Tech Briefs Magazine - February 2022 - 16

The Pursuit of an Uninterruptible Power Supply
TECHNOLOGY LEADERS Power Management
Electronics
A
n uninterruptible power supply
(UPS) is a great way to ensure
that power to important loads
is not lost in the case of a power
failure. When incoming power to the
UPS is lost, it immediately switches into
battery mode, which allows the connected
loads to run off this reserve energy.
But if the UPS itself fails, then any power
loss will shut down the entire system.
Therefore, it is important to make sure a
UPS is reliable and reaches its full lifetime
potential. Using the proper battery
for each application and constantly
monitoring the system to maximize
uptime can ensure the full life of a UPS.
No matter how good a UPS is, without
a battery, it can do nothing to buffer
power. If the UPS loses incoming power
and the battery is discharged, disconnected,
or dead, then the entire system
will shut down. It is therefore crucial to
use the proper battery for each application.
There are many types of battery
technologies, but two popular options
are valve-regulated lead-acid (VRLA)
and lithium-ion (Li-ion).
VRLA are a variant of lead-acid batteries,
which are commonly used in automotive.
Simply put, they operate by suspending
two plates of lead (the electrodes)
in diluted sulfuric acid (the electrolyte).
This enables the flow of electrons
when a chemical reaction occurs
between the lead and sulfuric acid. This
reaction produces lead sulfate and
water, and charging the battery reverses
this reaction.
Charging can also produce hydrogen
and oxygen through hydrolysis if the
charging current is too great. In a typical
lead-acid battery, these gases escape and
must be replenished with water or electrolyte.
Compare that to a valve-regulated
battery, where the gas is retained and
recombined into water (usually with the
help of a catalyst). If the pressure ever
gets too high, the safety valves open and
allow the pressure to return to safe levels.
Li-ion batteries are similar in concept
to lead-acid batteries, except they use
different materials. The electrodes, in
this case, are typically a metal-oxide for
the cathode (positive side) and
graphite for the anode (negative side).
This metal oxide is usually lithiumcobalt
oxide, lithium-iron phosphate,
or lithium-manganese oxide. The electrolyte
is typically a mixture of organic
carbonates.
To create power, lithium ions carry
current across the battery from the negative
to the positive electrode. When a
current
is applied,
this
process
is
reversed, and the ions travel back to the
negative electrode. Li-ion batteries can
catch fire if they are overcharged or
short-circuited, so various safety devices
are installed such as voltage regulators,
temperature sensors, and microcontrollers.
Many batteries and UPS systems
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Tech Briefs Magazine - February 2022

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