The 60 Hz grid is why we have HDDs spinning at 7200 RPM. Because of 60 Hz, it was simpler to design AC electrical motors to spin at 3600 RPM or 7200 RPM (1x or 2x factor). When DC motors were made, for compatibility with AC motors, they often spun at the same speed (3600 or 7200 RPM) even though there was no electrical reason to do so. When HDD manufacturers selected DC motors for their drives, they picked 3600 RPM models as they were very common. Then, for performance reasons, in the 1990s, 7200 became more common than 3600 eventually.
Maybe this was obvious, but I will spell it out for slow people like myself:
60 Hz = 60 cycles per second = 3600 cycles per minute
A simple 2 pole AC motor spins 1 rotation per cycle, so 3600 RPM. AC is a sine wave cycle of current. Current flows one way to attract it to one pole, the current flows the other way to attract it to the other pole.
For a big mainframe disc drive, it sounds like the obvious choice. Why they stuck with it after switching to DC, who knows. Maybe they didn't want to redesign the controller circuits.
I find it most annoying when moving your eyes. Anyone will notice the flicker if their eyes aren't stationary since then each "flick" will end up on a different part of the retina. So, instead of a normal motion blur you see a dashed line which is hard to ignore.
What's the cause? Alternators run at very high frequencies with good rectifiers, so I'm guessing the flicker is introduced by PWM dimming, but why would that be a low enough frequency to bother people?
I'm sensitive to flicker myself, but only on the more extreme half of the spectrum. For example, half rectified LED drivers on 60 Hz AC drive me nuts, but full rectified (120 Hz) I very rarely notice. I don't notice any problem with car tail lights, except in the case of a video camera where the flicker and the frame rate are beating. The beating tends to be on the order of 10 Hz (just shooting from the hip here) so if frame rates are 30/60/120 then I guess the PWM frequency is something like 110 or 130 Hz?
Yes indeed, but the German-Swiss-Austrian 16.7 Hz system is many orders of magnitude bigger than the Southend Electrification! The path dependency is much more understandable in that case.
Large parts of the NE corridor train line(DC to NY and New Haven to Boston) still operates at 25hz and has its own power system and generators because of it.
> Stillwell recalled distinctly the final meeting of the committee at which this recommendation was agreed upon. They were disposed to adopt 50 cycles, but American arc light carbons then available commercially did not give good results at that frequency and this was an important feature which led them to go higher. In response to a question from Stillwell as to the best frequencies for motors, Scott said, in effect, “Anything
between 6,000 alternations (50 Hz) and 8,000 alternations per minute (67 Hz).” Stillwell then suggested 60 cycles per second, and this was agreed to.
If we could magically pick a frequency and voltage for electrical systems to use (without sunk costs), what would it be?
What's the most efficient for modern grids and electronics?
Would it be a higher frequency (1000hz)?
I know higher voltage systems are more dangerous but make it easier to transmit more power (toaster ovens in the EU are better because of 240v). I'm curious if we would pick a different voltage too and just have better/safer outlets.
> If we could magically pick a frequency and voltage for electrical systems to use (without sunk costs), what would it be?
> What's the most efficient for modern grids and electronics?
I do not think it is possible to answer the question as posed. It is a trade-off. Higher frequencies permit smaller transformers in distribution equipment and smaller filtering capacitors at point of use. On the other hand, the skin effect increases transmission losses at higher frequencies.
If you want minimum losses in the transmission network, especially a very long distance transmission network, then low frequencies are better.
If you want to minimize the size and cost of transformers, higher frequencies might be better. Maybe the generator is close to the user so transmission loss is less important.
If you want smaller end-user devices, high frequency or DC might be more desirable.
You have to define some kind of objective function before the question becomes answerable.
I think the question could be constrained as "what frequency uses the minimum amount of copper to remake the electrical distribution network that exists today?"
This would be a pretty good approximation of the ratio of transmission lines to transformers.
Wouldn't it make sense to do both then? Low frequency or even dc long distance transmission that gets converted to standard frequency closer to the user?
You could push it to 100hz, MAYBE 200hz at most. Higher than that, transmission losses due to skin effect would make it a bad idea. Also generator motors would require too high RPM.
240v is a good middle ground for safety and power.
Higher Voltage: Less conductor material needed, smaller wires. But need more spacing inside electronics to prevent arcing, and it becomes more zappy to humans. Also becomes harder to work with over 1kV as silicon kind of hits a limit around there.
Higher Frequency: Things that use electricity can be made smaller. But losses in long transmission become much worse.
DC instead of AC: Lower losses in transmission, don't need as much spacing inside electronics for arcing. But harder and less efficient to convert to different voltages.
The skin effect causes AC current density J in a conductor decreases exponentially from its value at the surface J_S according to the depth d from the surface. The depth decreases as the square root of frequency. This means that the effective power a wire can carry decreases with increasing AC frequency.
Impulse Labs has built an induction range that has super high power; their trick is that they have a battery that they recharge from the mains. Might be expensive but the same technique could work for a toaster (or for a water kettle) to basically keep a whole bunch of energy in reserve and deliver it when needed.
That's a great idea - I wonder if electric kettles would be more popular in the US if they worked as quickly as they do on 240V? How large a volume of battery would one need to accomplish this, I wonder?
As an Aussie, it’s weird to think that induction and other cooking appliances are so slow or expansive. We have a $200 AUD induction stovetop from Aldi that draws up to 7.2kw across 4 pans
> Induction motors turn at a speed proportional to frequency, so a high frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft (and ships). Transformers can be made smaller because the magnetic core can be much smaller for the same power level. Thus, a United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power.
> So why not use 400 Hz everywhere? Such high frequencies cannot be economically transmitted long distances, since the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.
Very much true. A higher switching frequency means that a smaller transformer is needed for a given power load.
In reference to consumer power supplies, only reason why GaN power bricks are any smaller than normal is because GaN can be run at a much higher frequency, needing smaller inductor/transformer and thus shrinking the overall volume.
Transformers and inductors are often the largest (and heaviest!) part of any circuit as they cannot be shrunk without significantly changing their behavior.
Ref: Page 655, The Art of Electronics 3rd edition and Page 253, The Art of Electronics the X chapters by Paul Horowitz and Winfield Hill.
Correct. You can get the same power with half the voltage by doubling the current.
The trouble is the wires. A given wire gauge is limited in its ability to conduct current, not power. So if you double to the current, you'll need to have roughly twice as much copper in your walls, in your fuse panel, in your appliance, etc.
Additionally, losses due to heat are proportional to the current. If you double the current and halve the voltage, you'll lose twice as much power by heading the wires. For just a house, this isn't a lot, but it's not zero.
This is why US households still have 240V available. If you have a large appliance that requires a lot of power, like an oven, water heater, dryer, L2 EV charger, etc, you really want to use more voltage and less current. Otherwise the wires start getting ridiculous.
This is not to say that higher voltage is just necessarily better. Most of the EU and the UK in particular has plugs/outlets which are substantially more robust and difficult to accidentally connect the line voltage to a human. Lots of people talk about how much safer, for instance, UK plugs/outlets are than US plugs. If you look at the numbers though, the UK has more total deaths per year to electrocution than the US, despite the fact the US is substantially more populous. This isn't because of the plugs or the outlets, US plugs really are bad and UK plugs really are good. But overall, the US has less deaths because we have lower voltage; it's not as easy to kill someone with 120V as 240V.
So there's a tradeoff. There is no best one size fits all solution.
I don’t know is toaster are close to max power draw, but kettles certainly are.
Most places with 240V regularly have 16A sockets, allowing a maximum draw of 3840W of power. That’s the limit. Cheap fast kettles will often draw 3000W and boil 250ml of water at room tempature in 30s.
Kettles in the US are often limited to 15A and thus max 1800W (usually 1500W) and take twice as long (60s)
Houses are wired for 16A per circuit on both sides of the pond, with high-power appliances typically pulling around 10A to avoid tripping the fuse when something else is turned on at the same time. It's just a nice point where wires are easy to handle, plugs are compact, and everything is relatively cheap.
The US could have toasters and hair dryers that work as well as European ones if everything was wired for 32A, but you only do that for porch heaters or electric vehicle chargers.
More current needs thicker wires. The average US outlet is wired for 120v15amp. 20 amp circuits are somewhat common, though 20amp receptacles are not. Certainly not enough for commodity appliances to rely on.
Going to more than 20amp requires a multiphase circuit which are much more expensive and the plugs are unwieldy and not designed to be plugged and unplugged frequently.
Having more current running through a wire means thicker wires. Higher voltage means less current to achieve the same power, so thinner wires for the same power. The tradeoff for higher voltage is it's more dangerous (higher chance of arcing etc).
You need thicker wires for the same power. Which is why Americans live in constant fear of power extension cords, and people in EU just daisy-chain them with abandon.
You need the same thickness of wire for 10A regardless of which voltage you have. So with 230V, your 10A wire will let you draw 2.3 kW while someone with 120V and 15A wire would only get 1.8 kW and pay more for the wiring.
Today, with swichmode supplies, I think DC would make most sense. We lose much power to frequency deviation and inductive loads causing phase shift.
It would also make sense to have a high voltage and low voltage nets in houses. Low voltage for lighting and other low power equipment. High voltage for power hungry equipment. For example 48V and 480V.
Do we really lose much to phase shift? Increasing apparent load only causes a tiny fraction of that much waste, and local compensation isn't very expensive.
DC or a significant frequency boost would be good inside a house for lights and electronic items. Not so great for distribution.
I'm not convinced multiple voltages would be a net benefit outside of the dedicated runs we already do for big appliances.
Interesting to think about what the future could look like. What if breaker boxes were "smart" and able to negotiate higher voltages like USB-C does? It would avoid the problem of a kid sticking a fork in an outlet, or a stray wire getting brushed accidentally when installing a light fixture.
> What if breaker boxes were "smart" and able to negotiate higher voltages like USB-C does?
That'd be difficult; a breaker typically feeds an entire room, not a single outlet. (And when it does feed a single outlet, that's typically because it's dedicated to a specific large appliance, like an air conditioner or electric stove, which wouldn't benefit from being able to dynamically negotiate a voltage.)
Totally not, that would mean both worse skin effect and worse impedance.
Likely the best option (if you really don't care about the existing infrastructure) would be DC, 0Hz. There are some downsides of DC, of course.
This would be excellent for solar because it removes the efficiency loss from the inverters. AFAIK it's very hard to add/remove loads without spiking power to everything else on the line. A friend of mine applied for a job at a company that was trying to run DC in the home but it's not a trivial endeavor.
Normal LED lightbulbs shouldn't flicker on standard 60Hz circuits. Do you have a dimmer switch or smart switch in the circuit? I've noticed these cause flickering that's visible on camera or out of the side of my eyes.
Get better ones. I installed expensive LED lamps at home and they’re fine. The guys in the office picked the cheapest ones and I don’t want to turn these ugly things on.
Edit: Paulmann Velora are the expensive lamps at home.
Fun fact: Japan uses BOTH 60Hz and 50Hz for mains electricity due to historical generator purchases. This means the Japanese electric grid is split into two regions that cannot easily share electricity.
The US alone has 3 grids (East, West and Texas). With the same frequency but still not connected.
In Switzerland trains use 16.7Hz but they are connected with large frequency inverters. Before it was with large motors / generators. Now its just static with electronic.
I want to say this was part of the issue after the Tohoku Earthquake, my recollection was that some generators got brought in to support the ones that were flooded but were incompatible. However, I can not find any note of it in the timelines and after-action reports that showed up when I searched.
So possibly misremembering or fog of war reporting, or perhaps not important enough for the summaries.
I like the hypothesis by fomine3 on HN that "Japan's divided frequency situation made Japanese electric manufacturers to invent inverter for electrics (example: air conditioners, microwave, refrigerators). Inverter primary makes electrics controllable efficiently, also they can ship same product (same performance) for both 50/60Hz area in Japan."
(1997), which I wondered about due to the "Many people continue to be affected by the decisions on frequency standards made so very long ago" phrasing and the intro-bit about the need for adapters in the paper itself.
Because these days, voltage and especially frequency are pretty much irrelevant for mains-power AC, and "ignorant" will be more accurate than "affected" when it comes to "many people"...
They don't know it but they likely have a motor someplace in their house that runs at the speed it does because of frequency. They are ignorant but it affects them.
It is less and less likely... motor-based clocks are a thing of the past; hand appliances (like mixers and blenders) use either DC or universal motors to allow speed control. Even refrigerators feature "variable speed motors" nowadays, which means they are frequency-independent.
I think fans will likely be the last devices which care about frequency.. but new ones are often 12V/24V-based, with a little step-down modules.
Readit News
60 Hz = 60 cycles per second = 3600 cycles per minute
A simple 2 pole AC motor spins 1 rotation per cycle, so 3600 RPM. AC is a sine wave cycle of current. Current flows one way to attract it to one pole, the current flows the other way to attract it to the other pole.
For a big mainframe disc drive, it sounds like the obvious choice. Why they stuck with it after switching to DC, who knows. Maybe they didn't want to redesign the controller circuits.
Actually, still available. Good to have something quieter when performance requirements are not as high.
If anyone here works at a car manufacturer, please try to get this fixed. Apparently not everyone notices.
They could design it not to be that low of a frequency but apparently someone thought that 40-50hz was imperceptible to humans and went with it
I'm sensitive to flicker myself, but only on the more extreme half of the spectrum. For example, half rectified LED drivers on 60 Hz AC drive me nuts, but full rectified (120 Hz) I very rarely notice. I don't notice any problem with car tail lights, except in the case of a video camera where the flicker and the frame rate are beating. The beating tends to be on the order of 10 Hz (just shooting from the hip here) so if frame rates are 30/60/120 then I guess the PWM frequency is something like 110 or 130 Hz?
Deleted Comment
> Stillwell recalled distinctly the final meeting of the committee at which this recommendation was agreed upon. They were disposed to adopt 50 cycles, but American arc light carbons then available commercially did not give good results at that frequency and this was an important feature which led them to go higher. In response to a question from Stillwell as to the best frequencies for motors, Scott said, in effect, “Anything between 6,000 alternations (50 Hz) and 8,000 alternations per minute (67 Hz).” Stillwell then suggested 60 cycles per second, and this was agreed to.
What's the most efficient for modern grids and electronics?
Would it be a higher frequency (1000hz)?
I know higher voltage systems are more dangerous but make it easier to transmit more power (toaster ovens in the EU are better because of 240v). I'm curious if we would pick a different voltage too and just have better/safer outlets.
> What's the most efficient for modern grids and electronics?
I do not think it is possible to answer the question as posed. It is a trade-off. Higher frequencies permit smaller transformers in distribution equipment and smaller filtering capacitors at point of use. On the other hand, the skin effect increases transmission losses at higher frequencies.
If you want minimum losses in the transmission network, especially a very long distance transmission network, then low frequencies are better.
If you want to minimize the size and cost of transformers, higher frequencies might be better. Maybe the generator is close to the user so transmission loss is less important.
If you want smaller end-user devices, high frequency or DC might be more desirable.
You have to define some kind of objective function before the question becomes answerable.
This would be a pretty good approximation of the ratio of transmission lines to transformers.
240v is a good middle ground for safety and power.
Higher Frequency: Things that use electricity can be made smaller. But losses in long transmission become much worse.
DC instead of AC: Lower losses in transmission, don't need as much spacing inside electronics for arcing. But harder and less efficient to convert to different voltages.
https://en.wikipedia.org/wiki/Skin_effect#Formula
> So why not use 400 Hz everywhere? Such high frequencies cannot be economically transmitted long distances, since the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.
* https://aviation.stackexchange.com/questions/36381/why-do-ai...
In reference to consumer power supplies, only reason why GaN power bricks are any smaller than normal is because GaN can be run at a much higher frequency, needing smaller inductor/transformer and thus shrinking the overall volume.
Transformers and inductors are often the largest (and heaviest!) part of any circuit as they cannot be shrunk without significantly changing their behavior.
Ref: Page 655, The Art of Electronics 3rd edition and Page 253, The Art of Electronics the X chapters by Paul Horowitz and Winfield Hill.
Short protection at the breaker for every circuit would probably be necessary at that voltage
I guess there’s some internal resistance or something, but…
The trouble is the wires. A given wire gauge is limited in its ability to conduct current, not power. So if you double to the current, you'll need to have roughly twice as much copper in your walls, in your fuse panel, in your appliance, etc.
Additionally, losses due to heat are proportional to the current. If you double the current and halve the voltage, you'll lose twice as much power by heading the wires. For just a house, this isn't a lot, but it's not zero.
This is why US households still have 240V available. If you have a large appliance that requires a lot of power, like an oven, water heater, dryer, L2 EV charger, etc, you really want to use more voltage and less current. Otherwise the wires start getting ridiculous.
This is not to say that higher voltage is just necessarily better. Most of the EU and the UK in particular has plugs/outlets which are substantially more robust and difficult to accidentally connect the line voltage to a human. Lots of people talk about how much safer, for instance, UK plugs/outlets are than US plugs. If you look at the numbers though, the UK has more total deaths per year to electrocution than the US, despite the fact the US is substantially more populous. This isn't because of the plugs or the outlets, US plugs really are bad and UK plugs really are good. But overall, the US has less deaths because we have lower voltage; it's not as easy to kill someone with 120V as 240V.
So there's a tradeoff. There is no best one size fits all solution.
Most places with 240V regularly have 16A sockets, allowing a maximum draw of 3840W of power. That’s the limit. Cheap fast kettles will often draw 3000W and boil 250ml of water at room tempature in 30s.
Kettles in the US are often limited to 15A and thus max 1800W (usually 1500W) and take twice as long (60s)
Technology Connections has a great video on this: https://youtu.be/_yMMTVVJI4c
The US could have toasters and hair dryers that work as well as European ones if everything was wired for 32A, but you only do that for porch heaters or electric vehicle chargers.
Going to more than 20amp requires a multiphase circuit which are much more expensive and the plugs are unwieldy and not designed to be plugged and unplugged frequently.
Deleted Comment
It would also make sense to have a high voltage and low voltage nets in houses. Low voltage for lighting and other low power equipment. High voltage for power hungry equipment. For example 48V and 480V.
DC or a significant frequency boost would be good inside a house for lights and electronic items. Not so great for distribution.
I'm not convinced multiple voltages would be a net benefit outside of the dedicated runs we already do for big appliances.
Time will tell!
That'd be difficult; a breaker typically feeds an entire room, not a single outlet. (And when it does feed a single outlet, that's typically because it's dedicated to a specific large appliance, like an air conditioner or electric stove, which wouldn't benefit from being able to dynamically negotiate a voltage.)
One of the best things about living in the UK! https://www.youtube.com/watch?v=UEfP1OKKz_Q
https://en.wikipedia.org/wiki/High-voltage_direct_current
Totally not, that would mean both worse skin effect and worse impedance. Likely the best option (if you really don't care about the existing infrastructure) would be DC, 0Hz. There are some downsides of DC, of course.
Higher frequencies have terrible transmission (skin effect, transmission line length limit) and would start to interfere with radio.
Lower frequencies need larger transformers.
DC while nice is too expensive.
So about where we are now.
48VDC inside homes would be enough for most applications except heating and it would be kid-safe.
240V for heating applications.
Edit: Paulmann Velora are the expensive lamps at home.
In Switzerland trains use 16.7Hz but they are connected with large frequency inverters. Before it was with large motors / generators. Now its just static with electronic.
https://en.wikipedia.org/wiki/North_American_power_transmiss...
They can share power and are somewhat connected with HVDC interconnections however.
So possibly misremembering or fog of war reporting, or perhaps not important enough for the summaries.
Because these days, voltage and especially frequency are pretty much irrelevant for mains-power AC, and "ignorant" will be more accurate than "affected" when it comes to "many people"...
I think fans will likely be the last devices which care about frequency.. but new ones are often 12V/24V-based, with a little step-down modules.