IC- 

! 0 

% b 

I. 

1. 

MCR-85-641 / / 

FINAL REPORT 

FOR 

NICKEL CADMIUM BATTERY EXPERT SYSTEM 

NAS8-35922 

DEVELOPED FOR 

NASA/MARSHALL SPACE FLIGHT CENTER 

HUNTSVILLE, ALABAMA 

PREPARED BY 

MARTIN MARIETTA CORPORATION 

AEROSPACE DIVISION 

DENVER, COLORADO 

NOVEMBER 1986 

(EASA-CR-17903 1) NICKEL CACBlDll EASTEOP 

EXPER% sYsTE!! Final fieport (kartin aarietta 

Aerospace) 39 F CSCL 1oc 

. 

l07-2C47 1 

Unclas 

G3/33 45234 
,. . 

TABLE OF CONTENTS 

SECTION 1 . PURPOSE ............................................. 1 

SECTION 2 . PROBLEM ............................................. 1 

2.1 HUBBLE SPACE TELESCOPE TESTBED BACKGROUND ...... 1 

2.2 NICKEL-CADMIUM BATTERIES ....................... 3 

2.3 EXCESSIVE DATA ................................. 3 

SECTION 3 . OBJECTIVES .......................................... 4 

SECTION 4 . APPROACH ............................................ 4 

4.1 COMPUTER ENVIRONMENT ........................... 4 

4.2 DATA HANDLING LANGUAGE ......................... 4 

4.3 LOGIC PROGRAMMING LANGUAGE ..................... 4 

4.4 EXPERT SYSTEMS ................................. 5 

4.5 Knowledge Engineering .......................... 6 

SECTION 5 . IMPLEMENTATION ...................................... 6 

5.1 NICKEL-CADMIUM BATTERY CHARACTERIZATION ........ 7 

5.2 KNOWLEDGE AQUISITION ........................... 8 

5.3 NICBES DESIGN .................................. 8 

SECTION 6 . RESULTS ............................................ 10 

6.2 EXPERT SYSTEM ................................. 12 

6.2.1 USER INTERFACE ......................... 12 

6.2.2 FAC'LT DIAGNOSIS ........................ 12 

6.2.3 BATTERY STATUS ......................... 15 

6.2.4 BATTERY ADVICE ......................... 16 

6.2.5 DECISION SUPPORT SYSTEM ................ 18 

6.1 DATA-"DL. .................................. 10 

SECTION 7 . RECOMMENDATIONS .................................... 19 

7.1 STATISTICAL PREDICTION OF BAmY LIFE ........ 19 

7.2 MIGRATING NICBES TO A MORE POWERFUL 

ENVIRONMENT ................................... 20 

7.2.2 WINDOWS. MENUS AND MOUSE ............... 21 

7.2.4 EXTENDING THE CHRONOLOGICAL SCOPE ...... 22 

MODIFICATION ......................... 22 

7.2.6 System Control and Fault workaround .... 22 

7.2.1 MULTI-TASKING .......................... 21 

7.2.3 OBJECT-ORIENTED PARADIGM ............... 21 

7.2.5 GRAPHICS-DRIVEN SIMULATION AND 

REFERENCES ..................................................... 23 

APPENDIX A: LIFE CYCEL PERFORMANCE CHARACTERISTICS OF 

APPENDIX B: NICBES DATA FILES 

APPENDIX C: NICBES ADVICE ANALYSIS 

NICKEL-CADMIUM BATTERIES 

ii 
. . 

ILLUSTRATIONS 

TABLE 1: TESTBED TELEMETRY ................................ 11 

TABLE 2: TESTBED ALARMS ................................... 15 

TABLE 3: NICBES STATUS ANALYSIS ........................... 16 

TABLE 4: NICBES TEEND ANALYSIS PARAMETERS ................. 17 

TABLE 5: NICBES TRENDS AND DEVIATIONS ..................... 17 

TABLE 6: NICBES GRAPHIC DISPLAYS ......................... 118 

FIGURE 1: HST EPS TESTBED SCHEMATIC DIAGRAM ................ 2 

FIGURE 2: NICBES FUNCTIONAL DIAGRAM ........................ 9 

FIGURE 3: EXPERT SYSTEM FLOW DIAGRAM ...................... 13 

FIGURE 4: EXPERT SYSTEM MENU FLOW DIAGRAM ................. 14 

iii 
GLOSSARY 

AH1 

AH0 

BPRC 

ccc 

DOD 

EOC 

EOD 

EOF 

EPS 

HST 

MMDA 

MSFC 

NICBES 

sow 

SPA 

- ampere hours in 

- ampere hours out 

- battery protection and reconditioning circuits 

- charge current controllers 

- depth of discharge 

- end of charge 

- end of discharge 

- end of file 

- electrical power system 

- Hubble Space Telescope 

- Martin Marietta Denver Aerospace 

- Marshall Space Flight Center 

- Nickel-Cadmium Battery Expert System 

- Statement of Work 

- solar panel array 

iv 
, 

SECTION 1.0 PURPOSE 

This 

NAS8-35922, for NASA Marshall Flight Space Center (MSFC). 

the modeling and implementation of a prototype diagnostic expert system 

for Nickel-Cadmium Battery Health Management, as well as recommendations 

for future enhancements. 

Final Report details the work done under Contract Number: 

It includes 

SECTION 2.0 PROBLEM 

This section details the problems found-in Nickel-Cadmium Battery 

Management. 

data and a lack of consistency, except at a general level, between 

battery performance tests. 

The areas of difficulty are compounded by large amounts of 

2.1 Hubble Space Telescope Battery Testbed Background. 

NASA and MSFC are involved in the development of autonomous systems for 

spacecraft. 

several studies and by the Advanced Technology Advisory Committee as a 

leading candidate for implementing advanced automat ion approaches such 

as knowledge based and expert systems. 

EPS Testbed provides an opportunity to take a significant step toward 

autonomous operation of an EPS for spacecraft. 

The Electrical Power System (EPS) has been identified in 

The Hubble Space Telescope (HST) 

Power for the HST comes from a system of 20 Solar Panel Arrays (SPA'S) 

and six 23-cell Nickel-Cadmium batteries. 

Testbed at MSFC. 

it, divided into a single-SPA and a dual-SPA. 

power directly into the bus distribution system. 

supplies simulate the 20 SPA'S. 

testbed. 

The HST EPS is simulated by a 

A seventh dual-SPA brings 

Figure 1 is a schematic diagram for the 

Each battery has two power supplies associated with 

These 13 power 

The testbed at MSFC was built to simulate the HST EPS as closely as 

practical. 

the operation of various relays that disconnect when a temperature 

dependent voltage level is reached, and connect SPAs to the batteries. 

Each CCC controls 3 SPAs; a K2 relay controls one SPA and a K1 relay 

controls two SPAs. Thus only two power supplies are needed per 

battery. The 13th power supply simulates the two SPAs that are 

connected directly to the diode bus. 

There are 6 Charge Current Controllers (CCC) that control 

The batteries are diode isolated from each other. There are two 

batteries Connected to each of three diode busses. The diode busses 

then feed three independently controllable load banks. As on the flight 

HST, each battery can be switched to a reconditioning load and its 

associated SPAs can be switched to one of the other two diode busses. 

The batteries are mounted three each on two aluminum plates in a single 

temperature chamber. Each plate has a heater element that can control 

the battery temperature up to 10 degrees Celsius above the chamber 

ambient temperature. 

Also incorporated in the testbed is a microprocessor controller that was 

built and programmed at MSFC. 

temperature of the batteries, the load banks in either a 

09691/1526g 

This control computer (CC) controls; the 

1 
B 

!! 

r_ 

. .. .. 

i 

Q 

I 

" .,.' 

.,..I , . . ..I. 

. .. .. . .. ,. . ... , .. . .,;; . ;' , . : 

% 

a 

a X 

N Y LL 
constant current or constant power mode, the over voltage diode trip 

point, and, using sensed CCC relay operation it controls the 13 power 

supplies in much the same fashion as the HST DF224 flight computer 

controls the SPA trim relays for a step to trickle charge. 

maintain a trickle charge on the battries. 

It also can 

This testbed development work was performed by several people at MSFC. 

John R. Bush was responsible for the HST breadboard and controller. 

John A.Pajak was responsible for the data system and the associated 

wiring. 

and recontinuing circuits (BPRC). 

EPS Systems Team which has responsibility for this testbed. 

Rober E. Kapustka was responsible for the battery protection 

John R. Lanier is the team leader of 

2.2. Nickel Cadmium Batteries. 

Nickel-Cadmium batteries are appropriate energy storage media for a wide 

range of applications. 

long life and low maintenance requirements. 

that is unknown about the behavior of these batteries, in terms of 

design, manufacture, and operating characteristics. Even persons who 

have been working with these batteries for over 15 years, say that there 

is no such thing as a battery expert. Reference 1 documents a number of 

long-standing problems in this domain. APPENDIX A provides an overview 

of the Nickel Cadmuim Battery domain. The EPS requires constant 

monitoring for fault detection. A system which could predict anomalies 

by relaying battery status and battery trend information along with 

explanations as to why a particular battery is exhibiting such behavior 

would be extremely beneficial. 

performed to deter the expected fault(s). Although total automation is 

the desired final result, a prototype phase can demonstrate that such 

expectations are realistic. 

They exhibit a combination of-high capacity, 

There is, however, much 

Corrective measures could then be 

2.3 Excessive Data 

Extensive sensor data can be gained from batteries and battery testbeds 

sufficient to analyze their behavior. Data on cell pressure, voltage, 

battery current, temperature, solar assemblies and bus current are 

gathered from the HST testbed. As the system is operated over months or 

years, accumulations of this data fill hundreds of computer tapes and 

great heaps of printout paper. Information is hard to glean from the 

endless lists of numbers. 

paper to determine battery behavior. 

information is lost due to the overwhelming amount of work required to 

sift it from the numbers. 

Interested personnel hand-plot data on graph 

Unfortunately, other useful 

There is no reason not to automate some of this information gathering. 

Computers are very good at plotting values, finding averages, keeping 

running sums, and generally extracting desired information from vast 

quantities of data. 

their job better. 

This kind of assistance will help human analysts do 

3 

0969111526g 
SECTION 3.0 OBJECTIVES 

The major objective is to demonstrate the applicability of AI 

methodologies for the automation of energy storage management, in this 

case, Nickel-Cadmium Batteries. 

application domain, an expert system was to be developed which 

incorporates the physical characterization of the EPS, in particular, 

the Nickel-Cadmium Batteries, as well as the human's operational 

knowledge. The expert system will return not only fault diagnostics 

but also status and advice along with justifications and explanations in 

the form of decision support. 

developed by the use of rapid prototyping. This demonstration prototype 

is the first of many steps toward a truly automated reasoning system. 

With the HST EPS Testbed as the 

The requirements for the next phase are 

SECTION 4.0 APPROACH 

To meet the objectives described above requires several steps. 

needed to consider an adequate computing environment for a first 

prototype. It was then necessary to decide upon one programming 

language which could efficiently monitor the telemetry stream and 

another one which could not only provide a structure for the data but 

also for the human's "rules" for Nickel-Cadmium Battery management. 

expert system approach was taken. This involved the knowledge 

acquisition necessary to characterize the problems intrinsic to energy 

storage management and the design of a viable model which employed the 

gathered knowledge along with mathematical operations to build status 

and trend analysis. Finally, we implemented a prototype, the 

Nickel-Cadmium Battery Expert System (NICBES), which meets the 

functional and efficiency reqiiirements of the end users, the engineers. 

First we 

An 

4.1 Computer Environment. 

The IBM-PC AT was selected as the programming media. 

its memory and speed, and its support of various programming languages 

as well as graphics capabilities, 

of prototyping. 

Its availability, 

make it adequate for this first stage 

4.2 Data Handling Language. 

IC' is an excellent data manipulation language. It is both efficient 

and fast, an essential qualification for real time data handling. Such 

a language was needed to monitor the telemetry stream, to process the 

telemetry, and to write the output to data files. 

chosen due to its compatibility with the IBM-PC AT. 

MICROSOFT C was 

4.3 Logic Programing Language. 

PROLOG, named for PROgramming in LOGic, is a computer programming 

language that is used for solving problems that involve objects and the 

reiationships between them. 

statements, called clauses, that are either facts or ruies. A fact 

expresses something that is considered to be true. 

hand, expresses how new facts may be inferred from know ones. 

example, given the rule 

PROLOG programs are made up of a set of 

A rule, on the other 

For 

4 

09691/1526g 
. 

"If a battery cell has a hard snort, then its 'voltage is zero." 

"Cell 16 of Battery 5 has nonzero voltage." 

and the fact 

we can infer that Cell 16 does not have a hard short. 

PROLOG is designed so that it can draw conclusions from a set of facts 

and rules. It allows the programmer to concentrate on the logic of the 

problem, rather than on the flow of control as in a "standard" 

procedural language such as Fortran or Pascal. 

The natural independence of the facts and the rules allows great 

flexibility in a program written in PROLOG. 

together, with the only difference in syntax being the incorporation of 

an if then structure, and variables in the rules. 

run interactively by queries from the user, and in response to such a 

query, the rule that is called may make queries of its own upon the 

rules and facts it needs to answer the question. 

answers tlyestt if it can satisfy your question, and "nott if it. cannot. 

Facts and rules reside 

A PROLOG program is 

The PROLOG interpreter 

The mathematical theory underlying PROLOG encompasses the model that 

underlies relational databases, relational calculus. Thus, PROLOG is 

useful for information management applications. 

in natural language systems and representation of knowledge in expert 

systems. 

PROLOG is widely used 

Although PROLOG is not meant to be a "number-crunching" language, PROLOG 

implementations such as ARITY PROLOG, used in the NICBES program, 

support a number of arithmetical operations, as well as string 

manipulations and very simple graphical primitive operations. An 

excellent intrduction to PROLOG is given in the Clocksin and Mellish 

book, "Programming in PROLOG" (Ref ecence 2). 

Another important aspect of PROLOG is the ease of development that it 

provides. 

as it is written. 

(functions) and retested. 

simple predicates and for the larger groupings. 

context also makes it easily understandable and in some cases, 

self-documenting. 

systems such as NICBES. 

Each predicate (simple function) can be tested individually 

They can then be linked together in modules 

Changes can be made quickly for both the 

The English-like 

These methods are ideal for the rapid prototyping of 

4.4 Expert Systems. 

As put in the book "BUILDING EXPERT SYSTEMS" (Reference 31, The area of 

expert systems investigates methods and techniques for constructing 

man-machine systems with special problem-solving expertise." Expertise 

involves not only the facts in a particular field, but heuristics for 

problem solving. These are rules of thumb, hints, strategies, special 

methods that aid human experts in solving problems - drawn from both 

common sense and experience. 

5 

09691/1526g 
The definition above specifies a "man-machine system" rather than a 

computer-program. There is good reason for this since almost all expert 

systems run interactively, answering the user's questions, or asking for 

more information, or exploring a line of reasoning. 

give justifications for their decisions. 

Most are able to 

Expert systems are often termed knowledge based because of the central 

importance of the knowledge rather than any formal reasoning process. 

Most of the difficult and interesting problems do not have algorithmic 

solutions. In addition, formal reasoning does not have means for 

representing knowledge, using mu1 tiple levels of abstraction, or 

controlling complex processes. 

Knowledge is a scarce resource, usually transferred from a human expert 

to an apprentice, often over years of time. 

program is an even more difficult task, but the results can be 

reproduced many times to enable many people to use it or to learn from 

it. An important side effect of the knowledge engineering required to 

build an expert system is the quantification and refinement of the 

domain knowledge. This has often been useful to human experts and 

trainees, apart from its use in the program since in some cases the 

requisite knowledge has never before been written down in one place. 

Transferring it to a 

Battery testbed fault diagnosis and battery status advising are natural 

applications of expert system technology. 

in this field is highly heuristic, based upon intuition and years of 

experience. Logical operations in battery behavior diagnosis cannot 

readily be reduced to algorithms. The human interface for diagnosis and 

consultation fits the interactive nature of the expert system, answering 

questions ar?d giving advice. For these reasons, NICBES, an expert 

system, was developed to aid humans in this field. 

The nature of the knowledge 

4.5 Knowledge Engineering 

NICBES was developed by a standard method for expert systems. The 

knowledge engineer researched the subject of Nickel-Cadmium Batteries 

and their management through an extensive literature search. Upon 

feeling comfortable with the terminology and general theory of 

batteries, discussions were held with personnel at MSFC who have 

specific knowledge of the batteries and the testbed, and with the 

project manager who developed the goals of the system. 

SECTION 5.0 IMPLEMENTATION 

Upon identifing the critical parameters of the Nickel-Cadmium Batteries, 

their casual relationships and the heuristics used by human experts as 

energy storage management guidelines, the knowledge engineers were ready 

to design and implement a Battery Model. The design incorporates the 

representation of both the necessary data ana the icnowiedge of the 

experts. As previously stated, it was very important to also make the 

system easy to use as well as understandable. 

0969Il1526g 

6 
5.1 Nickel-Cadmium Battery Characterization. 

General statements can be made about Nickel-Cadmium batteries. The most 

important factors affecting their performance, ignoring design and 

manufacture, include ambient temperature, depth of discharge (DOD) and 

charging scheme. It has been observed that occasional changes in such 

operating parameters can be of marked benefit in the life cycle of the 

cell. 

As the batteries go through a great number of charge - discharge cycles, 

aging takes place, due largely to electrolyte migration, separator 

deterioration, hydrogen generation because of overcharging, and memory 

effect. 

part of the battery's capacity over a number of charge - discharge 

cycles, causing a change in the crystalline structure of the metals on 

the plates. 

holding it at a low potential for a period of time, then recharging the 

battery. This rebuilds a finer crystalline structure and restores much 

of the battery's capacity. 

and should not be undertaken lightly. However, it is a valuable tool in 

enhancing battery capacity. 

goes too far and reconditioning can no longer restore usefulness. 

This last condition results from utilization of only a small 

Reconditioning is done by draining a battery completely and 

Reconditioning is a strain on the battery 

Eventually, deterioration of the battery 

During the draining procedure of reconditioning, a weak cell can undergo 

reversal, causing permanent damage. 

BPRCs protect each cell of the batteries. 

The BPRC prevents this occurrence. 

During battery operation cell voltages tend to diverge, migrating into 

groups of strong cells and weak cells. 

carry their share of the load which then must be taken up by the 

stronger ceils. 

divergence, a low EOD voltage and particularly by both conditions 

together. 

recharge ratio (ampere hours in divided by ampere hours out), usually 

indicates that the battery is being insufficiently charged. 

As cells get weaker they do not 

The need for reconditioning is indicated by a high 

A low EOC voltage, particularly if accompanied by a low 

When a Nickel-Cadmium battery is overcharged hydrogen gas is generated, 

causing a sharp increase in cell pressure. 

an irreversible chemical reaction. Since the hydrogen is not recombined 

it is possible that a cell may rupture due to an accumulation of gas. 

Another problem due to overcharging is heat production, and causing an 

increase in the intake of current, causing more heat production leading 

to thermal runaway and battery self-destruction. Care must be taken so 

that overcharging does not occur, usually by shutting off power when a 

certain cell voltage is reached. 

battery remains on trickle charge for the rest of the charging cycle, a 

non-destructive "topping off" of the charge. 

The hydrogen generation is 

After main charge is shut off, the 

Decisims to recondition, change the charging scheme or adjust workload 

are presently made by rule of thumb and intuition gained from years of 

experience. Battery management remains a difficult subject. Further 

details are available in APPENDIX A, Life.Cycle Performance 

Characteristics of Nickel-Cadmium Batteries. 

7 

09691/1526g 
5.2 Knowledge Acquisition. 

Discussions with the HST EPS project manager revealed that, in addition 

to the fault diagnosis and battery status-responsibilities of the 

proposed expert system, an important goal was a user interface that was 

informative and easy to use for the users and other interested observers. 

In question and answer sessions with Mr. Bush, the operation of the 

testbed was explained so that this knowledge could be incorporated into 

the program. 

along with the malfunctions that could occur, and their probable 

causes. 

system and diagnosed their probable causes. 

Mr. George volunteered to serve as the battery "expert" despite his 

disclaimer of the term. .The theory and practice of battery management 

were discussed in great detail. The relative importance of various 

battery parameters was discussed, along with their relationship with 

battery management and expected useful life. The proper use of 

reconditioning was emphasized as a powerful tool that requires caution 

in its application. 

the battery and should be undertaken only when necessary to restore 

capacity. The knowledge engineer also determined the kind of 

information that was needed to aid in proper battery management and how 

best to display that information for maximum utility. 

The functionality of each part of the system was explained 

Mr. Bush decided upon the alarms that would be sent by the 

As stated above, reconditioning causes a strain on 

Following the knowledge engineering discussion a revised plan for NICBES 

was developed which incorporated suggestions of the NASA personnel. 

Then the expert system was coded in PROLOG and extensively tested to 

assure proper behavior. A systems programmer wrote the programs for the 

interface and file handler portion of the system. 

behavior for the testbed and batteries were simulated by "doctored" data 

files, as well as induced and simulated faults in data transmitted from 

the testbed. 

Faults and failure 

5.3 NICBES Design. 

NICBES was designed as a two-part system. 

to read telemetry output from the DEC LSI-11 and then to condense this 

data into current and historical data files which satisfy the input 

demands of the Expert System. 

pre-processed HST EPS Testbed data to perform Fault Diagnosis, Battery 

Status and Advice. 

Support Module which provides summary output information in the form of 

graphs. Since the IBM-PC AT does not support multi-tasking, the 

Data-Handler and the Expert System have to be executed independently. 

This is time consuming and inconvenient but no immediate alternatives 

have been found at this time. Therefore, the operator must first run 

the Data-Handler until enough data is processed to build the data files 

recpited by the Expert System. The Expert System can then be run after 

which the Data-Handler is reinitiated to generate the next set of data 

files. 

of the design. 

09691/1526g 

The first portion was needed 

The Expert System then utilizes the 

These functions are supplemented by a Decision 

Figure 2 provides an overview of the major functional components 

8 
NICBES FUNCTIONAL DIAGRAM 

E I 

DATA "DLER 

AND FILE SERVER 

cu 

Cr) 

cu 

v) 

a 

CALL 

ENGINEER 

FIGURE 

9 

NICBES: 

0 FAULT DIAGNOSIS 

0 STATUS AND ADVICE 

DECISION SUPPORT - 

GRAPHICS 

IBM-PC AT 

~ 

OPERATOR 

I STAR- 'SD -15 1 

2 
A central theme through out the knowledge engineering talks was the use 

of the computer as an informational tool. 

excessive amounts of data were produced. 

information from the data is time-consuming at best. 

learned about the operation of both the testbed and the batteries with 

better decision support on the part of the expert system. 

reason, the user interface and decision support system was accorded a 

position of importance in the development. A set of twelve plots was 

chosen, based upon discussions with NASA personnel, for their maximum 

utility to the concerned parties. 

on the IBM-PC AT resulted in a simple graphic style, but one which 

conveys the needed information. 

As mentioned in Section 2.3 

Extraction of useful 

More could be 

For this 

A fairly limited graphic environment 

The Status and Advice System of NICBES also uses these plots to support 

its statements about battery status and the generated advice. 

natural syntax of PROLOG as a query language was used to good effect in 

the question and answer organization of the interface. This meant the 

avoidance of a great deal of the work that would have been required to 

develop this program in a procedural language, where often the 

management of user queries and replies takes up the largest portion of 

the code. 

The 

SECTION 6.0 RESULTS 

An expert system prototype has been developed for the Nickel-Cadmium 

Battery Health Management process. 

Diagnosis, but also gives the engineer concise information on the 

battery's status, advice on what corrective measures can be taken for 

found battery problems, and supports its conelusions with ar! extensive 

set of graphics. Eventually this system can be expanded to give detailed 

maintenance procedures which may be performed by engineers or which can 

themselves be done automatically and thereby remove the engineer from 

the loop. Before this can happen, the Expert System's rules and 

reasoning must be validated to insure that all possible events are 

covered and that the conclusions reached are accurate. 

done by running the Expert System over a lengthy period of time with a 

Nickel-Cadmium Battery "expert" providing evaluations of the system and 

adding any additional rules or data which are deemed necessary for 

completeness. 

It provides not only Fault 

This can only be 

This section details the results of implementing the NICBES prototype. 

The Data-Handler and each module of the Expert System are detailed. 

6.1 Data-Handler. 

The Data-Handler's responsibilities include reading the telemetry, 

processing it and writing the condensed data to files which the Expert 

System can access. 

09691/1526g 

10 
Telemetry is sent from the DEC LSI-11 to the IBM-PC AT over a KS232, in 

six-second bursts, once every 60 seconds. Table 1 below details the 

information contained in the telemetry. 

TABLE 1 - TESTBED TELEMETRY 

Start of Telemetry Burst 

A 

Header Information (Integer) 

year 

day of year - 198X 

hour - 0 to 24 

minute - 0 to 60 

second - 0 to 60 

orbit - Positive Integer 

phase - 0 for discharge, 1 for charge 

day minute (minute in charge) - 0 to 70 

night minute (minute in discharge) - 0 to 37 

Battery Information (for each of 6 batteries) 

battery number Integer 1 - 6 

cell voltage 23 Reals -2 to +2 volts 

cell pressure 23 Integers 0 to 150 psi 

battery voltage Real 0 to 40 volts 

battery current Real -30 to +25 amps 

negative for discharge phase 

positive for charge phase 

BPRC current 

temperature sensors 6 Reals -15 to 30 (degrees C) 

battery reconditioning 

Real 0 to 5 amps 

Integer 0 for no, 1 for yes 

Miscellaneous Information 

Solar Array current 

Bus Voltage 3 Reals 0 to 40 volts 

Bus current 3 Reals 0 to 90 amps 

13 Reals 0 to 20 amps 

The Data-Handler, a program written in MICROSOFT Cy continuously 

monitors the telemetry data-stream. This program puts the data it 

processes into list formatted files so that the Expert System can 

easily analyze it. 

buffer, with data from the last 12 orbits. Each file is described in 

APPENDIX B. Each of the Data files has 6 rows of data, one for each 

battery. 

orbit, listed chronologically. The Current files are written every 

minute with only the required information for fault diagnosis. 

Many of the files are in the form of a circular 

In many of the Data files tnere are i2 columns, one for each 

11 

0969I/1526g 
This seems like a great deal of data to be stored in the system, but the 

telemetry sends 370 values per minute, thus 35,520 values per orbit of 

96 minutes, 532,800 per day. Data and functions of data stored in the 

files were carefully chosen for maximum information density. 

values from the last 12 orbits are kept in files from the 426,240 values 

sent. 

George, who said that 10 or 12 orbits would be enough for 

decision-making in most cases. 

keeping much larger amounts of data, this number was readily accepted. 

The Data-Handler continues to process telemetry for 12 or more orbits 

until the operator shuts down the system. 

is detected. At this time the entire set of data files is written and 

the system exits to make way for the Expert System fault diagndsis. 

Important 

The choice of 12 orbits was made based upon discussions with Mr. 

Considering the cost to the system of 

The exception is when a fault 

6.2 Expert System. 

The Expert System performs several functions. These include fault 

diagnosis, battery-status and advice, plus decision support. 

programmed in ARITY PROLOG and operates on the data files output by the 

Data-Handler. When PROLOG is called, the necessary data files and 

function files are consulted and the Expert System is initiated. 

Diagram is given in Figure 3. 

It is 

A Flow 

6.2.1 User Interface. 

The Expert System is menu driven, that is, user selections to various 

menus determine which system module will be activated. The exception to 

this is the fault diagnosis which is run automatically when the fault 

flag has been set to one. Figure 4 displays the Menu Flow Diagram. The 

user can view any portion of the Expert System and select any battery. 

Ths NICBES TJSER'S MANUAL describes the menus and their choices. 

Guidance is given on which choices will give the engineer the most 

information. 

using screen print commands. 

Hardcopy of any screen report or graph is available by 

6.2.2 Fault Diagnosis. 

This module diagnoses the cause of the alarm, and determines the 

malfunctions in the batteries or other testbed components. In some 

cases, more than one cause is possible. 

printed on the screen. 

Data-Handler when an alarm rings. 

diagnose the possible causes of the problems. 

All relevant explanations are 

As mentioned above, NICBES is alerted by the 

The Expert System is called to 

Table 2 shows the alarms. 

12 

09691/1526g 
EXPERT SYSTEM FLOW DIAGRAM 

- 

DECISION SUPPORT 

SHOWPAK. PRG 

SYSTEM IN ITlALlZATlON 

PROLOG.INI 

CONTROLLER AND 

MENU INTERFACE 

START.PRG 

b FAULTD.PRG I 

. 

I I I 

GRAPHICS 

GRAFPAK.PRG 

BATTERY STATUS 

STATUS.PRG 

BAlTERY ADVICE 

ADVICE.PRG 

PROGRAM SUPPORT 

FIGURE 3 

13 
NICBES MENU FLOW DIAGRAM 

NICBES MAIN MENU 

1. DECISION SUPPORT 

2. BATTERY STATUS 

3. BATTERY.ADVICE 

4. QUIT NIGBES 

I BATTERY SELECTION (1 - 6) 

A 

BATTERY 

I 

t 

STATUS 

1. ANOTHER 

BATTERY 

SELECTION 

MAIN MENU 

2. QUITTO 

L 

BATTERY 

ADVICE 

1. RECOND. 

2. CHARGE 

3. WORKLOAD 

4. ANOTHER 

BATTERY 

SELECTION 

MAIN MENU 

5. QUIT TO 

DECISION 

SUPPORT 

1. - 12. PLOTS 

13. ANOTHER 

BAlTERY 

SELECTION 

14. QUITTO 

MAIN MENU 

FIGURE 4 

14 
TABLE 2 -- TESTBED ALARMS 

1. Power Supplies 

a. SPA current < 5 amps during first 5 minutes of charge phase. 

b. SPA current > = 8 amps for 1-SPAS (1,3,5,7,9,11). 

c. SPA current > 5 amps during discharge phase. 

SPA current > = 16 amps for 2-SPAS (2,4,6,8,10,12,13). 

2. Batteries 

a. Cell voltage <= 0 volts for any cell in any battery. 

b. Cell voltage > 1.55 volts for any cell in any battery. 

3. Load Banks 

a. Sum of 3 bus currents > 99 amps. 

b. Load < 5 amps on any single bus during discharge phase. 

4. Temperature 

a. Average of the 6 temperature sensors > 25 C or < -10 C. 

5. Communication 

a. Missing 3 consecutive telemetry bursts. 

The Expert System will analyze the cause of any of these failures. Some 

of the failures may have more than one possible cause, in which case all 

relevant hypotheses will be displayed for the use of the engineer. By 

analysis of recent telemetry the most likely cause can often be deduced 

and this information will also be available. Diagnoses and supporting 

information will be printed on the screen automatically without specific 

human request. 

6.2.3 Battery Status. 

The Status portion of the Expert System checks the selected battery for 

reconditioning , temperature,- workload, charging scheme and divergence. 

A message is written to the screen as each check is performed, followed 

by a statement of "no problem" or adverse conditions found. The user 

may request the status of any of the six batteries in the testbed. 

NICBES will consult the appropriate files, and return an answer based 

upon the information found there. Where appropriate, graphs from the 

Decision Support System will be used to support these answers. Advice 

may also be sought on whether the battery is due for reconditioning, a 

change in workload, or a change in charging scheme. 

to see if the selected battery is being reconditioned. 

stops as the data may be misleading. 

called to check selected battery performance. 

averaged over 12 orbits) are used for the status analysis. 

details the conditions checked and what the implications are: 

Status first checks 

If so, Status 

Averages (battery data 

Otherwise, four procedures are 

Table 3 

15 

09691/1526g 
i 

TABLE 3 -- NICBES STATUS ANALYSIS 

CONDITION 

Temperature check (Data files 8 and 9) 

STATUS 

Temperature average over last orbit > 0 => Cold 

and over last 12 orbits < 0 

Temperature average over last orbit > 11 => Hot or possible 

and over last 12 orbits > 10 overcharging 

Temperature average over last orbit > 11 => Possible 

and over last 12 orbits < 10 overcharging 

Workload Check (Data files 1 and 13) 

AH0 average over last 12 orbits < 3. => Underwork 

(3.0 Ampere-hours) 

AH0 average over last 12 orbits > 14. 

(14.0 Ampere-hours) 

=> Overwork 

Charging Check (Data files 2 and 3) 

Recharge ratio average < 1.02 => Insufficient 

and average high-charge voltage < 32.5V Charge 

High-charge voltage > 33.8V 

Divergence Check (Data file 4) 

Divergence average > .8V between 

high and low cells 

High cell minus average greater than 

average minus low cells + 1 

=> Possible 

Overcharge 

=> High divergence 

=> Too many cells 

at low values 

6.2.4 Battery Advice. 

The Advice portion of the Expert System goes into further detail than 

the Status section on three subjects; whether a battery needs 

reconditioning, change in charging scheme or change in workload. The 

battery parameters used for trend analysis are given in Table 4, below. 

16 

09691/1526g 
TABLE 4 - NICBES TREND ANALYSIS PARAMETERS 

Reconditioning 

EOD batt voltage 

Charging Scheme Workload 

in-charge high voltage EOD bat t 

vol t age 

in-charge high voltage recharge rat io EOD cell 

diverge 

recharge ratio temperature Avg AH0 

EOD cell divergence 

in-charge cell divergence 

Avg in-charge cell diverge 

Avg EOD cell pressure 

Avg EOC cell pressure 

Divergence is simply computed by taking the differences between 

corresponding values of two lists as high-voltage cells and low-voltage 

cells. 

Trends are calculated by using two simple mathematical functions given 

below: 

n-J 2 - n 

1. 2 2- X(i) 2.2- i * X(i) 

i=l i=1 

where i <= 1 to 12 orbits and X(i> are the associated parameters. 

The first function weights all parameter values for a battery equally, 

while the second function weights the recent parameter values more 

heavily. 

The difference between the two weighting functions is taken and then 

compared to hand crafted deviation factors to determine the trends. The 

deviation factors were derived from the stacks of orbital data received 

from MSFC. Trends are expressed as none, slightly-up, up, strongly up, 

slightly-down, down and strongly down. These are displayed in Table 5. 

The trends of several variables make up the cases for evaluation. The 

conditions which are checked and their implications have been detailed 

in Appendix C, Advice Analysis. 

For a list of constant values, the two functions are equal. 

TABLE 5 - NICBES TRENDS AND DEVIATIONS 

-3 DEV -2 DEV' -1 DEV 0 1 DEV 2 DEV 3 DEV 

17 

0969111526g 
Messages are printed to the screen detailing which of the three choices 

is being examined and what the trends are for a particular battery. 

Given the condition, corrective action is recommended as reconditioning 

the battery, changing the workload or changing the charging scheme along 

with an explanation. 

viewing the plots detailed in the next section. 

Support for these decisions can be gotten by 

6.2.5 DECISION SUPPORT SYSTEM 

The display of information. in a useful form is an important part of this 

system.- The following 12 displays listed in Table 6, were chosen as 

being the most valuable. 

data for hundreds of orbits were rejected as being beyond the scope of a 

small system such as this. 

Other suggested displays which involved keeping 

Rather than using EOC voltage as the high value, it was suggested by Mr. 

George that more information about battery behavior can be obtained by 

using the high cell voltage during the charge cycle. This is done by 

comparing incoming values to the highest value so far, throughout the 

charge cycle of an orbit. 

time of maximum high cell voltage is also important information for 

battery analysis. 

Battery voltage and lowest cell voltage at the 

The Data-Handler handles the collection of this data. 

TABLE 6 -- NICBES GRAPHIC DISPLAYS 

1. 

2. 

3. 

4. 

5. 

. 6. 

7. 

8. 

9. 

10. 

11. 

12. 

Plot of EOD battery voltage for last 12 orbits. 

Plot of high cell voltage during charge for last 12 orbits. 

Plot of recharge ratio for last 12 orbits. 

Plot of high cell voltages, low cell voltages and average cell 

voltages at EOD for last 12 orbits. 

Plot of high cell voltages, low cell voltages and the average cell 

voltages, taken at high-charge, for last 12 orbits. 

Plot of cell voltages at EOD for the last orbit. 

Plot of cell voltages, taken at high-charge, for last orbit. 

Plot of average battery temperatures for latest orbit, taken at 2 

minute intervals. 

Plot of average battery temperature for last 12 orbits. 

Plot of EOC and EOD cell pressures during latest orbit. 

Plot of time on trickle charge for last 12 orbits. 

Plot of battery current during reconditioning, at 2 minute intervals, 

for the last reconditioning. 

Operators may request a hard copy of the dialogue or plots whenever 

desired. Further development of this portion of the system with other 

plots which can be added upon request of the system operators, will be 

relatively easy due to the development of the graphical primitive 

operations. A file containing the needed information must be created, 

then the existing functions can be called using that file and the other 

appropriate parameters of high and low values, scale and captions. 

18 

09691/1526g 
Based upon information from the Decision Support System, the operator may 

answer a number of questions about the cause of unusual behavior, such as: 

why high divergence? 

why temperature rise? 

why cell failed? 

why EOD voltage low? 

Simple answers are given by the system, based on its diagnosis of 

information found in the data files. The functionality-of this portion 

of the system is based upon discussions with Mr. Bush and Mr. George of 

MSFC . 

Plots were chosen rather than graphs due to the implementation of the 

system on an IBM-PC AT. 

provide an accurate graph. Changes may easily be made in the scaling of 

each plot, by the programmer, if a finer differentiation of values is 

needed. At present, this is not under operator control, due to the 

limitations in the resolution of the screen graphics. 

system is later moved to a high-resolution system (see Section 7.2.21, 

finer resolution of data would be possible. 

The resolution of the screen is not such as to 

If the expert 

SECTION 7.0 RECOMMENDATIONS 

In the course of working on NICBES, several rather exciting enhancement 

ideas came to mind. 

light many creative but useful techniques and methodologies. Presented 

below are several concepts that would make NICBES a far more powerful and 

effective system. 

A survey of similar AI applications also brought to 

7.1 STATISTICAL PREDICTION OF BATTERY LIFE 

The first, and quite practical, enhancement is to incorporate a 

statistical prediction of battery life. 

"Nickel-Cadmium Cell Cycle Life Prediction Equation for Low Earth Orbit", 

(Reference 4) appearing in the 1981 IECEC proceedings, details a method 

A paper by Hafen and Corbett, 

for using linear- regression to fit 

predicting battery life. 

Cycle of Mth failure = a -Cr (L 2M l)b 

2N 

where N = total number of cells 

M = failure number (Mth cell 

parameters into an equation for 

failed ) 

DOD is in % (note--we'll have to derive an approximation to this) 

T = temperature in degrees Kelvin 

a,b,c,d are regression coefficients 

19 

09691/1526g 
It is important to derive the regression coefficients from data which is 

specific to the battery type in question. 

considerably between batteries of different manufacturers, different 

designs, and to some extent even between one lot number and another. The 

operating regime of the battery also has an influence upon the regression 

coefficients. Calculation of cycle life using arithmetical averages for 

temperature and DOD give incorrect results since cycle life is nonlinear 

with both temperature and DOD. 

combine cycle lives from a variety of operating points. 

The coefficients will vary 

A method is given in Hafen and Corbett to 

A more general statistical model using the Weibull distribution has been 

described in the paper by Lurie and Steen, "Reliability Modeling of High 

Voltage Batteries", (Reference 5) appearing in the 1982 IECEC 

proceedings. The distribution of the two-parameter Weibull is in the form 

where a and b are parameters of the distribution, and t is time. The 

parameters must be found specific to the battery-type and charging 

scheme, and will change after a hard short or reconditioning. The 

parameter n is the number of cells in the battery, here 23 for the HST. 

Replacing t by (t - v) will give a three-parameter Weibull, where v is 

the location parameter. 

two-parameter Weibull ( where v = 0) runs the risk that the scale and 

shape of the curve will be in great error. 

model failure probabilities of a compound system such as a battery of 

cells. It is very sensitive to correctness of the parameters, since an 

extremely wide variety of curves can be obtained. 

Unless v is known to be close to zero, using the 

The Weibull is often used to 

Although the Weibull model bears investigation, we believe that the 

linear regression method given above will give a more accurate estimate, 

since it incorporates temperature and DOD, while the Weibull depends only 

upon time. 

To incorporate statistical prediction, a determination must first be made 

of the most appropriate type of equation, then the parameters must be 

determined by regression analysis of appropriate data from battery 

operation. Once the equation is derived, it could be used for 

predictions under various proposed operating schemes. 

would be incorporated under the Status and Advice system of NICBES. 

This capability 

7.2 Migrating NICBES to a More Powerful Environment. 

In order to more fully extend the diagnostic and predictive power of 

NICBES, and to make the user interface more productive, it will be 

necessary to port the expert system to a environment which supports a 

fuller cmplement of features, both hardware and software. There are 

four broad areas of enhancement which would improve not only the power of 

the system but also the ease of user interaction as well. 

' 20 

09691/1526g 
7.2.1. Multi-tasking. 

Personal computers, even those as powerful as IBM-PC/AT, do not give the 

type of support for multi-tasking which would serve to greatly improve 

the utility of NICBES. In its current implementation, the data 

acquisition module of NICBES must be interrupted in order to invoke the 

expert system module. Thus, it is certain that the data files stored on 

the AT will contain gaps; a more serious consideration is that faults 

which occur while the expert system module is invoked will not be 

detected or analyzed, without resorting to patching in data from the 

LSI. 

supports multi-tasking would allow the data handler to operate 

continuously and the expert system to be invoked without loss of data. 

The ideal configuration would be one in which the data handler detected 

anomalous values, invoked the expert system module with the proper 

information to load the appropriate data, and then continued to process 

data while the expert system diagnosed and analyzed the input information. 

Porting the data handler and expert system to an environment which 

7.2.2. Windows, Menus and Mouse. 

The current NICBES system interface is of two types; interactive menus 

and textual information which are constructed with the standard Arity 

PROLOG output predicates, and plots and graphs which are constructed 

through the use of calls to Arity screen-handling predicates, which in 

turn reference standard IBM screen-handling utilities. This necessarily 

limits the speed and effectiveness of the user interface and the 

precision of the graphical output. Use of an environment which supports 

high-resolution graphic monitors, multi-window interfaces and mixed-mode 

input (e.g. mouse, text, graphic manipulation) will allow a far greater 

ease of user interaction and far more revealing system output. 

7.2.3. Object-oriented Paradigm. 

A powerful method of knowledge representation is the object-oriented 

paradigm. 

combination of components and their attributes, relationships between 

components, and methods (procedural functions) which operate on the 

components and relationships. 

represented as an object which stands in the "has-a" relation to other 

objects representing individual cells. As data is input to the system, 

the cell objects are instantiated, and anomalous attribute values would 

trigger methods which would in turn instantiate l*fault*l objects. 

objects could be tied to graphical representations which would be 

continuously updated on the output display. 

The object-oriented paradigm lends itself to an easily maintained, easily 

understood logical system which can be readily adapted to changing 

situations and applications. If configurations are changed, or system 

parameters modified, the expert system can be quickly updated to reflect 

the new environment with a minimum of programming expertise and effort. 

Interfaces can aiso be modified rapidly by siiiiply altering the graphical 

object associated with a given logical object. Although object-oriented 

shells have been implemented on the class of equipment on which NICBES is 

currently installed, their performance on such machines will undoubtedly 

prove unsatisfactory, and their development environments are neither 

efficient nor straightforward. 

In this framework, knowledge can be represented as a 

For example, a battery could be 

All 

21 

09691/1526g 
7.2.4. Extending the Chronological Scope of NICBES. 

Personnel directly involved with the HST-EPS testbed have indicated that 

analysis of Nickel-cadmium life-cycle characteristics could best be 

served if data were gathered and interpreted over extended periods of 

time, such as 1000 orbits. 

make it impossible to load enough data into working storage to 

effectively deal with data of this quantity. 

be loaded into working memory, or virtual paging techniques implemented, 

the processing time would be extreme, even more so because the expert 

system and the data handler must function as independent processes. 

powerful environments which support working memories in the four to 

sixteen megabyte range, compared to the PC-DOS 640 kilobyte limit, would 

make this goal possible. 

The memory limitations of AT class hardware 

Even if enough data could 

More 

7.2.5. Graphics-driven Simulation and Modification. 

Another valuable enhancement to NICBES would be the addition of a module 

which affords users the opportunity to dynamically interact with a 

graphic representation of the power system. The user could induce 

faults at various components and invoke the expert system to diagnose and 

analyze the simulated faults, including those of a type not usually 

encountered, thus exploring both the effectiveness, the accuracy and the 

reasoning capabilities of the system. 

values would be facilitated, as well as the user's understanding of 

NICBES's behavior and logic. 

the system's scope is deficient as well as specify exactly where new 

rules and data are needed will make it easier to accurately extend the 

capabilities of NICBES. 

Experimentation with parameter 

The ability to interactively indicate that 

7.2.6 System Control and Fault Workaround. 

An extremely valuable extension of the NICBES is to add the capability to 

respond to faults with fault correction or workarounds. 

require additional expert system modules that could plan actions and 

execute them. Additional interfaces to the hardware and new hardware 

controllers or"effectors" to carry out the actions planned by the expert 

control and fault correction modules would be needed. This task is a 

significant extension of the existing prototype. However, as system 

complexity, numbers, and distances to space platforms increase there is a 

concomitant need for increases in system automony afforded by this 

extension. 

This would 

09691/1526g 

22 
REFERENCES 

1. S. Gross, "Unsolved Problems of Nickel Cadmium Batteries", 

IECEC Proceedings, 1981, pp 177-181. 

2. W.F. Clocksin and C.S. Mellish, Programming in Prolog, 

Springer-Verlag, Berlin, 1984. 

3. F. Hayes-Roth, D.A. Waterman and D.B. Lenat, eds., 

Building Expert Systems, Addison-Wesley, Reading, Mass., 1983. 

4. D.P. Hafen and R.E. Corbett, "Nickel-Cadmium Cell Cycle Life 

Prediction Equation for Low Earth Orbit", IECEC Proceedings, 

1981, pp. 199-204. 

5. C. Lurie and A. Steen, "Reliability Modeling of High Voltage 

Batteries", IECEC Proceedings, 1982, pp. 751-756. 

23 
APPENDIX A 

Life Cycle Performance Characteristics 

of 

Nickel-Cadmium Batteries 

1.0 The Life Cycle. 

Hickel-Cadmium batteries are appropriate energy storage media for a 

wide range of applications. 

long life, and low maintenance requirements. Unfortunately, stringent 

tests (i.e. experiments with strictly controlled parameters) of life 

cycle performance characteristics have never been done; 

certain generalizations can be made. 

They exhibit a combination of high capacity, 

nonetheless, 

1.1 Factors affecting performance. 

The factors affecting performance of nickel-cadmium cells are 

varied. Ambient temperature affects both the capacity and the charging 

characteristics of ni-cad cells. Depth of discharge is the primary 

influence leading to the "memory effect". Charging regimes can have 

great affect on the subsequent performance of cells, and it is claimed 

that variety (i.e. frequent changes, within reason, of depth of 

discharge, temperature, charging regimes and other parameters) can be of 

marked benefit in the life cycle of the cells. 

In this section, certain global and specific variables will be 

discussed which are of primary import on the life cycle characteristics 

of nickel-cadmium cells. 

1.1.1 Age. 

The age of a battery can be measured in two ways: chronologically and 

cyclically. Although the shelf life of a nickel-cadmium battery is not 

unlimited, deterioration is so slight, within reasonable time limits, 

that most applications can effectively disregard it as a factor. It is 

"cycle" age, the number of successive charge/discharge cycles that a 

battery or cell has undergone, which is of primary importance. 

analogy can be made to a piece of mechanical equipment, which if properly 

stored, might last years unused, subject to whatever unavoidable 

oxidation might occur. When the machine is put into use, however, "wear 

and tear" endemic to the application begins to exert its influence, and 

the life expectancy of the machinery begins to decrease. So it is with 

electro-chemical celis, and thus "cycle" age is a far more indicative 

measurement of the life cycle characteristics of the battery. 

The 

A-1 

09751/1526g 
Reconditioning (cf. below) is an effective procedure for rejuvenation of 

aging ni-cad cells, but its usefulness is limited. In recent tests of 

ni-cad batteries at MSFC, the batteries usually achieved 3000 cycles 

before notable performance deterioration occurred; after the first 

reconditioning, the battery exhibited "youthful" performance for 

approximately 1000 more cycles before critical performance faults became 

evident and reconditioning was recommended; subsequent reconditionings 

rendered the batteries rejuvenated for shorter and shorter periods. By 

the end of 8000 cycles, reconditioning was being performed every 200-300 

cycles. Although the other factors affecting performance were not 

rigorously controlled, and consequently improvement of these figures 

might be anticipated if effectively enhancing charging, reconditioning 

and other procedures are developed, the point is clear: the life 

expectancy of nickel-cadmium cells is not unlimited, and performance 

deterioration is only to be expected with increasing "cycle" age. 

1.1.2 Charging Regimes. 

There are no standard charging regimes for nickel-cadmium batteries. 

Charging schemes are limited by power sources for input, and by sensor 

configurations for cut-off, but within these limits various schedules 

have been tried in applications and tests. Charging may be done with 

constant current or constant voltage sources; current or voltage may be 

stepped-down as the battery approaches a charged state; high or low (i.e. 

"trickle") charges have been tried. Limiting charge by recharge ratio or 

actual sensor readings of cell voltage and/or pressure may be applied. 

In short, no stringent tests seem to have been done in order to determine 

what charging regime may be most effective in prolonging the useful life 

of ni-cad cells. 

An interesting, though unproven, suggestion by some experts is that 

the charge curve should as closely as possible approximate the discharge 

curve. Although this may be infeasible in some applications, where such 

fine adjustments to input current are awkward or too costly, a controlled 

test of such a scheme might prove extremely rewarding. 

Far more important, at least in the short term, is the development of 

effective techniques for limiting input current so that destructive 

overcharging does not occur. Although many systems use a strict 

numerical ratio to balance input and output of current to the 

electro-chemical system, such a controlling factor must necessarily be 

set conservatively, since other variable factors, both global to the 

battery and local to particular cells, may influence the actual amount of 

potential and capacity regained by specific cells. 

1.1.3 Depth of discharge. 

Depth ef discharge (Ed!) is the per cent of cell capacity used in any 

one discharge cycle. For example, if the capacity of a battery is 

50 ampere hours, and a 1 amp load is applied for five hours, the DoD 

is 10. Typically, operating a ni-cad battery at low ( < .20 ) DoD values 

for many cycles will result in diminished capacity through the "memory 

effect" (cf. below). Where possible, it is advisable to vary the DoD, 

A-2 

09751/1526g 
either through increased loads or through regular omission of charging 

periods to avoid this effect. 

many consecutive cycles, the "memory effect" is not evident, but other 

deleterious results, such as plate or separator breakdown, may result. 

In short, the consensus seems to be that extremes in DoD should be 

avoided, and that DoD should be varied wherever possible. This is in 

line with the remark made above that variety, anthropomorphic as such a 

term might seem, is perhaps a worthwhile method of keeping a ni-cad cell 

"happy" . 

If the DoD is extremely high ( I .80 ) for 

1.1.4 Reconditioning and the "Memory Effect". 

When Ni-Cad cells are utilized at a small percentage of their actual 

capacity for long periods of time, the capacity of the cell diminishes, 

as if the cells become accustomed to low discharge rates and lose their 

ability to sustain greater total AHO. This is due to a change in the 

crystalline structure of the nickel and cadmium metals on the plates. 

This condition is known as the "memory effect" and is perhaps the 

greatest single detrimental factor in long-term battery performance, 

aside from 

actual internal physical breakdown (e.g. short) of a cell. 

Reconditioning is a term broadly used to mean the procedure of 

draining a cell to its actual capacity limit, holding that cell at a low 

potential/low capacity level for a period of time, and then fully 

recharging the cell. 

structure of the nickel and cadmium plates, and depending on the number 

of previous cycles which the cell has undergone, can restore the actual 

capacity of the cell to a nearly "new" value. However, with increasing 

"cycle age", the restorative effect of reconditioning becomes more and 

more temporary, and reconditioning more frequently necessary. 

This procedure cause realignment of the chemical 

One point of particular and critical importance is cell reversal when 

draining a battery in the reconditioning procedure. 

reach the lower limit of their capacity, there is a tendency for them to 

reverse polarity and try to regain power from stronger cells. 

reversal at currents greater than 1 ampere can result in permanent damage 

to the reversed cell, and as such should be avoided especially. 

cell cannot be protected from such reversal, the load current on the 

battery must be kept at a low enough value to avoid damage. 

more cells are particularly weak, this diminishment in load can make the 

reconditioning procedure extremely time-consuming. 

ni-cad battery test, five days were necessary to bring all cells down in 

the first reconditioning procedure; needless to say, cell reversal 

protection circuits were quickly installed, and the reconditioning time 

was reduced to a matter of hours. 

As weaker cells 

Cell 

If the 

If one or 

In the recent MSFC 

1.1.5 Temperature. 

Ni-Cad cells perform quite well at temperatures between Oo and 

40° C. However, it is well to avoid sudden shifts in temperature, 

since they may adversely affect battery performance and make accurate 

evaluation of charging regimes and capacity values difficult. It is also 

A-3 

09751/1526g 
the case that internal faults within a cell, such as a short, may cause 

temporary rises in internal cell temperature, and that charging a cell 

also causes the internal cell temperature to rise. For this reason, it 

is advisable to have several temperature sensors on the battery, if it is 

not feasible to have one for each cell. 

1.2 Measurements and Evaluation of Parameters. 

1.2.1 Recharge Ratio (RR) and Efficiency (Eff). 

RR is a derived measurement, equal to Ampere Hours In (MI) divided 

by Ampere Hours Out (AHO); as used in some tests and applications, it 

serves as a limit on charging schedules and as an indication that battery 

reconditioning is necessary. In general, a RR of less than 1.04 would 

indicate that the battery is not being brought back to a fully charged 

state, and a RR of greater than 1.15 indicates that the battery cells are 

being overcharged. RR in the high end of the permissible range is a 

probable indication of diminishing capacity in the battery, although this 

judgement should only be made on the basis of examination of the current 

trend in RR, since short term fluctuations in RR may be due to 

idiosyncrasies of individual cells. 

Eff is analogous to RR; it is equal to Watt Hours Out (WHO) divided 

by Watt Hours In (WHI). Ideally, a battery would be 100% efficient; this 

is, however, never the case. Eff measurements of less than 95% will 

usually be equivalent to a high RR, and indicate the same conditions. 

1.2.2 Capacity. 

Capacity is measured in ampere hours of current deliverable before 

voltage falls below some arbitrary threshold. Since the discharge curve 

of nickel-cadmium cells is relatively flat through the greater part of 

capacity, usable voltage levels are obtainable through up to roughly 90% 

of capacity. Most applications, however, use a very small percentage of 

available capacity, and thus detection of lessening capacity (due to 

"memory" effect) is rendered more difficult. 

1.2.3 Individual Cell Measurements 

By far the most useful measurements are End of Charge (EOC) and End 

of Discharge (EOD) voltage and pressure values for individual cells in 

the battery. 

monitor voltage and pressure of each cell at both EOC and EOD. 

these measurements, derived parameters such as voltage divergence (VD) 

(i.e. the difference in potential between the highest and lowest cell(s)) 

and average voltage, as well as destructive overcharging, can be quickly 

determined. The significance of these values will be discussed in 

section 2 below. 

Ideally, any test or application of Ni-Cad batteries should 

From 

A-4 

09751/1526g 
2.0 Determining the Status of the Battery through Parameter 

Values 

2.1 Pressure 

High EOC cell pressure: A high EOC cell pressure indicates that the 

cell is becoming fully charged. Care must be taken, however, that 

overcharging does not take place. As the nickel plate becomes fully 

charged, oxygen is released, resulting in a gradual rise in internal cell 

pressure; upon discharge, the oxygen will recombine, and cell pressure 

will drop. However, when the nickel plate reaches full charge, the 

cadmium plate will begin to rapidly release hydrogen, and a sharp 

increase in cell pressure will result. Hydrogen will not recombine upon 

discharge, and a decrease in cell performance will occur. Extreme 

overcharging may even result in a "ballooned" or ruptured cell. 

For this reason it is recommended that cell charging be limited on an 

individual basis, using pressure and voltage sensors to indicate when a 

particular cell is fully charged. At that point, the cell should then be 

removed from the charging circuit. This is a safer, though more 

expensive, method than using RR as an indication of charging adequacy. 

In applications where replacement of damaged cells is dear or impossible, 

such a procedure may be greatly desirable. 

High EOD cell pressure: High EOD cell pressure is usually the result 

of non-recombinant hydrogen generation during the charging cycle. As 

such, it serves as confirming evidence of suspected overcharging. 

2.2 Voltage 

In the following, the terms "high" and 'llow" with respect to voltage 

are used in purely relative senses. A "low" EOD voltage at one level of 

depth of discharge might be a very high one at deeper levels of 

discharge. Although there are ideal values for the EOC level of new 

cells which are fully charged, "cycle" age may mean that a slightly lower 

value for full charge is acceptable. Thus, the terms "high" and "low" 

must be evaluated in terms of the other affecting parameters. 

A cell which exhibits high EOD and EOC voltages is a good cell, 

having a high potential at EOC and a strong capacity through discharge. 

Other combinations of high and low values, however, may be indicative of 

trouble. 

Low EOD voltage is an indication of lessened capacity, and is 

probably due to the "memory effect". As capacity decreases, the same AH0 

load will result in lower and lower EOD voltages, since the ability of 

the the cell to maintain an acceptable voltage level is a direct function 

of its capacity. 

capacity; if not, problems such as separator deterioration or plate 

breakdown may be suspected. 

Reconditioning will usually achieve a rebound in cell 

A-5 

0975Ii1526g 
Extremely high EOC voltages will usually be accompanied by high 

internal pressure values; see section 2.1. 

Low EOC voltages are usually the result of the memory effect; 

however, if all cells are displaying low EOC voltages, 

low, it is probable that the cells are being insufficiently charged. 

and the RR is 

2.3 Voltage Divergence 

Voltage divergence is the difference in the highest and lowest 

voltage values at a given point in time, usually EOD or EOC. Cells tend 

to group; the cell(s) with high voltage values at EOC usually continue to 

have them, and the cell(s) with low values usually remain low. 

time, the absolute value between high and low cell voltage increases, and 

cells tend to migrate from "average" values to either the high or low 

group. EOC voltage divergence is a usually higher than EOD voltage 

divergence, since stronger cells will "pick up" weaker cells under a 

load. EOC voltage divergence is a surer indicator of "memory effect", 

since, if battery charging is being limited by RR thresholds, cells which 

are losing capacity will be recharged less. Conversely, if charge is 

being limited through pressure and voltage readings, EOC divergence will 

be slight, but a rise in measured RR will indicate that certain cells are 

losing capacity. By monitoring the relative charge times of respective 

cells, low capacity cells can be identified. 

Through 

Voltage divergence of greater than 150 mv at EOC indicates that the 

low cell(s) is losing capacity, since if a "healthy" cell has a EOC 

voltage of 1.5 volts, a voltage level of 1.35 in any cell will be an 

indication that that cell is near the end of the discharge curve and has 

very little remaining capacity. 

2.4 Average Voltage 

Average voltage values are of primary usefulness in conjunction with 

voltage divergence values to give an overall indication of the entire 

battery status. If the average.voltage at EOC is at an acceptable level, 

while voltage divergence is high, it is indicated that approximately 

equal numbers of cells are migrating to high and low groups. If average 

voltage at EOC is dropping, and divergence is high, it may indicate that 

too many cells are moving to low values, and reconditioning is advisable. 

If average voltage at EOC is dropping, and voltage divergence is low, 

then the charging scheme should be reevaluated, since the total charge 

may not be great enough. If average voltage at EOD is low, and 

divergence is small, the DoD should be evaluated. If DoD is small in 

relation to projected capacity, then real capacity may be lessening in 

response to the memory effect. If average voltage at EOD is low, and 

divergence high, then "memory effect" is definitely indicated, especially 

if DoD is low with respect to projected capacity. 

A-6 

097511'1526g 
3.0 Therapeutic and Prophylactic Procedures and Prolonging the 

Life of Ni-Cad Cells. 

3.1 Prophylactic Procedures. 

There are three main points to be made in regard to protecting the 

viability of nickel-cadmium cells: one, cells should be protected from 

reversal during deep discharge; two, cells should be protected from 

destructive overcharge and the accompanying generation of non-recombinant 

hydrogen; and three, ambient temperature should remain relatively stable. 

The charging regime is one area in need of research. Since charging, 

just as discharging, llages'l a battery, optimal charging strategies need 

to be developed which minimize the "wear and tear" on the ni-cad cell. 

It is certain that some charging patterns are more destructive than 

others, and it is probable that different charging schemes will be found 

optimally beneficial at different times in the battery life cycle. That 

is, while it will undoubtedly be found that some charging procedures are 

undesirable under any circumstances, it may be discovered that a scheme 

judged optimal for a "new" battery will prove less desirable than some 

other at a later time in the battery's life cycle. 

3.2 Therapeutic Procedures. 

Only two long term therapeutic procedure are available in most ni-cad 

battery applications: reconditioning and variable DoD. As explained 

above, reconditioning, to a high degree, undoes the destructive "memory 

effect" in applications where consistently low DoD levels are utilized. 

On the other hand, variable DoD levels somewhat eliminate the "memory 

effect", but may not be feasible in some applications. Since 

reconditioning procedures make the battery unavailable for a period of 

time, it may be advisable to use a combination of reconditioning and 

variable DoD to prolong ni-cad cell life, where the application is 

amenable. 

3.3 Prolonging the Life of the Battery. 

As stated in section 1.1, the life expectancy of nickel-cadmium cells . 

is not unlimited. Critical or damaging faults due to poor construction 

or material can only be avoided through strict quality control. However, 

much can be done in the proper design of the components of the 

application to prolong ni-cad life expectancy. The steps advised in 

section 3.1 should certainly be taken. Further research should be made 

on the topics of optimal charging regimes, variability of DoD, and timing 

of reconditioning. Only by stringently controlling other variables can 

valid conclusions be reached as to the effectiveness of the therapeutic 

measures mentioned above. 

A-7 

09751/1526g 
Some suggestions for further testing may be in order: 

1. Preventive reconditioning or DoD. 

If the application permits, reconditioning or variance 

of DoD should be done before the first indications that 

capacity is diminishing. That is, do not allow the 

"memory effect" to become established in the "youthful" 

period of the battery's life. 

2. Prevention of destructive overcharging. 

Charging limits should be set conservatively and monitored 

closely. Failure to fully charge the cells may actually 

be beneficial, resulting in an inadvertent variance in DoD, 

while overcharge cause heat generation and increase in 

internal cell pressure through generation of hydrogen, and 

could never be deemed beneficial. 

3. Replication of discharge curve by charge curve. 

As mentioned above, development of optimal charge regimes 

could have great impact of life cycle pro-longment. 

Further testing in this area could reap great rewards. 

A-a 

09751/1526g 
APPENDIX B 

HICBES DATA FILES 

Fault file - Contains a fault flag = 1 if there was a fault 

= 0 if no fault was detected. 

Current file 1 - Contains the current orbit number and 

a reconditioning flag for each battery = 1 for reconditioning 

= 0 no reconditioning. 

Current file 2 - Contains Phase (charge or discharge) 

Day-min 

Current from 13 SPAS (Solar Panel Array) 

Current from 3 Busses 

Average Temperature for 6 Batteries 

Current file 3 - Contains 6 Battery Cell Voltages (23 per battery) 

Data file 1 (6x12) - File contains battery voltage taken at EOD per 

orbit for last 12 orbits. 

Data file 2 (6x12) - File contains the battery voltage at high in-charge 

for the last 12 orbits. There are 23 cells per battery. 

Data file 3 (6x12) - File contains the recharge ratio = AHO/AHI per orbit 

for 12 orbits. 

Data file 4 (6x36) - File contains cell voltages at EOD, with the high 

value, low value and average of all values, in this order per orbit for 

the last 12 orbits. So a row contains 12 high values, 12 low values and 

then 12 average values. 

Data file 5 (6x36) - File contains cell voltages at high-charge; high, 

low and average of all values, in this order, per orbit for last 12 

orbits. Each row contains 12 high values, 12 low values and the 12 

average values. 

Data file 6 (6x23) - File contains 23 cell voltages at EOD for each 

battery, from the latest orbit. 

Data file 7 (6x23) - File contains 23 cell voltages at high-charge for 

the latest orbit. 

Data file 8 (6x48) - File contains the average of the six temperature 

sensors (degrees C) per battery, at two minute intervals 

(lmin,3min, ... 95min) over the latest orbit. 

B-1 

09761/1526g 
Data file 9 (6x12) - File contains the average battery temperatures per 

orbit for the last 12 orbits. This is the average of the temperature 

averages in Data file 8. 

Data file 10 (6x46) - File contains the 23 cell pressures taken at EOC 

and then the 23 cell pressures taken at EOD for each battery in the last 

full orbit. 

Data file 11 (6x12) - File contains the time on trickle charge for each 

battery per orbit for the last 12 orbits. 

Data file 12 (6x49) - File contains battery current during 

reconditioning, at 2-minute intervals, for last reconditioning of each 

battery. It is recorded every 2 minutes, only when battery 

reconditioning flag is 1 and only for one orbit. Column 1 contains the 

orbit number for which reconditioning is occurring. The file contains 

zeroes until a battery is reconditioned. 

Data file 13 - File contains AH0 summed over discharge phase per orbit 

for last 12 orbits. 

B-2 

09761/1526g 
APPENDIX C 

NI CBES ADVICE ANALY S I S 

For reconditioning, 11 conditions need to be checked for a particular 

battery : 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

EOD voltage strongly down, in-charge divergence strongly up 

reconditioning advised. 

EOD voltage strongly down, in-charge voltage strongly down => 

recondition soon. 

EOD divergence strongly up, in-charge divergence strongly up => 

strongly rising divergence indicates reconditioning. 

Voltage trends strongly down or down, recharge ratio and divergence 

trends strongly up or up => reconditioning is indicated by all 5 

trends. 

Recharge ratio strongly up => reconditioning indicated. 

In-charge voltage is down or strongly down, in-charge divergence is up 

or strongly up => reconditioning recommended. 

EOD voltage down or strongly down, in-charge divergence up or strongly 

up => reconditioning indicated. 

EOD and in-charge divergence both up => consider reconditioning. 

Recharge ratio up => consider reconditioning. 

Both EOD and in-charge voltages down => consider reconditioning. 

None of the above => no need for reconditioning at present. 

=> 

To determine if the charging scheme for a battery should be changed, nine 

conditions are checked: 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

six 

1. 

2. 

3. 

4. 

5. 

6. 

Temperature strongly up, EOD pressure greater than 120, EOC pressure 

greater than 140 => overcharging causing high pressure. 

In-charge voltage strongly up => check for overcharging. 

EOD pressure greater than 110, EOC pressure greater than 135 => charge 

rate may be too high. 

EOD voltage strongly down, in-charge voltage strongly down => 

undercharging may be seriously affecting capacity. 

EOD voltage down, in-charge voltage down => undercharging. 

EOD voltage strongly down or down, in-charge voltage strongly down or 

down => undercharging may be causing loss of voltage. 

EOD voltage down, in-charge divergence greater than .8 => 

undercharging may be causing loss of voltage. 

EOD voltage strongly down, in-charge divergence greater' than .8 => 

undercharging may be causing serious loss of voltage. 

None of the above => no need to change charging scheme. 

conditions are checked to advise as to battery workload change: 

EOD voltage down, EOD divergence down, AH0 average less than 25 => 

loads probably too light. 

EOD voltage strongly down, EOD divergence strongly down, AH0 average 

less than 5 => losing capacity due to memory effect, try heavier load. 

AH0 average greater than 14 => possibly destructive overwork. 

AH0 average greater than 9 => heavy workload. 

EOD voltage down or stongly down, EOD divergence down or strongly down, 

AH0 average above 6 => losing capacity, consider reconditioning. 

None of the above => no need to change workload. 

C-1 

09761/1526g