4015 as input
  • There are two variable resistor on the module ( as in the picture) which we need to adjust current and voltage
    • Turn Anticlock : reduces voltage / current
    • Turn Clockwise : increases voltage / current
  • We need to set voltage at 8.4 first then set current to 3A
  • I need 2A as output and setting 1A for charging, the batteries
  • Based on the your lithium ion batteries, these value may vary. please check datasheet before setting these value
  • Tip : If the variable resistors do not respond, disconnect power and turn clockwise till you hear "click" sound or the end. Note that now you have max current (5A), make sure your ammeter can take more than 5A

Step 5: 2S Li-Ion Battery

  • I am using WH2S80A module as BMS for 18650 battery pack in 2s config
  • Make sure that both the batteries are fulling charged
  • Soldier connections as shown in circuit diagram

Step 6: Config MT3608

  • Connect the Battery pack to input of MT3608
  • Adjust the variable resistor to set as 12V ( Turn anticlock)
  • Sometime one needs to turn several times before the voltage starts to climb

Step 7: Charge the Battery

  • Connect the to the output of XL4015 and charge the batteries
  • The blue led on XL4015 will turn green when the battery is fully charged
  • We can test the whole circuit now and make sure that the output voltage at each module is correct
  • Do not test current !!! this will cause short circuit

Step 8: The Box

  • I have used 12mm MDF strip and 4mm MDF sheet for the case
  • The Box is 200mm x 45mm x 110mm
  • I have used PVA glue to stick the whole thing
  • Drill holes for wires and switch as shown
  • Paint the box with black acrylic paint and the varnish it

Step 9: Finishing

  • Carefully place all the components inside the box
  • Test the output again
  • And then close the lid to the box
  • Replace the existing power adapter with the new UPS

That's it : We are done!!!

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    Question 1 year ago

    Hello. How long does the battery last for 12V v3?


    1 year ago

    Hi, i have a router which needs same 12v 2a, but u said this circuit wont work for long term, can you please help with final circuit.


    Reply 1 year ago

    I have not shown battery connection, rest you can follow the circuit... Set current to 12.6v and constant current at 3amps


    Question 2 years ago

    i have made a 3s setup. but the balancer seems not working. i measured each cells individually. seems a bad bms

    the only missing is the charger. can i use a laptop charger and a step down buck converter LM2506 instead of SMPS?


    Answer 2 years ago

    Yes. You can use laptop charger, but use XL4015 to step down with constant current settings


    Reply 2 years ago

    Hi, when you say "with constant current settings", would it not be more appropriate to say a power supply with a current limit. So, I could use a 3A or an 8A supply as the batts only take what they need anyway. The load demands of course can vary.
    This may seem a play of words, but when I first read about your UPS found the wording misleading "with constant current settings". In that you were relating the constant current mentioned to the typical method of charging li-ion batts.

    Anyway, built it and will defo use thanks! PS. used BMS from Ebay...


    Reply 2 years ago

    sorry late reply but iv already ordered 5 lm2596 overseas and already on its way.

    Alex in NZ
    Alex in NZ

    2 years ago

    This looks really clear and do-able. Thanks for sharing your work :-)


    Reply 2 years ago

    You are welcome