DIY: Mini UPS for DSL Modem and WiFi Routers

Load shedding and power outages: For those who can’t live without their computers and internet for any or no reason, this situation can be a nightmare.

This is a rough, simple and not a sophisticated solution, but works in keeping your devices powered on! It can power not only DSL/WiFi routers, but also any other appliance that can work at 9V or 12V. Keep the internet alive, and use it on your laptop or cell phone, 24×7!

I use it to power my DSL router and a TP-Link WiFi router. PTCL DSL router’s ratings are 12VDC 500mA, TP-Link’s 9VDC 700mA.

That’s why I’ve taken two outputs.

Circuit Diagram – DIY UPS for DSL Modem/WiFi Router:

Parts:

• One 12V 7AH lead acid battery.
• One 16 or 18V laptop charger, max 2-2.5A current to charge the battery.
• Five 1N5404 diodes.
• One LM338T linear voltage regulator with a heatsink.
• One 0.1uF ceramic capacitor.
• One 1uF electrolytic capacitor (note the polarity of capacitor).
• Two resistors. R1 = 2.6kOhm, R2= 250 Ohms.

Things that you need to note:

• Make sure you check the specs of your appliances, in this case, router/modem first.
• If you are only using a single router, just remove the respective part from circuit diagram. E.g., if you are using a 12V router, you don’t need those 4 diodes and 9V output jack.

• You need to attach a DC pin to the outputs of the circuit. The same pin that is connected to your adapters, which go into your modem. Now, you don’t need that adapter. Just buy the same pin from market.

• You can give input from a laptop charger of 16V to 18V. Keep in mind the current rating of the charger, as higher current ratings can damage the battery quite quickly. Even 2A current is too much for a battery of 7AH. It should be around 700mA, but that will also cause slow charging.
• You must also attach a heatsink with LM338T IC. It gets extremely hot during operation!

I used a veroboard to build the circuit. You can use either that (will have to solder things), or use a breadboard.