is a UPS really needed?

westom said:

Either an earlier copy of the file was already saved on disk. Or the latest copy is already saved to disk. Does not matter if a new file is being written when power is lost. A disk file system reverts back to the last valid (uncorrupted) copy.

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That's not how it works. It does not make copies of files that are used by the operating system to run your computer.

If a file is marked open while a program is in execution and when the power shuts off, access to modify that file is locked out by other processes. Locking out files is a simple method to stop unauthorised programs with interfering with the operations of your computer at the file level.

When a system reboots, it will not be able to write to the file that is locked out (read only) and it will not allow a user to boot into the operating system. It will crash and fail!

This is just one example how loosing power and not cleanly shutting down your mac or pc can prevent it from ever booting up again.

Looking for good suggestions for a UPS where I can change out the batteries when they no longer hold a charge? Anyone?

No off event in AC sine wave

The AC sine wave does mometarily go through "0" (item #3), but this does not constitute turning the power off, an actual event of discontinued power. It creates no switching transients. It is merely a moment in an ongoing function. Hence your comparison is off. As to power surges readers might contact your local power company on their occurence and frequency. As to westom, giving your source information might lend some credence to your points. ipse dixit makes thin soup.

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westom said:

Let's undo some popular myths.

First, if a power loss occurs during a disk write or before a file save, then a drive simply reverts to a previously saved version. No data corruption. That corruption threat was eliminated by file systems developed before 1990. Unfortunately, a myth of data corruption lives on.

Second, get some numbers for a typical stepped sinewave (also called a pure sinewave) UPS. For example, this 120 volt UPS outputs 200 volt square waves with a spike of up to 270 volts. Is that destructive? Of course not. Because all electronics (including a Mac) contain superior protection. Protection that makes spikes from any UPS irrelevant.

Third, does power restoration created a surge? Only when myths exist. What is AC electricity? Power goes off and on 120 times every second. If power restoration creates a surge, then so does normal power that goes positive, zero, then negative, and then zero again so many times every second.

Fourth, two completely different devices are both called surge protectors. An adjacent one claims to protect from what is already made irrelevant by every Mac. Same internal protection also makes irrelevant 'dirty' electricity from a UPS.

Fifth, your concern is a completely different and rare transient that may occur once every seven years. An anomaly that can overwhelm internal Mac protection. And is only averted by the other completely different device with a same name.

That other surge protector must be installed where wires enter a building. Connected as short as possible to earth ground. Spec numbers that say it will earth direct lightning strikes and remain functional. And is a least expensive solution. This 'whole house' protector is provided by companies with superior reputations. Including Siemens, Square D, Ditek, General Electric, Syscom, ABB, Leviton, Intermatic, and Cutler Hammer - to name but a few.

Surge protection or 'temporary and dirty' power from a UPS are different solutions to different anomalies.

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Shivetya said:

Looking for good suggestions for a UPS where I can change out the batteries when they no longer hold a charge? Anyone?

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If you're in Australia, there's a place called "Battery World". In order to help you more, we'll need to know the country you're in, or try to google it yourself. Maybe a phrase like "buy battery to replace in UPS".

You'll need to open up the UPS at some stage and provide the shop with the details of batteries the UPS is using. With them being specialised in that industry, they can provide you a number of different batteries from different manufacturers that will do the job, what they have in stock and how much they are.

Raima said:

If a file is marked open while a program is in execution and when the power shuts off, access to modify that file is locked out by other processes.

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You are making assumptions based upon a the limited perspective of a programmer. How file systems work is completely transparent to programmers. And is why power loss does not corrupt a disk.

Describe in layman's terms is why unexpected power off does not corrupt files.

Either an earlier copy of the file was already saved on disk. Or the latest copy is already saved to disk. Does not matter if a new file is being written when power is lost. A disk file system reverts back to the last valid (uncorrupted) copy.

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Learn about journaled or journaling file systems.

A UPS provided temporary and 'dirty' power so that unsaved files can be saved.

Tucson Allen said:

As to westom, giving your source information might lend some credence to your points.

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I am a little confused why basic (layman) electrical knowledge requires source information. Should I quote my 1st semester circuit theory book? Exactly which concept requires citation?

Second, power restoration from AC mains or from a power switch is fundamentally same. One difference: a switch may also create noise (tiny harmonics).

Third, what happens inside a power supply? That 120 volts is converted to well over 300 volt radio wave spikes. If rumored spikes from power restoration or a power switch are destructive, then much higher voltage and frequency spikes inside electronics are more destructive.

Why do electronic appliances create rock solid 3, 5, and 12 volt DC power from well over 300 volt high frequency spikes? Because standard circuits inside electronics make irrelevant 'dirty' power from a UPS, rumored spikes from power restoration, and 'dirtier' power intentionally created inside electronics.

How is 'dirty' power made irrelevant? Best filtering and other solutions already exist inside all electronics. Electronics have been required to be that robust generations ago.

Fourth, sometimes a destructive anomaly is followed by a power outage. When power returns, the homeowner sees an appliance damaged. Did power restoration cause that damage? Yes, when speculation makes that conclusion. No, when one learns damage occurred before power was lost.

Fifth, power restoration causes a slowly increasing voltage - not a destructive spike. Electronics find this ideal. However this slowing rising voltage is potentially harmful to motorized appliances. Best is to power off motorized appliances until voltage is restored and stabilized. Because motors prefer voltage to be applied sharply - ie full voltage on and off 120 times each second.

westom said:

You are making assumptions based upon a the limited perspective of a programmer. How file systems work is completely transparent to programmers. And is why power loss does not corrupt a disk.

Describe in layman's terms is why unexpected power off does not corrupt files.
Learn about journaled or journaling file systems.

A UPS provided temporary and 'dirty' power so that unsaved files can be saved.

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I would think twice about calling everyone who's everyone a liar who's ever experienced a corrupt operating system after a power outage.

Your theory does not go hand in hand with people's results or experience.

Raima said:

I would think twice about calling everyone who's everyone a liar ...

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I never called or even implied anyone was a liar. However your are incendiary. If you knew a power outages corrupts a disk drive, then you should also say why. You don't even try. Instead you post accusations. And not one useful fact.

Your accusation also ignored a paragraph that already answered that accusation:

Fourth, sometimes a destructive anomaly is followed by a power outage. When power returns, the homeowner sees an appliance damaged. Did power restoration cause that damage? Yes, when speculation makes that conclusion. No, when one learns damage occurred before power was lost.

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Returning to the OP's questions. A UPS is temporary and 'dirty' power so that unsaved data can be saved. Effective protection is performed elsewhere using other hardware and installation practices proven by basic science concepts and over 100 years of experience.

westom said:

Let's undo some popular myths.

First, if a power loss occurs during a disk write or before a file save, then a drive simply reverts to a previously saved version. No data corruption. That corruption threat was eliminated by file systems developed before 1990. Unfortunately, a myth of data corruption lives on.

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In theory, however, the reality is that all too often file corruption is the result. Start a disk defragmentation and in the middle of it, pull the power to your computer. Do this over and over again and report back if you had no file corruption. Journaled file systems *should* prevent file corruption, but the advent of write-back caching makes that an iffy proposition.

Second, get some numbers for a typical stepped sinewave (also called a pure sinewave) UPS. For example, this 120 volt UPS outputs 200 volt square waves with a spike of up to 270 volts. Is that destructive? Of course not. Because all electronics (including a Mac) contain superior protection. Protection that makes spikes from any UPS irrelevant.

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Again, actual experience shows that stepped sine wave UPS's to be problematic for some power supplies.

Third, does power restoration created a surge? Only when myths exist.

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Incorrect, because power restoration often isn't a simple matter of simply turning on the power. High voltage switching centers have capacitor banks or inductor banks that cause voltages to swing if performed incorrectly.

Q. A big storm made my lights flicker several times during the past hour. What should I do?
Large storms often blow tree limbs onto PGE’s power lines, resulting in a fault that creates a power surge. A power surge can damage your electronics and appliances. If you do not have surge protection, you should turn off your more sensitive equipment like televisions and computers to avoid damage.
https://www.portlandgeneral.com/safety_outages/power_troubleshooting/home_power_troubleshooting.aspx

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and this, from General Electric http://www.eeel.nist.gov/817/pubs/spd-anthology/files/Protect techniques.pdf see "Switching Surges" on page 3, labeled as page 87.

Switching a 120v light switch on and off is simply not equivalent to switching 110Kv, 220Kv or even 500Kv lines with capacitor and/or inductor banks. Even the power you receive every day from your power company will generally have several spikes in it every day, due to load shedding and switching operations.

Fourth, two completely different devices are both called surge protectors. An adjacent one claims to protect from what is already made irrelevant by every Mac. Same internal protection also makes irrelevant 'dirty' electricity from a UPS.

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Nobody has suggested that an ordinary surge suppressor is effective against a lightning strike, that does indeed require protection at the service entrance.

westom said:

then you should also say why. You don't even try.

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It was said why and even provided links where computer systems failed to reboot after a power outage.

Yet you continue to spread misinformation to people that their systems are immune to system failures after power outages where systems were not shut down cleanly.

2Turbo said:

I still think you are insinuating a surge protector or ups unit is basically snake water as it won't protect better than the built in iMac protection.

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Surgex is a series mode filter. It will somehow stop what three miles of sky could not? Of course not.

Numbers say how well it filters. And other numbers for how well it will survive transients that blow through it. But it is only a filter. Its numbers define extremely limited filtering during a typically destructive surge.

BTW, it forgets to mention that a surge on its safety ground wire bypasses the Surgex and therefore bypasses protection provided by a Mac's power supply. They forgot to mention that part.

Surge protection means you know where hundreds of thousands of joules dissipate. Martzloff (and Nuke61) discuss some surge sources including switching transients and lightning. These occur during normal operation or belore power is lost (not during power restoration). The transient seeks earth ground.

If a path to earth is via an appliance, then the appliance is damaged. See Figure 8 in Martzloff's 1979 paper to understand why:
http://www.eeel.nist.gov/817/pubs/spd-anthology/files/Coordination 1980.pdf

What is a best protector on an incoming coax (cable TV) wire? Coax is hardwired low impedance (as short as possible) to earth BEFORE entering the building. A wire connects the coax to earth. What Nuke61 called, "protection at the service entrance." Then hundreds of thousands of joules dissipate harmlessly in earth. What does the protection? A wire connection to earth ground. No protector exists.

Telephone and AC electric cannot connect directly to earth. You make that same earth connection via a protector. A protector is one part of effective protection system when a surge connects to what does protection. Where are hundreds of thousands of joules harmlessly absorbed? Earth. What is the protection? Earth.

Yes, this typically is very hard to understand. Because one must first unlearn advertising myths and hearsay. Protector and protection are different components of a 'protection system'.

A reliable facility can have no protectors. But it must always have earthing - the protection.

Either a protector connects low impedance (ie 'less than 10 feet') to what does protection - earth ground. Or it only claims to protect from other (often not destructive) anomalies. Don't ignore that number.

So back to a Surgex or a UPS. Where is the always required and short connection to earth? None exists. Surgex spec numbers define a filter that will somehow block or absorb what three miles of sky could not stop? UPS claims near zero surge protection that gets hyped by hearsay into 100% protection? In both cases, no low impedance connection to what does protection - earth ground.

BTW, other surges exist. A USB device consuming too much power creates a different surge. Again, the word 'surge' describes something completely unrelated. The word 'surge' is even used to define a computer's undersized power supply. So what is one surge protector that protects from all these?

Without specific numbers, we have little idea which 'surge' is being addressed. Above discusses the one surge that does damage because it hunts for earth ground destructively via appliances (ie a Mac).

And yes, some surge protectors earth even direct lightning strikes harmlessly. Even the protector is unharmed. But most of your attention should focus on what does protection - single point earth ground.

westom said:

Surgex is a series mode filter. It will somehow stop what three miles of sky could not? Of course not.

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Once again you're bringing up a lightning strike when nobody else is talking about a lightning strike, just ordinary power loss and regaining power.

BTW, it forgets to mention that a surge on its safety ground wire bypasses the Surgex and therefore bypasses protection provided by a Mac's power supply. They forgot to mention that part.

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If you get a surge on the GROUND wire, then you've got much bigger problems than a simple voltage spike, you've got a lighting strike nearby. Once again, nobody has brought up lighting strikes except you.

Martzloff (and Nuke61) discuss some surge sources including switching transients and lightning. These occur during normal operation or belore power is lost (not during power restoration).

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It is absolutely FALSE that surges/spikes don't happen during power restoration. It is exactly the opposite, that it's *more* likely that they will happen during power restoration than during normal operation, because during normal operation the grid dispatch operators have very good idea of the loads on the grid, and switch in generation or voltage boost/buck as needed to support the mostly known loads. After a large power loss, they simply don't know with the same level of certainty how much load is on their system, and thus, the generation needed to get the proper voltage. They might switch in far too little or far too much generation capacity, and then counter it by switching again, either picking up or dropping generation or even large loads that can be dispatched by grid control. The result? Voltage swings and spikes as they switch loads and generation in and out until they match.

2Turbo said:

So can I just get a good surge protector and call it a day? Seems like the rare time it might go out, there will be minimal if any data loss.

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I absolutely hate the idea of the data loss, so these 15-20 min an UPS can give me to save my work / finish what I'm working on are more than welcome. I also use surge protection combined with UPS. Maybe it's an overkill, I'm not sure.