By Sol Jacobs, Tadiran Batteries
For remote battery-powered devices, this ‘seesaw’ battle
can lead to compromised solutions involving unnecessarily
large and heavy batteries that carry unforeseen expenses.
This results in more frequent battery replacements and costly
transportation from oversized batteries to remote, hard-to-access locations.
In order to make a more informed product specification
decision, the following parameters should be considered:
OPERATING VOLTAGE – Basic math tells you that
it takes more than twice as many 1.5 V cells to deliver the
same voltage as 3. 6 V cells. Selecting the battery with a
higher voltage could reduce size and weight, while also
saving money by requiring less cells.
COLD AND HOT TEMPERATURES – Exposure to
extreme temperatures reduces battery voltage under pulse.
If a battery with a limited temperature range is deployed in
a harsh environment, oversized batteries may be required to
compensate for an expected voltage drop under a pulsed
load. One solution may be to utilize a specially modified
bobbin-type lithium thionyl chloride (LiSOCl2) battery that
features extremely high-energy density, along with the
ability to handle high pulses at extreme temperatures, thus
eliminating the need for extra capacity and/or voltage.
SELF-DISCHARGE RATE – Certain battery
technologies suffer from high self-discharge rates of up
to 8 percent per month, thus requiring a larger battery to
compensate for the expected capacity losses. Choosing a
battery with a low annual self-discharge rate could enable the
use of a smaller battery, while possibly eliminating the need
for future battery replacements over the life of the device.
For example, superior quality bobbin-type LiSOCl2
batteries feature a self-discharge rate of 0.7 percent per
year, and are able to retain over 70 percent of their original
capacity after 40 years. By contrast, a lesser quality battery
made with the exact same chemistry could have a much
higher self-discharge rate of 3 percent per year, and exhaust
30 percent of its original capacity every 10 years, making it
impossible to achieve a 40-year battery life.
WHY IS YOUR BATTERY SO
LARGE AND EXPENSIVE?
BALANCING PERFORMANCE AND
COST REQUIRES TRADEOFFS
When developing an industrial grade, wireless device intended for long-term deployment, design engineers must
strike a balance between two inherently competing
goals: long-term robust product performance and
low initial cost.
Figure 1. Powering a surgical drill using four AA-size lithium-metal oxide
batteries in place of 12 alkaline cells can make the tool lighter and more
ergonomic for surgeons.