182 Agricultural Mechanics and Technology Systems
Copyright Goodheart-Willcox Co., Inc.
Battery-Operated Power Tools
Another common DC power source for a portable power tool is a
rechargeable battery. Battery-operated tools are also known as cordless
power tools and commonly use between 9.6 volts–36 volts DC power. Tools
equipped with similar motors deliver higher speeds proportional to higher
voltage inputs. Conversely, as more torque is applied to a power tool, it uses
more amperage or current.
Three main types of rechargeable batteries are used in cordless power
tools. Nickel-cadmium (NiCad) batteries are the oldest example. NiCad
batteries are the least expensive and last for about 1000 charge cycles, but
they can easily deteriorate when not charged and discharged properly.
Nickel-metal-hydride (NiMH) batteries can run two to three times
longer on a single charge than NiCad batteries. NiMH batteries, however, are
very sensitive to improper charging methods and storage conditions. Deep
discharging will shorten their life span, and exposure to extreme high or low
temperatures degrades the battery.
Both NiMH and NiCad batteries can develop a charge memory effect. If
they are improperly charged, a charge memory develops in these batteries,
allowing only a portion of the battery to accept a charge.
Lithium-ion (Li-ion) batteries, although more
expensive, outperform the other battery types used
in power tools, Figure 8-2. Due to their high power
density, Li-ion batteries offer a more uniform delivery
of power. The performance of NiCad and NiMH
batteries starts slowing down at about 70% charge.
Li-ion-powered tools deliver uniform speed and torque
down to about 20% of a full charge. Li-ion batteries last
only for 350 to 500 charges, but they do not suffer from
a charge memory effect.
The key to preserving the life of power tool
batteries is using a quality charging system. Battery
chargers use standard 120-volt AC current to fully
charge a battery in 1 to 16 hours. Fast charging is
not always best. NiCad and NiMH batteries last
longer using chargers that deliver a full charge in
about an hour, but Li-ion batteries can be damaged
by chargers that offer less than a 3-hour complete
charge time.
The run time on battery-operated tools varies greatly depending on the
energy demands placed on the tool. Tools for drilling or driving fasteners
may have a 30-minute battery life, while tools that are used for grinding
or sawing are often limited to a 15-minute run time or less before a fully
charged battery is needed. Contractors who rely heavily on battery-operated
tools address the limited run time by having multiple batteries and charging
stations set up on a job site.
Jeffrey B. Banke/Shutterstock.com
Figure 8-2. Manufacturers of cordless power tools
may use a single lithium-ion battery designed to fit
multiple cordless tools within their product line.
Safety Note
Although many of today’s
portable power tools are
capable of safely using
AC or DC current, check
for an AC/DC rating
marked on the tool or
in the manufacturer’s
instructions—especially
with older tools—before
attempting to connect to
a direct current power
source. Injury or tool
damage could result
from connecting to an
unsuitable power supply.
Safety Note
The cadmium in NiCad
batteries is considered a
heavy metal that is highly
toxic to the environment
when disposed of
improperly.