Please forgive me if my information is dated. However, I believe
this is still true. Please forgive me if I am not entirely accurate as
I've not re-investigated this in recent years when APC took over
the small "UPS/SPS" market by storm.
Since at least the early 80's UPS were basically of three
types (we'll leave out the motor generator types from years before):
The truly "online" types like SOLA sold. The "switching" types of
which most if not all APC units (at least the small ones) are and
one novel design that I first saw from Unison (later purchased by
Tripplite).
The Sola's used ferro-resonant transformers and capacitors to
regulate and store energy. It has been too many years and I don't
recall all specifics but basically the transformer would accommodate
voltage swings of 20%...all the time if necessary. This would help in
instances of deep prolonged brownouts and poor voltage supply in
general. All without tapping its batteries. The online UPS continuously
charges batteries where power is drawn from and inverted to a poor
to reasonable facsimile of an AC sine wave. So if the power goes out
you are just losing your battery charger. Power continues to be drawn
from the batteries. "No Break", as they were commonly referred to.
Topaz used rapid "tap switching" on their special transformers
to simulate the ferro-resonant action. Thus Sola, Topaz and others
also had voltage regulators without deep brownout or blackout
protection.
At that time the ability to "switch" in power from a battery source
within a few cycles or fractions thereof was not available (I presume).
Thus computers (perhaps the pickiest devices) needed true online
power supplies. Later, adequate "invisible" switching was possible
and companies like APC (American Power Conversion) based
their designs on that. This reduced the parts count and other
undesirable things like the relative inefficiency of the FR transformer
with its associated heat generation and tendency to have very
noisy windings (both part and parcel of the way it works).
Thus "Standby Power Supplies" or SPS's were born, which
technically most of the advertised UPS's are.
The disadvantage of SPS's are that they cannot correct for deep
brownouts or continuous low voltage (to a degree) or overvoltage.
They are relying on passive MOV (Metal Oxide Varistors) and
other such things to take out surges. They rely on switching
in and out (repeatedly if necessary) the battery supply for continuing
low voltage. Perhaps okay for our application but I hope you can
turn off the "alarm beeps" or have good headphones or "head-CW
filters"... :-)
The current SPS's are fine for most applications today but not in
all situations. I have seen some discussion about even using them
on linear amplifiers. The main point of contention being whether
there is a sufficient lag where the amplifier (or transmitter) power
supplies cannot ride through without affecting instantaneous peak
demands by modulation. Perhaps a moot point for all but the
"max power" or signal purists :-).
The third type, which I don't know if Tripplite still employs in
some or all of their designs, looked like a "T" configuration where
they used batteries in series up to 120VDC (or was it half that?)
and used the same circuit to charge them as well as invert to AC
when needed. Still truly uninterruptible (so they claimed) as
opposed to standby switched but with a lesser part count and
attendant complexity. Maybe achieving better reliability and cost.
So the moral is to understand your true power and (surge) load
situation. Then before you select a solution see if the kind you
select will really do the job. I have used all three with success.
Also, understand whether your loads will tolerate the often less
than perfect sine wave that some UPS produce. A good article I
saw years ago had oscilloscope pictures of the various "pseudo
sine waves" the tested units produced. Quite alarming. I hope
they have improved since then.
Please pardon the bandwidth and degree of "off topic" but
I hope this helps some understand the differences.
Oh, and motor generator types were mostly used in backing
up large main frame computer systems. Large, massive
wheel-type mechanical energy storage (then converted to
electricity) devices have been around for years before.
Aloha, 73
Kimo Chun, KH7U
To: <cq-contest@contesting.com>
From: Pete Smith <n4zr@contesting.com>
Subject: Re: [CQ-Contest] Buying a UPS
At 07:17 AM 3/9/02 -0500, Gerry Treas wrote:
>There is something that hasn't been addressed. Be sure
>that the UPS is always in the circuit, not one that gets
>switched in when AC mains fail. That would be OK for
>lights, but not computers. Working in TV (2 stations)
>corporate and local management do not want any failures, we
>are putting a bunch of smaller ones in to cover us while we
>plan the one that will be housed in a separate building to
>power our whole tech center and all the computer network
>servers. Somewhere around 500 kVA to 750 kVA. All have to
>be series type.
I think this is pretty much the design standard, at least for small
self-contained UPSes.
There are some amazing deals out there from time to time -- I got a new 300
VA APC UPS for $10 from Staples after a mail-in rebate. It's not enough to
power everything computer related in the shack, but it supports my CPU
quite nicely. Since installing it, I've never had an outage of more than
about 2 seconds, but I've had hundreds of the little glitches and dips that
would have caused my computer to reset otherwise. It's very pleasing to
hear the UPS beeeeep and know that I've just dodged another bullet,
especially in the middle of a good run.
73, Pete N4ZR
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