UPS Back Up Power: Your Protection May not be what you think
assets are becoming increasingly digitized, businesses rely more heavily
on computers and other essential electronic equipment. An
untimely power outage, without back-up power, can be a real headache
- or worse - causing lost data, scrapped parts, patient discomfort
Uninterruptible Power Supplies (UPS) are often used to protect sensitive
downstream digital equipment from power fluctuations and outages. At
least that is the plan.
In reality, depending upon the UPS backup power source technology
employed, the protection may not be what you think - leaving your business
with less protection than you bargained for.
Just as there are multiple ways to get from “point A” to “point
B” including cars, motorcycles, horseback, or walking - there are
several UPS technologies available. The two leading technologies
While they both do the same types of things - provide back-up power to
shut down systems, for example, how they achieve these can have significant
impact on the business assets that they are designed to protect.
Online Uninterruptible Power Supply vs Offline UPS — How Are
Off Line Uninterruptible Power Supplies
Offline UPS (aka line interactive UPS or single conversion
UPS) technology is the less expensive of these two technologies, and
that is one reason why it is also the most common.
of this type of UPS as “batteries in a box.” This
technology monitors the incoming line voltage and supplements it with
battery power when the voltage drops below a certain level.
interactive designs may include a tap-changing transformer which adds
voltage regulation by adjusting transformer taps as the input voltage
varies. The transfer time, which is inherent with the line-interactive
methodology, is typically 4-6 milliseconds - a period which is noticeable
to both human observers and more importantly - downstream sensitive
Online Uninterruptible Power Supplies
Online UPS (aka double conversion UPS) technology, on
the other hand, takes the incoming utility alternating current (AC) and
converts is to direct current (DC) which charges the batteries.
direct current (DC) is then converted back to AC (“double conversion”)
which is supplied to the protected load as clean power at the desired
the inverter is always connected to the output of the UPS, the double-conversion
technology produces a clean sine wave and also reduces harmonics -
further protecting downstream equipment.
Dropping the incoming voltage does
not cause activation of the transfer switch (to batteries) because
the input AC is not the primary source - it is the backup power source. An
input power failure, therefore, does not cause a transfer - so there
is no transfer time.