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An eloquent guide to buying an Inverter

When one talks about the basic necessities of life, primarily three commodities come to mind – food (including water), shelter and clothing. However, a modern definition of the basic necessities would see a new entrant, perhaps, a continuous electricity supply to power one’s home. Not just on a personalized scale, availability of continuous electricity propels the prosperity and growth of a nation and has a direct impact on the performance of states as industrial development requires continuous and reliable power supply that helps in enhancing the scale of production. Apparently, one often finds oneself out of luck when a power outage occurs in one’s locality, and the issue becomes all the way more accentuated in the sweltering humid summer months.Now, some might debate on the fact that they reside in one of the metropolitan cities where power outage is a term unheard of. However, what they might not be taking into account are the occurrences such as power grid maintenance, torrential rains, dust storms, earthquakes and other unforeseen instances that might dilapidate the power lines which might take several days to repair.
Under such circumstances what alternative does one have to resurrect the optimal standards of living?

Perhaps, a ‘power inverter’, or more commonly inverter.

Now, if you are a frequent visitor to the posts on this blog, you might be probably aware that we take each topic from the grass root level and we will do the same with this post as well. We will begin with the basics first, understand what an inverter is and how it works. Following which, we will discuss what all factors influence the specifications of an inverter that would be suitable for one’s home as per one’s requirements, taking necessary illustrations as well. Next, we will proceed onto discussing how some brands try to cut manufacturing costs and manufacture below par products that not only not perform as proclaimed but also have a very short shelf life. After which, we will move onto deciding which are some of the best inverters available in the market that not only offer efficient operation, but are also manufactured with components that offer long-lasting and reliable service, thus providing most value for one’s money.

You might be glad to know that my father works at a company that manufactures home appliances like water geysers, power inverters, voltage stabilizers, fans etc. So, at home, we frequently have a conversation about these appliances, what goes into making them, how some brands try to cut manufacturing costs to increase their profit margin etc.

Today, I will try my best to pass on the knowledge that I have acquired from my father over the years, to you so as to help you make a good buying decision.

So without further a do, let’s begin…

THE BASICS
All the electronic appliances in one’s home require electric current to operate, and electric current is produced by flowing electrons. In India, the supply of voltage that one receives in one’s home from the power grid is a 220–240 volt AC. For different countries, the supply voltage might be different. Most of the electronic appliances in one’s home are designed to operate on alternating current (AC). However, in times of power outages, the power grid doesn’t provide voltage to make the electrons flow in order to produce electric current. This is when the second type of voltage supply called as DC supply, majorly produced by batteries and photovoltaic cells comes into play.

A major drawback of DC power is that it can not be used to power electronic appliances, therefore, to power the appliances by the means of a DC supply, a need to convert DC power into AC arises, and the device that converts DC power produced by batteries into AC is called as inverter. It is used to produce an uninterrupted 220–240V AC supply in the absence of supply from mains.
In case of battery powered inverters, DC power is produced by the means of a chemical reaction that occurs in the battery, whereas, when solar inverters are placed in consideration, sunlight falling on the photovoltaic cells (arranged in rectangular panels) is harnessed by the semiconductor layers of photovoltaic cells. Semiconductor layers, usually made of silicon absorb sunlight, and this light energy sets loose the electrons in the silicon, hence DC power is generated.

(Image of a solar inverter setup depicting solar panels, DC batteries for alternate power backup and a solar inverter)

Now, having learnt the basics of how an inverter works, let us now proceed to discuss the various factors that help determine the specifications of the inverter and its battery that would accommodate one’s energy requirements:-

  • Power requirement of various appliances

This is one of the most crucial factors that heavily influences the Volt-Ampere (VA) rating one should opt an inverter with. Power requirement is the sum total of the individual power consumption of all the electronic appliances one wishes to operate on the inverter in times of outages. Typically, the most essential appliances such as few fans and lights, a refrigerator and a television are a few devices one would require running at all times.

Now, for illustration, we would keep into consideration these few devices that one would require to be in constant operation even in times of power outages and we would analyse the sum total of power consumption and correspondingly determine the VA rating one should aim to choose an inverter with-

4 Ceiling Fans – 75W x 4 = 300W
5 Fluorescent Tube – 50W x 5 = 250W
1 Double Door (3 Star Energy Rating) Refrigerator – 175W (approx.)
1 LED television (42 inches) – 75W (approx.)

Total power consumption = 300 + 250 + 175 + 75 = 800W

Now, if inverters, or any electronic appliance for that matter, operated on 100% efficiency then power supplied by the source and power consumed by the appliances would be equal. However, in reality 100% efficiency does not exist, primarily due to heat losses, and thus inverters operate on about 75–80% efficiency. An extension to the efficiency of an electrical appliance is a term called power factor and is the ratio of power required by an appliance to operate to the power supplied in the circuit.
Thus corresponding to 80% efficiency, the power factor would be approximately 0.8. The final Volt-Ampere (VA) rating one should consider buying an inverter with is found by dividing the Total Power Consumed by the Power Factor.

In our illustration, total power consumption is 800W, thus, dividing it by 0.8 would yield 1000VA. Therefore, the optimal inverter to pick for such kind of load requirement would be the one that has rating of at least 1100 VA.
Now, depending upon the requirement and usage, one can run large appliances such as air conditioners and water geysers on inverter power as well, by deciding on an inverter that has a significantly higher Volt-Ampere (VA) rating.

  • Types of inverter technologies

Inverters are primarily classified into two types based on the output characteristic – Pure Sine Wave and Square Wave

Pure Sine wave inverter technology delivers output voltage waveform that is a complete replica of sine wave, and since in most cases, voltage supply from the power companies has the waveform of a pure sine wave as well, the appliances operating on pure sine wave inverters run with higher efficiency, produce lesser heat and noise and chances of crashes in gadgets like computers and occurrences of glitches/noise in display screens such as televisions and monitors are almost nil.

Square Wave inverter technology does a satisfactory job running appliances such as fluorescent tubes and fans, however, when it comes to powering sophisticated devices such as laptops, electric motors, refrigerators, microwave ovens, televisions etc. the square wave inverter technology is not as efficient as pure sine wave one. Though, using a square wave inverter for powering the above stated appliances would not necessarily damage them, one might experience the devices getting warmer than usual which indicates efficiency loss is higher in case of square wave inverters than their pure sine wave counterparts. In some cases, when operating appliances like televisions and refrigerators on square wave inverter, one might encounter audible buzz/noise.


(Waveforms of Pure Sine Wave and  Square Wave Inverters)

  • Battery capacity

Battery backup is one of the pivotal aspects of owning an inverter. The time period for which a battery can provide power to the electronic appliances in absence of power outages depends on three factors – battery capacity, voltage of the battery and total power consumption.
Majority of the inverter batteries have a nominal voltage rating of 12V. Now, to illustrate, we would consider the power consumption of 800 W which we calculated before. Typically, power outages can last from about few minutes to several hours, and again, this depends highly on the locality as well. Therefore, for proceeding with the analysis, we would assume that a typical power outage lasts for approximately 4 hours.

So, to calculate what capacity of battery one would require under the given circumstances, there is a rule of thumb –

(Power consumption) x (Battery backup) / (Voltage of the battery)

i.e. (800W x 4 hours) / 12 volts = 266.67 Ampere-hours

For the considered power consumption and duration of power outage, a 266.67 Ah battery would be required, which can be easily constructed by connecting two 150 Ah batteries in parallel.
For various power consumption requirements, batteries of numerous Ampere-hour ratings are available in the market. Depending upon requirement, one may use the battery individually or connect two or more of them in parallel to increase the power backup times.

Now, having examined the several factors that assist in determining the specifications of the inverter and its battery, let us proceed to understanding the ways in which some manufacturers (names not taken) try to cut manufacturing costs in order to maximize their own profits and in turn deliver a sub-standard product to the customers, the components of which have a very short shelf life and may require frequent repairs/replacements.

COST CUTTING TECHNIQUES

  • Low-grade cooling fan. As discussed previously, electronic appliances do not operate on 100% efficiency. Most appliances function at 80% efficiency, the remaining 20% is lost to heat. In case of inverters, a high quality and potent fan is required to keep the inverter circuitry from overheating and keep functioning at optimal temperature. Unfortunately, most buyers do not pay attention to the cooling fan deployed in the inverter, and this gives some manufacturers a perfect opportunity to increase their profit margin and make use of an inferior cooling fan that is very inept in keeping the temperatures within the inverter casing in permissible range. As a result, over a period of few months, the excessive heat causes the components of the inverter to malfunction and finally melt, causing the entire unit to be non-operational. Cost of repairing the inverter might range from a few hundred bucks to more than a thousand bucks and this process is recurring.
  • Overstated Voltage-Ampere rating. In order to reduce manufacturing costs further, some manufacturers resort to exaggerating the VA capacity of the inverters they manufacture so as to lure innocent customers. However, obtaining near absolute power output from the inverter requires use of high quality components that have near ideal resistance and impedance, which again add to the initial cost. So, in order to keep the initial cost of the product low so as to attract buyers, those manufacturers make use of components that have higher impedance values which leads to loss of efficiency to heat. As a result of which, the inverter tends to beep continuously, displaying overload warning and trips just when the load reaches slightly higher than 65-70% of the stated Volt-Ampere rating.


Now, having learnt how some manufacturers reduce production costs in order to lure customers and to increase their profit margin, let us proceed to zero down on some of the best inverters and batteries, available in the market that not only offer efficient operation, but are also made of components that offer reliable and long-lasting service, thus providing most value for the money spent.

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