The Home UPS/Inverter Buying Guide

Enough of power cuts in the region I live and it became inevitable to buy an inverter/home UPS system. So I went ahead and did some very basic research before deciding upon buying the same. I am sharing the same over here in anticipation that it would help someone :-)

With loads of power backup options available in the market, it becomes quite a bit of an exercise to get to the right product. More so because of the aggressive marketing of the products, which may be misleading. Before even getting into the options, one needs to figure out the needs. For example, in my case I wanted a solution which would give a back-up of 2-3 hours for the following:

S. No. Equipment No. of Units Approx. Wattage / Unit Total Wattage
1. Fan 3 70 70*3 = 210
2. CFL 4 25 25*4 = 100
3.. Notebook 2 75 75*2 = 150
4. TV 1 120 120*1 = 120
5. Miscellaneous (Modem, Router etc.) NA 50 50*1 = 50
Total 630 W

So, I need a solution which can give me 630 W of power for 3 hours at a stretch (assuming I run all of the above for 3 hours). Now let’s do some high school physics calculations:

P (Power in Watts) = V (Voltage in Volts) * I (Current in Amperes)

Before we move ahead into the calculations, let’s clarify a couple of points:

What is the difference between an inverter and a UPS?

Well some think that these two are competing concepts, however the bottom line is that an ‘inverter’ is an equipment to convert Direct Current (D.C.) into Alternating Current (A.C.) where as an UPS (Uninterrupted Power Supply) is a circuitry which allows an instantaneous switch to the backup power source in case of a power failure thereby ensuring an uninterrupted power supply to sensitive equipments like a computer.

Now the only thing which needs an uninterrupted power supply in my list of equipments is the notebook, but that is anyway ensured by the notebook battery. So do I need a UPS? Well yes, I would want an uninterrupted internet connection in case of a power failure so I need the modem and router running in continuum.

Now that I know I need an inverter with UPS, do I need to look into anything else? Well yes, there are different types of inverters available in the market:

Square Wave Inverters: Popularly known as ‘Digital Inverters’ produce a Square Wave AC output which is not so great to run appliances as all the appliances are designed to run on a Sine Wave Alternating Current Pattern. Also, you would notice a humming sound in some of the appliances. Though electrical appliances would bear this, running electronic appliances over Square Wave is not at all recommended.

Sine Wave Inverters: These inverters produce the right wave pattern (Sine Wave) for which the appliances are designed. One can safely run most of the appliances on such current output.

Quasi Sine Wave Inverters: These fall somewhere in-between the above. I am not too sure about the internals. Also, didn’t find them in the market. But apparently they offer a low cost solution to run PCs and other electronic equipments on inverters.

Now what remains is the power storage medium, which, of course, is the battery. Again loads of options available which only confuse you. I didn’t think a lot over this and decided to go with an Exide Tubular Battery. Let’s have a real quick glance at the main options available relevant to inverters:

Standard Batteries: Loads of them available in the market. But they need maintenance i.e. putting in the distilled water on an ongoing basis.

Maintenance Free Batteries: While some claim they don’t need maintenance throughout their life-time, most of the maintenance free batteries need maintenance once a year or so.

Tubular Batteries: These batteries are superior in technology, construction and the quality of material used within. While you can figure out some nitty gritty here and here, they offer the following advantage:

  • They are maintenance free.
  • Long life (5+ years)
  • Faster Charging
  • More efficient

Though tubular batteries are a bit expensive, but considering their advantages I concluded that in the long-run, they actually turn out cheaper.

To wrap this up, let’s quickly get back to the calculations. So I needed a solution which could provide me with 630 Watts of power for 3 hours. Inverters available in the market are generally rated in VA/KVA.

Since, V*A=P, I need a 630 VA inverter. A very important point to keep in mind is the power factor. You would never get the rating mentioned in the inverter specifications. Considering a power factor of 0.8 (again figured out with some research) I would need an inverter with the following rating:

xVA * 0.8 = 630 VA

=> x= 630/0.8 = 787 VA

Luckily, for me we have 800 VA inverters available in the market, which perfectly fit to my needs. Note that this is a limiting factor w.r.t. the total wattage of appliances you can use. For instance I can’t run a 1000 watt appliance on an 800 VA inverter!

Now the battery. Inverter batteries are usually available in 12 V and are rated in Ampere Hours (AH). Since P=V*I and I need a backup for 3 hours,

630 W * 3 Hours = 12V * x (Ampere Hours)

=> x = (630 * 3)/12 = 157.5 AH

Again, luckily I discovered that we have batteries rated 165 AH in the market. So I decided to go with it.

Bingo! I have the details now. I need an 800VA inverter and a 165 AH battery for my needs. I just need to decide upon a brand based on the reviews.

Also, note that the above calculations are indicative. To quickly figure out how much back-up you would get while running a subset of the wattage considered at the time of buying, use the following:

Backup Time (Hours) = (Battery Voltage * Rating (in AH))/ Wattage required.

So if I just run 3 fans, i.e. 210 Watts, I would get a backup time of (on a fully charged battery):

12*165/210 = 9.4 hours

I can also run two moderate air coolers for about 7 hours. That’s sufficient for a night’s sleep :-)



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288 thoughts on “The Home UPS/Inverter Buying Guide

    1. Bokti

      1 fan is 70 w and 1 light is 20 w approx. so your consumption is 90.
      Calculation as per Amit would be 12×100/90…. So 13 hours plus,,,,,

  1. Arvind

    It is a Good post but still more information needs to be put.

    As few batteries have a rating of c20 , c10 wat does these mean. Please Post This information.

    1. Koushik

      C10 means that the Ah discharge was calculated on a 10 hr rate. (ie. 150 Ah was tested to ensure that it provides 15 Amps of Current for 10 hrs) Whereas C20 means it was calculated on a 20 hr rate.

  2. SA

    This manner of explanation would simplify plenty of supposedly complicated things ……good job Amit Srivastava, continue the good work!

    1. Renu

      Thanks for the information. I am looking to buy an inverter and this information is really useful. Hope I can get the required inverter in the shop.

  3. Shreyas Kurade

    Really an awesome explanation above..
    got cleared all my doubts technically & the most pleasing thing abt this article is the Calculations imposed which make each n every aspect in terms of home load just up-to-date.
    Thanks hope to hear more from you soon.

  4. Sirish

    It was very useful for my calculations. So which inverter and Battery you end up buying and how much did it cost. I have similar requirements

  5. V.G.Varshan

    I am a quite a analytical guy who is analyzing everything , each and every factor possibly would influence the products end use . CONSIDERING my this character , sir ur simple and complete information given in such a pin point structure is found to be very informative and easy to apply also , thanks for u for sharing this valuable information

  6. Pingback: The story of home inverter and more « Thinking Engine

  7. Ramesh C

    Thanks Amit, useful information.

    I plan to buy a inverter, the electrecian suggest Microtech inverter 800 with Exide Battery. Do you have any recomendation?

    1. RK

      Microtech/Luminious/Sukam(Rs 5k-6k) + Exide Tubular (150AH-Rs 13900/- or 115 AH-Rs 11900/- Bangalore Price)-Will be fine….i bought recently!!!!

  8. Sumit

    Hi. Amit glad to write you I planned to purchase a inverter my requirement is Microtek sine wave 875va with Exide 150ah battery.Will this good matching ? So how much cost ?

  9. The New India

    This article does not take into consideration the power factor and efficiency of the UPS, the efficiency and depth of discharge of the battery.

    Please check out The New India blog for UPS buying guide and also other information on power, energy and conservation in India.


    Dear Mr Srivatsa
    Have you analysed which make sine wave inverter is in the market.If yes can you please givr me the details.

  11. praveen

    i have exide tubular150 ah.and one year old.the battery back is only 4.30 hours load on 2oo watt bulb.this is normal back-up or not..please reply….

  12. Steven

    Hi Amit….. Great job… it gave me a basic idea about inverters… how to choose inverter for our requirement….. thanks a lot….. keep it up….

  13. PSR

    Nice calculations for a learner like me. I calculated using the above mentioned formulas and found the Inverter specs. for my home. Thank you very much.

  14. ro le

    Usually I don’t learn article on blogs, however I would like to say that this write-up very forced me to check out and do it! Your writing style has been surprised me. Thank you, very great post.

  15. Hasnain

    very nicely explained…well done and thanks for that.

    I have a query, am confused to buy an inverter or UPS. i don’t require to provide uninterruptable power supply as the devices I want on backup are fans and lights (may be refrigerator).

    Most backup solutions available in our market are Chinese inverters. A colleague of mine who imports UPSs suggested me not to buy one of these as an inverter is not much safe to use. He said, in case of voltage fluctuation or rise/dip the inverter may be damaged and the damage may be transferred to the connected devices, whereas UPS is safer to use, it provides better sine wave than inverter and does not hurt connected devices in case of any problem. Another thing that the inverter will not efficiently charge/discharge battery and thus the life of battery will be reduced much. This will not happen with UPS.

    Now i have no problem in buying UPS only that the UPS (1kVA) will need 2 batteries instead of one and that will make me spend 10k extra than with inverter as the inverter of same power rating can be operated with single battery. Kindly guide, if its safer and OK to use inverter or should I go for the UPS :(

  16. Umarani

    Dear sir ,

    Thanks for your useful things. But i want to tell one thing, the inverter itself take some watts. so we consider the total = (watt req. + inverter itself consume watts).
    it may be 100watts

  17. Avijit

    A suberb explanation by Amit…incredible …now buying an UPS or Inverter with adequate battery will not be any problems for us….good job done…keep it up

  18. swap

    for 3 tube lights, 2 fans, 1 computer ,1 tv, 1 refrigerator… for 5 to 6 hrs back up. ups or inverter and how much VT required in ups or inverter, which model will be good . and tell me about battery also..

  19. debashish ray

    awesome man, so much of details, i really liked it, i never put any comments in any forums but i am impressed with the survey privided by amit srivastava. thanks dude

  20. prasad jambhekar

    thanx dear. you have taken great pain in this research. it will be useful for a nontechnical person also.thank you very much.

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