Technology

How to Buy an Inverter for Backup Power

Power Inverters are Electronic gadgets that converts energy stored in a battery (or DC voltage) to AC voltage that will power your appliances. Their major selling points are their low noise and emission free operations as well as their convenience. This article will guide you on how to buy an inverter for backup power in the home or in the office.


The first challenge for a power inverter is that you need to charge the batteries.

You need electricity to charge the battery of your power inverter. This is a bit problematic if you live in a developing country like Nigeria where public power supply from the grid is not steady.

For example, I use my power generator during the day (if power supply becomes epileptic) and use my power inverter at night because they operate at low noise and are night-friendly. The generator also charges the inverter battery while it is on.

If you live in an area with less than 12 hours of public power supply, it will not make a lot of sense to buy an inverter, except you also have a power generator or you are willing to invest in a solar power system with solar panels.

It is also important to note that a power inverter is more suited for resistive loads like your household and office electronics like TVs, Computers, Printers, lights, etc.

Power Inverters are not best with inductive loads, so if you are going to be operating lots of machines with motors in them, a generator may be better, except you can find an industrial grade inverter.

Inductive loads like Refrigerators, Freezers, and Air conditioners can be powered by an inverter, just make sure you buy an inverter with high enough capacity and capable of handling their high start currents.

 

Your Power Needs

Once you are sure you need to buy an inverter, the next stage is to calculate your power needs. Simply note the gadgets that you will be operating with the power inverter.

For example, typical load may be 1 TV set, 1 decoder, 1 DVD player, 1 Fan, 1 Laptop, 3 light points.

Then note the power ratings of each of the gadgets. You can find the power rating on the back or side of the gadget. You can also check the manual of the gadget. For example for the load above, the rating could be:

  • 1 TV set (100w)
  • 1 Decoder (20w)
  • 1 DVD Player (20w)
  • 1 Electric Fan (70w)
  • 1 Laptop (20w)
  • 3 energy efficient light points (90w)
  • Total Load = 320w

The next step is to get a VA equivalent of the power, which if we assume a power factor of 0.8 gives 400 VA (i.e. 320/0.8)

After calculating your total load, the next step is to derate the power inverter to create some allowance for flexibility and to ensure it does not over work itself.

To derate, just multiply your total load by 2. In the example above 2 x 400 = 800VA. So, you will buy an inverter with a power rating of 800VA or higher like an 800VA Inverter.

You may also decide to multiply by 3 to give more operation allowance for the Power inverter. Note that the aim of derating is to ensure that your inverter does not operate at full-load or near full-load, which will ensure the longevity of the device.

Type of Battery

SMF Deep Cycle Battery Image

 

The best battery for your inverter is the SMF deep cycle inverter battery. SMF stands for Sealed, Maintenance Free. Though you can use the normal car battery, but they emit poisonous fumes which could have long term impact on your health. This means an SMF battery can be installed indoors making them very convenient.

Another type of battery to use if you do not mind some maintenance is the tubular battery, which are also deep cycle batteries, but require some maintenance.

They require less maintenance compared to car batteries. Tubular batteries are not advisable for installation indoors as they are not completely sealed and could be emitting gases.

deep cycle batteries last longer than regular car batteries because they are optimised for the loading characteristics of power inverters.

They may cost more, but we recommend you buy an SMF deep cycle battery for your power inverter. If you are looking for cost effectiveness and do not mind some maintenance, go with the tubular deep cycle battery.

Number of Batteries Required

An inverter is usually rated in this pattern X VA/Y V, where X is the rated power output and Y is the input voltage required.

For example an 800 VA/12 V inverter will give a maximum output power of up to 800 VA and require an input voltage of 12V. Similarly, a 1.5 KVA/24V inverter will output 1.5 KVA (1500 VA) and require 24V input.

Since batteries usually come in 12 volts voltage, the 800 VA/12 V will require a minimum of one 12V batteries, while the 1.5KVA/24V inverter will require a minimum of two 12V batteries connected in series.

In the same vein, a 3.5KVA/48V inverter will need a minimum of four 12V batteries. When you buy an inverter, make sure you know the minimum number of battery required.

What Battery Capacity

Batteries come in different capacities. The higher the capacity, the longer a battery can last before getting discharged, given similar loading.

A 200 Ah (Ampere-Hour) battery is recommended though a 100 Ah or 150 Ah battery can be managed.

For example, for our example load above (400VA), a fully charged 200 Ah battery can theoretically deliver 6 hours of power while a fully charged 100 Ah battery can only manage 3 hours.

Note that these are theoretical values, actual values may be less (as we ignored inverter efficiency and our power factor is assumed).

To increase the capacity and use time, you connect more batteries in parallel or reduce the load on the inverter.

For example, connecting two 200 Ah batteries in parallel will result in a theoretical energy capacity of 400 Ah and increase the theoretical use time to 12 hours. Note that to connect batteries in parallel you must account for the input voltage.

So, a 12V input inverter will require one 12V battery in each parallel set, a 24V input inverter will require two 12V batteries in each parallel set, a 48v input inverter will require four 12V batteries in each parallel set and so on.

Hence, a 48v input inverter will require eight 12v batteries for 2 parallel sets and twelve 12V batteries for 3 parallel sets.

sukam solar inverter - How to Buy an Inverter for Backup Power

Some inverters come with solar energy support. These inverters enable you connect solar panel(s) to your inverter and tap from the free energy of the Sun. This type of inverter is called a Solar Inverter.

The Solar Panel charges your battery ensuring you have enough energy when needed. Depending on the capacity of the Solar panel, it can charge the battery, while still providing power for your appliances. Solar inverters can also charge your batteries via generators or public power supply.

Note that if you do not buy a solar inverter, you can still upgrade a regular inverter for solar energy by buying a solar charge controller.

If you buy a Solar Inverter, you will not need to buy a solar charge controller separately, since they come with solar charge controller built-in.

You will have to buy the solar panels separately. If tapping energy from the sun is important to you, buy a solar inverter outright. However, you can always buy a regular power inverter and upgrade for solar energy anytime you want.

Inverter Installation

Except, you have above average electrical skills, you will need a technician to install your inverter. Thankfully, some retailers and online stores that sell inverters offer options with the installation kit, making installation easier for you or a trained technician.

The installation accessories come from the manufacturer of the inverter which ensures everything works well. When buying an inverter it is always advisable to take-up the installation kit.

The cost of the installation kit may be incorporated in the cost of the inverter or you will have to pay separately for it. Make sure you are present to inspect the installation.

Make sure that the cabling connecting the inverter to the battery is as short as possible. This will reduce energy losses.

It is also important to know that a lot of current moves (it could be double or triple digits) from the battery to the inverter, so make sure everything is properly sealed with no naked wires to prevent electrocution.

Installation cost for inverters ranges from 5,000 Naira to 25,000 Naira depending on the complexity of the system.

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