Bug Vanquisher

10 June 2007

Don’t use this cure. It worsens the symptoms!

Filed under: Things in life — Tanveer Badar @ 12:14 PM

Tired of load shedding? Constantly interrupted with power failure in the middle of that important chat? Finally, you convinced dad to install a UPS to fight all those chance of assignment not being completed on time? Wishing you had a laptop or owned KESC? You are that victim of constant power failure who couldn’t prepare for that DIFFICULT paper next morning? It is time to ride the band wagon to load shedding free summers in Karachi. You have three options, curse KESC all the time and do nothing else, not likely. Get a generator to fulfill your deepest desires. Buy a handy UPS for all you home, you are that generous person, you are. And in the meantime, get a small UPS for your computer too so that it does not suffer from jerks (electric and human included. It would be better if you could keep your hands off it for a moment.).

UPS come in all sizes in rating. They are for things as big as an entire office. They can provide power to an entire home if need be. Or they can be for things like computer we mortals have come to love. My office has a UPS that supports all machines in it and has a battery life of 15 minutes. The one at my home has a battery life of 6 hours and can power almost everything at once. Thankfully, they are designed such that battery life and load bearing capabilities are independent of each other. You can have as much battery life as you want if you add enough batteries. Load bearing can be as high as you want (well up to a certain point) by using power electronics and devices.

These preliminaries aside, have you ever given thought to what happens when power goes out, UPS begins its life as a power source and when power comes around, recharges itself for next cycle? For the illustration take my home as an example. Here is a typical day, 24 hour power consumption cycle for my home.

normal

Initial surge starting at 6 AM is due to everyone waking up. Things cool down a little from 9 AM to 12 PM. Then, those who don’t have a full day job return and the consumption surge begins. We have highest demand from 4 PM to 10 PM. Finally, one by one, we starting getting to bad, our share of electricity now served to someone else and a new cycle begins. 

Add UPS to the mix and see what happens.

UPS

The baseline power consumption for constant recharging and losses accounts for a couple of watt every day. This adds a certain amount to electricity bill each month. This is one part of the cost we pay for having power all day round. 

Overall, power consumption is increased by this base line UPS power consumption above what would be otherwise.

Result

Each day, we are consuming 24x/1000 units of electricity with no obvious gain. It is just like insurance, if the loss you have anticipated does not happen, you do not get all your money back, there is some amount taken. The operating charges and risk factor in case that catastrophe had happened.

From the last picture, can you guess what would happen when power fails?

power failure

UPS lost external power somewhere around 12:50 PM – 1:00 PM. This power out period lasts for about two hours. During this time, UPS’ internal power consumption has reduced to a bare minimum, sort of only for housekeeping jobs. So has total power consumption. It is very near what would be baseline power consumption in the absence of UPS. When power finally comes back around 3:00 PM, a sudden increase in power consumption happens. Difference of area under total power consumption from 1:00 PM to 3:00 PM in the last two pictures must be less than increased power consumption. What is the reason? UPS begins charging back itself and it is common knowledge that the energy it handed out during the last two hours must be more than compensated in the next few hours. UPS power consumption jumps to about double its baseline level. Similarly total power consumption stays at a high level for some hours. When UPS charging rate finally starts to come down, the solid curve assumes its normal profile. 

Now, do you see what the problem is? As more and more people install UPS in their homes, offices power consumption may be low for a part of the city while it is experiencing load shedding, but after that period is over, the amount that was conserved will be more than compensated by recharging devices. At the end, load shedding has not helped anyone conserve power but caused disruption for some and increased load on the system in the ensuing hours.

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2 Comments »

  1. You sure that a UPS takes double the input at charging when power resumes.

    Comment by Usman — 12 June 2007 @ 10:58 PM

  2. Of course that was just a rough estimate. But you must agree with me that increased power consumption must more than compensate.
    Recharging power requirements may be anything but equal to or less than baseline consumption.

    Comment by Tanveer Badar — 13 June 2007 @ 9:49 AM


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