0
\$\begingroup\$

First of all, I'm sorry if I had put this question in a wrong place, but I couldn't find a StackExchange site more suitable than this one. Basically, I'm asking if turning something on and off might be more costly than keeping it on. Let's imagine such situation: I'm in a bus and I have a phone with which I can buy bus tickets. Unfortunately, my phone battery is dying, so I'm keeping my phone turned off. I imagine two scenarios:

1. When I get on the bus, I turn on the phone and use the ticket app to but the ticket. Then I turn off the phone. If a ticket inspector shows up, I turn the phone on, open the ticket app and show him the ticket.

2. When I get on the bus, I turn on the phone and use the ticket app to buy the ticket. Then I don't turn the phone off. In case a ticket inspector shows up, I show him the ticket (the phone has been working all the time).

I think the thing that separates these two scenarios is the risk, that my phone won't work when I'll have to show the inspector the ticket, and I'm looking for the solution with the lowest risk. I've heard those sayings about the campaign where you turn off all your lights for one hour - people say, that actually turning these lights off and on costs more energy than keeping them on the whole time. Is it true and if yes, does this also imply, that actually the second scenario is less risky?

\$\endgroup\$

closed as off-topic by Leon Heller, Nick Alexeev, Matt Young, Ignacio Vazquez-Abrams, Daniel Grillo Feb 24 '14 at 19:44

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Leon Heller, Nick Alexeev, Matt Young, Ignacio Vazquez-Abrams, Daniel Grillo
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Check it: electronics.stackexchange.com/questions/55831/… \$\endgroup\$ – dext0rb Feb 24 '14 at 19:06
  • \$\begingroup\$ I'd turn the phone off as soon as it's not being used. Keeping ordinary lights on for a whole hour to save power is just plain silly. \$\endgroup\$ – Olin Lathrop Feb 24 '14 at 19:09
  • \$\begingroup\$ discovery.com/tv-shows/mythbusters/videos/… \$\endgroup\$ – Grant Feb 24 '14 at 21:43
  • \$\begingroup\$ Screen is one of the things that sucks the battery too much. For a smartphone, bootup takes a while, about 30 secs. By the time it is booting, the screen is on and consuming battery, also the CPU is probably running at full speed which also sucks battery. I would turn the airplane mode on and leave the phone on. Xperia Z for example uses less than 1% of battery when I am sleeping, that is about 8 hours. \$\endgroup\$ – abdullah kahraman Feb 26 '14 at 0:08
  • 1
    \$\begingroup\$ @abdullahkahraman nope, I'm not that Grant. :) \$\endgroup\$ – Grant Feb 26 '14 at 1:08
3
\$\begingroup\$

Leaving the phone on but disabling it from the telephone network (airplane mode) would ensure that the battery drain from it being interrogated by the cell network is minimized. Once on, I would suspect that after a minute or so (I'm thinking android at this point) all the apps you might normally have activated will be loaded and the phone can go into light standby. How long does a bus or train journey last? How much lower is standby power than normal power? How much power is re-used on turning the phone back on just to load the apps and power up the screen?

My phone currently tells me this about my battery usage: -

  • Screen 33%
  • Cell standby 22%
  • Phone idle 20%
  • Wifi 19%
  • Google play services (whatever that is) 6%

I don't have bluetooth enabled so that isn't draining anything.

Do some research and find out what the power consumption proportions are for each mode and I would suspect that if the bus journey is less than 15 minutes (gut feeling) it might be more economical to leave it switched on and doing nothing.

\$\endgroup\$
2
\$\begingroup\$

I don't buy that it takes any significant number of joules out of the battery to restart the phone.

On the other hand, there are two additional effects at work. When a battery is disconnected it tends to recover a bit from where it was (it's depolarization at the electrodes, that sort of thing, going on). In my experience, that's not a big effect in rechargeable lithium batteries, and in any case, it works in your favor. The negative effect is that the phone's battery protection circuitry may refuse to start with a battery condition that would allow it to continue running if it was already on. Since that algorithm is not known, it's hard to predict exactly what it will do.

Personally, I would turn it off as soon as possible. As well as likely saving the battery, you're not going to receive a phone call or text that you'll feel compelled to respond to.

You could also make (below schematic) (or, sigh, buy) a USB charger that uses throw-away batteries in order to save your butt if the inspector inspects.

enter image description here

\$\endgroup\$
  • \$\begingroup\$ My phone (SONY Xperia Z) gets warm just by booting. The OP should have stated what his phone is, really, we need this nowadays where no one can define what a phone is :) \$\endgroup\$ – abdullah kahraman Feb 26 '14 at 0:14

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