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 :-)

Comments

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289 thoughts on “The Home UPS/Inverter Buying Guide

    1. Abinash

      Hi Dan, your video Hi Dan, your video using the harbor fhgreit 45 watt solar kit prompted me to buy one and I personally think it is shit. I could not run a 450 watt inverter or a 750 watt inverter off the supposed 4 amp 45 watt solar panel setup. Yeah it can run a couple of stupid lights in the daytime and trickle charge a battery but it ends up being a waste of money. I have two 6 volt golf cart batteries that work great with my inverters but it would take the HF unit days to charge them, what gives?

  1. Abisheak

    Very good article… the only point is that the power factor is usually about .6 to .7 in most UPS and .8 in very less UPS models. So if the total necessary wattage = 600 watts and the UPS is 800 VA then the actual available watts will be 480-560 (.6-.7) and 640W in case of .8 power factor

  2. Pn

    Thank you Amit,

    These are basics one normally forgets and start thinking what to do and ends up rellying on sales pitch.

    this was simple and straight guidelines

  3. Maddy

    Very useful. Thank you, Mr. Srivastava. Can you suggest me any battery and inverter for using PC, 2 Fan, 6 CFL, Printer and broadband Net.

  4. sankara raman

    My rejoinder to Ed Soniat’s comments above: Fan and fluorescent lamps ( due to their choke circuitry) normally connected to inverter systems are inductive loads by nature. Hence power factor needs to be factored in VA calculations.

    However Amit, I need to be convinced for plumping for costlierTubular Battery option over the sealed ones. Amaron sealed Shield inverter battery 160 ah has lasted for five years on normal usage and little maintenance.

  5. sankara raman

    Fan and fluorescent lamps ( due to their choke circuitry) normally connected to inverter systems are inductive loads by nature. Hence power factor needs to be factored in VA calculations.

    However Amit, I need to be convinced for plumping for costlierTubular Battery option over the sealed ones. Amaron sealed Shield inverter battery 160 ah has lasted for five years on normal usage and little maintenance.

  6. Mutha Srikanth

    Thanks Amit.. could you help me to choose the best among these :
    1. Amaron 600 VA+ Amaron 150 Ah tubular
    2. Microtek 600 VA + Exide Inva tubular 150 Ah

    Regards
    Srikanth

  7. gspal

    I have an APC850va sine wave Home UPS (model BI850SINE-IN). An inverter cum ups (home ups) on mains does not provide any stabilized/corrected voltage. In other words on Mains, the mains voltage is passed to load if the mains voltage is between 100-250v for switch on Inverter mode and if the mains voltage is between 190-260v for switch on UPS mode. Only if the mains voltage crossed the range or is dead then the Home UPS would go to battery mode and provide output of 230v.

    Main voltage on UPS mode varying between 190-260v is not good for computers as they need constant voltage of 220v/230v +/- 1%/5%. Is it possible to insert a (say) 1 Kva voltage stabilizer between the Home UPS and Mains so that output from a Home UPS remains constant when there is mains. The voltage stabilizer would stabilize volatile fluctuations in voltage and spike and the problem of reverse polarity as does happen when the neutral gets become live and live become neutral. Pl do comment Amit. Thanks.

  8. Mohideen

    We are using SMF (42ah, 100ah) batteries with 3KV UPS past 2-1/2year completed. Now power back up is not come proper when power goes immediate shutdown all the PCs. So we plan to to move Tubular batteries. My Question is : 1. In UPS we can add Tubular battery or only add SMF battery. 2. Tubular means How many ah we will put and how many battery we can add? 3. Some companies told Tubular batteries are added only Inverter cannot suitable for UPS. Mohideen, Chennai

  9. vishnu

    wonderfully explained. I just purchased a home ups and this article was good enough to consider what type of purchase needs to be made. This is a one stop shop to understand the technicalities in purchasing a home ups

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