Once Bitten: the saga of computer power supply protection [part 1]

Like most people, I occasionally find it necessary to research topics with which I have no previous familiarity, in order to address certain nagging practical questions.  (“Is the risk of drug interaction between pseudoephedrine and vicodine overstated?” “Am I endangering my life by attempting to pry this thermocoupler loose from the furnace with a sharpened spoon?”  “Will writing this e-mail get me arrested for insider trading?”  Etcetera.)  Unlike most people, however, I frequently seem to find myself in the situation of having done that research, only to wind up with another hundred questions.  Such is the case with the exciting topic of computer power supply protection, the mention of which has invariably elicited a monosyllabic and confused “Huh?” from those friends with whom I have dared to broach it.  I am setting forth what I have learned about it and related matters here, not only to straighten it out in my own head, but in the hope that it might prove useful for someone else wrestling with these same issues.  If you’re that someone, read on…

First, a brief background.  Until a few weeks ago, my household desktop was a Dell PC with average stats running two high-end monitors off a single video card, plus a variety of standard peripherals (cable modem, ink-jet printer, and so forth.)  After four plus years of reliable performance, I awoke one morning to discover that it had died during the night, irretrievably.  Some quick on-line searches via a laptop, plus some simple experimenting with the plugs identified the problem as involving the power supply.  The reports of the technicians who examined it were more precise:  the capacitors on the mother board were blown, probably as the result of a power surge.  That confused me.  Wasn’t my computer plugged into a surge protector?  How did a surge get through the protector with enough juice leftover to blow the system?  How did it manage to blow the system without blowing everything else?  I started the research out by attempting to answer those questions, and also looking around to see if there was any kind of more advanced option available.

Second, some general, extremely non-technical terms, so we’re all clear on what we’re talking about here:

• A spike is a very short instance when your wall outlet is putting out more power than it should (presumably called such because if you look at a graph of the power over time, the line on the graph “spikes” upwards sharply then drops.)
• A surge is a spike that goes on for a long time, seconds or more.  (Some sources I’ve seen use “spike” and “surge” interchangeably for the short-term problem, and call the long term problem “high voltage”.  It’s all good…  er, bad.)
• A sag, conversely, is a very short instance when your outlet is putting out less power than it should.
• A brownout is a sag that goes on for a long time, seconds or more.

And of course, a failure is when the power goes off completely.  Simple, right?

And so we start with that rectangular bar the computer was plugged into, the one that was supposed to prevent this…

SURGE SUPPRESSORS

Surge suppressors (no one seems to calls them “surge protectors” anymore, presumably because to call something a “protector” implies that such protection is fail-safe) are a simple power supply protection tool that most people are aware of as being necessary.  It doesn’t take a genius to figure out that if a bolt of lightning hits the house next to you, the resultant surge through your electrical system is probably going to fry anything plugged in that doesn’t have some kind of defense line.  (If a bolt of lightning hits your house, whatever’s plugged in is probably going to fry regardless of how you have it set up, and you should be more concerned with having escaped with your life than with the condition of your electronics.)  The possibility of a fried appliance is no great concern if it’s a lamp.  It sucks colossally if it’s your high-end computer or world-destroying home theatre system.  So you need something to keep that from happening, and the surge suppressor is it.

Less obvious is just how surge suppressors do what they do.  There are a couple of different technologies they can use, but the garden-variety one that my computer was plugged into, and all the ones that I looked at to replace it, (and probably all the ones that you’re going to be looking at) rely on elements called Metal Oxide Varistors, or MOVs.  An MOV is a small electrical component that responds differently to different levels of voltage.  At the voltage of your wall current, it doesn’t conduct electricity at all.  At some level of current above that, it becomes conductive, and in your suppressor, drains the power away from your computer and into a ground line, where it dissipates harmlessly.  The voltage at which it performs this action is called the clamping voltage, so lesson #1 is:  lower clamping voltage = more stringent protection.

Unfortunately for you and me (and the varistor), the MOV degrades while performing this act–  physically breaks down.  And it’s not a binary, zero-one sort of degradation:  one overwhelming surge that exceeds the clamping voltage may render it useless in a single shot, but multiple smaller, shorter surges that are near the clamping voltage will also degrade it, reducing its effectiveness and potential protection.  This has the following implications:

1. You should probably replace any MOV-based suppressor periodically, even you haven’t been on the receiving end of a lightning bolt.  The one I was using was easily 6 years old or more;  it had undoubtedly been subject to many small surges that weakened it before the final blow.
2. The lower the clamping voltage and more stringent the protection, the higher the frequency of surges that will approach the clamping voltage over time-  and thus, the faster the degradation of the MOV.  (Tradeoff City!-  but whether that increased speed of degradation is meaningful- that is, whether we’re talking about two years vs. three years, or six months vs. three years-  I have yet to determine.)
3. On the product features list of a suppressor that you are considering buying, you might want to look for a fault light, some rudimentary indication that it will give you when it’s no longer working correctly.  Mine had one, and yes, it is now lit, lending credence to the surge explanation.  It is also entirely possible that it was faulted long before the evening in question, and I just never noticed!

Some suppressors include a circuit breaker or fuse in addition to the MOVs, so that a power situation that will toast the MOVs also cuts the line (unavoidably getting your attention).  Whether or not this is redundant given the pre-existing circuit breakers or fuses in your household, I don’t know-   but it will prevent you from using a compromised suppressor, and deprive you of the right to complain that you weren’t aware anything was wrong.

Also not necessarily obvious when considering surge suppression is the need to run whatever data line you’re using through the suppressor (the phone line for dial-up, coaxial cable for cable broadband)-   those lines conduct electricity just as readily as power lines do, and can provide a bypass that allows an incoming surge to hit your system if left unprotected.  Good surge suppressors allow for the connection of either, or both, right next to the power lines.  The one I was using was old enough that it only had a provision for a phone line; my cable modem, meanwhile, was blithely connected directly to the wall.  Did that factor into the collapse?  Hard to say…  but it certainly wasn’t doing it any good.

Some other terms and concepts associated with surge suppressors:

• The response time is how long it takes the suppression elements to become conductive and shunt the current.  Lower= faster= better.  Under 1 nanosecond seems to be a good current benchmark.
• The protection rating, usually given in joules, is how much energy the suppressor can shunt away at once before it itself fries.  Higher=better.  300-400 joules seems to be the minimum at this point;  I ran across a “home theatre grade” classified that was rated for 4000 joules with only 10 minutes of searching in Home Depot.
• The peak let-through voltage, for you technically-minded sorts, is the maximum “transient” (spike or surge) that the suppressor will let through before it intervenes.  It is, however, a measurement of “peak voltage”, which is not the same as “RMS voltage”, the average output of an AC current.  My understanding of it is tenuous, and if it’s meaningful to you, you probably don’t need me to lecture you on surge suppression.
• A Connected Equipment Warranty is the selling company’s way of saying that if the suppressor fails and your equipment gets zapped, you’ll get a payoff from them as compensation (provided it happens within a certain time-frame, of course;  that provision alone would seem to ratify point number 1 above about replacing it periodically!)  I have no first hand experience with attempting to redeem such a warranty, or any anecdotal accounts of anyone who did.  I imagine it has the potential for convenient fine-print exceptions, like any warranty.

Readers who have threaded their way through the above descriptions might have noticed some additional implications:  that your wall current is potentially full of all sorts of variations;  that spikes and surges lower than the clamping voltage are not really being affected by surge suppression;  and that  sags and brownouts aren’t being addressed at all.  If that worries you, congratulations:  you’ve progressed to topic 2:  power conditioning.

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If you have read this article, and you believe that I am seriously off-base or factually in error about any of the above information, please leave a comment and tell me!  I will happily revise it, and learn from my mistakes.