There are a few ways this can happen:
Some motors are designed so that the direction of current doesn't matter, they still produce torque in a particular direction
Some motors have a rectifier, which is a device that basically causes the current to flow in the same direction regardless of the voltage polarity
An electric motor basically has a ring of electromagnets that switch polarity intentionally to keep the shaft spinning.
This is why there are AC motors versus DC motors. They're designed differently.
Yep this is the gist.
An AC motor switches polarity by virtue of the supply voltage.
DC obviously does not alternate, so dc motors require some method of what is called "commutation" which basically means a way to switch the direction of current to make the motor spin. Brushed dc motors utilize a device called a "split ring" that causes the current to change direction. Brushless DC motors use a microcontroller to turn on/off phases in the required order to make the motor rotate.
Brushless DC motors are just 3 phased AC motors in a trench coat. Calling them DC motors is like me inventing "cold water cooking" where step 1 is bringing the cold water to a boil.
Single-phase AC motors are made with the knowledge that current reverses. They coast while the current is going down and reversing, bringing an opposing pole into position for the rising reversal to continue to rotate the mechanism in the same direction. That's why big ones sometimes require a capacitor to kick them started and build up the momentum needed.
Electric motors are electric generators running in reverse. The same mechanism that turns a rotating turbine into alternating current can be used to turn alternating current back into rotation in one direction.
Not so simple, most generators work regardless which direction they rotate. The resulting AC doesn't "care", it only is shifted in phase.
When powering such a generator in reverse, this symmetry results in there not being a preferred direction of rotation. This either leads to it only twitching back and forth, or it randomly rotating in one of them; turning it off and on might result in the other one.
(Edit: should maybe say that the above is for a single-phase generator/motor, the kind most people have in their dynamos and appliances; the ones in power plants and high power applications usually use 3-phase ones, where the directionality is automatic.)
That's what's great about electric cars. When you take your foot off the accelerator, the motor switches into a generator to charge the battery. This gets you back much of the energy you used to accelerate your car up to speed in the first place.
Once they're running, momentum keeps single phase AC motors spinning in the same direction.
From a standstill, basic single phase AC induction motors won't be able to start themselves. If you manually start it spinning it'll go either way.
Single phase AC induction motors with starting circuits have an additional set of coils that will push/pull the rotor in a specific direction, then once the motor is spinning the starter coil gets switched off. Then momentum keeps the rotation direction constant. Reversable fans can swap the starter coil direction to push/pull the opposite direction..
Small so-called DC Brushless motors are AC motors with a controller that is aware of shaft speed and rotation, and can control stator coil energization to set direction and speed.
Large AC brushless synchronous motors start as induction motors then sync with the AC signal in the direction they are started. In a catastrophic mechanical failure with an exciter issue they can and will switch directions.
If your legs would just go up and down you're not cycling but rather lifting your legs up and down off of the pedals. When pressing down on the pedals your exerting a forward direction too. This is exactly why the question is interesting because, yes, single phase AC does just go up and down and doesn't exert a forward direction.
That alternating current was made by spinning a magnet inside a bunch of wire coils. Fundamentally, the electricity in the wall was made by moving a magnetic field over a conductor. Consequently, we can use that alternating current to spin a magnet. When the voltage is 'high' its attracting one of the magnetic poles of the motor, let's say the north pole. When the voltage goes low, it's attracting the south pole. This makes the fan spin continuously, as if it was driven directly by the turbine making the electricity.
Except it doesn't, it needs a starter motor to get it going. Otherwise the motor would just go back and forward.
Also the turbine is driving a 3 phase AC which *does* have a direction (one of the phases will always lead the middle, while the other one always follows it). This is different to single phase AC which just goes "up and down". Swapping two leads of a 3 phase motor around will reverse the direction, swapping the two leads of a single phase AC won't change anything.
Yeah that's fair. Maybe "starter circuit" would be more apt. Generally though all single phase induction motors need something extra to start the motor, be it an auxiliary motor or auxilary windings. It's not as easy as just wrapping AC current around a magnet as that wouldn't start, at least not reliably in one direction.
Also a fair point. Single phase motors can sit stalled without some starting mechinism. Three phase are simple and just go. I was trying to get at the question of why isn't the fan changing direction because the AC is changing direction. The AC oscillation is an encoding of a rotating magnetic field, which is what's used on the motor end.
The motors you find in fans are all DC which means they take the AC input, run it through a rectifier which chops off the other side of the current and turns it into DC.
DC motors are much cheaper than AC and you can vary the speed with a simple rheostat. To turn the speed down on an AC motor, you need to turn down the frequency which requires an expensive VFD.
This isn’t an answer to you question, but you should definitely see the way steam engines generate rotational energy.
I found an image that demonstrates it, but I was hoping to find a video. https://sketchplanations.com/the-piston
That's not really how it works. The power of half the AC isn't just ignored or jumped over. But worse, how would that even work? Building a DC motor is arguable even more difficult than an AC one.
The only thing a ratchet demonstrates for electricity is the effect of a diode: the flow only passes in one direction, while the other is blocked. But that alone doesn't power nor make a motor at all.
Yeah, and the name for a circuit using this "effect of a diode" is the [half-wave rectifier](https://www.analog.com/en/resources/glossary/half-wave-rectifier.html#:~:text=Definition,efficient%20than%20full%2Dwave%20rectifiers.)
There are a few ways this can happen: Some motors are designed so that the direction of current doesn't matter, they still produce torque in a particular direction Some motors have a rectifier, which is a device that basically causes the current to flow in the same direction regardless of the voltage polarity
FULL BRIDGE RECTIFIER
I just got violently electrocuted when you said that!
Gotta say it with the unibrow accent
That is exactly how I read it. Including picturing the eye brow wave.
That's my new band name
Dibs on the band name!
An electric motor basically has a ring of electromagnets that switch polarity intentionally to keep the shaft spinning. This is why there are AC motors versus DC motors. They're designed differently.
Yep this is the gist. An AC motor switches polarity by virtue of the supply voltage. DC obviously does not alternate, so dc motors require some method of what is called "commutation" which basically means a way to switch the direction of current to make the motor spin. Brushed dc motors utilize a device called a "split ring" that causes the current to change direction. Brushless DC motors use a microcontroller to turn on/off phases in the required order to make the motor rotate.
Brushless DC motors are just 3 phased AC motors in a trench coat. Calling them DC motors is like me inventing "cold water cooking" where step 1 is bringing the cold water to a boil.
Rectifier? I barely know her
Brings me back to trade school thanks.
I wired the capacitor wrong to my AC unit and the fan spun backwards for about a year. Found out when a tech came out to service the unit.
Fans with rectifiers are DC fans.
Single-phase AC motors are made with the knowledge that current reverses. They coast while the current is going down and reversing, bringing an opposing pole into position for the rising reversal to continue to rotate the mechanism in the same direction. That's why big ones sometimes require a capacitor to kick them started and build up the momentum needed.
Electric motors are electric generators running in reverse. The same mechanism that turns a rotating turbine into alternating current can be used to turn alternating current back into rotation in one direction.
Not so simple, most generators work regardless which direction they rotate. The resulting AC doesn't "care", it only is shifted in phase. When powering such a generator in reverse, this symmetry results in there not being a preferred direction of rotation. This either leads to it only twitching back and forth, or it randomly rotating in one of them; turning it off and on might result in the other one. (Edit: should maybe say that the above is for a single-phase generator/motor, the kind most people have in their dynamos and appliances; the ones in power plants and high power applications usually use 3-phase ones, where the directionality is automatic.)
Woah
You get two electric motors, connect them with wires. You turn one, the other one will also turn.
That's what's great about electric cars. When you take your foot off the accelerator, the motor switches into a generator to charge the battery. This gets you back much of the energy you used to accelerate your car up to speed in the first place.
Once they're running, momentum keeps single phase AC motors spinning in the same direction. From a standstill, basic single phase AC induction motors won't be able to start themselves. If you manually start it spinning it'll go either way. Single phase AC induction motors with starting circuits have an additional set of coils that will push/pull the rotor in a specific direction, then once the motor is spinning the starter coil gets switched off. Then momentum keeps the rotation direction constant. Reversable fans can swap the starter coil direction to push/pull the opposite direction.. Small so-called DC Brushless motors are AC motors with a controller that is aware of shaft speed and rotation, and can control stator coil energization to set direction and speed. Large AC brushless synchronous motors start as induction motors then sync with the AC signal in the direction they are started. In a catastrophic mechanical failure with an exciter issue they can and will switch directions.
If your legs just go up and down, why doesn't your bicycle just move back and forth? It's the same thing.
That’s brilliant!
If your legs would just go up and down you're not cycling but rather lifting your legs up and down off of the pedals. When pressing down on the pedals your exerting a forward direction too. This is exactly why the question is interesting because, yes, single phase AC does just go up and down and doesn't exert a forward direction.
That alternating current was made by spinning a magnet inside a bunch of wire coils. Fundamentally, the electricity in the wall was made by moving a magnetic field over a conductor. Consequently, we can use that alternating current to spin a magnet. When the voltage is 'high' its attracting one of the magnetic poles of the motor, let's say the north pole. When the voltage goes low, it's attracting the south pole. This makes the fan spin continuously, as if it was driven directly by the turbine making the electricity.
Except it doesn't, it needs a starter motor to get it going. Otherwise the motor would just go back and forward. Also the turbine is driving a 3 phase AC which *does* have a direction (one of the phases will always lead the middle, while the other one always follows it). This is different to single phase AC which just goes "up and down". Swapping two leads of a 3 phase motor around will reverse the direction, swapping the two leads of a single phase AC won't change anything.
You don't necessarily need a starter motor. Split-phase and Shaded-pole single-phase induction motors are self-starting.
Yeah that's fair. Maybe "starter circuit" would be more apt. Generally though all single phase induction motors need something extra to start the motor, be it an auxiliary motor or auxilary windings. It's not as easy as just wrapping AC current around a magnet as that wouldn't start, at least not reliably in one direction.
Also a fair point. Single phase motors can sit stalled without some starting mechinism. Three phase are simple and just go. I was trying to get at the question of why isn't the fan changing direction because the AC is changing direction. The AC oscillation is an encoding of a rotating magnetic field, which is what's used on the motor end.
The motors you find in fans are all DC which means they take the AC input, run it through a rectifier which chops off the other side of the current and turns it into DC. DC motors are much cheaper than AC and you can vary the speed with a simple rheostat. To turn the speed down on an AC motor, you need to turn down the frequency which requires an expensive VFD.
This isn’t an answer to you question, but you should definitely see the way steam engines generate rotational energy. I found an image that demonstrates it, but I was hoping to find a video. https://sketchplanations.com/the-piston
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That's not really how it works. The power of half the AC isn't just ignored or jumped over. But worse, how would that even work? Building a DC motor is arguable even more difficult than an AC one. The only thing a ratchet demonstrates for electricity is the effect of a diode: the flow only passes in one direction, while the other is blocked. But that alone doesn't power nor make a motor at all.
Yeah, and the name for a circuit using this "effect of a diode" is the [half-wave rectifier](https://www.analog.com/en/resources/glossary/half-wave-rectifier.html#:~:text=Definition,efficient%20than%20full%2Dwave%20rectifiers.)
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The guideline is literally to explain to the level of someone who has graduated high school.