4 ms·

Older wall clocks used synchronous motors which would literally move the second hand using the waveform from the A/C power. As loads on generators went up, the

Older wall clocks used synchronous motors which would literally move the second hand using the waveform from the A/C power. As loads on generators went up, the effective RPMs went down, causing downstream power to run at slightly slower than 60Hz. It was so heavily used that power stations used to run "fast" catch up on any cycles they fell behind at night so that there were exactly 86,400 in a 24h period to prevent clocks from running fast or slow. Amusingly you'll see stories like this when power companies fail to maintain 60Hz on average over a day: https://www.reddit.com/r/explainlikeimfive/comments/xscztp/eli5_how_can_electric_company_maintenance_affect/ https://www.reddit.com/r/explainlikeimfive/comments/xscztp/e...

OptionOfT 2y ago
I remember this happening in Belgium, where they detected it quite like a month after the fact. Everybody got a letter in the mail (yes, snail mail!) explaining when they were going to run the system fast for a couple of hours to catch up.
userbinator 2y ago
These were very common in the last century and many continue to be used today: https://en.wikipedia.org/wiki/Telechron https://en.wikipedia.org/wiki/Telechron
ajb 2y ago
It may not be used so much for clocks now, but you can still buy cheap timed power switches that use this method. For example: https://www.argos.co.uk/product/5440524 https://www.argos.co.uk/product/5440524
rob74 2y ago
Wall clocks use batteries nowadays, but some clocks in devices permanently connected to mains power still use its frequency - e.g. my Siemens kitchen oven, which promptly was off when there were some synchronization issues in the EU grid a few years ago. You'd think that in an appliance that costs several hundred euros, a quartz crystal wouldn't really move the cost needle, but as long as they can get away with it most of the time, why spend more money?
- xnzakg 2y ago
  A quartz crystal can still drift, while the AC frequency is being regulated to stay within a few seconds per year, for free (for the manufacturer).

OptionOfT 2y ago

I remember this happening in Belgium, where they detected it quite like a month after the fact. Everybody got a letter in the mail (yes, snail mail!) explaining when they were going to run the system fast for a couple of hours to catch up.

userbinator 2y ago

These were very common in the last century and many continue to be used today: https://en.wikipedia.org/wiki/Telechron https://en.wikipedia.org/wiki/Telechron

ajb 2y ago

It may not be used so much for clocks now, but you can still buy cheap timed power switches that use this method. For example: https://www.argos.co.uk/product/5440524 https://www.argos.co.uk/product/5440524

rob74 2y ago

Wall clocks use batteries nowadays, but some clocks in devices permanently connected to mains power still use its frequency - e.g. my Siemens kitchen oven, which promptly was off when there were some synchronization issues in the EU grid a few years ago. You'd think that in an appliance that costs several hundred euros, a quartz crystal wouldn't really move the cost needle, but as long as they can get away with it most of the time, why spend more money?

xnzakg 2y ago
A quartz crystal can still drift, while the AC frequency is being regulated to stay within a few seconds per year, for free (for the manufacturer).