Re: UPS waveform question for SUN servers
- From: "DoN. Nichols" <dnichols@xxxxxxxxxxx>
- Date: 17 Dec 2008 03:10:46 GMT
On 2008-12-16, JJ <jj21@xxxxxxxxxxx> wrote:
I've been somewhat ignorant about UPSs. It was just recently that I
discovered that the main difference between the two UPSs we have is
that one produces a true sine wave (APC smart-UPS), while the other
(which was cheaper but with a higher VA rating) produces a stepped
approximation (APC smart-UPS SC).
O.K. The pure sine wave is better for systems with input
transformers (typically linear regulated supplies), which are more
likely to be found in audio equipment these days than in computers.
These UPSs sit between the wall outlet and two aging sun blade
workstations (a blade 1k - over 5 yrs old, and a blade 2k about 4 yrs
old).
The SB-1K and SB-2K use the same power supply. I've got a spare
(from a damaged chassis which I got from eBay -- but what I needed was
fine, so the damage did not matter to me. :-)
I not too long ago happened to take the power supply apart
(looking for a C-ring from one of the CPU modules which had gone into
hiding because someone had apparently tried unscrewing one jackscrew
completely before going to the other. :-(
The interior of the power supply is purely a work of art. And
It is a switching power supply with auto input voltage switching. I
doubt that it even knows that the waveform is only a stepped
approximation.
The more expensive UPS with the true sine-wave output just had its
battery die. During its life, this UPS has caused more trouble than
it has alleviated - with the battery sometimes discharging for no
apparent reason and the computer being unceremoniously shut off - why
in this eventuality the UPS would not just run the computers directly
off the incoming power is beyond me, but as I said, I'm pretty
ignorant about these things. I even had the UPS unit and the battery
replaced, but I've seen this type of anomaly occur about once a year.
Hmm ... circuit breaker tripped because too much load was on all
of the outlets serviced by that breaker?
Cat or dog knocked the plug from the wall? (This happened to my
wife's computer recently. I was hearing the alarm, but we have so
many things running that I could not track it down (I thought that it was
the keyboard beep). It communicated via the serial port to her SB-1K
and shut it down cleanly as intended, instead of suddenly dropping the
power from under the machine. If she had looked at the LEDs on the USP
front panel, she would have seen that it was running from battery power
and we could have prevented the shutdown entirely.
Automatic battery test with the VA load too close to the maximum
rating of the UPS and aging batteries? I've encountered this causing
the UPS to shut down for a short time when it shifts to powering the
system from the batteries to see how they handle the load. Normally,
all you may notice is a beep from the UPS when it switches to battery
power, and then silence. It typically gives beeps in Morse Code to tell
you what it is alarmed about. :-)
I thought a UPS was supposed to prevent unwanted shutdowns!
Not if it loses AC power long enough.
You need to have the audible alarm turned on, and to notice it.
(I failed the latter in that one case. :-)
Afterwards, the UPS battery would recharge and all would seem fine
again.
It sounds like the power cord connector loose in the outlet. Or
perhaps a house made during the period when aluminum house wiring was
legal. The aluminum crushes under the screws over time and starts to
make poor contact, which could leave your UPS without power for long
enough to discharge the batteries and to force a shutdown.
Anyway, because the battery is now truly dead (or so says the UPS
unit), I decided that now would be a good time to upgrade the unit to
one that is more dependable and with a higher VA rating. So I figured
I would get another of the SC units - haven't had any trouble with
that one since I got it about a year ago. Which is when I learned
about the sine-wave Vs. stepped approximation thing. Maybe the SC
unit has just never really been needed since I got it and has always
just passed the power directly through from the wall. At least it
hasn't shut off my system without warning.
I don't think that the SB-1K or SB-2k care whether it is true
sine wave, stepped approximation, or even just a square wave. :-
My real question is, do these computers (Blade 1k and Blade 2k) really
need a true sine wave of current from the UPS, or is a stepped
approximation good enough (especially for the short periods of time
they would be running off of the UPS)?
They should not care.
Would these machines just shut
down if they started seeing a stepped waveform?
Nope!
Would the stepped
waveform cause damage to any of the components if the power was out
for a long enough time?
Nope -- except perhaps for transformer-powered audio equipment.
Would I be better off with no UPS for these
computers than ones with a stepped waveform?
Nope!
My own preference is an UPS no longer made -- but available on
eBay (usually quite a few). Look for "Best power systems" and
"FERRUPS". These have a Sola type of constant voltage transformer, so
low power is just boosted to the proper voltage with no need for the UPS
to actually run from the battery, and surges are automatically reduced
to reasonable values. When the power actually goes away, the UPS starts
driving other windings on the transformer from the battery, and
continues to produce a clean sine wave.
There is a serial port on the UPS which an be connected to ttya
or ttyb and monitored by a dameon called "checkups" which can be
downloaded from the people who took over Best Power Systems if you don't
get the CD-ROM which includes it as part of the package.
It comes pre-compiled for several versions of unix, including
Solaris (and even SunOs 4.x.x IIRC), and with source code to allow you
to compile it for other systems.
You start it from an entry in /etc/init.d linked to one in
/etc/rc2.d (or wherever you want it to start). You can pass to it how
long before the UPS runs out of battery charge you want the system to
start shutdown, and how long you want to give the system to shut down
before you actually drop the power to preserve the batteries.
(Discharging them fully does terrible things to their life.) The UPS
shuts off the power when it is told to, and then returns power once AC
power returns. The system can be set up to boot on power restoration.
I've got a 700 VA BEST UPS powering my wife's SB-1K, a 1.4 KVA
one powering my SB-2K with a tray of seven 72 GB FC drives in a zfs
system, and a 2KV one with four 12V batteries in series powering the
server (Sun Fire 280R and two trays of seven 72 GB FC drives in zfs
filesystems, plus an Exabyte 430 tape library, and two Sun Ultra 10s,
two SPARCstaton 5s, a Sun Ultra 5 (acting as a firewall), a
router/T1-(CSU/DSU), several twisted-pair ethernet hubs, and
occasionally an Intel Mac Mini.
If you get a BEST UPS -- ask them to ship it without the battery
or batteries, and get a new one to fit it once it is at your home. The
UPS itself is quite heavy, and add a gel lead-acid battery and you will
have something too heavy to move. I did bring the 2KVA one up through a
trapdoor from the garage/workshop with a hoist and winch. The others
were carried upstairs as the main chassis, the case, and the battery,
and all were joined only when in the final location. (You will likely
need some wrenches to attach the cables to the batteries, and be careful
to not short across the two terminals with the tools. :-) Typically, I
needed a 1/4" drive ratchet set with sockets for 1/4-20 bolts and nuts
on the larger ones, and a 3/16" Allen wrench for the smaller one for the
700 VA unit. I got that battery (34 AH) at a hamfest (A vendor cycling
his stock which had been kept properly charged to sell newer stock to
his regular customers), and Batteries Plus for the larger 80 AH ones for
the 1.4 KVA unit and four of them for the 2.0 KVA unit.
As long as the batteries are replaced every four years or so I
expect no problems -- other than from my wife or the cats kicking the
plug out of the outlet -- and then I expect a clean and graceful
shutdown.
Good Luck,
DoN.
--
Email: <dnichols@xxxxxxxxxxx> | Voice (all times): (703) 938-4564
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