> On the consumer side, your microwave, coffee machine and even bedside clock will
I'd be very surprised. It's cheaper to build in a 32.768kHz crystal for timekeeping than try to access the grid frequency from the isolated low-voltage circuit.
It's cheaper to build in a 32.768kHz crystal for timekeeping than try to access the grid frequency from the isolated low-voltage circuit.
Those products don't use isolated power supplies --- normally they use a capacitive dropper. A high-value resistor to an IC pin is sufficient to drive the clock counter, and a resistor is definitely cheaper than a crystal.
A similar event happened in Europe a year ago (also due to problems in former Yugoslavia) and all electric clocks in my house (microwave, oven, alarm clocks) went out of sync temporarily. I was just as surprised as you.
Basically, it's exactly the devices that lose track of time in case of a power outage, and that you need to manually adjust for daylight savings time, that are synchronized to the grid. Devices that use a battery (such as laptops, mobile phones, and CMOS clocks in PCs) must necessarily use some other means.
It doesn't seem to be much correlated with price either: my alarm clock cost over $100 and it was still affected. Surely at that price point they could have afforded a crystal oscillator in the design, if they wanted to, but it seems this just isn't typically done.
As an industry, it requires a special customs declaration + fire safety measures on boats and planes when you transport an oven with a battery inside. That may be the reason for not using battery-backed ovens, and relying on the power supply.
The idea is that it wakes you up gently by flooding the room with light resembling a natural sunrise. One reason that it might be expensive is that it needs a lot of high luminance hue shifting LEDs, and possibly I overpaid a bit (there do seem to be much cheaper competitors) but it was still a good investment because it does make my mornings a lot more pleasant.
I have a microwave and oven from the same brand, and their digital clocks diverge about 2minutes in 24h. I just don't understand how it's possible to build a device that poorly in 2020 (they are new) and I also wonder which tech they use for timekeeping. Is it possible that one of them uses a crystal and the other uses the 50Hz? That would explain a small difference.
It's easy enough to mistune a 32768Hz clock crystal by shitty electronics engineering, unfortunately :/
50Hz might have temporary variations, but it's controlled so that over a longer period of time, you always get the correct number of cycles, e.g. 180000 in an hour.
This also means that going off the 50Hz power grid theoretically has better (or even perfect) long-term accuracy. Also means that if you adjusted your clock for this separation event, you'll have to adjust it back :D
It's either a poorly made bottom of the barrel crystal or they cheaped out even further and used a ceramic resonator. That is the price of race to the bottom globalization. Measuring line frequency is a no go because the safety compliance inceases costs.
US current is 60Hz. EU current is 50Hz. Maybe your over maker did some rounding when adjusting by 5/6 and here you go? Btw, does your oven have a 50-60Hz switch?
>> On the consumer side, your microwave, coffee machine and even bedside clock will
> I'd be very surprised. It's cheaper to build in a 32.768kHz crystal for timekeeping than try to access the grid frequency from the isolated low-voltage circuit.
IIRC, the grid frequency is usually more accurate. Probably because it's carefully monitored and managed by the power authorities like the OP describes. If you build a clock with its own frequency reference, than any error will accumulate and have to be monitored and managed by the user.
Maybe, but I bet those designs are very traditional and date from the time where it was cheaper to use grid frequency.
If not, why don't coffee machines that can start on a timer have a backup battery for their clock? That might be cheap enough too. And vital for those moments when there was a 10 second brownout which leads to your coffee not being ready in the morning...
> why don't coffee machines that can start on a timer have a backup battery for their clock?
As a European the thought wouldn't have come to me. Brownouts just don't happen (see this 0.5% frequency dip making headlines), and a blackout is a once-a-decade event for any given house (probably even less frequent than that).
So your answer is probably that demand for that feature is far from universal, and a coffee machine is much lower stakes than for example an alarm clock.
> Depends. I'm in a rural area, and I get 5-second power cuts every couple of months. It's the main reason I have a UPS under my computer desk.
This. Can't put the coffee maker on an UPS though. Or not on a cost effective UPS.
> So your answer is probably that demand for that feature is far from universal, and a coffee machine is much lower stakes than for example an alarm clock.
Actually for the alarm clock i'm just going to be late. Not having coffee hurts much more!
The grid is never exactly 50Hz, it varies quite significantly. On the long run, the grid operators try to average to 50Hz as close as possible, just so that clocks continue to operate somewhat accurate.
In fact, it is even in the FAQ of the article:
"The transmission grids of the countries of Continental Europe are electrically tied together to operate synchronously at the frequency of approximately 50 Hz"
Based on the article the control limits are 49.8 to 50.2 Hz (+-0.2hz). That's less than 1%, not very significant.
One of the places I lived in Austin, TX had a range with a clock that used grid frequencies (60hz in the US). It was dead accurate. I only changed it for daylight savings, it never need adjustment.
The US used to guarantee 5,184,000 cycles per day. That’s not, like, 1% or anything comparable, that’s zero (with temporary deviations). Any clock which referenced line frequency would be dead accurate over the long-term. There’s a system called Time Error Correction (TEC) which would do this (refer to WEQ-006 and the like). Obviously this error is measured relative to some reference clock.
I’m not sure what the current status is, but my understanding is that there are efforts to retire this system and allow the speed to drift more.
On the consumer side, your microwave, coffee machine and even bedside clock will.
Not sure on the industrial side.