Tech Briefs Magazine - February 2022 - 17

will disable themselves if unsafe conditions
are reached.
VRLA vs. Li-ion Batteries
Lead-acid and VRLA batteries, in general,
are among the most cost-effective
batteries on the market. Compared to
Li-ion batteries, which are often multiple
times more expensive, they have the
lowest purchase price. However, the purchase
price is not the only factor when it
comes to batteries. All batteries reach
end of life, and when they do, they must
be replaced.
In general, Li-ion batteries will last
longer, and therefore, need to be
replaced less often. This can result in Liion
saving money over the system's life,
which could justify the increased purchase
price. But based on initial cost
alone, VRLA is the better option.
In the same space, Li-ion batteries can
hold more energy than a VRLA. This
means Li-ion batteries are more energydense
and are useful when space is limited
in a system. This size savings extends
to weight as well. Their lighter weight
makes Li-ion batteries suitable for use in
mobile phones, tablets, and computers.
A VLRA battery should never be discharged
to lower than 50 percent of its
total capacity. This is referred to as the
battery's depth of discharge. A Li-ion
battery can be discharged down to 15
percent of its total capacity. This means
Li-ion batteries also have a higher
effective capacity and can sustain a
load for a longer duration when compared
to VLRA.
A battery has a maximum number of
charging cycles before it starts to
degrade and lose capacity. The number
varies based on the environment the battery
is operating in, as well as the depth
of each discharge. In general, a VRLA
battery provides 200 to 300 cycles, while
a Li-ion battery provides 500 to 1,500. If
used in a system that is constantly discharging,
Li-ion batteries will need to be
replaced less often than VRLA.
In general, batteries are very susceptible
to the temperature at which they
operate. Batteries stored at too high of a
temperature will discharge faster and
have a lower total lifetime. Batteries
stored at too low of a temperature will
lose performance and can be damaged
if charged.
Tech Briefs, February 2022
Cov
Battery
Type
VRLA
Lithium Ion
Cost
Size and
Weight
Higher Lighter
Depth of
Discharge
Lower Heavier Lower
Higher
Charging
Cycles
Shelf Life
Temperature
200-300 6-12 months 0° C - 40° C
500-1500 12-24 months -20° C - 60° C
Table 1: A breakdown of various factors and how VLRA compares to Li-ion batteries.
The optimal temperature for all batteries
is approximately 20° C (68° F), but
the type of battery affects the range that
it will operate in. The typical range for a
VRLA is 0° C to 40° C, while a Li-ion
ranges from -20° C to 60° C.
It may seem from these comparisons
that Li-ion batteries are the clear choice,
and in many ways, they are. The superior
size, weight, charge cycles, and operating
temperature make them a great
choice for any application. However,
there are still cases for VRLA. Besides
the upfront cost savings, there may be
no noticeable difference between the
batteries given the right application.
In cases where the batteries are in an
ideal environment, being properly
charged by the UPS, and not discharging
too often or deeply, VRLA batteries
could function identically to Li-ion. The
lifespan of the VLRA will be shorter but
could still be long enough that its
replacement costs are less than that of
the Li-ion. Table 1 gives a breakdown of
various factors and how VLRA compares
to Li-ion.
Maximizing Uptime
Even the best battery will eventually
reach end of life, so finding the optimal
time to replace it can save system downtime
and money. With system monitoring,
the user can obtain data on the
availability of each battery. This data can
also be used to find existing problems in
the system that may be prematurely
killing batteries.
In an installation with 100 batteries,
every battery is going to degrade slightly
differently. The easiest way to deal with
this is by replacing every battery after
some predefined period. The advantage
is that the maintenance is easy to schedule,
and there is no system downtime
(excluding a faulty battery). The downside
is the cost of replacing batteries that
potentially could have continued to
operate for much longer.
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ToC
The simplest way to monitor would
be an indication on the UPS that the
battery has not or will not support the
load. This could be accomplished with
local or remote indication, and it
ensures that only bad batteries will be
replaced. The advantage of this
approach is that there are no wasted
replacements. The disadvantages are
increased complexities in maintenance,
because failures can be random, as well
as the need for some way to constantly
monitor all the systems.
The most advanced form of monitoring
analyzes many different factors of a
battery and provides data based on those
factors. For example, Phoenix Contact's
IQ Technology analyzes batteries and
reports data such as remaining charge,
remaining lifetime, current temperature,
output voltage, and much more.
This sort of data allows the use of preventive
maintenance. Battery replacements
can be scheduled for a specific
period and, using data from the UPS,
only the batteries near their end of life
will be replaced. The main disadvantages
are setting up a system to collect all
this data and training users on how to
use any associated software.
To ensure the availability of a UPS system,
proper consideration must be
taken of each application and its
requirements. When there is a power
failure, the proper battery will make
sure the system does not go down, and
everything runs smoothly.
In conjunction with a good monitoring
system, maintenance can be regularly
performed, so there are no unexpected
failures. Combined, these two factors
will maximize uptime and ensure that
there is backup in the case of a power
failure.
This
article
was
written
by
Robert
Crittenden, Associate Business Development
Application Engineer - Power Supplies,
Phoenix Contact, Middletown, PA. For more
info visit http://info.hotims.com/82318-125.
17
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