power systems (UPS’s) are often being referred to merely as a “batteries in a
box”. While in fact, they are very complex systems which perform numerous
functions. Those important functions ensure clean power and continuous uptime
to sensitive electronic equipment.
However, without proper
maintenance, UPS’s are subject to failure, since
critical components wear out from normal use. Performing regular service by trained and experienced personnel is crucial to minimize the risk
of failure. Performing regular service enhances your own knowledge about
the power system. Understanding how the main elements of your UPS function is
of vital importance. This knowledge enables you to more easily identify, and
avoid, potential failures and unwanted delays.
Allow us to introduce you
to four primary components of each UPS:
This main component can be compared to a “heart”
of UPS system. When the system senses a loss of power
from the primary source the battery “kicks
in”. The main purpose of batteries is to support the connected load
during a utility power failure. This component is the most critical UPS
component since it guarantees system reliability. Nevertheless, the battery is
often considered as a maintenance-free product that doesn’t require much
attention or inspection. Such a mistake can prove costly and can potentially cause
a power failure.
Depending on the UPS configuration, each UPS
contains at least one battery string. In order to increase runtime and/or
redundancy, multiple battery strings can be added. Since the battery strings
are serially connected, a
single bad battery can cause failure of the entire battery string.
Experience shows that up to 20% of UPS failures happen due to a bad battery. This fact
underlines the need and importance of regular inspection and maintenance.
The most commonly used batteries in UPS’s
are valve regulated lead acid (VRLA) batteries, including Gel
and AGM (Absorbed Glass Mat) batteries.
A VRLA battery
uses a one-way, pressure-relief valve system. This means that the oxygen
normally produced on the positive plate is absorbed by the negative plate. This
suppresses the production of hydrogen at the negative plate. Water (H2O) is
produced instead, retaining the moisture within the battery. This type of
battery never needs watering, and they should never be opened as this would
expose them to excess oxygen from the air. In addition to damaging the
batteries, opening also voids the warranty.
(Absorbed Glass Mat) batteries
completely absorb electrolyte in separators, consisting of matted glass fibers.
Significant advantage is that they are spill proof, meaning they don’t leak
acid like a flooded design of battery, if tipped on their side. The AGM
batteries glass mats are wrapped around the positive plate, which helps prevent
damage from vibration and extend cycling. The battery strings are packed
tightly in the case partitions, which also protects their power producing
components. UPS batteries usually
have a life expectancy between four and six years, although individual quality
and charging technology can impact the projected lifespan. In the right
application, AGM batteries can have over twice the life cycle of conventional
or Gelled Electrolyte batteries
Instead of the
traditional liquid form, electrolyte in a Gel battery is permanently locked in
a highly viscous gelled state. Because there is no electrolyte in a liquid
state, this type of battery will also not leak if tipped on its side. The
thick, gelled electrolyte and tightly packed strings also protect the battery’s
power producing components. Gel battery designs have a superior deep discharge
resiliency and, if used in the right applications, can deliver over two to
three times the life cycle of an AGM battery.
A UPS rectifier performs two very important
roles: charging the batteries and converting incoming utility power from AC to
power loss occurs, the rectifier simply drops out of the circuit and the
batteries keep the power steady and unchanged. When power is restored, the
rectifier resumes carrying most of the load and begins charging the batteries,
though the charging current may be limited to prevent the high-power rectifier
from overheating the batteries. We
utilize a sophisticated charging method that prevents unnecessary charging of
the batteries, which significantly slows the wearing-out process.
The inverter within a UPS accepts the DC
from the DC buss, which is supplied by the rectifier and the battery. During a
power outage, the rectifier no longer provides current to the D/C buss, leaving
the batteries to support the load. But if power is not restored before the
batteries wear out, the system runs the risk of dropping the load unless an
external power source such as a generator kicks in. If power loss
the batteries drive the inverter, which continues to run. When power
is restored, either from the utility or a generator, the rectifier
delivers direct current (DC) to the inverter. The inverter runs full
static bypass is fitted to almost all On-line UPS. It forms the second line of defense.
Should the inverter fail, the static bypass ensures the load drops
automatically onto the mains input feed. This
component automatically closes the circuit and allows the incoming power to
divert around the rectifier, batteries and inverter. Although the power supply
is not conditioned, the static bypass lets critical systems continue
functioning even if the UPS’s internal components fail.
A static bypass is in almost all cases part of the UPS internal circuitry and
may be invoked manually using an external switch. In larger UPS, it
synchronizes the UPS output with the mains cycle before switching, so it may
take a few seconds to engage.
When you get familiar with
the primary UPS components, you are able to make more educated decisions and
keep your systems performing optimally. We recommend scheduling at least
two preventative maintenance visits yearly. These service visits,
which include a comprehensive range of inspections, are designed to ensure the
ongoing health of the critical UPS components.