Short-circuit events observed in ground test simulations of DSCS-3 battery in-orbit operations are analyzed. Voltage signatures appearing in the data preceding the short-circuit event are evaluated. The ground test simulation is briefly described along with performance during reconditioning discharges. Results suggest that a characteristic signature develops prior to a shorting event

Lurie, C.

English

NASA Technical Reports Server

CELL  SHORT  CIRCUIT,  PRESHORT  SIGNATURE 
C. Lurie 
TRW 
(Figure  4-85) 
TRW has  been  running  ground test  simulations  of DSCS-3 missions for  some  time  now. 
During the flight 7  simulation, several short-circuit  events were observed. 
In  the process of  our  looking  at  what  happened, we took  a very, very close look  at  the cell 
level data preceding each of the short-circuit events. In the process of this investigation, we 
discovered that  there was a voltage  signature  appearing  anywhere  from  days to  weeks prior to  this 
short-circuit  event. What I  would  like to  discuss  is what we saw and  what we think  it means. 
(Figure 4-86) 
It is necessary t o  describe  this  system just  a  bit.  The  ground  test  that we ran is a  simulation  of 
geosynchronous  orbit cycling. It is the familiar 45 eclipses  per  season. We run  real-time eclipses. 
There is no  attempt  to accelerate that  part  of  the  test. Mid-season maximum DOD is 40 percent, 
and that is at  72-minute  discharge. 
We reconditioned  after each  season. Reconditioning discharges into  a  44-ohm  load  to  a  l-volt 
per cell cutoff.  The solstice  period is accelerated to  the  extent  that  the  135 days is cut back to 
the  time necessary for  reconditioning  only, which is approximately 1 to  2 weeks. 
We have completed six seasons and  the  test is continuing.  The  test  battery is a 22-cell battery 
with the  indicated  12-ampere hour GE cells with  nylon  separator. The negatives are not  teflonated. 
(Figure 4-87) 
The  battely is mounted  on  a  thermal  electric baseplate. The  battery  baseplate  interface is 
adjusted to give us a  thermal  profile  equivalent  to  the  actual  orbital mission. The  battery is hooked 
into  the  battery  lab digital data  acquisition  system which gave us sufficient  data  on  a  continuing 
basis to  perform  this analysis. 
The battery is switched between trickle charge and full charge based on  temperature as 
indicated on  the right. As the  battery goes up,  it switches down to trickle charge at  about  76 
degrees. On temperature fall it goes to  approximately  70 degrees. 
(Figure  4-88) 
This rather  busy  looking curve is a  summary of a  typical  mid-season  profile  showing battery 
voltage, battery  current,  and  temperature. 
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https://ntrs.nasa.gov/search.jsp?R=19800012366 2020-03-21T18:19:02+00:00Z
This  portion  of  the  curve is the discharge. We come  out  of discharge, the  temperature  drops, 
and  the voltage  goes up. When the temperature  drops  sufficiently, we go  into full charge. In full 
charge the  temperature increases. While this is happening,  the  battery  voltage goes up  and reaches 
the voltage limit. 
As we come  off  this because  of temperature rise, the  battery is about fully  charged. It has 
taken  about as much as it can.  After  this,  everything  you see is overcharge. We have what  amounts 
to  a  series of overcharged  pulses.  This gives rise to  what  amounts  to  a  battery voltage  response to  
these  current voltages,  which looks very much like  a  series of  square waves. And if you  keep  that  in 
mind,  that is what  the  signature  turned  out  to be. 
(Figure  4-89) 
We saw  a number  of  different  types of short  circuits.  Hard  shorts, of course, are very easy to  
define  and  see. The  battery voltage  goes to zero. 
I  don’t want  to,  as  part of this  discussion,  get into a  discussion  of what  a  soft  short is, so we 
chose  a  simple  working  definition which I  think is valid for  what we have  observed.  Let me  just say 
any  time we saw anomalous voltage  decrease that wasn’t trivial, was greater  than 100 millivolts, we 
called it  a  soft  short.  There  should be  a  sense  of time  there.  This usually  occurred in minutes to  
hours,  rather  than  hours  to  days. 
Now, if you recall the voltage  response to  the  current pulses for  a  nominal  cell, it is about 
what this solid line  looks  like.  The voltage ramps up. We have an  initial  square wave which is 
charging. We have  a number  of  ensuing  square waves which, in fact,  are overcharge pulses. 
However, in all instances  the cells which exhibited  hard  or  soft  shorts,  what we saw at  some 
time  prior  to  the  short was something  that  looks  like  this  dotted  line. Where the voltage was 
depressed and  coming  into  the charge region, we saw a  feature  of  some kind at  the beginning 
and  a  ramping  up.  In  each of the  subsequent overcharge  pulses, instead of being squared,  it  ramped 
up. We defined our signature in terms of a  degraded overall voltage,  a  ramping  of the charge  and 
discharge  pulses and  this  feature  which  appeared at  the beginning of  this charge  pulse. 
(Figure  4-90) 
Now, some specific data is information taken during cycle 24 of the third season. We 
plotted six different cell voltages in pairs t o  show  the  superposition of the  data. In other words, the 
individual cells tracked  one  another. If they were nominal,  they  tracked very,  very well. We didn’t 
attempt  to superimpose all six,  because it wouldn’t  be  readable. 
You can see that  one cell, cell number  14, is showing  some  very,  very  slight  indication of 
ramping,  and  slightly  depressed  voltage. 
(Figure  4-9 1 ) 
368 
.% .., 
Now moving to cycle 34 of the same  season,  in other words, ten  24-hour  cycles  later,  three  of 
these cells exhibit  the  signature as indicated,  a generally  depressed  voltage feature  at  the beginning 
of  the  chart, falls, and  this  ramping. 
I should  point  out  during  these 10 days  battery  help  as we would  normally  judge it, based on 
the kind  of  information we would  have  from  a  battery  in  orbit,  battery  help  would  have  been 
excellent.  There  would  have  been no indication  that  anything was wrong or  about  to  be wrong, 
based on the normal  battery  telemetry.  In  fact,  at  this  point  the  battery was still  behaving  fine, 
accomplishing  its mission. We did  have the signature. 
(Figure  4-92) 
At  the  end of that season,  in other words,  almost  2  weeks  later  during  reconditioning, two of 
the cells which exhibited  the  signature  dropped  out of the reconditioning  discharge  very,  very  early. 
Cell number  14  and cell number  17  dropped  out  at  about 2  and  about 6 or 7 ampere-hours  in. Cell 
number  19 was just  included, as  an example  of  a cell which  did not  exhibit  a  short-circuit  signature. 
(Figure  4-93) 
If  we move to cycle 24 of season 5 ,  or  approximately 100 days  later, cell number  14  dropped 
out. Let me  explain  what we have  here. We have plotted six cells, and we have displaced the scales 
so the  data would be  readable  on the six cells. 
Cell number  14  started  out  low  but was remaining parallel to  the remaining cells. At  this 
point an inflection  occurred. At this  point  the second  inflection  occurred,  and we associate  some 
physical  process  with the  presence  of  the  inflection. 
Then,  the cell dropped  off fairly  rapidly and, in fact,  went  into reverse,  and reversed for 
about 1 ampere-hour  or so. Then, again immediately  prior to  this  reversal, battery  health  had been 
good. The only reason we would have expected something was wrong was the presence of the 
signature which persisted through  this  time. 
(Figure  4-94) 
So, what  do we think  the signature  means?  Probably  the  depressed  voltage is some  kind of a 
high impedance  shorting  that  exists. What is interesting  and  perhaps  a  little  difficult to  explain is 
that  it appears,  whatever it is, to be stable, to be  capable of being  stable  for  long  periods  of  time.  In 
fact,  that seems t o  be  unpredictable. When we see the  signature,  the cell may go out in hours, or it 
may  go out in weeks. But  it is capable of being  stable. 
The ramping is probably  the easiest part  to explain. If there is this  partial  short  you go into 
that pulse,  charge  pulse not fully  charged so the voltage isn’t going to  jump  up  immediately, it is 
going to  go  up gradually. 
369 
I 
That  little  feature  that we  saw at  the  beginning  of  the  charge  pulse  is  perhaps the most 
mysterious  part.  But  it  may  suggest  that the signature  itself  is  charge  dependent  and  that  we  are  at 
the  lowest  state  of  charge.  Whatever  its  manifestation, it behaves  differently  once  the  battery  goes 
past  its  first  stage  of  charge.  But  that  is  purely  speculation. 
Are  there  any  applications  of  this possible?  I think  the  question  that  has to precede  that is, 
how  general is the  phenomenon? Will we  be  able to use it  in  other  similar  situations?  That is 
something we  are  talking  about. 
If  we  can  and  if  it  is  reasonably  general,  perhaps  this  could  develop  into  short  circuit  early 
warning  system  if we had  some  microprocessor  capability,  an  algorithm  to  sense  the  curve  shape. 
What  we  are  doing  at  present is some  extensive  DPA  autopsy  work  on  these cells to  try  and 
correlate the degree of problem that we think we are having with physical observations during 
teardown  analysis. We hope  that will tell us a  little  bit  more  about  what we  are  seeing. 
DISCUSSION 
FORD:  I  couldn’t tell from  the  back  of  the  room,  what is the rise time  of  the pulse? 
LURIE:  The rise time is rapid.  I  don’t  know. 
FORD:  What was the  width of the  pulse? 
LURIE:  This is a  24-hour  charge. 
So that’s on  the  order of what? Half  an hour?  45  minutes?  That’s  a  function  of  the  thermal 
characteristics of the  system. 
LURIE: As soon as i t  heats up, it is going to drop  off. 
HENDEE: I find  that very  interesting.  There  are  several  other  preshort  signatures,  though, 
that  one  could  probably  observe.  It  depends  on  whether  it  is  a  short  on  charge - there is that  type 
which  may give you  problems. You may see that in your  subsequent  reconditioning. 
Then,  there  may be the  continuous  type  of  short. I have  seen  signatures  that  start  out  with, 
when you are  recharging  your  normal  voltage  peaking,  and  then  decrease,  you  just  start  seeing, 
instead of going up   t o  a  nice  peak  and  then  levelling  back  off, i t  goes up and  just  keep  smoothing 
out,  smoothing  out  until  you  are  just  approaching  it. 
I have  seen  other  ones  starting  to  go  up  and  then there’s  a clamp. I have  seen cells on  slow 
charge  which I will have  a  plot  of  tomorrow  on  my  presentation.  But  you  do  see an  oscillation in 
the  ampere  per  hour  voltage.  There  are  many  of  them. 
3 70 
SCHULMAN: Did you  try  to  correlate  in  any  particular cell,  where you  found a  signature  of 
a soft  short with  a  test that is  being  used  in battery  acceptance  testing, cell acceptance  testing,  that 
charge retention-type  test  which is supposed t o  indicate a short? 
LURIE: What we did correlate  with very successfully was capacity, voltage  decay in a  fully 
charged state. 
We charged the  battery  up  and  let  it  sit  for a period of 7 days. When we did  a  statistical 
analysis, we found  that all the cells except  two were  very,  very  close,  around  the  three sigma limit. 
Two cells dropped  out of the  three sigma limit,  and  the cell that was furthest  away  from  the  three 
sigma limit failed first. And  the cell that was closer to  the  three sigma limit  but  out of i t  failed 
second. So we did  get  very,  very  good  correlation  with  a more classical test. 
371 
4 
w 
N 
CELL SHORT CIRCUIT PRESHORT SIGNATURE 
e SEVERAL CELL SHORT CIRCUIT EVENTS WERE OBSERVED DURING A 
GROUND TEST  SIMULATION OF DSCS I 1  F7 BATTERY  OPERATIONS, 
0 CELL  EVEL DATA FOR THE PERIOD  PRECEEDING  THE SHORT CIRCUIT 
EVENTS \I,% INSPECTED FOR ANOMALIES, 
e THE  RESULTS OF THIS  . INVESTIGATION SUGGEST THAT  CANDIDATE  CELLS 
DEVELOP A  CHARACTERISTIC  SIGNATURE ANYWHERE  FROM  HOURS TO DAYS 
PRIOR TO A SHORTING  EVENT, 
Figure 4-85 
CELL SHORT CIRCUIT, PRESHORT SIGNATURE 
GROUND TEST --- TEST  PLAN SUKMARY 
w 
4 w 
0 THE GROUND TEST I S  A SIMULATION OF GEOSYNCHROYOUS OkBIT  CYCLING, 
00 45 REAL-TIME  CLIPSES PER SEASON:  MAXIMUM DOD = 402, 
00 RECONDITIONING  AFTER EACH SEASON:  BATTERY IS  DISCHARGED 
INTO A 44 LOAD TO A l V / C E L L  CUTOFF, 
OB TEE  SOLSTICE  PERIOD I S  SH9RTENED TO THE TIlYE REQUIRED FOR 
RECONDITION I NG AND RECtlARGE ONLY. 
e S I X  SEASONS HAVE  BEEN COMPLETED AFlD TtiE  TEST I S  CONTINUING, 
0 THE  TEST  BATTERY  CONTAINS 22 GE 12 AH CELLS, P/N 42B012AB20 
WITH NYLON SEPARATOR, NEGATIVE  PLATES  CONTAIN  SILVER  BUT' ARE NOT 
TEFLONATED, 
Figure 4-86 
CELL SHORT  CIRCUIT,  PRE-SHORT  SIGNATURE ............... 
___. 
GEOSYNCHRONOUS ORBITAL SIAIULL\T IOI \ I  
T E S T   C O , ' ! F I C U W i @ Y  
~~ 
S S T s  S V I I T C H  P O I N T S  
I C H A R G E l D l  SCHA'IGE T Z T  SET 
w 
4 
P 
S!VITCH T O   T C  ON 
TEI . :EQ4TU:< i  RISE 
Figure 4-87 
CELL SHORT CIRCUIT.  PRESHORT SIGNATURE 
SHORT CIRCUIT EVENTS 
a DESCRIPTION: HARD, SOFT, INTERRITTANT 
a "SHORT" D E F I N I T I O N  
F:R PURPEES OF THIS STUDY ,ANY ANOAALOUS VOLTAGE DECREASE 
GREATER THAN 100 t4V  WAS COHSIDERED TO BE  EVIDENCE OF A SHORT. 
a PRECURSOR OBSERVATION 
NOEl I RAL 
_ " " _  SHORT CIRCUIT PRECURSOR 
a "SIGFIATUkE" DEFI I : IT ISN 
am DEGRADED OVEMLL V O L T U E  
aa " R A E I P I I G "  OF CHARGE  AND DISCHAQGE PULSES 
ea "FEATURE" AT THE BEG1:INIPIG OF THE CHARGt  PULSE 
Figure 4-89 
CELL SHORT CIRCUIT, PRESHDRT SIGNATURE 
1 
ID 
Figure 4-90 
I 
...... CELL SHOTIT C!RCUIT, P2ESHO.ST S!GKATURE 
" .......-........ ." 
:.: :.: : I :  ::,: - :: . "  
"  . .  . . . . .  ..:: :::: - : a ,  .:*: I i: . i  
t i  
. -  . . I .  . -  . .  - . .  
x - :  . .  i..: :.: -:.E: . . . . . . .  . -  .. . . . . .  . "  -~ " .  "
"
OI 
-..:> _I.,i . I,i.. ::: ._ : ~" i.il "" .." .i I - L .  ~ L .. L- .I I .  . . . . . .  ........................................................... 
Figure  4-9 1 
;E?? Sr3RT CIRCUIT ,  PRESHORT S I G Y T L R E  
,- 0 CELL NO. 19 ?.ICC,:!>li:SS:Ni 3!IC<APGE 1 
C L l G  :4, i7, 19 
TIME (HRS) 
Figure 4-92 
CELL SHORT CIRCUIT. PRESHOPT SIG:!ATURE 
a PHYSICAL  INTERPRETATION OF THE  SIGIlATUPE 
#a DEPRESSED  VOLTAGE------HIGH  IMPEDANCE  SHQRTIEIG  PATH :,%ilCH CCII 
BE  STABLE FOR A PEFt l03  OF !.:iiKS. 
am "RREIPI#G"--------------RATTERY IS PARTIALLY  DISCHARGED  AT T h i  
@a ANOMALOUS CHARGE-------THE PHYSICAL  S16i:IFICAIICE IS NOT C L E M  .li 
BEGlHNl l lG  OF THE  PULSE. 
PULSE  FEATURE  PRESENT BUT IT KAY SUGGEST THAT  THE RATUgE 
OF THE  SlGllATURE IS STATE OF CHARGE DEPEIDENT. 
0 APPLICATIONS-----------------AS A SHORT CIRCUIT EARLY  ARNIKG  SYSTEII, 
a WORK Ill PROGRESS-------------DPA TO COFRELATE  TEARDOIW  ORSERVATIOE!S  WITH 
SIGNATURE/SHORTIHG EVEfiT HISTORY I 
Figure 4-93 Figure 4-94 


Cell short circuit, preshort signature

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