Things to Keep in mind before buying an inverter

Buying Guide 334 comments

Boiling summer is just few weeks ahead, scheduled and unscheduled power cuts are expected as usual. Inverters are one of the most demanded products of summer season. Are you planning to buy or upgrade your inverter in this season? Then instead of being trapped in the marketing gimmicks, understand some basic facts and do a little bit home work. Here some facts you must know before buying an inverter

inverter thumb Things to Keep in mind before buying an inverterCalculate your power requirements

Before going to purchase an inverter- You have to make a rough estimation of your power requirements. remember- Inverter is not a Generator. Inverter has it’s own limitations. You can’t power and run your complete home with a normal inverter. If your power requirement is  more than 3000 VA, then an inverter alone can’t cater your demands effectively. No doubt a high power inverter can run your refrigerator and air conditioners, but how long?  Here your battery will not last more than few hours. Hence it it better to go for a home generator. However if you don’t want a single minute power downtime, then a power inverter – electric generator combination is a good option.

 Wattage rating of typical home appliances

Appliances  Power
Fan (Ceiling) 50-75 Watts
Fan (Table) 25-50 Watts
CFL 18 Watts 18 Watts
Computer (Desktop) 80- 150 Watts
Laptop 20- 75 Watts
LCD TV (32”) 150 Watts
Refrigerator 160 – 250 Watts
Tube Light (4 Feet) 40 Watts

Starting power and running power

Starting and running power requirement of all electric appliances are different. An 18 Watts CFL takes around 25 Watts power to start and after few seconds it stabilizes to 18 Watts. Some appliances like Refrigerator, Washing Machine etc take almost double power to start as compared to the normal running power. Hence before selecting an inverter you must calculate the starting power requirement also.

Difference between VA and Watts

Often people confuse with the difference between Watts and VA ratings of inverter or other home appliances. Manufacturers use both these terms according to their requirements to confuse and mislead the consumers. Power drawn by the equipment (Power using equipment like Bulb, Fridge, Washing Machines, ACs, Stabilizers etc.) and Power generated by the equipment (Generators, Inverters, UPS etc) can be expressed in Watts or VA (Volt Ampere). In general Power generating or stabilizing equipment manufacturers use the term VA to specify their ratings and power consuming products use Watts to specify their ratings. Here comes the difference. Power in Watts is the real power drawn or supplied by an equipment, this is the real value. VA is the apparent power (more theoretical)  which is obtained by multiplying the Voltage and Current drawn/supplied by an equipment. We can equate the VA and Watts ratings:

Power in Watts = Power in VA- Losses

or

Power in Watts = Power in VA x Efficiency of the equipment

The ratio of Power in Watts to Power in VA is termed as Power factor. Unfortunately manufacturers often don’t specify the power factor or efficiency in their products.

Let’s see an example. You are purchasing an inverter with 650 VA power ratings. This 650 VA indicates, it can supply 650 VA power under ideal situations( means efficiency of the inverter is 100%). If we take 80% as a typical efficiency figure, the said inverter can supply 80% of 650 = 520 Watts only. Now you can understand why inverter manufacturers only publish the VA rating on their products. If an inverter or UPS is coming without mentioning power factor, you must take a safe value of 0.6 (60%) as power factor while connecting appliances.

Inverter or Home UPS?

Nowadays we can see a new segment in inverter market- Home UPS. Functionally both inverter and UPS do the same job- Converting Direct Current from batter to Alternating Current which is  used as a backup power generating device in case of mains power failure. UPS as the name suggest provide Uninterrupted Power Supply to equipment. The equipment will not feel the switching delay from mains to UPS supply. Switching over time of a typical UPS is 3 to 5 Milli Seconds only. A standard inverter takes around 500 Milli seconds which is unacceptable for the electronics devices like computers, Modems, Routers, printers etc.

Home UPS is a combination of Inverter and UPS. Here the switching delay of inverter has been brought down to UPS standard. Hence you need not to go for a separate UPS for PCs and associated devices. One thing you must remember- UPSs are further classified in to three- Offline, Online and Line interactive. Home UPS are normally Offline only, hence they cannot replace your online UPS requirements to drive sophisticated devices.

Digital Inverter

What is digital in inverters? First generation inverters were using power transistors as switching devices and transistorized circuitry for  monitoring/controlling applications. That is an old story. Nowadays inverter technology has changed a lot. A complete transition from old square wave technology to Pure Sine wave technology with the help of advanced Digital Signal Processing (DSP) techniques. Micro controllers are extensively utilized for précised monitoring and controlling applications. Switching transistors are replaced with high efficient MOSFETs.

Battery

Batter- the vital part of inverter. Performance and life of an inverter is greatly depends upon battery. We can see several classifications of inverter batteries. Normally high power Lead Acid batteries are used to power inverters. Lead acid batteries are classified in to different types as per application, design, technology etc.

Battery Capacity

Capacity of a battery is expressed in terms of Ampere Hour (Ah). It indicates the rate of current a battery can supply for a given duration. If the capacity of a battery is 100 Ah, that battery can supply 100 Ampere current for 1 Hour or 1 Ampere Current for 100 Hrs, 2 Amps Current for 50 Hrs .Capacity of inverter batteries are generally 100 Ah, 150 Ah or 180 Ah.

Why automotive batteries are not suitable for inverters?

Lead acid batteries used for automotive purpose are termed as “High Cycle” lead acid batteries. These batteries are designed to provide high current for a very short duration (To start the vehicles). Automotive lead acid batteries are not designed to be regularly discharged by more than 25% of their rated capacity. Here the requirement of inverter is totally different. Inverter require “Deep Cycle” type batteries to provide continuous power which can be discharged at least 50% of their rated capacity. Some good deep cycle batteries can be discharged over 80% of their capacity. Deep Cycle batteries have specially designed thick plates to withstand frequent charging and discharging.

Maintenance Free batteries

Lead acid batteries require regular maintenance. You have to check the electrolyte level and require to be topped up on regular intervals. Moreover these batteries release poisonous gases during charging and discharging. If you don’t keep the batteries in a properly ventilated place, it can invite serious health problems. You have to keep the terminals of normal lead acid batteries corrosion free by applying petroleum jelly or grease regularly.

Maintenance free batteries are sealed lead acid batteries which do not require topping up or additional ventilation.

Disadvantages of Maintenance free batteries:

  • Cost of Maintenance free batteries are very high as compared with normal lead acid batteries.
  • Life- Life of maintenance free batteries are comparatively low. For example if a normal lead acid battery run for 3 years, you can expect 2 years from a maintenance free battery.
  • Scrap value- You will not get much more from a maintenance free battery as scrap.

If you like a fit and forget inverter system or your situations don’t permit you to do periodic maintenance of batteries then go for a maintenance free battery. Let me quote one example- My friend uses Maintenance free batteries in his home because his old aged mother is living alone and she don’t have enough knowledge on battery maintenance. In that situation maintenance free battery is a right choice.

Tubular batteries

This is the most popular segment of inverter batteries-Tubular batteries have several advantages compared to flat plate batteries.  More complex design increases the manufacture cost but the high electrical efficiency and extra long life make tubular batteries suitable for both domestic and industrial applications. A good maintained tubular battery can run unto 8 years or more. Tubular batteries comparatively require less maintenance. Cost of tubular batteries can go up to double of a normal flat plate battery, however if you have a high efficiency inverter then go for a tubular battery, you will not regret. Almost all popular battery  brands in India like Exide, Prestolite, Amaron etc have specially designed tubular batteries for inverters.

Batteries from Inverter manufacturers

We can see that almost all inverter manufacturers supplies battery along with inverter. I strongly suggest-don’t go for such batteries. This is a simple business technique, often they just market batteries on their brand name. As battery costs more than inverter, it is always better to go for a  reputed and trusted battery brand. I have personal experience with Exide and Prestolite tubular batteries. Exide Invatubular batteries run flawlessly upto 5 years.

Local made batteries

We can see a common trend- People often go for branded inverter and local battery combination. Local batteries costs around 60% of the cost of same rated tubular batteries. However I don’t recommend local batteries because of the following reasons:

  • Poor life: A well maintained local battery can run maximum up to 3 years.
  • Poor efficiency: Electrical efficiency of local batteries are very poor, which requires more time to charge.
  • Safety hazards: Lead acid batteries are very much prone to explosion if not maintained well. We have witnessed several battery explosion incidents. Poor quality of safety vent plugs, casings, impure lead and acids increase the chances of accidents.
  • More maintenance: We can see that local batteries require more maintenance because of poor efficiency.
Flat Plate Batteriesexide inverter battery thumb Things to Keep in mind before buying an inverter Tubular Batteries
exide invatubular thumb Things to Keep in mind before buying an inverter
Maintenance Free Batteries (Sealed lead acid)
exide smf thumb Things to Keep in mind before buying an inverter
Battery Life Span Low (~ 3 Yrs) High(~ 5 Yrs) Medium (3 to 4 Yrs)
Maintenance High Medium Low
Cost Low High High
Safety Low Low High
Efficiency Low High Medium
Scrap Value High High Low

Warranty/Guarantee of Battery

First of all understand the difference between Warranty and Guarantee- Under the terms of Warranty you will get the maintenance and repair of items in free of cost but no replacement. A product under Guarantee will be get replaced in case of malfunctions. Normally we can see batteries are marketed under guarantee + warrantee combination , ie first few years Guarantee and after that warranty. Some brands offer even 48 months warranty. As battery is the costly and vital part of your inverter system, go for a brand which offer long term guarantee/warranty and after sales support.

Inverter output (Sine wave, Square wave, Stepped Sine wave)

inverter waveforms thumb Things to Keep in mind before buying an inverter

Our commercial power supply is 50 Hz pure sine wave (see the figure). However most of the inverters don’t output pure sine wave. Old inverters generate 50Hz square wave or 50Hz modified Sine wave (Quasi Sine wave , Trapezoidal wave or Stepped Sine Wave). Then the question comes. This wave shape really matters? Yes it does.

All commercial instruments are designed to run on pure sine wave. Characteristics of such devices are greatly depend upon the input wave shape. A change in wave shape will affect the performance of the appliances. Appliances like Motors, refrigerators, Ovens etc will generate full power on pure sine wave input only. Distortion in the sine wave creates humming noise in transformers, and audio devices. Some instruments like light dimmers, few battery chargers, toasters etc require pure sine wave to work. Prolonged operation of appliances in Square or stepped waves will considerably affect the life of such equipment due to the generation of heat.

You may be noticed that  audio amplifiers, Televisions, Fluorescent lamps etc make noise on inverter power. This indicates that inverter output is not pure sine wave. Sine wave inverters are costly as compared to square wave and stepped sine wave inverters, however it is always advisable to go for a pure sine wave inverter for the safety and effective performance of your appliances.

Square Wave Stepped  Sine Wave Pure Sine Wave
Safety of Appliances Less Moderate High
Life of Appliances Less Moderate High
Battery Life Less Moderate High
Noise Level High Moderate Normal
Heat generation High Low Normal
Suitability for sophisticated appliances No Not recommended for prolonged use Yes

Inverter efficiency and No load power consumption

Efficiency of an inverter is proportional to the amount of power drawn. It can varies from 90% to 50% from full load to light load. Here the notable factor is that inverter efficiency is high on maximum load. Generally an inverter is in its most efficient capacity when being used at around 1/3 to 3/4 of it’s full rating.

Power Consumption of inverters

Inverters take mains power supply to  charge the batteries. If the charging section of an inverter is not energy efficient, it will waste electricity even after the battery is fully charged. This will inflate your electricity bill. It is very difficult to check this aspect in shop before purchasing an inverter. However you can test the same at your home. Switch off all appliances except the  mains supply to inverter, disconnect the battery and measure the power consumption for a specific period.

Battery backup duration

Here we have an equation to find the battery life on load

Time(in Hrs) = Battery Voltage (In volts) * Battery Capacity (in Ah)*efficiency of inverter

                                                                           Load (in VA)

Let us have a sample calculation

Battery voltage = 12 Volts

Battery Capacity = 150 Ah

Load = Two fluorescent lamps (40 Watts each) and one ceiling fan (75 Watts )= 155 Watts

Inverter efficiency = 80%= 0.8

Backup Time = 12 * 150*0.8/155= 9.29 Hrs (Approx)

Other features

Solar Panel input: In typical Indian situations even eight hours of continuous commercial power supply availability can not be assured. Hence many people use the most reliable and alternate non conventional power source- Solar energy. Nowadays inverters facilitates the usage of Solar Panels also. Those inverters are embedded with solar charging circuits and regulators.

LCD Status Indicators: Modern inverters come with LCD status indicators to display various status like Battery charge level, Load, Input/Output voltages, Battery life etc.

Voltage stabilizer , High/Low voltage cutoff : Normal inverters don’t stabilize the mains supply, means the commercial supply is routed directly to the appliances without monitoring. Some inverters comes with in built voltage stabilizer , which protects your appliances from voltage fluctuations.

Earth Leakage Protection: Earth leakage protector is a safety device used to protect users from electric shock and appliances from damage. Modern inverters come with in built earth leakage protection circuits, which continuously monitor earth leakage and cut off the supply to safeguard the users.

After Sales Support

We can’t give a blanket suggestion in favor of a particular brand or model. All electronics equipment are prone to damage, hence after sales support is always paramount which varies from place to place. As inverters are static devices, go for a dealer or brand who offers on site warranty repair and maintenance.

Read this Home Solar Inverter Buying Guide



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  • Samir Patnaik 07/13/2014, 9:22 PM Reply

    Hi Sujith,

    I got an idea how to choose an inverter but still a doubt before purchase that which company you will suggest to go for? My requirement is as below based on that kindly inform which company inverter, battery i need to purchase,

    CFL Light – 4 NOS (27 W – 1 NOS / 15 W – 3 NOS)
    Fan – 2 NOS (1 Celling / 1 Standing)
    Mixer – 1 NOS (Only for emergency)
    LED TV – 1 NOS
    Mobile/Lapto – 2 NOS
    Charging point

    Regards,

    Samir Patnaik
    9011070527

  • Magesh 07/13/2014, 10:36 PM Reply

    Hi Sujith,
    Can we keep the inverter and its battery in a closed loft, will that create any problem? Please advise.

  • sarita 07/14/2014, 5:04 PM Reply

    I Understand all things, I am going to purchase the inverter and I came to know all the details about inverter. Thank You.

  • Samardeep Singh 07/15/2014, 8:37 AM Reply

    Sir, my requirement is

    3 Fans , 3 Tube lights, and about 7-8 Hours back up. Which inverter battery (both) would u suggest me for installing.

    • Anil Chauhan 08/14/2014, 2:32 PM Reply

      Kindly suggest me an adequate capacity and of inverter and the battery for 7-8 hrs. back up for my home.

  • khargeswar 07/15/2014, 3:05 PM Reply

    sir

    i have 3 cfl 60 w.2 fan 100 w.1 laptop 100 w and one tv 150 w. i want to buy a 2000 va invertar and also order it in homeshop 18. but i am confiuse…what power betrry i have to buy? how much volt….pl pl pl pl replay….kindly…

  • Pawan kumar 07/17/2014, 10:57 PM Reply

    Hi please solve my problem,i have a 1500 VA microtek inverter with two 200ah battery when i bought this inverter several time it became faulty. Now i plan to buy a new inverter. As per your article,i visited a inverter shop for pure sine wave inverter but seller tells me if in a pure sine wave inverter got faulty after warrenty it circuit not repair,only changed. Please solve my problem . And also suggest which inverter i buy microtek,sukam,luminious or arise. I m living in a village in haryana where long power cutt often. Yours sincerely pawan kumar

  • Pawan kumar 07/17/2014, 10:59 PM Reply

    Hi sir i have a little confusion if i run a celling fan on my 200 ah double battery, how many hours it can run and what is the calculation method.

  • Azamuddin 08/01/2014, 5:23 PM Reply

    Dear Sir i have UPS 850 Savegard Brand & Luminious Tubler 150ah Battery i want to user 4 tubelights 2 Fans 4 CFL what can i do in ups Direct N- P+ take output for that or Only P+ Take from ups & N- From Govt. Supply

    Some Budy told me user BOth N- and P+ from UPS

    Some Budy told me User P+ from Ups Like Invater N- from Govt Suply

    Thanks for Advice

  • shahebaz 08/29/2014, 1:46 AM Reply

    Please suggest me which invertor and suitable battery I purchase

    My requirement :- 4 ceiling fans, 1 wall mounted fan, 2 tube lights, 1 television 21″,

    Power cut:- 6am to 9am and 12pm to 3pm
    Total 6 hours

    Please give me a suggestion

  • kvaiphei 09/13/2014, 11:22 AM Reply

    The Basics you have given are really useful. Many a times we live in ignorance,doubt and being cheated. Your article is really useful.

    Kindly discuss more on the safety part.

    1. Dos and Donts for Safety

    2. What are the dangers ?

  • kirthy 09/16/2014, 12:15 PM Reply

    Dear sujith,
    I just wanna buy a best ups for my home.
    cud u pls. suggest a suitable one for me.

    3 =tubelights
    2 =ceiling fans
    1 =32 inches led tv
    1 = 1.0 samsung a/c(optional)
    2 =plug points(occassional)
    1 = refrigerator(optional)

    mention WHICH BRAND to buy?
    waitn fr ur response.
    BR//
    Kirthy

  • Ronak 09/22/2014, 9:34 PM Reply

    Sir
    Can i use single 150 Ah battery with 1450 VA Inverter
    Bcz of my back up hour requirement is 1.25 hr only & i want consume 1100 watts load at a time.
    Plz reply on email
    ronaktongya@gmail.com

  • Ruby Johnson 10/04/2014, 10:30 PM Reply

    I want to buy a Microtek inverter of pure sinewave, very confused to buy about the VA of either 900 or 1500 and the battery to be tubular type and maintenance free one. I want to run 2 desktop computers, one ceiling fan, one light for 6 hours. When 2 computers not in use i want to run Normal 28 inch TV, setoff box, 2 fans and 3 tube lights. Kindly suggest me the the Invertor va requirment and battery requirements. I am planning to buy immediately, so please reply me. Awaiting for your reply

  • gopi 10/11/2014, 9:43 AM Reply

    Sir

    At present indian solar pv panels able to with stand with lightning strike,some manufacturers are saying able to hold lightning strikes
    pl.guide me

    Gopi

  • R A AGARWAL 10/11/2014, 10:01 AM Reply

    Sir,

    Can I connect three exide battery of 150AH(Invertor Plus 1500) with my 1400 VA Su-Kam invertor for battery long life and long power backup ?
    Beacuase one old battery of 150 AH exide make in good condition lying with me as ideal.

    regards.
    r.a agarwal

  • varun jain 10/11/2014, 11:31 PM Reply

    i want to need inverter with ups supply,5-cfl,4-fan,1 hp 1-phase motor.which company i buy and suggest me with price.

  • DEEPAK SONI 10/21/2014, 3:39 PM Reply

    i need inverter for 2 ciling fan and 3 light 40waat 1led tv how much power i req..

  • rakesh 10/26/2014, 6:04 PM Reply

    I have new exide 150 ah battery and iget only 2.15 hour in 400 watt.

  • Ashok Patnaik 10/28/2014, 11:32 AM Reply

    Hello Sujith,
    Thanks for contributing lucid article on Inverters; I am benefited. I admire your patience too.

  • Ramesh Balaji 10/29/2014, 8:54 AM Reply

    Hello Sir
    Previously I used WEP inverter which was producing sine wave output. It got failed recently. I want to purchase a new one. As you mentioned in the above article, I want to go for a inverter which should have LCD display, voltage stabiliser, ELCB and other latest technologies.

    Kindly suggest me a new branded inverter.

    And also tell me about the inverter which supports the solar technology. This will help me to upgrade solar technology in future.

    Regards,
    Ramesh Balaji
    9994901969

  • K.Rajeshkumar 10/30/2014, 4:58 PM Reply

    Sir, I want to purchase Inverter for the requirements of following description

    1.Tube light – 2Nos
    2.Refrigerator – 1 No
    3.LED TV (24 inch) – 1 No
    4.Ceiling Fan – 2 Nos
    5.Laptop – 1 No
    6.Mobile – 3 Nos.

    Kindly give ur suggestion for Inverter, cost of that Inverter, and Brand

    Thanks & regards
    K.Rajeshkumar
    Coimbatore
    Tamil Nadu
    919943866211

  • Dharmendar Reddy 11/03/2014, 9:54 PM Reply

    Hi, I purchased Luminous 875 VA UPS Inverter/Sine wave UPS and 180 Ah Luminous battery in 2011 May. I am using 4 tubes, 4 Fans, 4×18 Watts CFL bulbs, 3 zero bulbs and desktop computer. Only I see when the distilled water is less,I fill it thats all. Still now no problem.

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