I'm new to this area and know very little about electrons and how electrical components work. I'm always curious about Inverter/UPS usage.

I'm from India and we have a inverter at home. It is attached with two batteries which will supply the power for my home for 8 hours (TV, 4 ceiling fans, 4 lights). When there is interruption in power supply I drain out the inverter completely and when power comes back it gets charged fully in 2 hours.

I was always thinking that if it can charge up fully in 2 hours and supply power for 8 hours then I can save electricity for 6 hours which I'm paying to supplier by disconnecting power supply after my inverter charge up completely.

I know this is silly thinking but I want to have some explanation from experts saying that my thinking is incorrect, because if that happens then everyone in this world can save lot of power.

  • 2
    \$\begingroup\$ Do you pay per hour that the electricity is turned on, or do you pay per unit of energy that you use? :) \$\endgroup\$
    – endolith
    Apr 5, 2011 at 14:23
  • \$\begingroup\$ Inverter link is broken. \$\endgroup\$
    – Gunnish
    Jan 11, 2014 at 17:25

2 Answers 2


Electricity isn't simply on or off... you're missing the quantity of electricity which is measured in Amperes (Amps for short).

So, while your UPS is charging, it's using lots of electricity to charge your UPS storing a large amount of power as well as the relativity small quantity of electricity powering your house.

When the power is switched off, your UPS is just providing the relativity small quantity of electricity for your home appliances.

So, in the space of time it takes to charge your UPS, your electric company will charge you the cost of 8 hours worth of electricity, plus 2 hours of normal use, plus a tiny bit extra for the inefficiency of your UPS.

If you do this, it will likely cost slightly more than you are paying now, due to the UPS inefficiencies.

  • \$\begingroup\$ The only way I could think that you could do this to save money is if the electric company charged different rates depending on current demand, and you charged the UPS during the cheapest time (low demand hours) and switched to it during peak demand hours. \$\endgroup\$ Apr 6, 2011 at 10:38

Imagine a situation where you store water in a bucket for use in your garden when the taps run dry. The bucket is like your battery. The flower pots are your loads.

Let us say It takes about 4 minutes to fill the bucket from the bathroom faucet, and it takes one minute pouring out water from the bucket into your flower pots.

You havent saved water just because filling the bucket took longer than emptying it.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.