[mythtv-users] Power outages and UPSs

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Mon Jul 30 22:51:23 UTC 2007


    > Date: Mon, 30 Jul 2007 16:41:09 -0400
    > From: "Michael T. Dean" <mtdean at thirdcontact.com>

    > That sounds like a very real possibility.  Florida is, after all, the
    > lightning capital of the US.  Though I almost always have power, I get a
    > lot of spikes (with both the up and the down that follows--I've heard
    > the down is usually worse on electronics).

[Down is only sometimes worse.  And "good" UPSes (midrange APC's for
sure) will also compensate for slight drops w/o having to go
on-battery.  Big dips will be compensated-for by the UPS battery, of
course.  The UPS -must- be rated to take these dips---that's its
design function!  "Down" will increase the current drawn by switchers,
but that's irrelevant unless it's prolonged (things get hot).  It
absolutely destroys AC motors via overheating, but that's not your
problem today.  And at least "down" can only go down so far, whereas
"up" can be as high up as you can imagine, so at some point "up" is
far worse... :) ]

There are commercial powerline analyzers that can watch for spikes,
sags, frequency deviations, and the like, and log the output.  (I have
one myself.)  You may be able to rent one, or get the local utility
company to park one on your premises for a while and see what happens.
If all you care about is HV surges, you can also kludge a solution; as
I recall, about 25 years ago I built the cheesiest imaginable version
using a resistive divider hooked to the line, and some sort of fast
latching logic element (e.g., the SET input (not the clock! :) on a JK
TTL flipflip or something) that would light an LED and keep it lit if
the line ever spiked to the point that the divider yielded a logic 1.
This was for somebody's phone line, and sure enough, it tripped after
a week or so and explained why cheap electronic phones kept getting
fried.  (A complete solution for a power line would be one on hot, one
on neutral, referenced to your true ground, and see my PS below.)

Unfortunately, if that's your problem, there aren't many good
solutions that are particularly inexpensive.  You can get whole-house
surge suppressors that mount in your breaker box; they're the moral
equivalent of a giant MOV.  They're not cheap.  OTOH, there are
probably lots of qualified installers for them in Florida... :/

You can probably get purpose-built quality surge suppressors and put
them -before- any CPU or UPS.  This can backfire; I had one from
Tripp-Lite that fed several UPSes.  It worked for low load, but it
hummed annoyingly at higher load (30-50% of its rating?  I forget)
and since it was in a quiet room, it pissed me off and I bypassed it
and plugged the UPSes in directly.  (It continues to protect phone and
video connections, though, or at least is claiming to do so... :)
It took me a while to finally figure out -where- that annoying hum
was coming from, since I didn't expect it from an essentially passive
component with no transformers in it.

P.S.  Don't overlook the possibility that your house is poorly
grounded, especially in a lightning-prone area.  A bad ground can
allow damaging HV spikes in via a variety of nonobvious paths and
damage things even w/the cleanest utility power.  A nice reference on
this for the typical electrically-minded homeowner is _Wiring a House_
by Rex Cauldwell; he talks a lot about how to drive real grounding
rods (where, how many, etc) that will perform much better than the
typical cold-water-pipe ground.  I recommend also that you use the
thermite-based fast-welding solutions rather than attempting even an
outdoor-rated ground clamp; I don't trust the latter not to go ohmic
over time.  I can look up where you get such things if you care.  (And
they're fun to use!  Smoke!  Fire!  Red-hot glowing stuff!  And the
grounding rods (typically 10' lengths of 1/2" or 5/8" copper, with one
very sharp and pointy end) are still amazingly cheap (less than $10)
at Home Depot, even considering the outrageous price of copper these
days, and make excellent javelins if you're tired of the prosiac
lethality of lawn darts.)


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