Notices
Results 1 to 28 of 28

Thread: How do different sources of power determine whether or not an appliance remains running?

  1. #1 How do different sources of power determine whether or not an appliance remains running? 
    Forum Freshman
    Join Date
    Sep 2008
    Location
    The United States
    Posts
    65
    When I unplug my laptop, it remains on, but when I turn off the switch that operates the outlet which the computer is connected to, the laptop shuts off. Why do the two work differently?


    Reply With Quote  
     

  2.  
     

  3. #2  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    16,517
    That seems rather odd. I can only assume it is some sort of hardware or software bug where turning the power outlet off causes the computer to think the battery has got low. I have never come across this before though.


    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
    Reply With Quote  
     

  4. #3  
    Forum Bachelors Degree One beer's Avatar
    Join Date
    May 2013
    Posts
    442
    Hi Theresa, I guess the software has been arranged so that unplugging the mains causes your laptop to switch over to the onboard battery. That makes sense - that is what you would want if say you wanted to move your laptop away from the outlet, but continue working with it.

    Switching off the outlet though; the logic must assume that you wouldn't deliberately leave it plugged in but switched off*, so the software assumes there has been a power cut and shuts down the laptop, otherwise it would run down the onboard battery. Supposing this happened at night, you would wake up to find a flat battery, which is not what you want.

    I would guess that somewhere in the power set-up default menus, you can tell it what you want it to do in each case, but I couldn't advise you on the specifics of this. Try looking under power management, energy saving, and sleep modes perhaps.

    {*The hardware must have a way of detecting if the laptop is plugged in but the outlet is switched off. I am not sure about USA domestic power, or if your power cord uses the earth connection, but here in the UK, you could conceivably detect a plugged-in-but-switched-off condition by comparing the earth and neutral and live lines.}
    Last edited by One beer; May 2nd, 2014 at 03:51 AM.
    Reply With Quote  
     

  5. #4  
    Suspended
    Join Date
    Apr 2007
    Location
    Pennsylvania
    Posts
    8,822
    Quote Originally Posted by One beer View Post
    I am not sure about USA domestic power, or if your power cord uses the earth connection, but here in the UK, you could conceivably detect a plugged-in-but-switched-off condition by comparing the earth and neutral and live lines.}
    All the laptop power supplies I've seen just have a 2-prong plug. I don't see why there would be a difference between unplugging it from the wall and shutting off the power to the receptacle. If "unplugging" the laptop means disconnecting it at the point where the a-c adapter plugs into the computer, there might be a difference. There could be a switch that tells the computer when the a-c adapter plug is pulled out of the computer.
    Reply With Quote  
     

  6. #5  
    Forum Freshman
    Join Date
    Sep 2008
    Location
    The United States
    Posts
    65
    Thank you. This has not been a problem for me, I have just been wondering why it happens. In America earth lines are not as common. Their usage is typically limited to specific needs, but I'm sure that you could find homes here and there throughout the country that use earth lines in general.
    Reply With Quote  
     

  7. #6  
    Forum Freshman
    Join Date
    Sep 2008
    Location
    The United States
    Posts
    65
    Thank you everyone. Harold14370, I mean unplugging the computer either way: removing the cord from the computer or removing the plug from the outlet.
    Reply With Quote  
     

  8. #7  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    16,517
    Quote Originally Posted by Theresa View Post
    Thank you everyone. Harold14370, I mean unplugging the computer either way: removing the cord from the computer or removing the plug from the outlet.
    Hang on: are you saying unplugging the adaptor from the outlet has the same effect as unplugging the supply from the laptop?

    Which implies that unplugging from the outlet has a different effect than switching the supply off at the outlet? That is ... inconceivable!
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
    Reply With Quote  
     

  9. #8  
    Forum Freshman
    Join Date
    Sep 2008
    Location
    The United States
    Posts
    65
    Yes, that's precisely what I'm saying. This is why I puzzle over it.
    Reply With Quote  
     

  10. #9  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    16,517
    Reminds me of this: A Story About "Magic"
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
    Reply With Quote  
     

  11. #10  
    Forum Freshman
    Join Date
    Sep 2008
    Location
    The United States
    Posts
    65
    That story is close to mine. Are you suggesting that this happens to my laptop because of a voltage drop?
    Reply With Quote  
     

  12. #11  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    16,517
    Quote Originally Posted by Theresa View Post
    That story is close to mine. Are you suggesting that this happens to my laptop because of a voltage drop?
    Not really: I am suggesting I don't have a clue!

    Perhaps if the switch contacts are very bad, it is injecting a lot of noise into the supply which causes .... but no, the noise rejection of the PSU shouldn't let that through so .... again: no clue.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
    Reply With Quote  
     

  13. #12  
    Suspended
    Join Date
    Apr 2007
    Location
    Pennsylvania
    Posts
    8,822
    I was wrong about the 2-prong plug. I don't have a laptop, so I was thinking of phone adapters and so forth. The laptop computer adapters do have 3-prong plugs.

    Now, I'm thinking that the switch that controls the a-c receptacle just interrupts the "hot" wire, but leaves the "neutral" connected. The "neutral" bus is supposed to be connected to the ground bus back at the breaker panel in the house. But sometimes you can get a little bit of voltage on the neutral due to loads on the circuit. Or if there is a wiring problem in the home, it could be more than just a little voltage. So there could be a little bit of voltage to one side of the power supply. How that shuts off the computer, I don't know.
    Reply With Quote  
     

  14. #13  
    Forum Sophomore
    Join Date
    Dec 2013
    Location
    27°20'06.53"N 82°32'48.35"W
    Posts
    176
    My guess on this would be, unplugging the power completely switches the device straight to the battery. Switching off the outlet just kills the hot wire, potentially allowing the battery to bleed dead through the neutral wire.
    Reply With Quote  
     

  15. #14  
    Suspended
    Join Date
    Apr 2007
    Location
    Pennsylvania
    Posts
    8,822
    Somehow, I think there must be a small voltage on the receptacle when the switch is off. Then the computer is probably shutting itself off to prevent damage if the voltage is low (like a brownout) but not low enough to trigger the switchover to battery power. This could be a clue that there is something wrong in your house wiring, so if I were you, I'd take a voltmeter and see what kind of voltage is on that receptacle with the switch turned off.
    Reply With Quote  
     

  16. #15  
    Forum Sophomore
    Join Date
    Dec 2013
    Location
    27°20'06.53"N 82°32'48.35"W
    Posts
    176
    then attach a jumper from the neutral to the neutral in the outlet see if that shuts it down.
    Reply With Quote  
     

  17. #16  
    Forum Bachelors Degree One beer's Avatar
    Join Date
    May 2013
    Posts
    442
    Quote Originally Posted by Harold14370 View Post
    I was wrong about the 2-prong plug. I don't have a laptop, so I was thinking of phone adapters and so forth. The laptop computer adapters do have 3-prong plugs.

    Now, I'm thinking that the switch that controls the a-c receptacle just interrupts the "hot" wire, but leaves the "neutral" connected. The "neutral" bus is supposed to be connected to the ground bus back at the breaker panel in the house. But sometimes you can get a little bit of voltage on the neutral due to loads on the circuit........

    This was my thinking in post #3. Most AC outlets only switch the live - they leave the neutral and of course the earth (ground) connected. Easy then to build a circuit to 'look at' the voltage on the live and neutral, relative to the earth (ground), and have the laptop react differently if the live disappears, or the plug has been pulled out.

    OB

    (In the UK; the 'earth' is what you call 'ground')
    Last edited by One beer; May 5th, 2014 at 03:03 AM.
    Reply With Quote  
     

  18. #17  
    Forum Bachelors Degree One beer's Avatar
    Join Date
    May 2013
    Posts
    442
    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Theresa View Post
    Thank you everyone. Harold14370, I mean unplugging the computer either way: removing the cord from the computer or removing the plug from the outlet.
    Hang on: are you saying unplugging the adaptor from the outlet has the same effect as unplugging the supply from the laptop?

    Which implies that unplugging from the outlet has a different effect than switching the supply off at the outlet? That is ... inconceivable!

    It's not necessarily inconceivable to an electronics engineer!
    Reply With Quote  
     

  19. #18  
    KJW
    KJW is online now
    Forum Professor
    Join Date
    Jun 2013
    Posts
    1,134
    Quote Originally Posted by Theresa View Post
    When I unplug my laptop, it remains on, but when I turn off the switch that operates the outlet which the computer is connected to, the laptop shuts off. Why do the two work differently?
    Has anyone answered why rather than how?
    There are no paradoxes in relativity, just people's misunderstandings of it.
    Reply With Quote  
     

  20. #19  
    Suspended
    Join Date
    Apr 2007
    Location
    Pennsylvania
    Posts
    8,822
    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Theresa View Post
    When I unplug my laptop, it remains on, but when I turn off the switch that operates the outlet which the computer is connected to, the laptop shuts off. Why do the two work differently?
    Has anyone answered why rather than how?
    If you're asking why the computer would be designed to shut itself off on a low voltage condition, this might explain some of the reasons:
    power supply - Why are brownouts so harmful? - Super User

    A zero voltage condition is different. That's what normally happens when you unplug the laptop and take it somewhere away from the a-c power source. Then, you want it to switch to the battery spurce without shutting off.
    Reply With Quote  
     

  21. #20  
    Forum Bachelors Degree One beer's Avatar
    Join Date
    May 2013
    Posts
    442
    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Theresa View Post
    When I unplug my laptop, it remains on, but when I turn off the switch that operates the outlet which the computer is connected to, the laptop shuts off. Why do the two work differently?
    Has anyone answered why rather than how?

    Er, yeah I did. You didn't read very far into the thread ! Check out post #3

    OB
    Reply With Quote  
     

  22. #21  
    KJW
    KJW is online now
    Forum Professor
    Join Date
    Jun 2013
    Posts
    1,134
    Quote Originally Posted by One beer View Post
    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Theresa View Post
    When I unplug my laptop, it remains on, but when I turn off the switch that operates the outlet which the computer is connected to, the laptop shuts off. Why do the two work differently?
    Has anyone answered why rather than how?

    Er, yeah I did. You didn't read very far into the thread ! Check out post #3

    OB
    Yeah, I actually did see that but thought the implied design logic was flawed. For example, if there is a power failure, is this equivalent to switching off at the wall or pulling the plug?
    There are no paradoxes in relativity, just people's misunderstandings of it.
    Reply With Quote  
     

  23. #22  
    Forum Bachelors Degree One beer's Avatar
    Join Date
    May 2013
    Posts
    442
    Hi KJW. To quote myself:


    Quote Originally Posted by One beer View Post
    ..........Switching off the outlet though; the logic must assume that you wouldn't deliberately leave it plugged in but switched off*, so the software assumes there has been a power cut and shuts down the laptop, otherwise it would run down the onboard battery. Supposing this happened at night, you would wake up to find a flat battery, which is not what you want.......

    ...........{*The hardware must have a way of detecting if the laptop is plugged in but the outlet is switched off. I am not sure about USA domestic power, or if your power cord uses the earth connection, but here in the UK, you could conceivably detect a plugged-in-but-switched-off condition by comparing the earth and neutral and live lines.}

    So it could conceivably be arranged that the logic could detect that the lead is still plugged in, but that there is no live voltage present. This would be the case if the outlet was switched off OR if there had been a power failure.

    OB
    Reply With Quote  
     

  24. #23  
    KJW
    KJW is online now
    Forum Professor
    Join Date
    Jun 2013
    Posts
    1,134
    It seems odd to me that a laptop would be designed to respond differently to the different ways of losing mains power, considering that I would expect the laptop to continue operating under battery power regardless of how the mains power was lost, especially in the case of a power failure. It especially seems odd to me that in order to continue running the laptop under battery power after running from mains power, the plug has to be disconnected while the mains power is still on.
    There are no paradoxes in relativity, just people's misunderstandings of it.
    Reply With Quote  
     

  25. #24  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    16,517
    Latops and their power supplies do "communicate" at a basic level. For example, plugging a PSU intended for a different model laptop can pop up a warning message. So I can imagine that if the PSU thinks there is something seriously wrong with the mains supply, that the system might think it is safer to shut down.

    I read a story about someone who had problems charging his laptop when travelling. The PSU was providing power but was unable to charge the battery. He tried all sorts things and eventually found it was the cord from the outlet to the PSU that was the problem. Which sounds similar to this (i.e. no rational reason why the power cord should stop it working but ...)

    These things are never as simple as you imagine with modern technology. A while ago I had to replace the battery in a laptop. It came with a software update CD with very serious warnings about not replacing the battery with installing the update. For an "identical" battery.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
    Reply With Quote  
     

  26. #25  
    Forum Freshman
    Join Date
    Sep 2008
    Location
    The United States
    Posts
    65
    Thank you everyone, for the helpful background. KJW, in electrical issues, 'why' and 'how' tend to overlap each other. The others have addressed my issue sufficiently, but I appreciate you defending my question nonetheless.
    Reply With Quote  
     

  27. #26  
    Forum Professor
    Join Date
    Aug 2013
    Location
    San Diego
    Posts
    1,970
    Quote Originally Posted by Strange View Post
    Latops and their power supplies do "communicate" at a basic level. For example, plugging a PSU intended for a different model laptop can pop up a warning message. So I can imagine that if the PSU thinks there is something seriously wrong with the mains supply, that the system might think it is safer to shut down.
    Agreed, but there is no method that the laptop can use to determine the "state" of the supply other than its output voltage and available current. The only other communication I know of is Dell's ID pin, which is used to validate that the charger is really a Dell charger. It doesn't communicate anything else other than ID, and the only action the laptop takes is to refuse to charge the battery.
    Reply With Quote  
     

  28. #27  
    Forum Bachelors Degree One beer's Avatar
    Join Date
    May 2013
    Posts
    442
    This 'feature' certainly seems unusual, and very advanced if true, but I can think of ways it could be done.

    As I've said, it might be possible in the default menus to specify how the laptop reacts when there is a domestic power cut or it's just switched off at the outlet, because some users might want it to automatically switch over to the onboard battery, other users might not.

    If you ever find out, please let us know.

    OB
    Reply With Quote  
     

  29. #28  
    Suspended
    Join Date
    Mar 2014
    Posts
    1,041
    Just change the power options settings.
    Reply With Quote  
     

Similar Threads

  1. New power sources planned to replace nuclear plant
    By Harold14370 in forum Environmental Issues
    Replies: 35
    Last Post: April 3rd, 2014, 06:25 PM
  2. Diseases through monkey remains?
    By lucky13 in forum General Discussion
    Replies: 1
    Last Post: December 22nd, 2013, 08:46 AM
  3. Refurbishing legacy equipments by modern power sources(!!NEW!!)
    By Lawrenzo in forum Electrical and Electronics
    Replies: 1
    Last Post: November 12th, 2012, 09:46 AM
  4. Possible human remains
    By WVBIG in forum Criminology and Forensic Science
    Replies: 3
    Last Post: May 20th, 2009, 03:55 PM
  5. Herbst appliance
    By MariƩ in forum Health & Medicine
    Replies: 0
    Last Post: August 20th, 2006, 03:00 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •