In the vast majority
of cases the design and cost to
employ a UPS is left to the end
user. This deprives the end user
from a choice of options. Since
he dares not redesign the systems
(to include other means for backup,)
he has no choice but to purchase
a stand alone AC UPS and place
it between the utility and the
system. On face value, this seems
to be an easy and straightforward
solution, which will result in
the satisfaction of both the user
and (undoubtedly) the maker of
the UPS. It is evident, however,
that this is a fallacy. From an
overall point of view, the use
of stand-alone AC UPS does not
result in a cost effective, high
reliability or high efficiency
solution to the backup problem.
In fact, the overall efficiency
of this arrangement is rather
poor, and its cost burden is rather
substantial. The maintenance cost
of this inefficient system is
ongoing, and for the duration
of the system’s life cycle,
it may add up to a sizable amount.
A far better solution
is to satisfy the requirement
for uninterruptible power by the
use of a DC UPS (DUPS or USPS)
within the system itself. However,
this embedded approach requires
that the system’s architect
takes responsibility of either
implementing the DUPS as part
of the system design, or at least
planning for such option should
the need require its inclusion
in the future. This approach pays
well at the end in a more efficient,
less costly and far more reliable
system for the end user.
The main purpose
of this article is to advocate
the embedded DUPS approach or
any form of a DC UPS in lieu of
an AC UPS. The article further
highlights a severe incompatibility
problem (not known to most users)
between AC UPS and Switchmode
power supplies (SMPS). Consider
that for external UPSs, the SMPS
within the system is a highly
non-linear load, which demands
its current in high pulses, thus
causing havoc within the UPS that
feeds it.
This incompatibility
problem is at the core of many
unpleasant surprises to the end
user, as he can connect an AC
UPS to his system and as a result
endure many unforeseen problems.
These problems are related to
the dynamics of the AC UPS and
the SMPS within the host system.
