Dim LED Display - Old LM8560 Mains Driven Clock - Page 1
Forum section: electronics / repair

author: t1d
author_rank: Super Contributor
timestamp: November 15, 2021, 11:13:32 pm
content: Background: I am a still-learning hobbyist, but I have very nice lab equipment. PSUs, Freq Gens, Freq Counters, Scopes, Mutlimeters, Soldering Stations, etc... So, if you can tell me what to test, I can tell you what I find...I am wanting to repair this clock for the learning experience. Yes, I know a new clock would be the better investment, so, let's stick with discussing the repair, please and thank you.This is a very minimal circuit... I have only started my investigations, but I am only finding...- a 120 to 4.7VAC-0-4.7VAC transformer to a couple of rectifying diodes... No voltage regulator- the LM8560 takes its timing from the 60Hz mains AC. The is no external oscillator can.- various other diodes, resistors, caps, inductor, etc., but no transistors. I replaced the 330uF e-cap with a 470uF (what I had in stock,) just as a matter of maintenance. The 330uF tested as good. The LM8560 data sheet spec's a 470uF e-cap. This did not improve the display brightness.- I do have 10.87=11.00VDC fluctuating on the LM8560 supply pin, with 0.47VAC. This chip runs on -15V to +0.3V, so I probably had my meter probes inverted.The minimal components seems to be in keeping with the DS common circuit diagram. See attached.I think this chip is meant to drive a common cathode display. So, what might cause the display to dim, equally, over all the digits?Thank you for your help.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 15, 2021, 11:58:55 pm
content: It's a special kind of common cathode display where half the segments are driven on each half of the mains cycle. Biplexed if you like. So you may not have any luck finding a replacement unless it's for/from a similar kind of clock. So you will have to repair it.I picked up a similar cheap clock from e-waste once, checked that it was working and gave it away. I think it was deliberately dim because it was for bedside use. Or maybe the displays had aged.

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 12:15:07 am
content: Thanks for your reply!Here are some pictures. I am still investigating, but it looks like they skimped on everything. Look at page 7 of the DS. There should be transistors on the switches. They skipped those, for example.Look at the return for LED cathode. It looks like the DS has two switching diodes on the display returns. But, the board only has one glass diode. Maybe they combined the returns into the one diode? And, maybe that diode is leaky? Would that cause dimming?The glass diode does test as good, but I only checked it in-circuit, which I know is not legitimate. If you think it being leaky would dim the LED, I will pull it and test it out-of-circuit.Thanks for your help!

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 16, 2021, 12:19:13 am
content: I think that glass diode is not for the display current. Maybe the reverse protection for the mains sensing circuit. Those 1N type rectifiers are the display cathode returns. They are very visible on the RHS of the board.You could check the cathode limiting resistors but it's unlikely that both would rise in value so you would see half the segments dimmer than others. You could reduce them in value to increase the brightness perhaps at some cost to the life of the display.

author: james_s
author_rank: Super Contributor
timestamp: November 16, 2021, 12:37:10 am
content: Are you sure there's anything wrong with it? Old LEDs were a lot dimmer than modern ones, it should be bright enough that you can read it in normal room light but it won't be blinding like a modern LED display.

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 03:14:07 am
content: Quote from: retiredfeline on November 16, 2021, 12:19:13 amThe two 1N diodes below the red-black-red wires of the transformer secondary, which are nested between the resistors, are the rectifying diodes. I have not checked the connection of the other 1N, but I will.Quote from: retiredfeline on November 16, 2021, 12:19:13 amAgreed.Quote from: retiredfeline on November 16, 2021, 12:19:13 amI fear I am losing the display, so that may be a solution to squeeze a little more life out of it. But, I will check everything else, first.Thank you so much for your input.

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 03:16:06 am
content: Quote from: james_s on November 16, 2021, 12:37:10 amThat is a fair question, but I am sure that it has been dimming, significantly, over the last month, or two. I can barely see it at all, in the daytime.

author: floobydust
author_rank: Super Contributor
timestamp: November 16, 2021, 03:57:23 am
content: So far it's not making sense to me. All the LED's shouldn't go dim, B and C segments age the fastest and E or G ages the least, I forgot.Used to actually repair these things in a shop, for manufacturer's warranty. Flat rate $5 if it had a radio. They are very low cost.Common failures were an LED here and there for a dead segment. The clock IC does experience mains surges which can damage it, and rural electricity can be high mains voltage which ends up with too much DC for the IC. Most had bad counters, on fast set they would skip and jump 1.2.3...6.9.10.11 kind of thing.You can try illuminate an LED using a multimeter to judge how their brightness is. Not a multimeter that puts out over say 3V on diode-test, to damage the IC. That will test if the display is to blame.*The digit bank dropping resistors, at the far end, are chipped and likely damaged. 47R or 470R? Did you nail them with a screwdriver.I had an alarm clock using this IC with blue LEDs and it was super bright, with no dimmer, I couldn't use it and went back to a 1970's Randix cube clock radio with VFD I still use lol.

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 08:17:17 am
content: Quote from: floobydust on November 16, 2021, 03:57:23 amNot making sense = agreed. For them all to dim, there would have to be a cause that is common across all of them. That lends itself to the common cathode side, I would think...Quote from: floobydust on November 16, 2021, 03:57:23 amI don't think we have those kinds of power problems, were I am. The label states that the power supply is to be 120VAC. Meaning, it is not an older unit that is only rated to 110VAC/etc.Quote from: floobydust on November 16, 2021, 03:57:23 amI like that idea. I have a couple of ways to get at it... I have a Siglent DMM which has an adjustable voltage threshold on the diode function. Or, I could just use my PSU at some voltage and with the current limited. What voltage and current values do you suggest?Quote from: floobydust on November 16, 2021, 03:57:23 amNo, I am very confident that I did not nick them with a screwdriver. Best I can tell, those marks are not chips, but are smudges - of what I do not know. I have only tested those two resistors in-circuit, but they are reading just 5R/5 Ohms, each.

author: timenutgoblin
author_rank: Regular Contributor
timestamp: November 16, 2021, 10:01:40 am
content: Quote from: t1d on November 15, 2021, 11:13:32 pmIs the display consistently dim regardless of the time being displayed? Is the display brighter at 1:11 compared to 10:58 (12 hour time) or 22:58 (24 hour time) ?The transformer has self-regulation when it's being loaded. The greater the load, the lower the output voltage on the secondary winding.According to the datasheet for the LM8560 it requires 15VDC nominal, but can operate at lower voltages hence the battery backup feature (9V).Are the rectifier diodes working properly? Of course they are...

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 10:29:22 am
content: Quote from: timenutgoblin on November 16, 2021, 10:01:40 amThe unit is disassembled, presently, so operating the switches may prove difficult, but I will give it try, tomorrow.Quote from: timenutgoblin on November 16, 2021, 10:01:40 amI'm not sure I know about the effect you are speaking of... I do know about voltage "droop."Quote from: timenutgoblin on November 16, 2021, 10:01:40 amFrom a previous post = "- I do have 10.87=11.00VDC fluctuating on the LM8560 supply pin, with 0.47VAC. This chip runs on -15V to +0.3V, so I probably had my meter probes inverted."I did not have my probes inverted; this chip can run on positive voltage, as well. See pg7 of the DS. With the GND Probe on Pin 20 and the Positive Probe on Pin 15, the DMM reads a positive voltage.Quote from: timenutgoblin on November 16, 2021, 10:01:40 amGiven that we have the expected voltage at the chip and that the diodes test okay in-circuit, I think that they are operating. Secondary = 4.7-0-4.7 = 9.4VAC - 2 x 0.7Diode Drop = 8VAC x 1.414Factor = 11.31VDCAs I mentioned, I checked the Cathode resistors in-circuit. I went back to double-check that the smudges were not breaks; they are not. But, the paint rings did not make any sense to the values I had read in-circuit. So, I pulled them.I checked them out of circuit, with the Kelvin/Four Wire feature = ~4.7R, each. I looked at the paint rings, under my microscope. The first, yellow ring was not visible to the naked eye. Yellow_4 - Magenta_7 - Gold_/10 - Gold_5% So, they are good.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 16, 2021, 11:07:44 am
content: Quote from: t1d on November 16, 2021, 10:29:22 amActually you do not have a sqrt(2) factor since the cathode supply is rectified but not smoothed because no capacitor. This is another cost saving measure. Also avoids current peaks tthrough the transformer and rectifiers. Each half bank of LEDs is actually getting half-sine waves and would emit a 60Hz visual hum if only your eyes could see it.The positive/negative voltage supply thing is just a matter of perspective. With PMOS technology, usually voltages are referenced to the most postitive voltage so are usually stated as negative.

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 01:20:08 pm
content: Quote from: retiredfeline on November 16, 2021, 11:07:44 amThanks, retiredfeline. I haven't slept, so I will have to let this information soak, until I can process it fully. lol

author: t1d
author_rank: Super Contributor
timestamp: November 16, 2021, 01:45:31 pm
content: I re-installed the two cathode resistors and reflowed the display ribbon cable, on the controller PCB. Then, I considered the illumination, again, at typical room light levels.There is a minor difference in brightness, between the characters, left to right, as you would expect, with age. However, it is just too dim to be seen across the room.I have determined that the display is just plain used up and that's okay. I have checked what there is to check and I learned some things, thanks to you good folks. I think we can call this one "Concluded", but not "Solved."Time to buy a new clock. (There's a joke in there, somewhere.) Or, maybe I will use the clock drive, from this clock, and build a giant character display with three LEDs per character segment. I guess that would require driving some transistors with the clock to power the multiple LEDs... Or, I have been wanting to DIY a clock with a PIC microcontroller. I think I have all the needed parts. The problem is that I am not much of a coder. Maybe I will find a complete project, on the internet? There are lots of fun possibilities.Thank you, all, again, for your help and support. The EEVBlog Community is the best forum I know of, regardless of topic. You make it that way!

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 16, 2021, 01:49:18 pm
content: Instead of discrete LEDs to make a segment, you might consider what I'm thinking, and that is to buy those LEDs in the shape of filaments that are used in retro looking bulbs. You can make quite tall digits with them. Don't know how bright they are but one filament model takes 12V and 45mA. I don't think you want that glowing in your bedroom.

author: james_s
author_rank: Super Contributor
timestamp: November 16, 2021, 07:10:43 pm
content: You could just buy some 7 segment LED displays and solder them up on a piece of perfboard to replace that one. Or if you want a challenge, you could scrap the LED dies off the board in the existing display and solder some 0402 SMT LEDs in their place.

author: tooki
author_rank: Super Contributor
timestamp: November 16, 2021, 07:19:10 pm
content: Quote from: james_s on November 16, 2021, 12:37:10 amThe snap domes make me think it’s notthatold. The one board could be indicating a 1994 date code. Red LEDs were a perfectly mature technology by then. 1970s LEDs were dim, but not 80s/90s. (Sure, we now have LEDs way brighter than that, but indicator LEDs aren’t meant to be blindingly bright.)

author: tooki
author_rank: Super Contributor
timestamp: November 16, 2021, 07:20:26 pm
content: Quote from: retiredfeline on November 16, 2021, 01:49:18 pmI just found a vendor on AliExpress this week that sells 3V LED filaments, from 20mm all the way to 300mm!! I am SO going to build a clock with some of those!!!

author: floobydust
author_rank: Super Contributor
timestamp: November 16, 2021, 08:57:12 pm
content: I was going to use some too for a big display thermometer, but I thought all are high voltage series strings 45-70V. For 3V they must run a wire through and all be in parallel. Hmmm.

author: tooki
author_rank: Super Contributor
timestamp: November 18, 2021, 08:29:25 pm
content: The last time I’d searched was a few years ago, and indeed all I found then were high voltage filaments.

author: Runco990
author_rank: Frequent Contributor
timestamp: November 19, 2021, 12:17:16 am
content: I just looked at that LED clock. I have a few very much from that era, and man.... they are DIM!!! REALLY DIM. And work just as they should. We are spoiled by today's super bright LED's, but you could not see the old one's in bright room light. They were pretty terrible.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2021, 12:52:30 am
content: Well remember that they were mostly meant as bedside clocks, you probably don't want a blinding beacon on your nightstand while you're trying to sleep. I have a Heathkit digital clock I built back in the 80s that has a light sensor that automatically dims the display at night but I don't recall ever seeing that feature on a store bought clock. I don't know why because it isn't complicated.

author: floobydust
author_rank: Super Contributor
timestamp: November 19, 2021, 01:09:58 am
content: TheLM8560LED's are multiplexed duplex at mains frequency, so each pair of digits is on 1/2 time driven by sine-wave, and then that pair is further reduced in perceived brightness by whatever this IC mux operates at. The only RC clock is 900Hz supposedly for the AC fail and alarm beeper, I could not see what it uses for muxing the pair.Point is the LED's may be extra dim due to the oddball (=cheap) multiplexing scheme. The flicker would be annoying.I added a dimmer to my VFD alarm clock and it did not work out. A front-facing phototransistor can only see what's in front of it, which is my dark furniture/bed so it always registers dark. I'm going to change it and make it point up at the ceiling which is white.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2021, 04:20:47 am
content: Now that you mention it, I have a Heathkit VFD clock at our cabin and it has a light sensor too. It's a CdS cell pointed forward at a slight upward angle, seems to work really well.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 19, 2021, 07:37:29 am
content: Quote from: floobydust on November 19, 2021, 01:09:58 amThe multiplexing is at mains frequency coordinated by the sense pin which is also the timebase. No mutiplexing on top of that. Nothing particularly odd about the scheme, just increase the current to about 2x (and perhaps a bit more because the conduction angle isn't the full 180°) and it's a standard multiplexing (biplexing) scheme. Maybe the 60Hz flicker might be noticeable in the corner of your eye but obviously they can get away with it.

author: floobydust
author_rank: Super Contributor
timestamp: November 19, 2021, 03:16:38 pm
content: The common cathode is for a pair of digits, so during that AC mains 1/2 cycle I figured you need to mux those two digits in the pair. It might be 1/4 cycle to accomplish that, so 1/4 perceived brightness, actually less because it's a 1/2 sine not a square -wave. The kooky LED display looks interleaved as well.Clock chips like old MM5314 etc. have their own RC oscillator e.g. 1kHz for doing the display multiplexing and fast set, just the time counter is sync'd to mains AC REF.Edit: The IC is actually a TI TMS3450, so those datasheets seem better.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 19, 2021, 03:50:09 pm
content: Quote from: floobydust on November 19, 2021, 03:16:38 pmNo, look at the pin designations on the datasheet. Half the segments have one common cathode and the other half have another common cathode. Not grouped by digits the normal way. So for say 24 segments, 14 pins are required, as opposed to 11 for 7 segments + 4 digit cathodes. (The number is actually a little different because some segments can be grouped.) That's why you will not be able to use a normal multiplexed display. There's no need to assume it's a TI chip. You can find the datasheet for the model number that OP posted here:https://pdf1.alldatasheet.com/datasheet-pdf/view/41215/SANYO/LM8560.htmlYes, other clock chips use multiplexed digits, but that's neither here nor there.

author: floobydust
author_rank: Super Contributor
timestamp: November 19, 2021, 04:08:38 pm
content: I found details for the LED display, it's like you say some segments per digit are multiplexed- rather than each digit. I think this interleaving would be to lower perceived flicker from them using mains frequency for the biplex.You've got 14 pins and 4 digits plus colon, AM/PM etc. so they aren't saving anything for pins doing this. The only savings is the IC doesn't see high-current "digit" drive on one pin.My reckoning, TI came up with the idea then Sanyo etc. rolled with it.I was tying to figure out the resulting duty cycle for the LED's and what the human eye ends up with.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 19, 2021, 04:13:07 pm
content: Duty cycle would be somewhat less than 50% due to the conduction angle less than 180° as the LED has a forward voltage. The advantage of using the mains cycle for biplexing is it allows the LED supply to be unsmoothed.Some National Semiconductor clock chips also use this biplexing method. Someone on this forum found a handful and wondered how they could use it. I wonder if it was patented. Maybe it is obvious to a person skilled in the art in patent law jargon.

author: quadtech
author_rank: Regular Contributor
timestamp: November 22, 2021, 10:15:15 am
content: The clock display uses a 2 phase clock to mux the display segments at the mainsWe have frequent power outages in my area, so I converted an old LM8560 clock radio torun off battery power, with a CD4541 based crystal oscillator, to generate a 50Hz clock.The output of the CD4541 output is used to drive the 2 phase LED mux; these outputs are gated sothe display is powered on only when the mains supply is present.The attached schematic may explain this better.A replacement duplexed LED display with discrete LEDs is available here -https://easyeda.com/Trajectory/testsAnd a whole clock on pcbway -https://youtu.be/hoPcHzMy-98

author: floobydust
author_rank: Super Contributor
timestamp: November 22, 2021, 08:07:09 pm
content: Interesting project, I see the clock chip has 2 x 14(pin) mux or 28 LED capability. Cute to combine AM/PM and 10's hrs seg B.For the same pin count, I think they could have used fewer pins with traditional 4x7 mux but then the IC would need four high current digit driver outputs. The filter cap is the usual 470uF either way so I don't think those are the pennies they were after. It might be silicon die size and a standard package number of pins.OP's clock, because the common cathodes are 1/2 sine-wave, you're getting less average current (brightness) than a square-wave drive there. RMS would be roughly 71% and the 1/2 time would that not be 35% compared to straight DC?

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 22, 2021, 08:56:40 pm
content: Besides eliminating the capacitor for the LEDs (there is still one for the chip DC supply), going with no smoothing also reduces the peak current through the transformer and rectifier. (Edit: Actually eliminating the cathode drive transistors that would be needed for digit multiplex would be another reason. Remember this was the age of PMOS and high current MOS transistors we have now were not available then.) Lower effective current through LED can be compensated for by lowering the 2 current limiting resistors. A few more pins say 24 to 28 is no big deal. In any case this biplexing scheme was invented many decades ago, who knows what the market justification then was, so if one wants to use this chip one just deals with it. The main drawback is the need for a special display. A search found that this chip can still be purchased but I couldn't find suitable integrated displays.

author: Marcus72
author_rank: Newbie
timestamp: January 12, 2024, 09:13:26 am
content: Hello to everybody, I am new here. Sorry if I resume this old topic. If required I open a new one, but this already contains many info I would like to talk about.I have many questions about the LM8560 and some schematics posted in this thread. I would appreciate if some expert about this chip would explain me. I like electronic, but my knowledge is no more fresh (30 years ago at high school).I still find that the LM8560 is one of the cleverest IC ever produced, and one of the longest living. Even today there some clocks which are still produced with this chip.In the schematic posted by quadtech (3 posts above this), it looks that the AC voltage to drive the display and to be sent to the counter of the LM8560 is not generated by a quartz. This would make the clock not usable (too much drift).https://1.bp.blogspot.com/-qmePruE8o84/X4yLIXyYnFI/AAAAAAAAEe0/it6jztgPmewMNRbRkK5EwqpQn_L1wo2gQCNcBGAsYHQ/s1760/LED%2BDigital%2BClock%2B24Hr.pngAlso in this schematics posted by floobydust I don't see a quartz oscillator. Or am I wrong?:https://www.eevblog.com/forum/repair/dim-led-display-old-lm8560-mains-driven-clock/?action=dlattach;attach=1327064;imageThe LM8560 has many mysteries. I don't understand how the display driver manages the current to the single LED segments:- There is only one resistor for each group of common cathodes- The current that flows through the resistor is almost the same when only few segment are lit (at 1:11 time) and when many segments are lit (at 20:08, or 10:08 for 12h clocks).The brightness of the display decreases significantly between 1:11 and 20:08, but not so much in proportion to the number of lighted segments (I suppose). Does it mean that the MOSFETs that drive the segments also modulate the current (their conduction resistance), so that the current on the single segments does not vary too much, depending on how many segments are lit? But the LM8560 is always cold. It doesn't dissipate heat.As far I know, it is technically wrong to use only one resistor placed on the common cathode line of a multi segments display, because the current does not get equally distributed among the segments. Some segments would drain a consistently higher current than the others. This would short the life of some segments. Therefore I wonder whether the MOSFETS of the LM8560 regulate the current to the segments individually.Does someone has idea about these questions? And there are even some mysteries more

author: retiredfeline
author_rank: Frequent Contributor
timestamp: January 12, 2024, 11:40:31 am
content: Actually in many countries the mains frequency is good enough and will not drift long term because generators are required to fulfull the number of cycles generated. Especially if the clock shows minutes but no seconds, then it's even less important. I have quite a few mains frequency clocks and they work well enough. Your microwave probably has one.It is possible that the chip has a constant current drive for each segment. For a few mA, you will not notice much heat from the chip.The main problem is you may not be able to find duplexed segment displays to suit the chip. I guess some Chinese mfrs may make it for bedside clocks using this chip or similar ones.

author: tooki
author_rank: Super Contributor
timestamp: January 12, 2024, 10:08:49 pm
content: By “many countries” you really mean “all of them” because industrial machinery would break if the mains frequency changed too quickly, and transformers would overheat if the frequency stayed too low for too long. So as you said, they keep track of cycles and don’t drift toooo far. In the long run mains frequency is a better timekeeper than a quartz crystal.

author: Marcus72
author_rank: Newbie
timestamp: January 12, 2024, 10:13:43 pm
content: Yes, as far I know in the modern power plants, the AC frequency is constantly monitored, and the unavoidable drifts that occurs are compensated with opposite sign over the time. Therefore, AC based clocks can result more accurate than quartz clocks, on the mid and long time. Depending on the quality of the AC power grid. I have experienced it with my clocks. But on power grids with unstable and not compensated AC frequency, they are not good clocks.It is strange. Even considering few mA per segment, multiplied by 25-26 segments, it should dissipate some heat, if there is as a constant current regulation, I think. But maybe I am wrong.I will try to measure the current on a single segment in the different conditions.Another mystery of the LM8560 is that when it is powered with its traditional way, using an AC transformer with a central tap, the eye doesn't notice any flickering, even if you put the display direct close to your eye.Instead, if you power a LED with a rectified single half wave using only 1 diode, the LED flickers noticeably. It should have actually the same duty cycle as the segments of the LM8560. I have measured it with an oscilloscope, and the segments of the LM8560 looks to have even a slightly shorter duty cycle, but on them you don't notice any flickering, if you put them direct in front of your eye. I can't explain this.This very reduced flickering maybe is also one of the reasons why the designers adopted this half duplex solution, instead of the traditional multiplexing.The unpleasant thing, is that the spread the 2 groups common cathodes among all the 4 digits. If they had grouped them differently, making 2 whole digits for each group, it would be possible to use normal common cathodes 7 segments modules.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: January 12, 2024, 10:46:50 pm
content: It should dissipate some heat but your finger is not a good measuring instrument. Also your eyes are not good at measuring duty cycle.Modern LEDs are quite bright at a few mA. A bedside clock is designed to be not too bright so each segment may only be a fraction of a mA. Multiply by 20 odd segments and you get maybe tens to a hundred mW dissipation.Traditional LED mutiplexing runs at higher frequencies than mains, hundreds to thousands of Hz. There is usually a relaxation oscillator on the clock chip for the mux.I think there might be places that use uncompensated local generators so I wouldn't be so brave to say all of them. But even back in the third world country where I grew up, mains was accurate enough as a clock source.

author: tooki
author_rank: Super Contributor
timestamp: January 13, 2024, 12:00:05 am
content: Quote from: Marcus72 on January 12, 2024, 10:13:43 pmSuch as…? As I explained above, deviating significantly in either the short or long run causes severe problems that cannot be tolerated; every power grid must constantly adjust its power generation to match the load, so they match frequency as they do this. There isn’t some place with horribly incorrect frequency and frequency stability because that can’t be allowed to happen, and there’s no reason to let it go wrong, since you have to adjust production constantly anyway.On the rare exceptions that a grid is overloaded and struggling to keep up, it may end up getting disconnected from its parent grid, and if the frequency drifts too far, protection circuits will kick in and shut the grid down rather than run it at the wrong frequency, because the wrong frequency could destroy millions (billions?) of $/€ of machinery, and the power company doesn’t want to be liable for that kind of damage.Consequently, I am extremely skeptical of any claims that any electrical grid anywhere in the world has significant frequency stability issues.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: January 13, 2024, 12:20:36 am
content: Someone once measured mains derived time in NL (I think) over a period, I think a year or two and wrote a paper on it. I'm sure you can find it by searching.The kind of drift that was measured was in the order of seconds, so not signiificant to cause harm to consumers and was invariably made up for. I think the actual reason for the control is financial. If the power supplier hasn't delivered the correct number of cycles in the long run then they have under or over supplied the consumer with energy. That works out to a lot of money for the power dealt with.

author: tooki
author_rank: Super Contributor
timestamp: January 13, 2024, 07:06:56 am
content: How do you figure? The amount of energy doesn’t depend on the frequency.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: January 13, 2024, 07:21:15 am
content: Rotating machines.

author: tooki
author_rank: Super Contributor
timestamp: January 13, 2024, 06:01:13 pm
content: Please elaborate. I still don't see how it would make a financial difference.

author: floobydust
author_rank: Super Contributor
timestamp: January 13, 2024, 11:01:49 pm
content: The power plant I worked in, the province grid operator has designated clock freq. correction days where many generators were sped up/slowed down at night. You can do this easily when there is light (night time) load. It's just to correct mains clocks drift over the long term.I have an old alarm clock using mains and it does just fine keeping time, so far beating my Aliexpress LED clock with counterfeit DS3231 lol that thing drifts like junk.For an AC mains failure, the alarm clock switches to a phase-shift oscillator/battery power.