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Things to Keep in mind before buying an inverter

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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

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 Tubular Batteries
exide invatubular
Maintenance Free Batteries (Sealed lead acid)
exide smf
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

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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456 comments… add one
  • S. Kumar

    Thanks for the education. I wish, I had read this before I installed my first inverter instead of blindly following the electrician’s advice. My tubelights make a humming sound and now I know the reason. Moreover I installed a flat battery with poor backup. Now I can educate others. Bravo, keep it up.

    • ashish

      Hi Kumar,
      Can you please tell what is the reason of humming sound of tubelights ?

  • akash meher

    I have 2 cfl bulb of 18 watt and 3 mobile total battery =7500mah and i need backup for 8-9hrs how much va of ups would be required

    • VKB

      Wonderfully simple, yet extremely useful. The only flip side is some grammatical mistakes in the language. Great job well done. Keep it up.

  • Rekha C

    Hi Sir,

    Having small new firm with 6 desktop computers with LCD monitors, request you to please advise what combination of UPS or Inverter (VA) and batteries (AH) should I purchase so that I can have atleast 4 to 5 hours auto power backup. If possible please assist good brands too.

    Thanks for your kind support in advance.

    Regards
    Rekha

  • Anjum Rizwi

    Excellent Article. Very useful. I would say read whoever want to buy UPS/inverter.

    • I would suggest you go for a 12v dc inverter with a battery of 150ah with 3 yrs warranty which will cost you approx 14000/ which is most suitable and reliable

  • K Ramesh

    Dear Sujith
    Very good article. Thanks for the same. Keep continuing this good work.

    I want to buy inverter and need your guidance. My requirement is minimum 3/4 hrs of back up
    Usage will be
    CFL 20W – 3 Nos
    Ceiling Fan – 3 Nos
    32? LED Tv – 1

    please suggest me which capacity inverter and battery is best suited for my requirement. Also the approximate cost.

    Regards
    K Ramesh

  • Raheem

    I need your advice as to which inverter is good for nigeria that I can buy for my 3.5 kva consumption and type of battery that will last for me .thanks

  • ABHISHEK CHUARASIA

    THANKS, IT’S REALLY HELPFUL 😉

  • Samy

    K Ramesh. you need 1000va inverter cost. RS-7,000. and 20V 300AH battery cost.RS-18,500. It is the cost of 1 battery total cost is RS-25,500. You afford it easily. Thank you.

  • Dinesh yadav

    Thanks for providing such an important things about inverter .

  • Panicker

    This article is helpful- thanks.

  • A.K.Roy

    I want to run 3fans/5 LED lights,40in LED TV, water filter,cooking chimney,modum what is the capcity of inverter will be required

  • A.K.Roy

    back up time 6hrs

  • Vijayakumar

    This is very nice explaination with examples. I planning to buy an inverter. So it is really good for me to get educated. Thank you so much

  • Neepa

    Dear Sir ,

    Your article is really helpful for points to be considered before purchasing inverter , thank you for sharing valuable knowledge

    I need to buy inverter to run
    3 Fans
    3 Tubelights
    1 40″ LED TV
    1 Desktop
    1 Wifi Router
    1 Fridge ( Optional )

    Pls guide me I should Purchase how many VA Inverter + hw many AH Tubular Battery

    Also please suggest me which brand model of inverter covers maximum features like Display of Battery Charge Level, Load , Input / Output Voltage , Battery Life , Voltage Stabiliser & Earth Leak Protection in it

    Please reply me ASAP

    Regards ,

    Neepa

  • Sunil

    Please suggest me the best inverter for following
    1) 2 desktop computer with monitor
    2) 2 LED tubes 28 watt each
    1) Laptop
    Thanks in advance

  • NH

    Dear sir,
    I want 6-7 hours running battery + inverter …
    I need to run

    3 ceiling fans , 2 cfl bulbs (11watt), 2 Zero power light …..

  • Barry baker

    Very informative , a must to know before purchase of my inverter

  • Neema

    Which inverter is most useful profitable & long life ….to use 3 cfl & godrej 1 ton inverter A/C..

  • Abhishek Joshi
  • Syed Sirajuddin

    Dear Sir ,

    Your article is really helpful for points to be considered before purchasing inverter , thank you for sharing valuable knowledge

    I need to buy inverter to run
    2 Fans
    3 CFL 18 watts
    1 32? LED TV
    1 Wifi Router
    1 Fridge 165 litres

    Pls guide me I should Purchase how many VA Inverter + hw many AH Tubular Battery

    Also please suggest me which brand model of inverter covers maximum features like Display of Battery Charge Level, Load , Input / Output Voltage , Battery Life , Voltage Stabilizer & Earth Leak Protection in it

    Please reply me ASAP

    Regards ,

    Syed Sirajuddin

  • Gursharan

    I am looking for a good power back up(UPS) for my gaming PC and a ps4. Would appreciate if anyone could point me in the right direction. Ps4 – 90-150 watts, PC – ??

  • varun

    hi
    i have 4 fans
    5 tubelights
    1 refrigerator
    40” tv
    2 charging points
    1 dish tv
    1 wifi router

    please suggest me which capacity inverter and battery is best suited for my requirement. Also the approximate cost

  • Ashish

    Sir, I have heard that repair cost of pure sine wave inverter is more ,compared to normal inverter (ie. one have to change complete kit in sine wave inverter if there is need of repairing on other hand normal inverter doesn’t require full kit to be replaced…)

    is it true sir…..plz guide..and make me correct is i am making any mistek…

    Thank you..!!

  • Udaya Bhaskar

    Really helpful and worth reading!!! Cheers.

  • Yakin Patel

    Grate…… Perfect and best suggestion….

  • karan

    i am looking for maintaince free battery for home

    which battery is good

    please advice brand name

  • Nirmit Naik

    Thank you so much for such descriptive information, with quality and important details.
    These technical value found to be very useful to buy me a new UPS inverter with inverter battery.
    I am going to buy Luminous Zelio 1100 with Exide Tubular Battery 150Ah, as per your guidance.
    Thank You.

  • Souptik Gupta

    Hi, I want to run 4 CFLs, 3 15W Coloured Bulbs, 2 Ceiling Fans, 1 Table Fan, 1 LCD TV(with Set Top Box), 2 Laptops, 2 Mobile Phones(incase of charging), 2 Routers, 1 Modem and 1 Inverter Refrigerator 280 Lts. during power cuts. I don’t want the routers to restart when the power supply is being transferred from mains to battery. I am planning to buy Luminous Zelio 1100 inverter and Exide IT-500 Battery. I want to know if this will be sufficient for my needs ? Please help.
    Thanks.

  • gurpreet

    I purchased invertor in 2012 luminous invtr and exide battery.but backup was not good.now battery gravity is down.its 7.so please guide me which battery I should buy.i am confuse between luminous and microtec.

  • Shankar

    very useful information to buy inverter

  • prasanna

    hi
    i have 1 fans
    1 tubelights
    1 refrigerator
    22” tv
    1 charging points
    1 dish tv
    1 mixi
    2 led 9 w

    please suggest me which capacity inverter and battery is best suited for my requirement. Also the approximate cost

  • kamlesh jha

    I need to buy inverter to run
    2 Fans (one ceilling & 1 table)
    3 CFL 20 watts
    1 32 inch colour TV
    please suggest me which capacity inverter and battery is best suited for my requirement. Also the approximate cost

  • Mohammed Inamullah

    I need your help on selecting a inverter and battery for the below items
    5 CFL Bulbs 20 watts
    TV 32 ”
    2Ceiling fan 48”
    1 Refrigerator
    1 air conditioning

  • shivanand h

    Hello Sir,
    Thanks a lot for your honest inputs.
    I have read your tips on inverter & battery,
    my need is around 800 va can you suggest the brand & model according to the technology.
    And rgds batteries of 150Ah , should i go for tall tubular or normal tubular. (exide)
    please feel free to speak out your mind, I will understand you & not misunderstand
    shivanand

  • Tony

    Hello.

    Thanks a lot for the information. It was worth the read.

    As you’ve observed, most of the comments are requests for individuals aiming to determine their inverter power supply.

    I want to suggest: Why dont you arrange a payment option, where these people can pay to have their questions answered. Then you can, possibly, hire a staff who would pay detailed attention to their power needs, and provide responses to them, preferably, via their emails.

    The advantages are, you get to help them with detailed information on their power needs, and also, you get to help reliable inverter firms, sell their products.

    I would be interested in helping out, if you do consider this.

    Regards,

  • Tony

    Hello.

    Thanks a lot for the information. It was very comprehensive, and worth the read.

    As you’ve observed, most of the comments are requests for individuals aiming to determine their inverter power supply.

    I want to suggest: Why dont you arrange a payment option, where these people can pay to have their questions answered. Then you can, possibly, hire a staff who would pay detailed attention to their power needs, and provide responses to them, preferably, via their emails.

    The advantages are, you get to help them with detailed information on their power needs, and also, you get to help reliable inverter firms, sell their products.

    I would be interested in helping out, if you do consider this.

    Regards,

  • z R Khan

    hello sir
    i need best battery for my house the battery should be work atleast 7-8 hours and battery warranty must be 5-6 years

  • Satyajit Parhi

    Dear Sir ,

    Your article is really helpful for points to be considered before purchasing inverter , thank you for sharing valuable knowledge

    I need to buy inverter to run for my home
    3 Fans
    4 L.E.D. Bulbs having 15-20 watts each
    1 24? LED TV

    Pls guide me for purchase how much power VA Inverter + how much power AH Tubular Battery

    Also please suggest me which brand model of inverter covers maximum features like Display of Battery Charge Level, Load , Input / Output Voltage , Battery Life , Voltage Stabiliser & Earth Leak Protection in it

    Please reply me ASAP

  • Ranjit

    Very good information.Thanks for sharing

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