Sunday, April 3, 2016

Power backup

I am living in a village after deciding to move out of city and buying the farm. Apart from being a farmer, I am still a software architect too. Every day I spend almost half a day on software projects. Therefore I need reliable electricity supply. Being a village there are some challenges for electric power. This post provides information about how I solved the problem. Please note - I don't have any affiliation or any relationship whatsoever to any brands I mention in this post. I am describing what I did to solve my problem hoping that will help someone with similar challenges.

As you know cities get major share of electric power. Villages are the most neglected places by the power sector. We have 6 hours scheduled power shutdown in this village. Apart from that power may go and return at any time - that is unscheduled. Mains voltage may vary anywhere between 170 to 240 V. Electric power is unreliable here. That is why I need a power backup. I ended up buying a lead acid battery backed inverter for power. General tendency is to buy some inverter and battery combination recommended by the dealer. Some dealers push whatever is best for them (who pays them more commission), not for the customer. Therefore I did my home work to decide which one to buy.

When it comes to large storage battery for the inverter currently available options are lead acid battery and Nickel Iron battery (also called as Ni-Fe battery or Edison battery - named after the inventor Thomas Edison). Almost all the batteries you have seen in an inverter installation are lead acid batteries (either a flat plate battery, tubular battery, tall tubular battery, absorbed glass mat or gel). Lead acid batteries are very toxic; both lead and sulfuric acid in the battery are toxic substances. Lead acid batteries need lot of careful maintenance and don't last more than 5-6 years even with best maintenance. Compared to this Nickel Iron batteries are less toxic and last really long. Frequent deep cycling does not damage Nickel Iron batteries. Nickel Iron batteries can last several decades. There is a study done on almost a century old Nickel Iron batteries indicating they are still working well! Looking at that Nickel Iron battery is the winner. But there are challenges in using Nickel Iron batteries. Lead acid and Nickel Iron battery charging and discharging characteristics are very different. All our mass market equipment are designed to run with lead acid batteries, not Nickel Iron batteries. Therefore if I decide to use Nickel Iron battery I will have to design and fabricate a special inverter for working with Nickel Iron battery. Another challenge with Nickel Iron batteries is difficulty of sourcing them. There are very few manufacturers and sellers of Nickel Iron batteries because of low demand. It will remain a maintenance nightmare even if I import few pieces of Nickel Iron batteries. Therefore practically only viable option was only one - some kind of lead acid battery. Tall tubular type is the choice out of flat plate, tubular, tall tubular, gel, and absorbed glass mat type lead acid batteries because tall tubular are the most widely used ones. My goal now is to make sure this battery I buy lasts as long as practically possible so that I don't need to throw another 15-20 thousand rupees for another heavy box of toxin [ unfortunately that is what a lead acid battery is :-( ]

Once it was a given that I have to live with a tall tubular lead acid battery I had to find an inverter which does the best job of charging the battery for longest battery life. I had a 6 year old Su-Kam brand Sturdy-i model inverter. This inverter has served me well so far. However this inverter does not consider fine variations between different lead acid battery types charging and discharging characteristics. Therefore it cannot maximize the battery life.

Another challenge is battery charging voltage vs. battery temperature. As the temperature rises battery electrolyte becomes more conductive. Therefore lower charging voltage should be used at higher temperatures and higher charging voltage should be used at lower temperatures. Any inverter not taking battery temperature into consideration for charging the battery will under charge the battery in winter and over charge the battery in summer. Both are damaging to the battery. That shortens battery life. Since my goal was maximizing battery life I wanted my inverter to adjust charging voltage according to battery temperature.

Once my requirements were clear, I spent some time on Google. I zeroed in on Su-Kam brand Falcon+ model inverter. Falcon+ has several innovations in it. You can set it to flat plate, tubular and tall tubular batteries to consider battery specific characteristics for charging/discharging. It also differentiates between a small size battery and large size battery (VA rating of the battery). Best thing about this inverter is - it reads battery temperature to decide battery charging voltage. This inverter also has ability to play well with solar charge controllers. I am planning to go completely off-grid when I build my farm house. This inverter implements 6 stage charging technology (de-sulphation, soft start charging, bulk charging, absorption charging, equalization, and float charging) controlled by a microprocessor. I believe this is the best inverter technology available in India at this moment. I have couploed a 200 AH tall tubular battery (60 months warranty) to this inverter. This gives me more than one full day autonomy for one wireless router, a desktop with LED monitor, 2-3 10-15 W LED bulbs (only in the evening), and 2-3 hours of a DTH receiver & 34 inch LED TV.

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