Talking about the home appliances and electronics, if it is single phase that we are using in houses and currents get to zero every half cycle, how do the home appliances (using AC) and electronics (using AC as rectified to DC) continuously function (inspite of periodically recieving 0 current)?
\$\begingroup\$
\$\endgroup\$
2
-
1\$\begingroup\$ By home appliances, do you mean things with motors, like vacum cleaners and blenders and mixers? I think we can thank Nicola Tesla for working that out. Or things with just heating elements, like toasters and toaster ovens? That's probably more Thomas Edison. \$\endgroup\$– CrossRoadsCommented Dec 27, 2018 at 13:42
-
\$\begingroup\$ I'm asking about them all. (But not the ones which work on DC, if that's the case with toaster ovens.) \$\endgroup\$– VyunCommented Dec 27, 2018 at 21:52
Add a comment
|
3 Answers
\$\begingroup\$
\$\endgroup\$
3
how do the home appliances (using AC) and electronics (using AC as rectified to DC) continuously function (inspite of periodically recieving 0 current)?
A full wave rectifier and reservoir (smoothing) capacitor are used to "hold-up" the voltage during the time that the AC is close to zero volts: -
It acts like a water tank - if the main water feed into the home gets shut down for a period of time, the reserve water tank will keep the home supplied in water until the main water feed flows again.
answered Dec 27, 2018 at 13:35
-
\$\begingroup\$ Thank you so much. (Unfortunalety, I couldn't see the gif) \$\endgroup\$– VyunCommented Dec 27, 2018 at 19:46
-
\$\begingroup\$ @Vyun that's odd - I've changed it to a png file now. \$\endgroup\$– Andy akaCommented Dec 28, 2018 at 11:09
-
\$\begingroup\$ Hey, I can't see it because it is on Imgur, it is banned here. :) \$\endgroup\$– VyunCommented Dec 29, 2018 at 19:01
\$\begingroup\$
\$\endgroup\$
7
how do the home appliances (using AC) ...
Because motors have inertia:
When you spin a motor using single-phase AC, the torque goes to zero when current goes to zero. The actual torque being transmitted from the windings to the armature is roughly sinusoidal at twice the line frequency (so, 120Hz for a 60Hz line frequency). The motor spins because the average torque is in the desired direction, but it is kept spinning through the current zeros by inertia.
and heaters have heat capacity:
The situation is the same for a heater -- the actual heat being dissipated in the heater is AC at twice the line frequency, plus some average heat. (It goes as \$(\cos \omega t)^2\$). Heaters generally have long time constants, so the temperature is averaged out.
and eyeballs have persistence of vision:
Similar to the above, it take some time for your visual receptors to respond to changes in the light striking them. Most lighting (even incandescents, to some extent) flash on and off, or at least vary in intensity, at twice the line rate. You perceive the light as steady because the light-sensitive cells in your retina time-average the light coming into them.
answered Dec 27, 2018 at 15:41
-
\$\begingroup\$ I got a little confused about the motor and inertia explanation. Can we talk according say washing machine? \$\endgroup\$– VyunCommented Dec 30, 2018 at 20:31
-
\$\begingroup\$ I think talking about a washing machine may complicate things too much. Imagine just a motor, with a pulley or something on the shaft that you can grab. If you give that pulley a kick, the motor will turn for a while after you let go. Keep kicking it, and it'll turn at a fairly constant rate. Now imagine that it's being kicked at 120Hz -- it'll be speeding up and slowing down at 120Hz, but not by very much at all. For all but the most demanding applications, it'll be going at a constant enough speed to do its job just fine. \$\endgroup\$ Commented Dec 30, 2018 at 20:34
-
\$\begingroup\$ Alright, but I am confused about the 120 Hz part. And isn't the rated current still 0? (sorry if sounds stupid-ish) \$\endgroup\$– VyunCommented Dec 30, 2018 at 20:52
-
\$\begingroup\$ I mean, I got that inertia does the work, but don't we need current (electron flow), so how is that the sine wave give us 0 rated current? \$\endgroup\$– VyunCommented Dec 30, 2018 at 23:22
-
\$\begingroup\$ I believe you mean average current -- rated current is the current that a manufacturer guarantees a device as being able to withstand. The reason that you get average torque at zero average current is because the current sloshes back and forth, and the motor is arranged so that you get torque in the same direction for either direction of current flow. \$\endgroup\$ Commented Dec 31, 2018 at 0:11
\$\begingroup\$
\$\endgroup\$
2
The home appliances and other devices that do not use rectifiers use thermal and mechanical mass to smooth operation under pulsating power. The element of an incandescent light bulb does not cool very much when the power drops to zero for a small fraction of a second, so we don't notice the lights flicker. Single phase motors vibrate and make more noise than that three-phase motors, but inertia keep the speed relatively constant. Some single-phase motor have capacitors that are continuously connected, that smooths the power somewhat. Other motors get some smoothing from the difference in resistance and inductance in two current paths inside the motor. Loops of wire, called pole shades, around a portion of the magnetic core also help to reduce vibration and smooth torque in motors and reduce vibration in electro-magnets.
-
-
\$\begingroup\$ In fluorescent lamps, electric energy converts mercury vapor to plasma. Ultraviolet energy of the plasma causes the fluorescent coating inside the tube to emit light. The mass of the plasma reduces energy energy fluctuations. The fluorescent coating has a persistence that cuts down on the visible light intensity fluctuation. For the casual observer, the light fluctuation is generally not noticeable, but some people are bothered by it. Many people can detect it in some tubes by looking at the light through moving fingers. \$\endgroup\$– user80875Commented Dec 29, 2018 at 19:19