The Handbook of FMA, Inc.

Lithium Polymer Battery Systems

Section 1 – FMA LiPo Systems

July 2005

This document is a work in progress.

Latest revision: July 24, 2005

FMA, Inc.

Distributor  for Kokam Lithium Polymer Cells

5716A Industry Lane

Frederick, MD  21704  U.S.A.

Section 1 Contents

Introduction

A brief history

FMA Li Po Systems

Building Li Po packs

The basic cell

Wiring an individual cell

How cells are connected

Series connected cells

Parallel connected cells

Series/parallel connected packs

How modular packs are manufactured

The Li Po modular pack connection system

Building a modular Kokam Li Po “Super Pack”

Unitized packs

Stick Packs

The FMA SKYVOLT System

SKYVOLT Application Examples

Balance Pro and Scorpion for the Two Cell Packs

BalancePro Application Examples

Cell Pro Balancing System  (Coming mid-2005)

What Li Po packs can do

What goes in to design of FMA cells and packs

A brief history

Lithium Polymer batteries are a new generation portable electric power source.  They are different from other batteries used for RC.  In 1959, when Fred Marks became involved in RC, only carbon zinc batteries were available to RC.  Lead-acid batteries were used with a converter to generate 180V for the tubes used in transmitters, but all else was done with carbon zinc batteries.

The first time anything other than carbon zinc was used in RC was when the great Walt Good came to a meet in the early 1960s with some extraordinary cells he had obtained from Johns Hopkins Applied Physics Lab where he worked.  The small Silver Cadmium cells were of great interest, but far out of reach of the average modeler.

Surplus wet Nickel Cadmium cells began to appear from the Nike missile program (they had to be replaced periodically) and found good use as glow plug lighters.  In 1962, Fred obtained his first NiCd button cells from the ABC Battery Company.  In due time, cylindrical NiCd cells came on the market with General Electric and Gulton as the first mass producers.  It wasn’t long until the Japanese acquired the technology and rapidly drove down the price of NiCds.

NiCd technology has seen steady if slow growth over the ensuing 40 years.  NiMH became a new technology only in the early nineties and has grown a bit faster than NiCd.  The primary attraction for NiMH was lighter weight and better environmental characteristics.

About 1980, Lithium Ion (Li Ion) cells began to be used for light duty, lightweight applications.  Li Ion cells began to be modified for RC from retired cell phones and surplus sources only about four years ago.  Li Ion cells can tolerate only modest discharge rates but found some use in powering electric airplanes.

Lithium Polymer (Li Po) cells began to see use in 2001 in a small way.  The “small way” was primarily in the form of the Kokam Engineering Co., Ltd. 145 mAh cell.

A brief history of the development of Li Po technology follows:

Early in 1980, Motorola and Sony decided to apply lithium ion technology to the mobile phone to reduce weight and improve energy density, even though there were safety issues as there are now.  They developed a safety module, the so-called PCM (protection circuit module).  Up to now there have been few accidents from Li Ion.

Meanwhile, the Bellcore Lab in San Diego announced that they had developed the lithium polymer battery to increase energy density and safety by using a plastic pouch packaging/stacking method (different than Kokam’s system) using an ion conductive separator named PVDF (polyvinyldifluoride) which has good binding characteristics at 100° C.

Sony, Toshiba, Panasonic, Samsung, Saft, Varta, Valence, Ultra-life, Polystar and perhaps 30 companies bought licenses to commercialize the Bellcore technology during the period since.  No one was successful due to the difficulties of mass production technology when using this technology.  Everybody gave up or went bankrupt.  Sony started a new method  which modified conventional technology with PVDF material only, but closely related to winding technology.  With this material (PVDF), it is very difficult to achieve high power drain due to the limitations of the ion conductive material itself.  Wound cells cannot achieve high discharge rates because of high current drain from the anode tab.  Winding has a longer electrode which increases the internal resistance at high current draw.

Kokam, too, evaluated Bellcore technology as an alternative, but realized that it is not a practical technology for commercialization due to the processing difficulty.  Thus, Kokam decided to develop new technology with assistance from the Korean government agency named KIST (Korea Institute of Science and Technology).  A new system was invented system that permits Kokam to make the battery easier with significant improvement over Li Ion and providing better safety.  Kokam acquired patents world - wide and started to design the full process and equipment suitable for mass  producing Kokam cells.  German and Chinese companies licensed Kokam technologies.

With the Kokam technology, we have successfully created the first 20C discharge rate commercial Li Po battery

In June 2002, FMA, Inc. and Kokam Engineering Co., Ltd. signed an agreement for FMA to serve as the agent for Kokam in North and South America.  In October 2002, FMA, Inc. began actively shipping Kokam Lithium Polymer (Li Po) cells.  As of this writing, over 2,000,000 cells are being used in RC models.

At this time, FMA Direct has been actively promoting the use of Li Po cells and packs for three years with gratifying results.  In the past three years, Li Po technology has advanced farther than NiCd technology advanced in nearly forty years.  In 2002, the standard Kokam cell was capable of continuous operation at three to four times the multiple of capacity (3 to 4C) with 5C as the upper limit.  In the past two years, FMA/Kokam has introduced, and FMA now has on the market, cells capable of sustaining up to 20C with loss of but a few percent capacity and with the capability to withstand pulses of current of < one second duration at up to 40C .  Detailed performance data are available as Data Sheets in the FMA Li Po Compendium.  During 2004, FMA/Kokam reduced Li Po cost by one-third.

From the beginning of its involvement with Li Po technology, FMA has anticipated the need for a system of Li Po components.  Several factors influenced this approach:

·         Li Po batteries require different chargers than other chemistries.

·         The 3.7V cell output requires that packs and ESCs must be designed and sized differently.

·         It was desired to make it as easy as possible for the NiCd/NiMH user to make the transition to Li Po.

·         Li Po cells have unique safety and operating rules.

·         Over the past four years, FMA has addressed and optimized all aspects of successful use of Li Po batteries.

By providing all the elements needed (below), FMA hopes that Li Po will continue the rapid rate of acceptance and success seen to date.  We truly believe that glow engine power will be largely replaced by Li Po power over the next few years.

See all products needed to make you successful with Li Po batteries at www.fmadirect.com

From the tiniest to the BIGGEST, FMA Li Pos power and control them all!

The basic cell

Using Li Po cells was challenging for early users, and only the most persistent did what it took to use them.  The first cells had only bare tabs that were thin and fragile, and one tab was aluminum that required special solder and techniques.

The first improvement was to weld a nickel tab to the aluminum tab that, in turn, could be soldered.  The next improvement was incorporating a small pc terminal board on each cell that made soldering as easy as for any cell with terminal lugs. Such cells are available still for certified pack builders who purchase in quantity. *