does a cell phone charger consume power when phone is not connected?

Discussion in 'General Electronics Chat' started by PG1995, Sep 21, 2011.

  1. PG1995

    Thread Starter Active Member

    Apr 15, 2011
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    Hi :)

    Two stupid people were having a discussion, by the way one was me, that whether the cell phone charger consumes power or not when it is not connected to the phone (assuming it is connected to the mains). I was of the opinion that it does consume power. It outputs DC current which can be thought of as a continuous push of electrons. Think of someone pushing a wall. Although, in physics terms, no work is being done, 'biological' energy is still being invested. Likewise, electrons at the tip of charger's pin which goes into the cell phone are continuously pushed but they can't flow outward. It's just like a water pump which is continuously pumping water but the pumped water is not used for any useful activity. I have noticed that charger, connected to the mains, gets hot even when no cell phone is connected. Please let me know if I'm correct. Thank you.

    Regards
    PG
     
  2. Crispin

    Member

    Jul 4, 2011
    88
    2
    It would be consuming power but very little which would be due to losses, not nearly what you would see when it is charging.


    Not sure on your explanation, someone cleverer than I will be along and give a proper explination :D
     
  3. colinb

    Active Member

    Jun 15, 2011
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    You have some right ideas and wrong ideas here. Yes, you can think of current flow as electrons being pushed through the wire, or water in a pipe. But if no electrons are flowing, then the current (I, in amps) is zero. If current is zero, then power P=IE is zero as well. Therefore in order to consume power (and thus energy), current must flow.

    That is a good observation. The increased temperature of the charger means something is converting electrical energy to thermal energy, thus consuming electrical power.

    The cell phone charger is an offline ac-dc switching regulator, which should consume much less power when nothing is being charged, but there is still going to be some quiescent current draw, the standby power.
     
  4. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Unless your chgr has an onboard "off " switch, it will continue to draw thru the primary of its T1. whether hooked to the phone or no.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Most chargers have a light (LED), so there is some power used for it too. Not much, but still...
     
  6. colinb

    Active Member

    Jun 15, 2011
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    That would be so on a linear power supply, but is not necessarily true for offline ac/dc converters, depending on the specific topology. The transformer winding may not be connected directly to line power, but switched on and off by the control electronics as needed.
     
  7. VoodooMojo

    Active Member

    Nov 28, 2009
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  8. colinb

    Active Member

    Jun 15, 2011
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    Has anyone considered that these “energy usage monitoring devices” such as the popular Kill A Watt use power themselves? How much power is wasted by the measurement device?
     
  9. tom66

    Senior Member

    May 9, 2009
    2,613
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    Power Integrations make an offline AC-DC converter controller IC which (in combination with all other components) uses only 5mW, which is practically zero power. It would take 1.75 years to cost a single penny of electricity with that where I live.
     
  10. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    so, plug a Kill A Watt into a Kill A Watt so we could measure the power consumption of the power consumption metering device :D....
     
    VoodooMojo likes this.
  11. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Well, the only way to be sure is measure one. However, I've taken mine apart and from inspecting the construction, I would be quite surprised if the whole thing dissipated more than a watt. See attached picture.

    I've had mine for about 6 years and paid $20 for it on Amazon (delivered too). It's a quite useful tool to own, especially if you make electrical measurements. I use mine sometimes to power my Variac when I'm testing AC things and it's nice to be able to see the power, power factor, and current being consumed.
     
  12. BMorse

    Senior Member

    Sep 26, 2009
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    Adafruit industries has a conversion kit for the kill A Watt so that you can tweet about your power savings with the wireless "Tweet A Watt"....
     
  13. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
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    We've all probably seen that commercial where the girl denies that her cell phone charger is plugged into the wall. The commercial is trying to make us more energy conscious.

    Anyway, I decided to see just how much one of those modern cell phone chargers was consuming and plugged it into a Watt-o-meter. It would end up costing $1.00 - $1.50 a year if left plugged in.
     
  14. Smoke_Maker

    Active Member

    Sep 24, 2007
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    Been in that discussion myself, the conclusion we came to is YES. If it get warm like you said then it is consuming energy. We also came up with some other interesting observations,

    1. How accurate is the power company meters? and at what what will it see current flow.

    2. We don't pay for BAD power factor just the current flowing through the meter.

    3. Electrons have mass.

    This is my understanding at this point in my education. :)
     
  15. CraigHB

    Member

    Aug 12, 2011
    127
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    Standy power consumption for consumer devices can be a big concern. Most electronic devices these days do not actually turn off, but go into a standy mode when you hit the power button. For some of them, standby power consumption is pretty liberal, just bad engineering in my opinion.

    People have been saying to use power strips for your devices and turn them off via the power strip when not using them. I do that whenever I can, but some devices do wierd things (like failing to retain user settings) when turning them on and off that way.

    The solution is that enginners need to build consumer devices with very low standby power consumption. With modern electronics, it's really not hard to do.

    The same can be said for things like cell phone chargers. They can be designed for minimal power consumption when idle. The fact they get warm indicates they still consume some power when not doing anything.
     
  16. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
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    My Kill-A-Watt draws 21.66 mA from a 120 VAC line. The real power is .215 watts. The apparent power is 2.656 VA with a power factor of about .08

    The charger for my LG cell phone draws (with the phone not connected) 1.72 mA from a 120 VAC line. The real power is .086 watts with a .41 power factor; that's impressive!

    With the phone charging, it draws 1.48 watts and the power factor goes up to .86
     
  17. colinb

    Active Member

    Jun 15, 2011
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    Well, 215 mW may not sound like a lot, but with all the commotion about standby power consumption of household electronics (aka vampire power aka phantom power), an extra 215 mW continuous for your energy measurement device seems like a lot to me. Once again, poor engineering. All it needs is a tiny MCU (less than 30 mW) and an ADC (a few mW) as well as a segmented LCD driver (less than 1 mW).
     
  18. VoodooMojo

    Active Member

    Nov 28, 2009
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    sounds like a profitable venture for an entrepreneurial spirit....maybe another opportunity for loosewire to exploit?
     
  19. colinb

    Active Member

    Jun 15, 2011
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  20. colinb

    Active Member

    Jun 15, 2011
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    Have you analyzed the circuit board? I am curious about how it works. If you have a chance to post high resolution close-up photos of the circuit board (ideally both sides), we could draw some conclusions about the device's power supply methods, and I am curious what kind of microcontroller is used and what type of ADC or dedicated power measurement IC is used, if any.
     
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