UPS Inveter: How to Construct Yours

1200va 12V UPS
An old UPS can be used to construct a simple power inverter to power gadgets like laptops and small fans when public power is unavailable.
A power outage can be the most frustrating thing to any business owner. The complaints are legendary. But that dusty old UPS sitting in storage could be the thing that solves your problem.
For those who don’t know, a UPS is an electronic device used for converting DC current to AC current. Connecting it to your electronic gadgets automatically prevents them from going off during a power cut.
How long it powers your gadgets depends on the size of the battery inside the UPS. Typically, most UPS don’t last for more than 30 minutes.
And when the battery becomes weak or dead (after a couple of years of usage), we normally abandon them (UPS) and get new ones.

UPS as Inverter

Most people know power inverters as electronic gadgets that cost an arm and a leg to purchase and install. The fact is, your old UPS abandoned in storage is also an inverter.
There is only one major difference between your old UPS and the Power inverters:
Power inverters, depending on their rating, can power bigger loads than your ordinary UPS. UPS, because of their design are good enough for just small basic electronics like TVs, fans and laptops.
Even at that, you can power only a limited number of electronics simultaneously with the UPS.
So, this guide is for those who need to be on their laptops or computers for a long time and at any time. You won’t have to depend on public power supply completely again.

The logic behind using UPS as an Inverter

It is worth repeating that a UPS is already an inverter. The only difference is, it has a smaller capacity.
What happens is this: you simply extend the time the UPS can power your gadgets. For example, if your UPS time limit was about 15 minutes, you would now extend it to hours.
The length of time depends on the load attached to the UPS at any time. That would be looked at in details later.
So, to keep your UPS on longer, you need to exchange the battery with a bigger one. It is that simple.

Batteries for your inverter

The batteries are generally maintenance-free batteries. They are completely sealed. There are different brands and kinds.

12v 40Ah VRLA battery
The most common types are known as valve-regulated lead-acid (VRLA) batteries. There are many of them in the market and they come in different capacities.
Your old UPS also comes with a VRLA battery of about 7Ah. What you are looking for is to change that 7Ah 12V battery to at least a 40Ah, 12V battery.
Now, you can go as high as 200Ah or more. It all depends on how much money you have. For students, if your laptop is your main concerned, 40Ah, would do just fine.

Making your own inverter using your log UPS


If you don’t have an old UPS, you can buy one from the market. They are rather cheap.
Other materials you need are:
Flexible wires – these must be at least 3.5mm thick. This is important not to cause overheating in the wires. The wires must come in two colors, preferably black and red to denote negative and positive respectively
Battery charger – you need this to charge the battery. This is connected to the public power supply. When there is power, it charges the battery. It is also important to get a smart charger.

12V 20 amps smart battery charger
The main advantage of smart chargers is they stop charging once the battery is full. These are also available in the market.
Crocodile clips (optional) – this is to clip the wires to the terminals of your VRLA battery
Screwdriver, insulation tape, razor.


1 Unscrew the outer cover of the UPS. The screws are easy to remove
2 Remove the cover to expose the UPS circuit. Inside you would see the small battery.
3 Detach the wires from the battery. The wires are two. You can remove the battery if you want to.
Note that the red wire is attached to the positive terminal of the battery and the black to the negative terminal
4 Using the 3.5mm flexible wire you bought, extend the length of the wires you detached from the UPS battery by removing the insulation from the tips of the wires and joining them together.
Make sure similar colored wires are joined together.
5 Then attach the other end of the now extended wires to the two terminals of your new big battery. The red wires to the positive terminal and the black wire to the negative terminal.
6 The battery charger also has two wires coming out of it with crocodile clips at the end. The clips are also appropriately colored negative (black) and positive (red). Clip them to their respective terminals on the battery.

Simple schematic diagram of your inverter
7 Use the insulation tape to wrap the point you joined the 3.5mm flexible wire to the UPS wires. This is to prevent short circuiting.
Plug the UPS and the battery charger to an extension socket. The extension socket should already be plugged to the public power supply.
Though the UPS can work without being plugged into the public power supply, plugging it would ensure automatic switch-over to public power when the power comes back.
As for the charger, it needs the public power to charge your battery.
8 Congrats! You’ve created your own inverter. Just connect your gadgets to the output terminals of the UPS.

How long your new inverter would power your laptop

Most laptops come with a power pack (power adaptor used for charging laptops) with different power ratings ranging from about 60W to 90W.
The power rating is written on the body of the adaptor. Let’s assume your adaptor has a power rating of 65W, and your new inverter has a battery capacity of 40Ah. Since the whole setup is a 12V affair, your inverter can power your laptop on battery power alone for
12 V × 40Ah ÷ 65W = 7.4 hours.
Or if your fan is rated at 50W (the power rating is usually written on a sticker at back of the fan or carved into the body of the fan) your inverter setup with just 40Ah battery would power the fan for
12V * 40Ah ÷ 50W = 9.6 hours;
implying you can use your fan all night during the heat period on battery power only.

Miscellaneous issues

1. If you are not comfortable doing it yourself, the neighborhood electrician or technician can do it for a small fee. Just buy the materials and tell them what you need.
2. If you want longer time on battery, just buy a bigger capacity battery.
3. If you want to add more batteries to increase the capacity, make sure to connect the batteries in parallel.

Parallel connection
That is, connect the positive terminals to each other with flexible wires. Do the same for the negative terminals.
4. Your UPS is not strong enough to power electric heaters, fridge and other equipment with high power rating.
5. Be careful not to buy defective batteries. You should consult a knowledgeable and trusted person before getting the battery, whether new or second hand.
All things being equal, as long as you get at least 3 hours of public power supply every day, you won’t have any problem using your laptop at any time of the day.
With time and with enough money, you can upgrade to bigger batteries and get more life out of your simple inverter.
You can even connect energy efficient bulbs if you wish. The simple trick is to make sure the total load is not too much for the UPS.

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