DIY Mini UPS for WiFi Router V4.0

The pandemic COVID-19 outbreak forced companies to continue with work-from-home policy to maintain social distancing and for business continuity. More and more of us are working from home these days, and that means your home's WiFi networks are more important than ever.

Anyone with a fixed-line connection will know that their WiFi drops whenever the power goes out. It is annoying if you are in an important meeting/webinar through Zoom, WebEx, or MS-Team, and there is an interruption due to power cuts.

Solutions :

1. Using a conventional UPS ( Bulky and Costly )

2. Mini-UPS ( Light and Cheap ) I have already posted Instructables on DIY Mini UPS, but I have received so much feedback for making a UPS that can be run by using the power bank.

In this Instructable, I will guide you on how to make a mini UPS for your Router that can run by using the power bank.

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Features:

1. Light Weight ( 80 grams )

2. Output: 9V / 12V - 1.5A

3. Back up time depends on power bank capacity

5. Output Voltage Display for setting 9V or 12V

6. 3D Printed Enclosure

Components Required :

1. Boost Converter Module - LM2587S ( Amazon )

2. 0.28" Voltmeter Display ( Amazon )

3. DC Jack - Male ( Amazon )

4. DC Jack - Female ( Amazon )

5. Rocker Switch ( Amazon )

6. 12V Relay ( Amazon )

7. Diode- 1N5822 ( Amazon )

8. Resistor- 330 Ohm ( Amazon )

9. Resistor - 580Ohm ( Amazon )

10. Red LED ( Amazon )

11. Green LED ( Amazon )

12. Heatshrink Tube ( Amazon )

13. 22 AWG Wire ( Amazon )

Tools Used :

1.Soldering Iron ( Amazon )

2. Hot Glue Gun ( Amazon )

3. Wire Cutter ( Amazon )

4. Wire Stripper ( Amazon )

5. 3D Printer ( Amazon )

6. Hot Air Gun ( Amazon )

The working of the circuit is very simple, in normal condition, power from the mains is drawn by a 12V DC adapter to provide power to the router and energize the relay coil ( COM contact connects to NO contact ). When the mains power fails, the relay coil will be de-energized, the COM contact will be connected to the NC contact and the stored energy in the power bank will be fed to the boost converter input.

The two diodes 1N5822 are used to block the reverse current flow. Two LEDs are used for indicating the healthiness of the two power sources. The voltmeter display is used to display the output voltage so that you can easily set the output voltage as per your requirement ( 12V or 9V ).

The positive terminal of the input DC jack is connected to the positive terminal of the output DC jack through a Schottky diode ( 1N5822 ). The relay terminals C1 and C2 are connected to the positive and negative terminals of the input DC jack. A 5mm green LED with current limiting resistor is connected to 12V and Ground

The power from the power bank is fed to the UPS through a micro USB port. The positive terminal ( Vbus) is connected to the relay COM contact. The NC contact of the relay is connected to the boost converter LM2587 IN+ terminal. The negative terminal ( GND) is connected to the boost converter IN- terminal.

The boost converter LM2587 Out+ terminal is connected to the positive terminal of the output DC Jack through a Schottky diode ( 1N5822 ) and the Out- terminal is connected directly to the negative terminal of the DC jack.

The voltmeter positive terminal is connected to the positive terminal of the output dc jack through a rocker switch and the negative terminal is connected to the negative terminal of the output dc jack.

Disclaimer: Please note that you are working on a Li-Ion battery which is potentially very hazardous. I cannot be held responsible for any loss of property, damage, or loss of life if it comes to that. This tutorial is written for those who have ample knowledge of rechargeable lithium-ion technology. Please do not attempt this if you are a novice. Stay Safe

The two 5mm LEDs are used to indicate the healthiness of the two power sources (12V adapter and Power Bank ). In the normal condition both the LED are turned ON, when there is a power failure the green LED will be switched off and only the red will remains in ON condition.

The series resistors are used to limit the LED current. You can calculate the resistor value by using this online calculator. Here I have used 330 ohms for RED led and 580 ohms for the green LED.

First, trim the extra legs of the LED and then solder the resistor with the positive terminal ( longer leg )of the LED. Then solder a red wire to the resistor and black wire to the negative terminal of the LED. To insulate the bare conductive part, use a heat-shrink tube.

Note: Though these LEDs are useful for indicating the status, at the same time we are wasting energy. So in my view, at least the RED led may be removed because it will draw power from the power bank continuously. As a result, we will lose the back time. Give your feedback, I will modify the design accordingly.

Hare I have used a 5 pin micro USB module for feeding power from the power bank. It is very cheap and handy for use in the 3D printed enclosure. If you don't want to buy this module, you can use a USB charger cable too.

Solder the positive terminal of the red LED and a piece of red wire to the VBUS terminal of the micro USB module and the negative terminal of the LED and a piece of black wire to the GND terminal. Here I have used 26 AWG wire for connections.

The objective of using the 0.28" Voltmeter display is to display the out voltage so that you can set the output voltage of the boost converter module as per your router voltage ( 9V or 12V ). The rocker switch is connected in series so that you can switch off the display when it is not required. In this way, you will not waste energy unnecessarily.

First cut the trim of the red wire of the display unit as shown in the above picture. Then solder the small piece of trimmed wire to the one terminal of the rocker switch ( 15 x 10mm ) and the other terminal to the positive terminal of the voltmeter display. Insulate the soldering joints, by using heat shrink tube.

In this project, we will use two Schottky diodes ( 1N5822 ) to prevent reverse current flow. You can also use general-purpose diodes but the main reason for using the Schottky diode is that they have a lower forward voltage drop than the general-purpose diode.

The negative terminal of the diode is indicated by a silver ring on it. Trim the two legs of the diode by using a nipper and then solder two pieces of wire to them. Then apply heat-shrink tubing to the terminal joints as shown in the above picture. The datasheet of the 1N5822 diode is attached below for your reference.

Here I have used two 5.5mm DC jacks, one for connecting the 12V adapter and another one for 12V Output.

It is sometimes very difficult to solder extension wires to the DC jack terminals, so preconditioning is required. Apply a small amount of flux to the terminals and add a small amount of solder by using a soldering iron. Now it is very easy to solder the extension wires.

Now you have to prepare the adapter to connect the UPS output to the router input. First, check the specification of your router to confirm the size of the jack ( Sleeve size ) and the tip polarity. Your router will have a small diagram indicating the polarity expected by it; care should be taken to adhere to this, as an improper power supply may damage the device.

In my case, the size of the jack is 5.5mm and the tip polarity is positive. According to the size, order two male DC Jack. Then solder red wire to the tip (smaller one ) and black wire to the sleeve.

To give a nice commercial product look, I designed an enclosure for this project. I used Autodesk Fusion 360 to design the enclosure. The dimensions of all the components are measured by a vernier caliper then the same were considered during the design.

The enclosure has two parts:

1. Main Body

2. Cover Lid

The Main Body is basically designed to fit all the components including the battery. The Cover lid is to cover up the main body opening.

Download the STL files from Thingiverse

I have used my Creality CR-10 Mini 3D printer and 1.75 mm Grey and Yellow PLA filaments to print the parts. It took me about 4 hours to print the main body and around 1 hour to print the top lid.

My settings are:

Print Speed: 60 mm/s

Layer height: 0.2mm ( 0.3 also works well)

Fill Density: 25%

Extruder Temperature: 210 deg C

Bed Temp: 55 deg C

Install the DC Jacks, Rocker Switch, Relay, and Voltmeter display unit to the slot provided in the 3D printed enclosure. Apply hot glue to mount the charging status LEDs and Voltmeter. Similarly mount the TP5100 charging board, battery pack, and the LM2587s boost converter by using hot glue.

Note: Mount the charging board, battery pack, and the boost converter only after completion of all the connections as per the schematic.

Follow the schematic diagram to make the circuit.

I will recommend taking a printout of the attached schematic diagram and make the circuit as per it. Before connecting the input DC adapter, double-check all the connections.
Note: Red and black wire in the schematic represent positive and negative respectively.

After connecting the wires to the Input and output screw terminal of the Boost Converter, you have to set the output voltage.

Place your multimeter probe at the output terminal and adjust the trim pot until you get 12V.

The last step is to test the UPS, connect the power bank to the micro USB port through a good quality USB cable, you will notice the red LED will ON. Then plug in the12V adapter jack to the input DC jack. Now you will notice the green LED will glow. Now you can check the output voltage by switching on the rocker switch.

Plug in the DC jack cable prepared in the earlier step into the female jack at the output. The other end of the cable will connect to the Router power input port. The router status LED starts to glow and after a few minutes, your router is ready for providing internet service. At this stage, you can unplug the input DC adapter, you will notice the router is still working flawlessly. You can check the backup time in this condition.

Power Backup:

Back up time of the UPS depends on the battery capacity of the power bank. In general, a 10000 mAh power bank will give you 2-3 hours of power backup very easily.

Drawback:

You may face some delay in switching the relay from dc adapter to power bank, some time the router will reboot once because of slow switching of the relay.

This problem may be eliminated by using fast switching circuit ( MOSFETs ). Please suggest me a proven circuit using MOSFET, I will be happy to adapt it in my design.