AC-synchronized clocks in Europe?

So, I heard this on the radio yesterday, and I, honestly, couldn’t believe it. Since there are lots of Europeans and electronics folks here, I figured I would ask.

I found several articles, but they’re mostly like this one:

I’ve never seen a digital clock that didn’t run off DC, and almost always has a crystal oscillator. But I’ve never been to Europe.

I can see mechanical clocks that run off synchronous AC motors being dependent on the AC frequency, but I haven’t seen one of those in decades. Is Europe really full of them, or some weird digital clocks that don’t have crystals and depend on the accuracy of the 50hz AC?

A oven in a kitchen can easily last 10 or more years and it has been common to have a clock in them. There is probably also a lot of clock controlled equipment that uses 50Hz as base. Usual it is very stable over time, i.e. the clock will basically never have to be adjusted (Except summer/winter time may spoil that a bit).

Several of the articles talk about microwave clocks and digital clocks. Every digital clock I’ve ever opened up (and that’s been quite a few since I was a kid) had a crystal. So I still suspect the reporters are misunderstanding and overstating their case.

But I admit I’ve never torn apart a European digital clock.

I have had mains synchronized digital clocks, but that is some time ago.
Again: the advantage is the precision over time. Maybe US do have have that precision in the mains frequency?

Synchronizing to mains was basically free to do when a ordinary transformer was used for power supply, but today with everything using switch mode supplies I doubt much new equipment uses it.

In my house alone there are 3 clocks than run 5 minutes slow atm, 2 bedside clock-radios and indeed the clock of the (not that acient Samsung) microwave.

I haven’t seen anthing like that happening here in the UK, but our grid only touches the rest of the EU via a handful of interconnectors, and those are usually high voltage DC, which means that our grid AC frequency would be entirely independent from the rest of the EU.

What kind of clocks are they, and do they normally keep accurate time, or do you think you’re seeing the phenomenon from the article?

MM5316N is a very old digital clock chip, runs from 50Hz or 60Hz of electric frequency.

They normally keep accurate time and I’m indeed seeing the phenomenon from the article. The clocks from my wife and kid are 5 minutes slow, while my own bedside clock radio is dead on time because I’m nerd enough to have a clock that is radio-controlled by the DCF77 signal from Mainflingen, Germany :expressionless: :nerd_face: :nerd_face:

I see your nerd and raise. I have two Casio watches that set themselves every night using the NIST’s WWVB radio signal from the atomic clocks in Fort Collins, CO, USA. I’m also fascinated by the implementation of NNTP. That’s why this issue caught my attention.

The only clock with a synchronous AC motor I’ve ever seen was the one built in to my mom’s stove as a kid (I’m 51). I actually never saw it functioning, it was broken for as long as I can remember.

Crystal oscillator clocks (eg, run by battery) are accurate in the short term, but inaccurate in the long term (drift).

Mains-synced clocks (eg, plug-in) are somewhat inaccurate in the short term, but accurate in the long term. That’s why your microwave oven or plug-in digital clock pretty much never have to be reset at the minute level, but usually only for daylight/standard time swaps at the hour level.

With talk about de-synchronising the AC grid into several distinct regions in the US, there won’t be a continent-wide uniformity anymore if that happens.

I imagine the EU has different regions based on the supplier of the electrcity, and they want to do the opposite of here and link ’em up into one Übergrid.

Until the 1950’s parts of Ontario Canada near Niagara Falls had 25 Hz AC power (talk about flicker!). When they converted to 60 Hz, trucks roamed the affected residential neighborhoods converting appliances that were frequency dependent, mostly by replacing motors/ballasts.

I managed to find an original vintage 25 HZ mains powered synchronous motor driven Canadian “mantle clock” on eBay almost 20 years ago. It was fun to periodically plug it in to 120 VAC 60 HZ and literally watch time fly.

Here’s an article about the history of the Canadian Rankine Niagara 25 Hz generating station:

50 Hz grid frequency is (usually) a precisely maintained standard which is used for long term (days, weeks, months, years, decades) timekeeping.

Through the day it can vary slightly as loading varies, but this is averaged out over 24 hours, with great precision.

For example, my UK electricity supply is “Economy 7” meaning my metering switches at night to a much lower price for 7 hours, during which I run e.g. an immersion heater for hot water, dishwasher and washing machine.

This switchover is performed by a marvellous electro-mechanical clock, locked to grid frequency, which has kept perfect time for at least 34 years (since my house was built). It has clockwork spring backup to keep it running through power cuts, and I’ve had plenty.

The electricity meter itself has been replaced three times, and is now a solid state digital device with barely readable faded LCD displays, (and I am being pressured to have it replaced with a “smart meter, but that’s another can of worms in the UK at the moment.) But the Economy 7 switch has never been. When I questioned the technician who fitted the last meter replacement he explained that no digital device had the reliability or stability of the electromechanical clock.

Certainly no inexpensive quartz oscillator, nevermind backup battery. The electronic meters have to be replaced every 15 years if they even last that long. The old spinning disc meters last pretty much forever (my parents one is at least 57 years old, probably much much older, and has never been replaced).

The UK grid is disconnected from mainland Europe, except for DC interconnectors which are converted back to UK AC frequency, so we are not suffering this frequency loss.

You can see what’s going on on the UK grid at e.g. including how the frequency can drop at times of peak demand, and how this is corrected later. It was interesting to see how we survived our recent cold snap and gas shortage, just, thanks to coal, nuclear, a lot of wind, backup diesel generators, and major industrial users being severely rationed or shut down. Gas was severely rationed for power generation to keep domestic supplies available for heating and cooking. Our gas storage facilities are out of action and, ironically, tankers of LNG from Russia have been helpful during the crisis.

So yes, mains frequency is very much an important time source here. After every power cut I have to re-set at least my cooker, oven, microwave, combi-oven and a couple of electric heaters because all their clocks depend on it.

Yes we also have an atomic clock time signal broadcast on 60 kHz, but that could be an expensive thing to add to consumer devices for perhaps little benefit. That said, all my clocks, and one wristwatch can lock to this, and other such broadcasts. Time and frequency MSF radio signal - NPL

the synchronous clocks usually look like this:

(school and 'train station' clocks are also commonly AC sync, or used to be)

at that frequency, it would lose a minute in 8.68 days, which is a lot

that article didn;t say the euro clocks that lost time, were digital, in fact it specifically said digital clocks and cell phones were immune


Most clocks tell time using internal mechanisms or, like cellphones, get the time from a radio signal, and those have been fine. But clocks that measure time by that alternating current have been fooled by the drop in frequency.

These old AC ones have their uses..
If the power cuts off for hours, you can see that (up to 12 hours) later, like if you come home from and think the power went off while you were gone.
(You have to set them accurately though, to tell that)
Also, if power only goes out for a second - the thing does not reset and blink 00:00 annoyingly!

Yes, the USA traditionally has very high precision in AC mains frequency.

They measure it constantly, and when it gets off, they make it up.


I rebuilt this late 1950’s General Electric wall clock about 10 years ago. It still has the original synchronous motor, still keeps perfect time.


what did ‘rebuilding’ entail?

don’t the motors and the neon backlight last pretty much forever?


Took the clock completely apart. Cleaned and painted the case and hands. Changed the bulb sockets and wiring, including a new backlight switch and line cord.

The clock was in bad shape when a buddy of mine gave it to me. It looks almost brand new now.

Point of information: The USA does not have an overall synchronised grid. It is divided into at least nine separate regions, with various DC and AC interconnections for load sharing etc.\_power_transmission_grid

Nevertheless I trust that every effort is made to maintain 60 Hz average frequency, long term.

Personally I am dismayed that some “local difficulties” have been allowed to slow down the grid across mainland Europe for weeks now, not that it affects me, on my little island.