Wouldn’t leaving it unplugged for 2 seconds accomplish the exact same thing?
Ditto for any other device that requires you to disconnect from the power source. (Smart phones etc…)
WAG, when I shut down my computer normally, it takes a while for all the programs to unwind and revert back to a position from which they can restart. Just an assumption, that there are programs running in your modem, which need time to close out before restarting, and powering up too soon interrupts this shutdown process.
It depends on the device. Some electronics don’t have hard reset functionality, charge left in capacitors can leave the device in an unknown state until they’ve fully discharged. Other devices can fully reset themselves on power up to a known state. So it’s just a precaution for any device to make sure it’s completely powered down before restarting.
I also understood that the ISP will hold your address (assuming it is dynamic) for a while before reallocating it. If you want to change your IPA, you need to leave it off for long enough for that to happen.
For all the ISPs I am familiar with, that time (the DHCP lease time) is one day.
The 30 second shutdown is to guarantee that the modem actually resets. I usually ignore that suggestion, and give it a few seconds.
I think 2-5 seconds max. for any such device ensures the caps drain.
What I usually see is 10-15 seconds. While technically too large, it’s enough to ensure that people who are ansty and try to rush it a few seconds wait long enough.
It’s also a good idea for many devices to not immediately stop and restart it just to reduce stress on the components.
I usually cave in after 10-15 seconds and it always works.
So no, 30 seconds is not necessary.
Are you suggesting that any programs are running (even if they are just gracefully finishing what they need to do) in your modem after you turn off the power? If there is no power how can they be running?
If the modem has a capacitor, the device might be drawing power from that, and will continue to do so until the capacitor is fully discharged. So anything that is resident in memory on the device will still be ‘running’ until that time.
Most chips have a “reset” line; the system resets when this lead on the chip transitions from zero volts to say, 3 volts. Standard electronics that runs a boot sequence would have the reset line tied to a resistor-capacitor circuit tied to + voltage, so that the line did not go “on” until after a slight delay, so that full power is applied to all parts of the circuit and they are ready before the boot sequence statrs.
Meanwhile, there’s the process of converting AC to DC (all these electronics use DC to run). AC is converted by a set of diodes to a lumpy DC (imagine cutting the sine wave in half and flipping the bottom half up). This lumpiness is smoothed by large capacitors and RC (resistor-capacitor circuits), typically.
When you unplug electronics, it takes a few seconds for those capacitors to drain. If they don’t drain enough, the “reset” line does not go below the trigger threshold, so applying power will not trigger the boot sequence and the electronics “freeze” - some parts may be stuck in arbitrary states.
So the usual advice I have heard is “turn it off /unplug it, wait 10 seconds, turn it on”. I assume most phone help lines make it 30 seconds because some people would be impatient. I would think 2 or 3 seconds should work. This just guarantees that the device begins from boot sequence, any residual settings disappeared when the power fully drained.
Every pulled the plug on a device like a laptop power supply and watched the LED slowly dim for the next 2 or 3 seconds?
speaking from a call center perspective, when giving troubleshooting instructions, “30 seconds” is typically interpreted by the caller as 5 seconds. I can’t count the number of times I’ve instructed someone to power something off, wait for 30 seconds, then power back on. I’ll time it, and 30 seconds after they say they turned it off, I’ll tell them to go ahead and turn it back on. I’d say about 90% of the time, the caller responds that the machine is already turned back on, booting up. Perhaps their perception of 30 seconds while waiting on a phone is altered, or they just don’t care. But especially when powering off hardware that contains moving parts (ie. spinning hard drives), you really should wait at least 10 seconds before powering it back on. You might just turn your hard drive into a paperweight if you attempt to power it on while it’s still spinning down. Modems, Routers and devices with SSD storage, not so much…
The better quality modems are designed to be able to handle a few seconds of no power – this prevents them from resetting when your electrical power drops for a moment & your lights flicker. Otherwise it would reset annoyingly often.
So to force a reset, they suggest waiting 30 seconds. People usually only wait 5-10 seconds, but that’s enough to reset most modems. But unplugging & immediately replugging usually isn’t enough.
I have a laptop that, several years ago, developed a severe display-screen problem that rendered it almost unusable. I left it powered down for hours — still the same display bug. Fortunately it was possible to copy its files to an external despite the severe display problem, so I just bought a new laptop and moved on.
One day, several weeks later, I thought of taking it somewhere for possible repair. I powered it on since I needed to reconfigure something to avoid confusing repairer. The laptop worked fine!! A few more experiments seemed to confirm it: Let the machine run hottish for a few hours and a severe display bug occurs. To recover, leave the machine powered off for several days, not several hours.
Was this an intermittent bug that, by chance, seemed correlated with ultra-long off-periods? It seemed logical to me that some flaw might cause a net in an IC to develop a charge that would discharge only very slowly. I almost posted an “Is this possible?” query here at SDMB — well, I’ll ask the question now.
A similar tale has I. One day computer forgets how to talk to the router. I’ve turned both them off and on again several time, spent a couple of hours in the googlepants to no avail. Finally I come upon a suggestion to leave the computer off for an extended period rather than a few seconds, and bugger me if it didn’t do the trick.
But does that require 30 seconds?
How does delaying the stop and restart reduce stress on the components?
Or they know from experience that it just doesn’t matter.
Given that this has happened so often that you “can’t count the number of times”, why haven’t you changed your instructions? Either you should emphasize that it is really important to wait 30 seconds (and not one second less) or tell them whatever actually works for their particular device.
Paxx: Given the naiveté of your questions, I don’t think it would be worth the effort to give the necessary extensive education to clear up your confusion.
Just take it for granted that people who know these things better than you have posted sufficient information already assuming a reasonable understanding of electronics (and human nature). If you don’t have that background, it would take a really large amount of effort to explain it all.
If you’re still not satisfied, I’d suggest taking a couple of college level courses in Electronics as well as perhaps some Psychology courses.
Again, at least 3 to 5 seconds no power is required to clear the capacitors in the power supply and ensure all power is drained from the system, to ensure a clean restart.
Also, yes, when electronics act erratically, odds are it’s because of overheating. Chips that work within spec when cool may overheat with warm environments and constant use to the point where they do not perform properly; possibly because the chip is slightly out of spec. A transistor uses energy (creates heat) every time a transistor changes state; there are thousands to millions of transistors on some chips, so the type of activity a chip is doing will also determine how hot the chip gets - so you may not re-create the circumstances of failure again, or for a long time.
(My father-in-law’s computer would boot up and within a few seconds the video stopped. After a while, the video did not work at all. Looking inside, the heat sync had popped off the video chip. Overheating killed the video chip.)
That part above about “capacitors” is your answer!
Capacitors are sort of like short term batteries. They will keep something running for a short period of time after power is removed. And this happens more so as devices become more energy efficient. Unplug something and you may notice the power light continues to stay on for a bit. That is a capacitor continuing to power the device.
These days, that’s mostly an “old wives tale.”
There’s no modern device that I know of that requires a long interval between power-off and power-on for longevity reasons. In Ye Olde CRT days, the degaussing coil would have a PTC thermistor is series so that it would only run for the first few seconds after power up. If you turned the set off and then back on again immediately, it would not run, but, so what?
Also, some switching power supplies have NTC thermistors to reduce in-rush current. If you flip them off and then back on quickly, the inrush current might be enough to blow the fuse, but no permanent damage will be done.
Thanks. That’s what I thought.
Also, previously in this thread, you said:
[QUOTE=beowulff]
The 30 second shutdown is to guarantee that the modem actually resets. I usually ignore that suggestion, and give it a few seconds.
[/quote]
That’s what I’ve done over the years but I continue to be told by support techs to wait 30 seconds, which is interesting given this web page: Why support tells you to wait 10 seconds before rebooting.