Festool C12 EC-TEC User Manual

Technical Review of
the C12 EC-TEC
Cordless Drill

By Rick Christopherson

Once again, Festool has shattered the expectations
of the drill industry with the release of the new
C12 cordless drill. The C12 is not just a cosmetic
change made to an existing design. The C12 is
packed with revolutionary motor and control
technology on several levels. Festool didn't just
leap forward in one area of this drill; they made
huge leaps forward in ALL areas of this drill. From
the motor, to the electronics, to the geartrain; this
drill raised the bar just past the fingertips of the
competition.

EC-TEC® Motor Technology

The heart of the C12 is the revolutionary EC-TEC
brushless motor. This isn't just your run-of-the­mill motor. This is a permanent magnet, remotely
commutated, 3-phase, AC motor. This is the same
type of motor used as servo motors in robotic
systems where high torque, high speed, and
extreme durability are crucial.

To circumvent the
losses of the
brushed motor,
Festool
incorporated a
brushless DC

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motor

into the
new C12 drill.
The electrical
connections to
the windings are
permanent, and
don't suffer from
the inefficiencies
of constantly
connecting and disconnecting as the motor rotates.

The brushless DC motor lasts longer, and requires
no maintenance, as compared to the brushed
motor. It is also smoother and quieter.

So just how unique is this motor? Well, if you
mechanically turned the motor, it would generate
a 3-phase, sinusoidal AC output; just like
industrial diesel-electric generators do. (Do not
attempt this.

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)

For years, the motor technology of cordless tools
has not changed. The brushed DC motor has been
the staple—albeit inefficient—motor for ages. The
brushed motor is simple, compact, and
inexpensive, but it suffers from inefficient use of
limited battery power. The greatest weakness of
the brushed motor is that the electricity to the
motor's windings passes through an electrical
connection that is constantly changing and
moving. Every time you see the brushes spark
inside of a brushed motor, it is a waste of energy
that is not available for use by the motor.

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Never attempt to manually turn the output shaft of any

Festool drill or connect this drill to the output shaft of
another drill. The C12's output shaft has a mechanical lock
for bit changing and cannot be rotated manually.

Electronics

There are some popular brand drills on the market
that are known to destroy themselves under a
normal, but heavy load. I know this first-hand
because I "smoked" a couple drills during my
investigation of drills (including the most
expensive drill my local home center carried).

A powerful drill is of little value if it is easily
damaged. The C12 has an intelligent electronic
controller that not only powers the motor, but
more importantly, monitors its health. Unlike
other drills on the market, the C12 won't let you
destroy the drill (or the battery) no matter how
hard you try.

It took less that 30 seconds to destroy a $270, 18­volt drill, yet the 12-volt C12 handled the same

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Even though this is a 3-phase, AC motor; it is the electronic

industry's practice to refer to this as a brushless DC (BLDC)
motor because the AC power signal is electronically created
and controlled from a DC (battery) power source.

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load without causing damage.

The C12 monitors the electrical power to the motor
to ensure that the motor operates within safe
parameters. However, make no mistake; the C12
was designed properly in the first place, so it
won't overheat under normal use. The drills
mentioned above were under-engineered so the
manufacturer could claim higher performance
than the drill is realistically capable of
providing.

Power Control

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Virtually all drills on the
market (including AC and
DC motors) use a similar
design for controlling the
power to the motor. The
trigger switch contains a

ll of

the electronic controls.

to fail. It is a sensor that detects the position of
rare earth magnet located on the push button.
More importantly, the electrical power of the
motor is not flowing through a set of s

witch

a

contacts like it does with other drills.

Battery Sizes

Whether you're an occasional picture hanger, or a
professional contractor, the C12 is flexible enou

gh

to meet everyone's

needs. The C12 is

available with three
sizes of batteries to
choose from: 1.

3 Ah

NiCd, 2.4 Ah NiCd,

a

nd 3.0 Ah NiMH.

The higher the amp-hour (Ah

)

rating, the longer the battery

will last.

A small electronic circuit
creates a pulsating signal
for controlling the

speed
of the motor, and a
mechanical switch
controls the motor's
direction (refer to How

Variable Speed Controllers
Work on page 5). All of the

power to the motor passes
through this small circuit,
and what's more, passes
through the me

chanical
contacts of the
forward/reverse switch.

The C12 uses six high power amplifiers to control
the power to the three phases of the motor. These
are located on the main control board where the
is ample room for a heatsink. The only con

re

trol
circuit inside the power trigger is a small,
solidstate resistor

that is part of the frequency

generator circuit.

Even the forward/reverse control of the C12 is
solidstate. There are no moving parts or contacts

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This is not a new concept. U.S. tool manufacturers frequently

overstate their claims for marketing purposes. Festool does
not play these marketing games.

Battery Protection

There are two common w

ays

that battery life gets

shortened; over-charging, and

over-discharging. The C

includes an inte

lligent

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battery charger to prevent

over charging. The

microprocessor controll

charger rapidly charges

ed

the

battery, and when full

charge is detected, th

e

charger switches over to

maintenance mode.

A common misconception with tool batteries is

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that they should be fully discharged before
recharging. While there is some truth to this,

fully
draining a battery to the point of stalling the moto
can actually cause permanent damage to the
battery. The cells inside the battery pack can
actually change polarity, called cell reversal, under
deep cycling. The C12 monitors the battery to
determine if it is capable of providing the power
required. If the battery cannot supply the powe

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With daily use, the batteries can be left in the charger until

needed. However, the charger should not be used for long­term storage of infrequently used batteries.

r

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