UPS Diagrams

offline means it will operate whenever there is main power fails.online means it will operate continuously even the mail supply is on also when power fails for the backup time provided.

1. Standby power supply (SPS). In this type of supply, power is
usually derived directly from the power line, until power fails.
After power failure, a battery powered inverter turns on to
continue supplying power. Batteries are charged, as necessary,
when line power is available. This type of supply is sometimes
called an " off-line" UPS.

The quality and effectiveness of this class of devices varies
considerably however, they are generally quite a bit cheaper than
" true" UPSs. The time required for the inverter to come online,
typically called the switchover time, varies by unit. While some
computers may be able to tolerate long switchover times, your
mileage may vary. [ Some articles in the trade press have claimed
that their testing shows that modern PCs can withstand transfer
times of 100ms or more. Most UPS units claim a transfer time to
battery of about 4ms. Note that even if a computer can stay up
for 100ms, it doesn't mean that 100ms switchover is okay. Damage
can still be done to a computer or data on it even if it stays
up. ]

Other features to look for in this class of supplies is line
filtering and/or other line conditioners. Since appliances
connected to the supply are basically connected directly from
the power line, SPSs provide relatively poor protection from
line noise, frequency variations, line spikes, and brownouts.

[Some SPS's claim to have surge/spike suppression circuitry as
well as transformers to " boost" voltage without switching to
the battery if a modest voltage drop occurs. An example is the
" APC Smart UPS" which claims it will switch to this boosting mode
if voltage drops below 103V (from the normal expected 120V) and
switches to battery only at 90V and below. This, it is claimed,
allows operation of the equipment indefinitely under brownout
conditions as long as voltage does not drop below 90V. I have
not tested this, and would be interested in independent data.
There are other vendors products that make similar claims.]

2. Hybrid UPS systems. I only know one vendor who sells them -
Best Power, Inc. The theory behind these devices is fairly simple.
When normal operating line power is present, the supply conditions
power using a ferroresonant transformer. This transformer maintains
a constant output voltage even with a varying input voltage and
provides good protection against line noise. The transformer also
maintains output on its secondary briefly when a total outage
occurs.
Best claims that their inverter then goes online so quickly that
it is operating without any interruption in power. Other UPS
vendors maintain that the transition is less than seamless, but
then again it's not in their best interest to promote Best's
products.
Best has a sizable part of the UPS market.

[ Note: According to some sources, ferroresonant transformers in an
UPS system can interact with ferroresonant transformers in your
equipment and produce unexpected results. The Moral: Again, test
before you buy. -npc ]

3. What I call " true" UPS systems, those supplies that
continuously operate from an inverter. Obviously, there is no
switchover time, and these supplies generally provide the best
isolation from power line problems. The disadvantages to these
devices are increased cost, increased power consumption, and increased
heat generation. Despite the fact that the inverter in a " true" UPS
is always on, the reliability of such units does not seem to be
affected. In fact, we have seen more failures in cheaper SPS units.
[ Note, though, that given the same quality inverter, you'd expect the
one that runs least to last longest. ] Check www.powerstream.com

On-Line UPS - The power flow is through the Battery Charger and Inverter under normal condition. For the UPS abnormal condition, the load is automatically transferred to utility power (or regular power) by automatic static transfer switch.

On-Line (or standby) UPS - The power flow is directly from the utility power (or regular power) under normal condition. UPS is used only when the utility power fails. The transfer of the load to the UPS supply is done by automatic static transfer switch.

- MS