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While You Were Sleeping  
 

It has been over 2 years since I moved back to India after spending a decade in the United States. The first thing that a lot of friends and family ask me is – how has the experience been so far. Most of them are in disbelief that an individual who has been at the forefront of technology development would want to come back to India (of all places) to be an technology entrepreneur.

It has been wonderful. I am working on problems that I would have by no means been able to work on while I was abroad. I find myself truly lucky to be able to enable solutions that are critical to our society and nation. There is immense job satisfaction. Although, let me not sugarcoat it. I have had my challenges. Especially, with the limited infrastructure and resources here in India.

To give you an example, I have recently experienced a windfall of batteries failing on my personal electronics. Over the last 2 years, 2 batteries on my IBM Thinkpad X60 and 1 on my iPhone 4s had to be replaced. I am quite certain that, in the near future, I am going to see a failure on my Macbook Pro as well. I was able to operate the laptop for 6 hours without needing to recharge. At present (2 years since I bought it) I need to recharge it every 3 hours. My iPhone 4s did not even last a year before battery capacity degraded to 10% and had to be replaced.

These battery troubles are new to me. I have never seen battery failures prior to these events. My usage pattern has not changed. I still charge my laptops and cellphone overnight, So why am I seeing these battery failures in India?

As I discussed my problems with others, I received advise on how to charge and maintain electronics. Most of the suggestions have been about when and how long I should charge these devices. There is a common belief that charging electronics overnight will cause these premature failures. I find this hard to believe. I am certain that device manufacturers are building in protection circuitry to ensure that the batteries do not overcharge. To further investigate this, I looked in to the charging behavior of the products that were failing. I found this rather interesting chart on Apple's support website (http://www.apple.com/batteries/).

 
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Figure 1: Charge cycle on Apple products
 

Apple products opt for a 'fast charge' cycle for the first 2 hours where they reach 80% charge capacity. Charging the last 20% is achieved using a 'trickle charge' and may take 4-6 hours (to reach full capacity of 5V). It appears that the device manufacturers are ensuring that batteries can be charged over larger periods of time. In the case of Apple, they are insisting that the product be charged over longer durations. In theory it appears there is nothing wrong with charging batteries overnight.

With that out of the way, I started analyzing the quality of power. Our team has collected data at different locations in Maharastra (Nashik, Pune, Nagpur and Mumbai). Data was collected over a 24 hour period with 3 second intervals. Studying the data I did not find anything odd with the frequency (except in the case of power failures). I was considerably alarmed by the daily voltage level fluctuations. Although there are several short duration (<10sec) variations. The worst of which are sags that cause up to 10V drop. I am shocked to see the variations in the voltage levels across a longer duration. We should be expecting a supply voltage of 230V.
However the measured voltage is consistently higher and ranges from 235-260V. In particular between 9 pm to 9 am the voltage is maintained over the 8% overvoltage limit.

 
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Figure 2: Voltage measured in 4 different cities in Maharashtra. 24 hour window.
 

It is not surprising that my personal devices are seeing battery failures, while I sleep. I concede that the general consensus is right, I should not be charging my electronics at night. For me, the move to India warrants a change in habit – From now on, the only thing I will be recharging overnight is myself. Good Night and sweet dreams!

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