The secret life of batteries

The secret life of batteries
mike miller
CAN Unit Diagram
The secret life of batteries
a breakthrough in battery monitoring technology is delivering
major benefits across the electric vehicle industry, from
battery manufacturers and vehicle OEMs to the end users
Battery management is a complex issue for
fleet managers and other end users. For
reasons of productivity, safety and cost control, it is
essential to know how long the battery life will be,
what the state of charge is, how healthy the battery is,
and other key aspects of battery functionality.
Damage, premature depletion and improper battery
maintenance can lead to vehicle downtime or costly
battery replacement.
Concerning the science of battery life, Eugene
Finger wrote The Battery Book. Finger was a Curtis
Instruments engineer whose comprehensive analysis
of battery functionality became the standard industry
reference. His book is still available, and can now be
downloaded from the Curtis website.
Battery monitoring
Last Charge Cycle
215 A-hr
(0 - 255 A-hr)
Last Discharge Cycle
204 A-hr
(0 - 255 A-hr)
% of RATED
Historically, Curtis Instruments – a global leader in
integrated systems technology for electric offhighway vehicles – has also been a leader in battery
monitoring. Founded in 1960, Curtis patented
Battery Discharge Indicators (and coined the term
BDI) in the 1970s. However, while these early battery
fuel gauges were the state-of-the-art in battery charge
measurement, they only indicated discharge.
Early-generation BDIs were mostly used on forklift
trucks that typically ran in three shifts. These gauges
Battery information is displayed in real time on the Curtis enGage VII or any other CAN-based display
rode on the vehicle, measuring only the voltage of the
battery. The management method was to use the
battery almost to the point of depletion, then drive
right across the industry, to battery manufacturers,
battery life, state of charge, maintenance and abuse
the vehicle to a battery-changing station, where a
vehicle OEMs and end users alike.
incidents. Many decades of battery expertise have
crane would lift out the drained battery and replace it
During the Acuity development process, Curtis
enabled its development.
with a fully charged one. An expensive, awkward and
engineers sought to fulfil three key value points:
Acuity resolves the ongoing debate between
time-consuming system, to say the least.
• Provide the highest accuracy SOC information
vehicle manufacturers, battery manufacturers and
Finger dreamed of a better solution. He foresaw
possible, clearly quantifying the amount of energy
end users as to when battery performance is not as
more accurate measurements and readings by
remaining at any given time;
guaranteed. It provides proof positive of compliance
understanding not just the voltage, but also the
• Serve as a warranty witness (validating that the
or non-compliance within warranty guidelines.
current of the battery, and what specifically happened
battery has or has not been operated within its
The technology also enables end users to manage
during the charge cycle. He realised that if you could
conditions of warranty);
their fleets with far more efficiency. They can get the
measure both current and voltage, and if the device
• Function as a productivity tool, indicating the
most work out of each charge and each battery; can
travelled with the battery, then you would achieve the
condition of the battery in addition to SOC.
know in advance what will need replacing, and when;
most accurate assessment of the state-of-charge (SOC).
The new Curtis Acuity mounts directly onto the
identify abuse patterns that can be rectified; and, in
Now Curtis has achieved that goal, and made it
battery for exact readings of both voltage and
general, achieve more control over fleet performance.
affordable for the marketplace. The Acuity battery
current, delivering the most accurate SOC possible.
In order to technically solve the problem of a more
monitoring system is a revolutionary step in modern
As the industry’s most reliable battery monitoring
complex, comprehensive battery reading, a new
vehicle battery monitoring. It is a highly intelligent
tool, Acuity is a viable warranty witness and
algorithm was needed. The old maths calculated SOC
monitor that
productivity tool, providing detailed information on
by integrating the battery voltage over time. As work
Rev. 11_9_12
xxx November 2012
The Curtis Acuity device connects directly to the vehicle battery, where it collects and transmits accurate battery state-of-charge and battery-condition information.
was done by the vehicle, the battery voltage
decreased and the time that the voltage was below a
reference voltage was accumulated, with the resulting
SOC being displayed on the gauge.
The new algorithm to calculate a more accurate
SOC takes into account multiple charge and discharge
scenarios. Acuity calculates SOC by integrating
current, voltage and temperature (using an integrated
temperature sensor) at multiple discharge rates. It is
far more precise than previous algorithms and is what
Curtis engineers like to call ‘the secret in the sauce’.
Each Acuity device mounts onto the battery, has a
unique serial number, and is intended to spend its life
on the battery. It provides a full and constantly
updated history: how long the battery has been in
service, how often it has been charged, and to what
level discharged. Any discrepancies in usage are
noted. There are about two dozen data points – see
box (overleaf) for a sample listing.
Installation could hardly be more simple, without
any hardware or brackets involved. You basically just
put the battery cable through the Acuity current
sensor, connect the CAN wires, and tie it into place
for plug-and-play performance.
All solid state, Acuity has no moving parts, and is
designed to last at least 10 years – the average life
cycle of a forklift truck. It is equally at home on golf
cars, aerial lifts, sweeper/scrubbers, scissor lifts, etc.
Although the device attaches to the battery and is
meant to stay connected for the life of that battery,
Acuity is not averse to remarriage. It can be remounted
on a new battery if it outlasts its first companion.
The standard Curtis Acuity system enables users
to access battery data from the vehicle’s CANbus
either via the on-vehicle display or via the handheld
programmer or equivalent device using VCL. Once
the device is in place, you get information, not just
data. Tools to program, read, interpret and apply the
information include an on-vehicle display, PC software
tools and a handheld programmer connected to the
Rich information
Curtis has created a standalone software program –
an optional Acu-Set software kit that greatly enhances
this process. The kit consists of software and a dongle
which allows the Acuity data to be read by a PC. This
proprietary software reads the data and translates it
into clearly accessible and actionable information.
Longevity and ease of use
Acuity connects to the vehicle’s CANbus system,
integrating seamlessly into the Curtis drive system. It
also communicates effortlessly with all standard Curtis
products and tools, including all enGage displays, all
CAN-based motor controllers (including AC), and is
accessible with Curtis handheld programmers via
Curtis’s Vehicle
Language (VCL).
ABOVE: The Curtis Acuity Battery Monitoring System is easy to install. Shown is the Curtis Acuity on the battery
of a Class 3 powered pallet truck November 2012
Keeping track
The Acu-Set software translates the Acuity battery data into easy-to-read performance data. It also calculates
Percent Rated Capacity (PRC) – the actual energy the battery can deliver as compared to its rated capacity
The Acu-Set tool also allows easy programming of
the Acuity, the ability to read instantaneous battery
data and store battery data into the PC. Matching
Acuity parameters to a specific battery brand and
model is easier than ever: most models can be
selected from a comprehensive pull-down menu, or a
custom battery profile can be manually entered.
Reading battery information for productivity,
maintenance and warranty witness is extremely
simple with this software tool. The user can see
instantaneous or historical data of the measured
values in comprehensive displays, including in chart
format. Fleet managers can easily access the full range
of battery data points via wired or wireless means.
The Acu-Set software also stores the data collected by
the Acuity battery monitoring system.
With battery costs running in the range of
US$5,000-7,000, the economical Acuity can very
quickly pay for itself by identifying faulty batteries and
preventing abuse that shortens battery life. It
therefore presents an extremely affordable battery
monitoring solution with excellent ROI by saving
abuse and forcing warranty terms.
Acuity to communicate via Zigbee, WiFi or Bluetooth.
Any time the device is in range of a WiFi hotspot, the
operator or manager can access and ‘talk to’ the
vehicle from anywhere in the world. Readings can be
made from the fleet manager’s office, warehouse or
company HQ, supplying vital data for superior battery
management and optimal fleet performance. iVT
Mike Miller is director of product management, Curtis
Instruments, Inc.
Based on Acuity readings, operators can avoid the
leading causes of battery damage:
• True accuracy in measuring depletion avoids
usage below 80% depth of discharge, the
recommended recharge level;
• Because batteries are strongly affected by
temperature extremes, Curtis Acuity includes a
temperature sensor integrated into the harness.
Acuity provides data – translated by Curtis
software into readable information – on the
following points:
• Battery voltage;
• Battery current;
• Battery temperature;
• Ampere hours in;
• Ampere hours out;
• State-of-charge (SOC);
• State-of-health;
• Battery serial number;
• Highest voltage measured;
• Lowest voltage measured;
• Highest temperature measured;
• Lowest temperature measured;
• Current measured at highest voltage;
• Current measured at lowest voltage;
• Highest SOC measured;
• Lowest SOC measured;
• Date;
• Time;
• … and more!
Looking ahead
Curtis Acuity presents the possibility of a new business
model: a rental approach to EV usage. Dealers can
approach their customers and say: “Only pay for the
energy you are using” – similar to paying for mileage
on a rental car or truck.
Also to be seen in the near future, a working model
of a wireless communications version is now in the
Curtis engineering lab. This variation will enable
The Curtis Acuity monitors the voltage, current and
temperature (with integrated temperature sensor)
of a battery to determine accurate state-of-charge,
battery warranty status and battery productivity
iVT November 2012
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