Fans; High is next to Off on purpose

fans what would we do without them even before we figured out that air is a fluid we've been pushing it around at our whimsy and thanks to electric fans things are better than ever they keep us and our things cool by speeding up the transfer of heat energy they make your voice all funny when you talk through them and if they're old enough they are a clear and present danger to anything with fingers yes the world's a better place thanks to fans fans it's what's for dinner but the common electric fan has a depending on who you ask mildly perplexing to intensely irritating design quirk you see most fans run at multiple speeds most commonly three and nearly all of them have a speed selector switch with the order of off high medium low why are they in that order it may seem more logical for the speed to increase as after all things like volume knobs and dimmer switches tend to increase intensity the more you turn it but fans they're like the opposite why well there are two basic reasons for this the first is that this is just how it is and we're all used to it by now so why bother changing it and the second more real answer is that this protects the motor inside the fan and increases customer satisfaction by reducing the likelihood of a stall condition what's a stall condition i'm glad you asked electric motors are weird i mean they're also amazing and wonderful but they're also weird at their core it's really just some sort of magnet that we figured out how to make go all spinny then we put some sort of output shaft on the spinning magnet and we can make other things spin like paddles which push air forward and thus create a constant stream of moving air or the little dish at the bottom of your microwave or a train or a car or really anything at all but getting the magnet to spin isn't as easy as you might think obviously we can create a magnetic field that attracts something to it coils of wire make excellent electromagnets but we can't simply create a magnetic field around a magnet and get useful motion sure it will attract the magnet to itself but once it's done that well then it won't spin will it it'll just sort of move a bit and then get locked in place so we need the magnetic field itself to spin then the magnet in the core of the motor is being attracted to a continuously moving target and not a stationary one there are a whole bunch of ways we can do this and we don't even need to use magnets at all in fact we usually don't instead the spinny bit which i should probably add is called the rotor can itself be another electromagnet or if we want to get real fancy can be made of steel and copper and thanks to our friend electromagnetic induction fields from the stator induce currents in it and it becomes its own electromagnet attracted to the very fields which created its attraction in the first place and yes i'm oversimplifying so anyway to make a motor spin we need a rotor which may or may not contain a permanent magnet somewhere which is attracted to a spinning magnetic field induced by the stator which surrounds it that's the stationary electromagnetic bit now this is all well and good except for one thing household electricity doesn't spin it just pulses three-phase electricity does spin though grid scale electricity generation and transmission is done as three-phase power that's why you always see transmission lines in multiples of three we do this because thanks to math and stuff it allows us to transmit more power with a given amount of conductive material going from two wires to three allows you to transmit triple the amount of energy and that's economical right there the three phases are staggered 120 degrees apart from one another each phase on its own is just pulsing on and off but in sequence they chase each other just like the lights on a movie theater's marquee if your name is tesla or ironically ferraris no relation and you design a motor with a three-phase stator and ensure they're in the correct order you'll get natural rotation of the field thanks to the chasing effect of the phases lots of big industrial motors are built like this and so are the motors in modern electric cars with a motor on the grid it will have a fixed speed thanks to the fact that the electric grid itself has a fixed frequency but in an electric vehicle the motor is hooked up to some fancy power electronics which turn the dc power from the battery into three-phase ac power at whatever frequency and voltages you like this is called a variable frequency drive and they're not exclusive to electric vehicles and in fact in evs they're usually not called that but that's a story for another time wasn't this video about fans ah well i promise we're getting there three-phase power is generally not found in the domestic environment the closest you'll typically get in the u.s anyway is in a situation like an apartment building where the building has a three-phase supply and there might be things like elevators or large hvac units with three-phase motors in them but you'll only have two of the three phases in your personal breaker panel and large appliances like electric stoves will be put across two of them giving you 208 volts rather than the standard 240. our electrical system in the u.s is weird but that's a story for another time so anyway with only a single phase you ain't getting rotation you're just getting power unless a magnetic field which pulses on and off and changes polarity with each cycle now you can design a motor to work with that just fine the universal motor is one such design here a commutator and brushes are used to provide its own spinning field by switching the polarity of that field as the rotor which typically is itself also an electromagnet spins therefore always creating attraction in one rotational direction they even work on dc power which is why they're called universal but the carbon brushes which carry current through the commutator wear out over time they're not usually super efficient they create a lot of electrical and often audible noise there's usually some arcing going on and so they're typically only used in certain applications which don't run them for long periods at a time like power tools or food processors for something like a fan which may run for days at a time you'll want to use an induction motor these don't have brushes that wear and will generally last as long as their mechanical bearings do and you can make an induction motor work with a field that isn't rotating because the rotor itself rotates keep in mind that from a spinning motor's perspective the stator is what's spinning so the electromagnetic field itself is two even if it's not rotating from our global perspective but of course when you first turn on the fan it's not spinning and this is bad see the amount of torque an induction motor produces is a function of its slip slip describes the difference in speed between the rotating magnetic field and the spinning rotor the rotor actually has to be moving through the field produced in the stator in order for it to react against it and produce mechanical force and this means that single phase induction motors are not self-starting if both the field and the rotor are stationary no torque is produced in contrast a stopped three-phase induction motor will immediately produce torque when it receives power because the field is rotating around the stationary rotor and that means that the rotor is consequently moving through it even when it's stopped from a standstill the rotation of the field around the rotor will induce the necessary currents in it for it to start moving and will accelerate until it's almost but not quite to the same speed as the rotating field it never reaches synchronous speed with the field because then it would not be slipping at all and no torque would be produced and this is exactly the reason a single phase induction motor cannot start itself there is no slip when nothing's moving so now you've got a problem how do you get the rotor to start rotating well you cheat and create your own rotation somehow there are a ton of different ways to go about this you can use capacitors you can use shaded poles you can use a separate out of phase start winding which gives a temporary kickstart you could just give it a push the specifics don't really matter but what does matter is that you've got to generate a rotating field at least temporarily to produce enough torque to get the motor going after which point the rotor's movement relative to the stator produces the necessary currents within the rotor's windings to keep itself going and we're happy and yes i am still oversimplifying we'll talk about fleming's rules and lenses laws when you're older one of if not the simplest ways to create rotation with only one phase is with a shaded pole motor let's look at one it's a good thing i still haven't put the selection accumulator back in the jukebox because it's got one of these now this is a c frame motor these look a lot like transformers and indeed operate a lot like transformers but they're actually decepticons instead of another coil on the other side of the iron core for converting voltages it's got a squirrel cage rotor this is the bit that has currents induced in itself producing electromagnetic fields which react against the fields created in the stator which in this type of motor is the hole in this side of the core but that's not what's important right now instead it's these little bits of copper these are called shading coils and their job is to react to the flux created by the field coil over here and slightly delay its phase in these two locations electromagnetism is weird and complicated and i'm getting deeper than i need to really as always but here's the upshot these coils break the uniformity of the magnetic field produced in the stator causing a very slight delay in flux in these two locations which will in effect produce a bit of rotation in the field overall thanks to that shifting in time these shaded poles provide just enough rotation in the field to get the rotor spinning from a standstill and once it has enough speed the induction currents in the rotor become quite substantial as it moves through the bulk of the pulsing field and now it really takes off so what does this have to do with fans and their switches well everything you see the shading coil isn't really that great of a way to start a motor it works but the amount of starting torque it creates is quite small they are after all completely passive components sort of stealing a bit of the output from the stator that weak saw starting force means that this style of motor is really only suitable for loads like well a fan where the force required to start it spinning is relatively low and the load increases as rotational speed does to start it really just has to overcome static friction but once it's spinning it can really induct and that's the main reason that high is typically the first setting next to off while a shaded coil motor isn't super great at producing starting force it's cheap and entirely passive you don't need a component like a capacitor or a centrifugal switch to disable a start winding you just give it power and it goes but the amount of starting torque you get depends on what speed the fan is set to the different speed settings are usually accomplished with different windings within the motor that produce varying amounts of power and thus torque and since the shaded pole affects all the windings equally on lower speeds you get proportionally less starting torque making the first selectable speed high will ensure that the motor will at least briefly produce the maximum starting torque it can whenever it's switched on that way it's more likely to successfully start this hand chopper is nearly a hundred years old and it too has its switch in the order of off high medium low now it's probably got a shaded pole induction motor that design certainly isn't exclusive to c-frame motors but this motor is literally an antique and i would rather not take it apart to find out for sure anyway since i can just easily reach out and grab the fan blades i can demonstrate how weak the starting torque is it's surprisingly easy to hold the blade back even set to high this little fan moves a lot of air on high and that obviously produces much more force than it is exerting on my fingers right now this is seriously much weaker than you might expect now if i dared to reach in and grab the blade while it was spinning i would regret it but also i'd find it would be producing much more torque than it is right now because well that's just how induction motors work but you don't want to find a motor in this stalled condition why well because current is still flowing through the stator windings when it's stalled i mean you can hear it and in fact there's more current flowing through it right now than would be if it were spinning this fan uses about 42 watts when it's on high and right now with the motor stalled it's using more than 70. that's getting dissipated as heat in the motor's windings and before too long it could burn itself up if the fan switch were designed with low in the first position you could turn on the fan and find that the blades didn't start spinning this would not only be annoying but could hurt the motor and in a fan like this potentially start a fire now to be clear modern fans are required to tolerate being stalled for indefinite periods of time without burning your house down after all you could have left it on low had a power interruption and not get the benefit of the starting kick new fans will either have some sort of thermal protection or simply have a stator design which can't possibly pass enough current through it to get dangerously hot still though you don't want a stalled motor it's bad and also just annoying now i should add that it's not like most fans can't produce enough starting torque on low if i have this set to low and then plug it in it gets going just fine but it doesn't hurt to play it safe and fun fact i have encountered a ceiling fan on a fan control which was in fact stalled on low i had switched it on and you could hear it humming but it wasn't turning i needed to increase the speed to medium which produced enough torque to get it spinning and then i can move it back to low and it turns out that these modern electronical smart fan controls i installed because i couldn't help myself are designed to prevent that very thing from happening by always initially switching the fan too high this here is my biggest fan and i last had it set to low so when i turn it on it will go back to that same setting but for about 2 seconds the fan control gives it full beams to make sure it starts spinning and then it switches to low power pretty neat huh in fact these fan controls are themselves pretty neat just because they're bypassing the fans internal speed controls and creating its own and i should also add that ceiling fans often use capacitors as part of the speed control schema really there are just a gazillion types of electric motor out there and you can lose your mind trying to keep track of all of them and the ways we control them but that's a story for another time now it could very easily be argued that this high comes first positioning isn't really required anymore after all how frequently would a fan motor stall anyway at least one like this and you could argue it was never required anyway i mean this thing's a hundred years old and it starts fine even on low and there could very well be fans that don't use shaded pole motors in fact there are certainly exceptions out there and even fans which do in fact put low first whether that's because they use a different motor design or just because somebody did the math and realize we've been worried about a very unlikely thing is unclear but one thing is certain the fan switch isn't or at least wasn't designed like this just to annoy you there is in fact a method behind this madness when you take an already not great method of starting a motor and weaken it with lower power settings it doesn't hurt to give it a kickstart first maybe at this point it's more tradition than it is actual need as a matter of fact i've had this very fan on a separate switch for years with it always set to low and it never once stalled it clearly produces enough torque on its own to get going in any speed and it's almost a century old but the fact that these modern fan controls always kick the fan on high from a stop is i think a sure sign that putting high first is very intentional besides even if stalling weren't likely well how else are you supposed to know how many times you're gonna need to pull the ceiling fan chain to get to the speed you want [Music] there's nothing with the delivery of that line which i didn't particularly like did that say i better record that because asked might have sounded a little different the three phases are st with a motor on the grid i should silence that shouldn't i then i should remember to do that before i start moving anyway we're good we'll be back there's usually some arcing going on and so they're typically not used in most only used not used only used that's fine that's fine just go ahead and that's fine if i have this set to low and plug it in but i need to turn the quarter in for design to prevent that very thing but from happening [Music] [Applause] [Music] [Applause] you

Channel: Technology Connections

Views: 3,488,609

Keywords:

Id: hQ3GW7lVBWY

Length: 17min 48sec (1068 seconds)

Published: Tue May 12 2020

Reddit Comments

[u/Lorddragonfang]

These look a lot like transformer, and indeed operate like transformers, but are actually decepticons

I snorted into my coffee.

Also two three "that's a story for another time"'s? Are you Grey now? :P

[u/Shawnj2]

“Bb..But Alec, I’m your biggest fan!”

[u/bobnine]

On my fan off is next to high and low: https://i.imgur.com/onvLrHnr.jpg

(Yes the switch goes both ways)

[u/Jack-M-y-u-do-dis]

I have to appreciate how you can make pretty much any mundane topic sound very interesting to the point that I almost dig out my cheap desk fan just to admire the starter mechanism and to check if it starts on the lowest setting.

[u/[deleted]]

This used to bug me too and the only guess I had come up with was that it makes it very obvious when you've actually turned it off, whereas if low was next to off you might accidentally only flip to low, hear/see the speed drop, and assume it was coasting to a stop. Which makes way less sense than the actual answer lol.

[u/Blovnt]

Technical question: How do you film those smooth, closeup panning (tracking?) shots?

Is that done on a tripod, or a model trail, or...?

[u/mystica5555]

I wonder if any of these fans are meant for 100-120V - as in they could be used in Japan as well. And, if 100-120 50-60hz ranged, as it would have to be since Japan has a power system split, there *might not* be enough force to get it turning at 50hz, 100v, unless at the greatest power setting. I honestly wonder if this is a real scenario though, I've never had a fan made in Japan before to check.

[u/ThrowdoBaggins]

In the description:

" Do you have the rumblies that only links can satisfy? "

I see someone is a fan of llamas too! (Unless I'm wrong, and something else came first and LWH referenced the original?)

[u/[deleted]]

cool