5/16/2024 at 10:24:11 PM
> grids were owned by many small regional power companies; thus, voltages and frequencies (42Hz was quite common) could vary a lot between each otherIt always amazes me that some countries are still operating on multiple mains voltages and/or frequencies while sharing a common plug standard, such as Brazil or notably Japan (where the 50/60 Hz division apparently runs through a densely populated area)!
Fortunately most devices I bring with me when traveling don't care and adapt to whatever, but being able to plug a 110 V hairdryer into a 230 V outlet without any form of adapter sounds scary.
by lxgr
5/17/2024 at 12:08:42 AM
A difference in frequency is much less of an issue than a difference in voltage, I would have thought. Especially as 50 and 60Hz are fairly close to each other.The only big problems I can think of are devices that use the frequency as a reference, such as motors and clocks. But even then, they wouldn’t break, they’d just run at the wrong speed.
by LeoPanthera
5/17/2024 at 2:18:12 AM
A difference in frequency is not that big of a problem... except for the fact that you can't easily transfer power across the two grids.Japan has some power conversion stations, but when the Tohoku earthquake and tsunami of 2011 knocked off several powerplants in the 50 Hz half of the country (including Fukushima), they could not transfer enough power from the other side, and the suffered many blackouts, even though the 60 Hz half of the country had power to spare.
by pezezin
5/17/2024 at 11:39:23 AM
> A difference in frequency is not that big of a problem... except for the fact that you can't easily transfer power across the two grids.And for everything, which uses the frequency as a clock.
by johannes1234321
5/17/2024 at 1:15:18 PM
True. Nowadays it is not a problem, but it makes me wonder how they could make 60 Hz television run on a 50 Hz grid.by pezezin
5/17/2024 at 4:57:30 PM
I've been wondering that too recently, and apparently it wasn't that big of a deal [1] – more recent analog TVs weren't that susceptible to mains interference of the sort that benefited from being synchronized to the frame rate.In other words, the mains frequency was never used as a frequency source for TVs, and the apparent frequency match was only to make interference patterns not wander around the screen.
[1] https://electronics.stackexchange.com/questions/164249/is-th...
by lxgr
5/17/2024 at 12:29:22 AM
> The only big problems I can think of are devices that use the frequency as a reference, such as motors and clocks.This was my March mindfuck:
That there are periods every couple weeks when the WHOLE ELECTRICITY GRID of a country is run with higher/lower frequency for a period of time to get your Chinese oven clocks back into sync.
by rrr_oh_man
5/17/2024 at 12:37:48 AM
Long-term grid frequency stability is something you take for granted, until it suddenly fails, like in most of Europe back in 2018, due to a political disagreement between Serbia and Kosovo: https://www.reuters.com/article/idUSL5N1QP2FF/I also find it quite funny that our cheap oven clock is probably among the most precise (non-internet connected) ones in our apartment :)
by lxgr
5/17/2024 at 12:46:04 AM
WWVB de-rating has got us all a bit down in North America. Lots of consumer level “atomic clock accuracy” devices just don’t update any more.https://www.watchuseek.com/threads/wwvb-operating-with-reduc...
by Scoundreller
5/17/2024 at 4:17:07 AM
It’s a shame there aren’t more time tower sites broadcasting in a distributed manner for redundancy.by toomuchtodo
5/17/2024 at 1:25:36 PM
Like the 6 independent 24-satellite (plus spare) constellations that constantly orbit Earth and output synchronized beacons accurate to nanoseconds?by smallmancontrov
5/17/2024 at 2:10:40 PM
How effective is receiving precision time from a GNSS constellation within structures, urban areas, and other challenging SNR envs? Another comment mentions cell towers broadcast this unencrypted and without the need for service, so perhaps the solution is to instead require strong SLAs around that service, with the gov potentially paying for that service level?by toomuchtodo
5/17/2024 at 5:01:33 PM
I feel like once you're concerned about SLAs for precision timekeeping, you need to start worrying about spoofing as well, which is tricky to combat in an inherently unidirectional protocol.Galileo has an interesting signal authentication service [1], but even that is subject to replay attacks by definition (although you can't skip ahead a receiver's time).
In comparison, networked bidirectional protocols like NTP are almost trivially secure-able, by including a challenge in the request and a cryptographic signature over the response.
[1] https://berthub.eu/articles/posts/galileos-authentication-al...
by lxgr
5/17/2024 at 2:44:36 PM
Yep, reception is a real problem with straight GNSS. WWVB suffered from it too, and cellular (which is locked to GPS) is a big upgrade. I suppose that now the thing to do is wait for the $0.10 cellular clock chip that makes it easy.by smallmancontrov
5/17/2024 at 3:38:21 PM
My interest is as a bit of a precision time enthusiast and an advocate of public goods. We’re awash in “good time”, GNSS, RF, NTP over IP, cellular, but it still feels like there is a gap to fill to make precision time super cheap and ubiquitous. Getting time over mains power or other previously convenient but potentially low precision sources should be over, but getting precision time should be as easy and reliable as mains power. Thanks for riffing with me!by toomuchtodo
5/17/2024 at 8:21:07 AM
Noted my car got time from GPS the other day and it got me thinking, why aren't there unencrypted packets on all wifi that distribute NTP time so my oven/microwave/alarm/etc can grab it from any wifi it can see (even if it's not paired to them) - bonus points if APs also hand out local TZ databy Taniwha
5/17/2024 at 10:42:14 AM
Phone networks can already do this. And its true broadcast, you can decode it passively without ever connecting to the network, so no SIM/transmission required.I have no idea this is actually enabled in networks in practice, but the specification exists.
by joha4270
5/17/2024 at 1:34:32 PM
And in my experience, it's often wrong on some towers. I can't enable the setting on my phone to automatically set the time from the network, because if I do, it gets several minutes out of sync with the real time, which breaks TOTP generation.by cesarb
5/17/2024 at 3:36:19 PM
Yeah, a large German cell provider had their time off by a couple of minutes some years back, which made the news as it resulted in people's alarms ringing late and them being late to work/school etc.Hopefully modern phones prioritize GPS or NTP derived time and timezone information over NITZ (which is how networks provide it). At least Android has the capability to do so, but it's ultimately up to device manufacturers, as far as I understand [1].
by lxgr
5/17/2024 at 4:03:10 PM
Could the detection and reporting of this inaccuracy be crowdsourced, either with mobile devices or perhaps SDRs? Fetch tower time, fetch real time over GNSS or NTP, report delta with tower ID and drift to a central server? Perhaps even include a map, like the map of GPS error rates derived from ADS-B data feeds.by toomuchtodo
5/18/2024 at 3:24:06 AM
Then you'd need Internet access to get the data, and if you had that, you could just use NTP.by eternityforest
5/17/2024 at 4:35:32 PM
I'm almost certain that at least Apple already has such a database on the operator level, i.e. a list of MNCs and the (non-)trustworthiness of NITZ. I vaguely remember seeing some carrier settings keys to that extent somewhere.by lxgr
5/17/2024 at 5:57:35 PM
Why bother? If you can download data from a central server you have an internet connection, so you can also retrieve time via NTP instead.by crote
5/17/2024 at 6:20:21 PM
Distributed monitoring and centralized reporting would be used to correct anomalous towers providing bad time and can provide independent verification of precision. It is not enough to provide a service; you must also have a system to validate it, and correct when needed.by toomuchtodo
5/17/2024 at 4:42:17 PM
Unencrypted broadcast NTP timestamps sound like a good idea until your neighbor starts broadcasting false timestamps to prevent your loud smart leaf blower from charging overnight :)by lxgr
5/18/2024 at 9:33:34 AM
Best practice would be to listen to all the local APs and choose what most of them sayby Taniwha
5/18/2024 at 12:30:32 PM
Making one AP look like thousands is trivial.by lxgr
5/18/2024 at 3:22:21 AM
It's probably about time for an update that can work with more compact receivers.Governments(Or an industry group, or really anyone) could publish digitally signed timestamps every second with a a key that doesn't change, and you could have a BLE profile for sharing them.
by eternityforest
5/17/2024 at 8:17:25 AM
There used to be a local hydro generation that fed the local city, they had 2 clocks on the wall, one on the local grid and one on the national one - some time late at night they'd speed up/slow down the local grid to keep the clocks in syncby Taniwha
5/17/2024 at 3:03:15 AM
It's surprisingly hard to keep a clock accurate over time. Typical crystal oscillators can gain or lose seconds per day. If you want to do better than that, you either need internet access (for NTP), a radio receiver of some kind (for atomic clock broadcasts, GPS, etc.), or a significantly more expensive oscillator. Having a frequency reference with perfect long-term accuracy that any electrically-powered clock can use for free is pretty convenient!I've often wondered how hard it would be to make portable battery-powered clocks use 60 Hz noise as a timekeeping source. Maybe I should make a project out of it.
by AdamH12113
5/17/2024 at 10:15:32 AM
> Typical crystal oscillators can gain or lose seconds per day.Are you sure?
I only owned a quartz watch when I was a kid, but all sources I find on the web say even the lowest quality quartz watch movements are accurate to +- 20-30 seconds a month.
For comparison: my several decades old manual Poljot loses some seconds per day.
by rrr_oh_man
5/17/2024 at 5:49:26 PM
The Casio G-Shock I got in the 90s was ~66 ppm fast, which worked out to ~5 seconds/day. There are cheap crystals on Digi-Key with ~10 ppm accuracy, which is around 0.86 seconds/day. But crystals drift with age (and a tiny bit with temperature). Perhaps watches have improved since I last looked, but I would want to measure the actual real-world accuracy before believing anything better than 1 second/day.by AdamH12113
5/17/2024 at 6:08:36 PM
Yeah, that sounds about right. Crystal oscillators typically have an accuracy of about 20ppm, which is 1.73 seconds per day.Keep in mind that those number are a guaranteed worst-case performance - real-world performance is often much better.
by crote
5/17/2024 at 6:19:08 PM
The problem is that grid frequency has terrible mid-term performance. The frequency itself will be reasonably close to 50/60Hz, but it's guaranteed to be off by a little bit due to the way it operates - and that small offset accumulates over time.For example, the European supergrid only makes time corrections if it has drifted by more than 20 seconds. That's good enough for the clock on your microwave, but it's pretty bad compared to literally any other time source.
by crote
5/18/2024 at 12:03:15 AM
Wow, that's pretty bad! In Texas it's +/- 3 seconds[1]. Which I wouldn't want to use for precise event logging, but for human use is fine.by AdamH12113
5/18/2024 at 3:28:48 AM
I wouldn't be surprised if you could do it in software alone, using a wire on an ADC as the receiverby eternityforest
5/17/2024 at 2:30:06 PM
how more expensive is a "more expensive" oscillator?by agos
5/17/2024 at 4:50:55 PM
A few cents, as far as I understand, but that's not the only problem:You can get significantly more precision using an oven-controlled oscillator (frequency is temperature-dependent, and it's easier and more precise to control temperature to a known high setpoint than to compensate for the temperature-frequency curve using a thermometer), but these are, as the name implies, small ovens that consume additional electricity (on the order of 1-2 W, as far as I know).
An additional base load of 1-2 W per oven and microwave would be pretty bad for the energy budget on a global scale, so just providing a time source from the power line they're already connected to is more efficient :)
Other than oven-based oscillators, you can also use temperature-corrected oscillators; the Apple Watch does that, for example, and is supposedly about four times more accurate than a non-temperature-corrected MEMS, which in turn is already better than a quartz oscillator [1].
Not that it matters much, given that all models have at least a GPS receiver these days, as well as a battery life of about a day without charging, but I suppose it's a real benefit to all Apple Watch users working in faraday cage isolated bunkers without Wi-Fi :)
[1] https://www.watchuseek.com/threads/apple-watch-oscillator-an...
by lxgr
5/17/2024 at 5:59:04 PM
> A few cents, as far as I understand, but that's not the only problemNitpick: looking on Digi-Key, in quantity, a sub-ppm oscillator is ~5x more expensive than a 10 ppm crystal -- ~85 cents for the cheapest TCXO I can find vs. ~18 cents for a crystal. The frequencies are also much higher (tens of megahertz), which won't help with the power consumption.
You're right about the power consumption, though.
by AdamH12113
5/17/2024 at 9:51:14 PM
It depends. On the lower end of the spectrum, there are high volume products that offer somewhat better performance for just a tiny increase in cost, as mentioned in other comments. On the higher end of the spectrum there are laboratory-grade oscillators, for example the legendary Hewlett-Packard 10811 [1] and similar, which cost hundreds to thousands of dollars. These overlap in price with the lower end atomic clocks.[1] http://etoysbox.jp/Memo/3_Test_Equipments/HP_10811_OCXO/HP_1...
by generuso
5/17/2024 at 3:35:24 PM
A motor running at 20% higher/16% lower speeds might break some things, I could imagine?by lxgr
5/17/2024 at 6:34:55 PM
If the motor is designed for it, then no. Many motors these days are built to handle variable frequencies on account of VFDsA variable-frequency drive is a motor controller that adjusts the frequency of the power delivered to a motor to speed it up or slow it down.
It could possibly damage a motor that isn’t designed for use with a VFD.
by quickthrowman
5/17/2024 at 1:21:30 AM
Here in Brazil we have voltages in different regions but we also have different voltages inside the home. My washer has its separate 220v circuit while the rest of the home is 110v.by mateus1
5/17/2024 at 2:07:00 AM
As far as I know that’s usually a split-phase system: You get 110V between either phase and neutral, and 220V between the phases.In a three-phase system (like the ones used in most of Europe), that effect isn’t as pronounced since you usually have at most 120 degrees phase difference instead of 180 and the voltage between two phases is less than double, so less appliances make use of that (I think some stoves do).
by lxgr
5/17/2024 at 2:45:12 AM
> As far as I know that’s usually a split-phase system: You get 110V between either phase and neutral, and 220V between the phases.We Brazilians tend to call it "110V", but it's often a three-phase system with 127V between phase and neutral and 220V between phases.
Or sometimes it's 115V from phase to neutral and 230V from phase to phase (probably a split-phase system like you said). And in that case, us Brazilians would still call the lower voltage "110V", and the higher voltage "220V".
You can't trust a Brazilian when they say the voltage is "110V" or "220V". These numbers are only an approximation, which might have been correct for some places a century or two ago.
And yes, it's a mess. Check the official list at https://www2.aneel.gov.br/aplicacoes/srd/frmConcessionaria.c... (link found at https://www.gov.br/aneel/pt-br/centrais-de-conteudos/relator...), which shows which voltages can be found in each city for the whole country. For instance, take a look at the city of São Paulo in the state of São Paulo (yes, it's the same name for the state and its capital city, this is also the case for Rio de Janeiro):
- 115V / 230V
- 120V / 208V
- 127V / 220V
- 220V / 380V
- 220V / 440V
At least the frequency is always 60Hz (unlike the rest of South America, which uses 50Hz; we have to use HVDC links when importing or exporting electricity to the neighboring countries).
by cesarb
5/17/2024 at 9:20:28 AM
Fascinating!Using HVDC to interconnect async grids is very common.
This presentation is a nice deep dive on the situation in Europe: we are even building HVDC “corridors” embedded inside some of the sync grids. Pricey gear but valuable too!
http://catedraendesa.us.es/documentos/jornadas_uimp_2015/201...
by davedx
5/17/2024 at 12:42:07 PM
HVDC corridors make sense because it's functionally impossible to build new overhead transmission lines anywhere, so operators are forced to bury the transmission lines. But buried AC transmission lines have terrible loss and are super expensive, buried HVDC lines are slightly less expensive (but require expensive terminal stations), and have much lower losses.by formerly_proven
5/18/2024 at 2:22:38 PM
> it's functionally impossible to build new overhead transmission lines anywhereThis isn't really true, new overhead lines are being built all over the place. It definitely depends where they're being built and there is definitely strong opposition from councils in e.g. some parts of Germany, but see for example in the Netherlands there are definitely new overhead lines being built: https://www.tennet.eu/nl/projecten/provincies/groningen/eems...
That being said it's true that it's much more challenging than it used to be to get planning permission.
by davedx
5/17/2024 at 2:28:11 PM
> we are even building HVDC “corridors” embedded inside some of the sync gridsWe also have that here in Brazil; the Xingu-Estreito and Xingu-Terminal Rio HVDC links run in parallel with the high-voltage AC links. On the other hand, the Madeira HVDC link (https://en.wikipedia.org/wiki/Rio_Madeira_HVDC_system) is AFAIK normally disconnected from the AC grid on the generation end (it has a direct connection, probably used to start up the power plants, but normally uses a back-to-back HVDC converter instead of it).
by cesarb
5/17/2024 at 11:45:01 AM
My local power company (in the USA) is known for running slightly higher voltage than the spec. In the past I have seen 127V - and wrote a letter complaining about it. Which probably got me on their list of annoying customers...Currently it's at 121.8V - either they have finally adjusted the tap on the neighborhood transformer or there's a heavy load at the moment (hot water heaters running from people showering this morning?)
by chiph
5/17/2024 at 1:24:59 PM
According to ANSI C84.1 (which I believe is the relevant US specification), there is a tolerance of +/- 5%, which would put 127V just barely out of spec.I could imagine that utilities calculate some average base load and adjust transformers accordingly to accommodate the expected voltage drop, given that 110/120V is relatively low and drops can be significant?
by lxgr
5/17/2024 at 11:33:03 PM
Obviously not an expert, but I wonder if they run a higher voltage in order to give them some margin from frequency dropping too far below 60 Hz (caused by generators slowing down) during high load periods?by chiph
5/17/2024 at 8:25:11 AM
Just for comparison other countries that claim "230v" have that last one - 220-240v between the phase you get and neutral and 440v between phases if you get 3-phaseby Taniwha
5/17/2024 at 3:32:04 PM
440V would be split phase. We have 400 3phase hereby Bene592
5/17/2024 at 6:34:40 PM
Europe also just doesn't need split-phase systems. A regular outlet will provide 230V @ 16A, or about 3.7kW. That's enough for virtually all household appliances, and single-phase 32A circuits for 7kW stoves are quite common too.Households these days often do have a 3-phase hookup, but it's quite rare to have 3-phase equipment. Maybe a stove, and with the energy transition larger solar setups, electric car chargers, and large heat pumps. But most of the time that 3-phase hookup is just treated as three separate 1-phase sections.
by crote
5/17/2024 at 1:43:09 AM
Didn't know that was done outside north America.by coryrc
