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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 ๐Ÿ™‚

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 โ€˜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 โ€˜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 ๐Ÿ™‚

Comments

comments

Amit Srivastava
 

Click Here to Leave a Comment Below 293 comments
Anitha - September 30, 2011

The details provided was very useful and for a new person who want to select inverter or UPS its very useful link

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Dhruv - October 1, 2011

Hey Amit, this was v v useful! all the battery sellers say for 100 amps we can use 1 fan 1 lite for 2.5 hrs only!

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    Bokti - June 21, 2012

    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,,,,,

    Reply
ROMIL KITROO - October 1, 2011

I FIND IT VERY HELPFUL EVEN ANY NON TECHNICAL PERSON CAN SELECT THE INVERTER & BATTERY. THANKS FOR THE DETAIL.

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Arvind - October 2, 2011

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.

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    Koushik - March 1, 2012

    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.

    Reply
SA - October 11, 2011

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

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Amit Srivastava - October 11, 2011

Thanks everyone for the comments!

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    Renu - October 12, 2011

    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.

    Reply
Raja - November 28, 2011

Thanks for this very good information.

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Shreyas Kurade - December 6, 2011

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.

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Kumar - December 22, 2011

Superb Knowledge sharing Amit.

Now I can confidently decide what type and VA i need for my home with AH battery ๐Ÿ™‚

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Vijay ananth - December 24, 2011

Good One

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Sugandhar - January 3, 2012

Thanks Amit, this info is really helpful.

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KC Harihara - February 3, 2012

Thanks a lot Amit. It’s really helpful for me.

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Janardhan - February 8, 2012

Superb Amit!! Good job!!

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SivaJ - February 9, 2012

Thanks Amit,

Good info, helped me to choose the right one at right time.

Regards,
SivaJ

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B Kabirdas - February 26, 2012

Thanks Amit,
Your detailed informed helped me in finalizing my requirement. Keep it up guys.

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Srinivas TR - March 4, 2012

Thanks. Was very useful.

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Sirish - March 4, 2012

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

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smruti ranjan - March 5, 2012

sir, this is very good and easily understandable information

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V.G.Varshan - March 5, 2012

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

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Muttanna - March 6, 2012

Thanks amit …very usefull …information ….

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suresh - March 11, 2012

Thanks!!!!!!!!!!!!!!

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kiran kumar - March 12, 2012

Thank you very much.
these calculations are helpful me a lot.

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Jadoo - March 13, 2012

Nice article…..Thanks……

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Mubarak - March 25, 2012

Very good information. You saved me lot of time. Thanks.

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Neil - March 26, 2012

Thanks for the information. Usually batteries come with 2 year warranty , can I expect more life out of it ?

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The story of home inverter and more « Thinking Engine - March 28, 2012

[…] found this link useful. If you want to do some calculation for your requirements use it. http://www.amitsrivastava.net/2008-06-01-the-home-upsinverter-buying-guide/ Rate this: Share this:FacebookTwitterEmailLike this:LikeBe the first to like this post. […]

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RK - March 28, 2012

Xlnt…but if can give what price you have bought 800 VA + 165 AH (Tubular)….it will help us to compare the price!!!

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Ramesh C - March 28, 2012

Thanks Amit, useful information.

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

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    RK - March 29, 2012

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

    Reply
Sumit - April 9, 2012

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 ?

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The New India - April 27, 2012

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.

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Rajesh - May 13, 2012

Excellent Article Amit. Are you a physics prof or something??

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V MOHANARAO - May 23, 2012

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

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praveen - May 26, 2012

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….

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Steven - May 30, 2012

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….

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PSR - June 8, 2012

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.

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ro le - June 14, 2012

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.

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Hasnain - June 19, 2012

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 ๐Ÿ™

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raman - June 24, 2012

realy helpful.Thanks

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Kadappa - June 26, 2012

very good analysis. Thanks for sharing

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Umarani - June 27, 2012

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
thanks

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Avijit - July 1, 2012

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

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swap - July 2, 2012

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..

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debashish ray - July 13, 2012

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

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manigandan - July 15, 2012

how much computer voltage ? and i’m using ups voltage 1000

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Tinku Mani - July 30, 2012

Thanks Amit for the clear description of inverter. Keep writing. Very well written.

GOOD JOB DONE!!!!!!!!

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prasad jambhekar - August 6, 2012

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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Rockey - August 10, 2012

sell solar power inverter , Pure sine wave power inverter , solar powered systems

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guru sahay - September 15, 2012

a 875va luminios ups & branded battery 150ah is not taking load on a laser printer 2.5amp + a computer why?

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guru sahay - September 15, 2012

what funda diference in offline&online ups. a computer wattage rating.

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deepak - September 24, 2012

which is better lead acid or tubular batteries..

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