Home electricity.

Discussion in 'General Electronics Chat' started by therock003, Jan 10, 2009.

  1. therock003

    Thread Starter Member

    Jun 25, 2008
    13
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    Sorry for the weak topic tile, but i would like to ask some basic question concerning matters of home electricity.

    Guys what does it happen exactly when you plug an electronic appliance into the wall's socket?

    -If you have something plugged in but it is idle (lets say a hair drier that is switched off) does it still consume electricity?

    -And most importantly when you use a charger to charge a device, does it continue charging even when the battery as at max capacity?

    -What happens if there's nothing at the end of the charger or power supplier?

    -Why is the input voltage that much greater than the output? Considering you have a 100-240V input on a mobile charger and the output is only 3-6v. Where so the rest of the input go? Does it ecycle? Does the 240v has a potential of givning 240v output maximum(Theoretically asking, cause i dont even know what could use 240v as input)?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A lot happen but in simple words the mains voltage causes current to flow through the device and the device works.

    No, it doesn't unless the device is power by a transformer and the switch is after the transformer (on the secondary). In this case the primary of the transformer consumes a little amount of energy.

    This depends on the charger circuit itself. There are many types of chargers. Mobile phone chargers stop charging when the battery is full.

    A little energy is consumed inside the device if the switch is on.

    Because the voltage of battery of a mobile is lies in this region (3-6V). The 240V AC is stepped down with a transformer or with a switched mode technique, converted to DC and then fet to the mobile. Also, 240V is the rms value of the mains voltage, the maximum value is about 339V. Don't try to use the mains voltage directly on electronic devices or what ever if you don't know what are you doing. It can be lethal.
     
  3. therock003

    Thread Starter Member

    Jun 25, 2008
    13
    0
    Thank you for your reply. No i don't have any intention to do anything hazardous, i'm only gathering information so i can understand the electricity consumption of a household and the main laws that apply.

    -So how do mobile chargers (and possibly other kind of chargers) get notified of when a battery is full?

    -Also do you mean that such chargers contain step-down transformers inside their circuitry so that they can transform mains voltage to the necessary output voltage? I mean so far I've heard of transformers doing upconversions and downconversions for use of power suppliers on different countries. But are you telling me that each device on its own, contains a step down transform in order to downconvert mains voltage to the voltage it needs to feed the device? So in this case the 240 rms input gets downconverted to 3.5v right?Am i gettting this so far?

    -BTW is the input constant or is that rms too? So for example if you need to calculate the wattage that a device consumes, is tha voltage and the current and therefore the wattage constant or do they differ ever so slightly?
     
  4. floomdoggle

    Senior Member

    Sep 1, 2008
    217
    2
    Hey Rock,
    From your post, I gather you are trying to save money on "ghost" power. The power used when devices are not in use, but on standby. Unless it has a transformer, as per Mik, off is off. Only potential is there.
    However, many electronic devices that use electricity still use "ghost" power. Think of all the clocks and timers on your DVD, microwave, etc...
    If not, look up potential.
    Dan
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Here you have to know about electronics. A circuit senses the voltage across the battery and when it reaches a value it stops charging.

    Mobile chargers don't contain transformers (they are small as you can see). They convert the mains voltage directly to DC and then chop it to reduce its amplitude. If you want to know more search in google about DC chopper circuits.

    The main's voltage is supposed to be constant. However, in practise it varies due to various reasons. To calculate the power a device consumes measure the voltage across it and the current it draws and multiply them (P=V*I).
     
  6. therock003

    Thread Starter Member

    Jun 25, 2008
    13
    0
    Well honestly i do try to save some money since every day electronic usage has become gruesome and the electricbill is becoming worse and worse. But it is the first i hear of the so called "ghost power". Now that you mentioned it i will do some research though and find out more about it.

    Moreover i just want to study more thoroughly the concept of electricity.

    Does it stop charging completely thought or does it send short packets of electricity if it senses loss of voltage, let's say in the case you forget it plugged.

    For example you leave your mobile phone charging overnight. After 2-3 hours the charge is fully complete, but what happens during the next hours till you wake up? Will the capacity deteriorate (drop) or will the charger keep feeding it current when it detects that it dropped less than full, and how often does that occur?

    Well yes, they are small indeed but still they have some kind of a "Head" instead of just the plug so i thought that something more must have gone on inside there.

    Well one of the few things i know are the ohms and joules laws so i do know this formulae, but what makes m suspicious is the constant property of current and voltage. What devices are used in order to measure such values so i can compare them with the ones indicated in order to see if they stand correct?
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I've never heard the term myself, the concept is simple. Many devices take a trickle of power to maintain things like clocks, programing, whatnot. It amounts to less than a $1 per year most cases. We had a similar thread long ago where we calculated the cost of leaving a LCD monitor on full time to around $7.50 a year or so. What the gadget does is everything. A refrigerator, for example, has to run full time.

    *************

    Found it, wasn't the monitor, it was the power off LED...

    http://forum.allaboutcircuits.com/showthread.php?t=10717&highlight=watts
     
    Last edited: Jan 11, 2009
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The charger keeps the battery always charged.

    You can use a multimeter to measure the current flowing into the device and the voltage across it. Then multiply the current by the voltage to get the power dissipated by the device. Also, you can buy a watt meter which plugs into the wall socket and you plug the device in the watt meter.
     
  9. duffy

    Active Member

    Dec 29, 2008
    44
    0
    Yeah, buy a "Kill-A-Watt" for twenty bucks. Most of this "ghost power" crap is overblown.
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    For the last 75 years or so electrical appliances sold in the UK have had to carry a 'rating plate'. Nowadays this is usually a stick on label not a plate.

    The plate or label must display the average power consumed by the device and the working voltage. Respectable manufacturers expand by adding further information such as 'standby power'.

    A medium sized television might be rated at 225 watts active and 7 watts standby.

    Over one year 7 watts works out at 7*24*365/1000 kilowatt hours = 61 Kw-hrs or units.

    These days a unit costs arount £0.13 so the cost per year of that television on standby is £61 * 0.13 = £8

    A modern large screen telly can easily be up to treble this.
     
  11. duffy

    Active Member

    Dec 29, 2008
    44
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    Yeah? You actually measured those trebles? I've made several measurements. The big stuff pulled no more on standby than the small stuff. Didn't find anything pulling more than a couple of watts.
     
    Last edited: Jan 11, 2009
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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  13. duffy

    Active Member

    Dec 29, 2008
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    Perhaps you should make measurements instead of perpetuating myths.
     
  14. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I should be interested to see your mathematical proof that my calculations are incorrect.

    In fact I should be interested to see any calculations at all from you, since you have yet to publish any.

    Perhaps you could post a photograph of the rating plate from a 400w -600w plasma screen, showing the standby power.

    However this site posts many measurements, the most revealing being 197 watts for a Play Station 3 on standby!

    http://www.avforums.com/forums/plas...out-plasma-screen-electrical-consumption.html
     
    Last edited: Jan 12, 2009
  15. italo

    New Member

    Nov 20, 2005
    205
    1
    WHAT happens is totaly dependent on the loads dryer. oven whatever you plug is is a load of some kind. To get to low voltage for chargers ect. we need a transformer which as the nomecleture inply it transform to one level to another level of voltage . It can be higher or lower as needed. For a normal house everything that plugs in is a load meaning it is not a source of power but a sink of power.
     
  16. italo

    New Member

    Nov 20, 2005
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