-3
$\begingroup$

Question
Many things( hairdryers etc etc ) that plug into the wall / mains for power, use a transformer inside, so are not physically connected to the mains, do they consume mains energy ?

  • I assume that more resistance ( load ) on the secondary windings of the transformer causes more resistance on the primary windings / wall-mains wiring, and thats power consumption.

  • For example - If an incandescent-light-bulb puts more resistance on the secondary windings of the transformer which causes more resistance on the primary windings / wall-mains wiring, thats power consumption

Surely this question has been asked before on this site, any links ?

Improve this question
$\endgroup$
5
  • 1
    $\begingroup$ I'm not aware of any hair dryers that use transformers. Can you cite any examples? $\endgroup$
    – Bob D
    Commented Dec 29, 2021 at 22:45
  • 3
    $\begingroup$ there is no such thing as a free lunch $\endgroup$
    – shai horowitz
    Commented Dec 29, 2021 at 22:59
  • $\begingroup$ hotel hair dryers, look to me like they just use a transformer, for safety $\endgroup$
    – infomtn
    Commented Dec 29, 2021 at 23:13
  • 1
    $\begingroup$ Surely this exact question has been asked before on this site, any links ? $\endgroup$
    – infomtn
    Commented Dec 29, 2021 at 23:14
  • $\begingroup$ Well, if you are sure this question has been asked before on this site, you should look for links on this answers... This is the purpose of this site anyway... $\endgroup$
    – ZaellixA
    Commented Dec 29, 2021 at 23:41

2 Answers 2

Reset to default
1
$\begingroup$

Used to be such devices were called "vampires." Two pointy teeth sucking up a little bit of power. Although some of them have a ground pin as well as the two ordinary pins.

Most devices with transformers have more than just transformers. They usually have rectifiers and batteries and a circuit to charge up the batttery. Some examples are the charger for your phone or other such hand-held device, the power supply for your lap top computer, the backup power for your LED alarm clock, etc. They have an isolation transformer to reduce the possibility of ground fault. Then there is a rectifier of some kind. Then a cirucuit to check out your batttery level and decide if it needs charging. Possibly one or more LEDs to indicate their current operating mode, whether they are connected to the AC power, if the battery is charging or charged, maybe some other things.

Such devices usually consume a very small amount of power when the main device is not in use. If you leave your phone charger plugged in it will be using a small amount of power all of the time. Same for your lap top charger, etc.

There was a push during they early 2000's to try to get people to switch to devices that used less standby power. The idea is that, even if they only use a few watts each, there are 10's of millions of them. Anybody with two or three hand-held devices will have similar numbers of them. Maybe more since they might have one for the office and one for home. You might find it annoying to have to carry your charger around, and they are usually not too expensive. So it might be the case that having people unplug these things when not in use would save many MW of power in a large city. It would be possible for the device to know when something was plugged in for charging and only use power when it was. However, the media chose to mock the president at the time for calling them "vampires." So this particular thing went away.

Improve this answer
$\endgroup$
0
$\begingroup$

You can look at the answer I gave to a different question, but which explains how the transformer consumes energy from the mains.

Improve this answer
$\endgroup$
7
  • $\begingroup$ so putting more of a load ( resistance ) on the secondary means more strain on the primary $\endgroup$
    – infomtn
    Commented Dec 29, 2021 at 23:19
  • $\begingroup$ @infomtn Well, rather the contrary ! Putting more load, therefore more strain, is obtained by putting a smaller resistance that allows a larger current to flow ! The voltage of the mains is constant, and also the voltage between the plugs of the secondary coil. The smaller the resistance, the larger the current in the secondary, thus the larger the "useful" (real rather than imaginary) current in the primary circuit. $\endgroup$
    – Alfred
    Commented Dec 29, 2021 at 23:31
  • $\begingroup$ What I meant was, and removing the word strain - More resistance ( load ) on the secondary windings of the transformer causes more resistance on the primary windings / wall-mains wiring, and thats power consumption. - If an incandescent-light-bulb puts more resistance on the secondary windings of the transformer which causes more resistance on the primary windings / wall-mains wiring, thats power consumption $\endgroup$
    – infomtn
    Commented Dec 30, 2021 at 1:36
  • $\begingroup$ Well, did you read my answer at he link gave you ? More load is obtained with less resistance. A powerful bulb, that gives a lot of light, has less resistance than a weak bulb that gives little light. If you do not plug *anything at all, the resistance is not zero, it is infinite ! $\endgroup$
    – Alfred
    Commented Dec 30, 2021 at 7:31
  • $\begingroup$ Apart from the fact that you understand the word "resistance" the wrong way, if you use "conductance" (inverse of resistance) instead, you are right. More conductance on the secondary causes, in some sense (see my post there), more conductance on the primary, thus increasing consumption, yes. $\endgroup$
    – Alfred
    Commented Dec 30, 2021 at 8:44