The performance of two types of batteries, lead-acid and nickel-zinc, was measured as a function of the charging and discharging demands anticipated from electric vehicle propulsion systems. The benefits of rapid high current charging were mixed: although it allowed quick charges, the energy efficiency was reduced. For low power (overnight) charging the current wave shapes delivered by the charger to the battery tended to have no effect on the battery cycle life. The use of chopper speed controllers with series traction motors resulted in a significant reduction in the energy available from a battery whenever the motor operates at part load. The demand placed on a battery by an electric vehicle propulsion system containing electrical regenerative braking confirmed significant improvment in short term performance of the battery

Bozek, J. M.

Cataldo, R. C.

Ewashinka, J. G.

Smithrick, J. J.

English

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DOE/NASA/1 044-7
NASA TM-81515
(NASA-TM-81515) AN ELECTRIC VEHICLE
	 N80-24756
PROPULSION SYSTEM'S IMPACT ON BATTERY
PERFORMAVC;E: AN OVERVIEW (NASA) 10 P
HC A02/MF A01
	 CSCL 10B
	 Unclas
G3/44 20957
John M. Rozek, John J. Smithrick,
Hobert C. Cataldo, and John G. Ewashinka
National Aeronautics and Space Administration
Lewis Research Center
Work performed for
U.S. DEPARTMENT OF ENERGY
Conservation and Solar Applications
Transportation Enar gy Conservation D ivision
Prepared for
Third International Electric Vehicle
Exposition and Conference
St. Louis, Missouri, May 20-22, 1980
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DOE/NASA/1044-7
NASA TM-81515
AN ELECTRIC VEHICLE PROPULSION
SYSTEM'S IMPACT  ON BATTERY
PE1IFORMANCE^AN OVERVIEW
John M. Bozek, John J. Smithrick,
Robert C. Cataldo, and John G. Ewashlnka
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
Work performed for
U,S, DEPARTMENT OF ENERGY
Conservation and Solar Applications
Transportation Energy Conservation Division
Washington, D.C. 20545
Under Interagency Agreement EC-77-A-31-1044
Third International Electric Vehicle
Exposition and Conference
St. Louis, Missouri, May 20-22, 1980
AN ELECTRIC VEHICLE PROPULSION SYSTEM'S IMPACT
ON BATTERY PERFORMANCE r AN OVERVIEW
by John M. bo;ek, John J. Smithrick,
Robert L. Cotoldo, and John G. hwashinka
National Aeronautics and Space Administration,
Lewis Research Canter
Cleveland, Ohio 44135
INTRODUCTION
Many of the performance limitations of
an electric vehicle are due to the bat-
Cary. Certainly the range, in some cabda
the acceleration and hill climbing capabil-
ity, and to some extent the "suet" costa,
are all affected by the battery. Beyond
tiles" immediate affect#, the long tens cost
of keeping nit
	
vehicle dapends
heavily on rte cycle life of the battery.
The longer a battery Insta l the longor the
time over which one call nmortizo the cost
of the battery.
Civet. 5n electric vehicle battery,
there are two primary operations that af-
fect t ►te short term and long term perfor-
ntanca of that battery. charging and dis-
charging of the battery. Under the spon-
sorship of the DOE Electric and hybrid
Vehicle program, the NASA-Lewis Research
Center line been involved in quantifying
battery performance all
	
function of the
ebargiog and discharging demands placed oil
the battery by electric vehicle propulsion
systems. Tile questions that arc+ addroased
and discussed in this paper are: Which
quick ehnxging technique can shorten charge
times and how does it affect energy affi-^
Clancy? Is pulse charging with slid without
small discharging (depolariration) pulaea
an effective quick charging technique?
Does the current waveforin of all
charger affect the life of a battery? Does
pulse discharging, characteristic of the
Demands placed vo a battery by chopper
speed controllers, affect battery perfor-
mance? How does Cite electric vehicle's
method of regenerative braking affect bat-
taxy performance? In it better to reg
Ate via a meebnnical system like a flywheel
or is it bettor to regenerate electri-
cally? These are the questions we are at-
tempting to answer. The answers will help
us choose sit vehicle propulsion
systow that not only will be inexpensive.
small. light weight and durable but also a
propulsion ayatem that will treat the bat-
tery in a way that would efficiently ex-
tract energy from the battery without ad-
vaarsoly affecting tite battery's durability.
ASSULTS
Many of the allergy related quostions
have been answered but most of the Jurabil°
ity questions are still awaiting completion
of long tone tests.
Ch a.rgilist
Ra p id char i►Uj, The objective of ttese
tests was to date nma.ne it olectrochemical
calls call 	 efficiently charted in less 1
hour (ftei. 1).
Two electruchemical systems, 300 A-it
lead-arid and 300 A-h nicker-zinc calls,
were tested. Thca charging current profile
having promiso wars a high rate taper direct
current WKTDC) profile, which takes ad-
vantage of the high coulombic charge offi-
ciancy of a battery at low etates-of-charge.
A typical charge curve is shown in
Fig. 1. This happens to be for Lila nickel-
zinc cell, however, data for load-acid
calls are similar. In tile, HHTDC method
need, the initial charge current was 500
amperes. Periodically during the charge,
the current wits reduced in 50 ampere it ►cre-
tmcnts until the final charge current was
100 amperes. Excessive gassing or rate of
temperature rise were the criteria usvad to
reduce tite current o^ end the charging.
t
L_ - 	 ._V
During the first part of the clisrge,
the stepdown in charge current wall dictated
by a rapid Visa in temperature. In the
middle of the charge, gasiing became the
dominate criteria. Tito tertsination of the
charge was due to the battery approaching,
10 or 20% coulombic efficiency is measured
by the &easing rate.
Results of Clio i1HTik: tests are shown
to Table 1. 'the %;oAacities removed from
the two t,i.ns of electrochemical cells dar-
ing disci+.ago were 71 And 03% of tite rated
capacity. Tito charging time was 53 minutes
for the nickel-tint system+ and 4b minutes
for the land-acid system, both less than an
hour. The charge-discha gse energy effi-
ciency was 522 for tine nickel-zinc cell and
04% for the leAd-acid cell. Typically, tit*
enorgy efficiency of a loud-acid cell that
is charged overnight (i.e., about d hours),
would be about 75% (Re(. 4). and a nickel-
zinc somewhat higher (Hof. 3). We sae that
quick charging is possible, but one pays
the priceof lowered available capacity and
a lowered energy efficiency,
Pulse char 'n . Tito variations in the
performance of 300 A-h land-acid cell#, of
the type and design found in electric velti-
cle delivery vans, were studied as a func-
tion of quick charging techniques other
then the 11RTLIC method discussed above. Tito
tochniquea varied front a baseline constant
current charge to high frequency, pulse
type charges with and without dopolariza-
tion pulses (Ref. 4). Figure 2 allows schr-
statically the type of chaYUing pulses used
And the nonH•nklnturo that is used to iden-
tify the pulses. The time Averaged current
and frequency for Lite wnv* shapes were
equal, about 147 amperes and 60 Hz, rospec-
tively, yet the duty cycle and the ntagni-
tude of the charge and depolnrization
pulses vary.
All charges were terminated, as in tite
previous discusoion, whoa either the gass-
ing or temperature of the cello reached
unacceptable levels.
Table 2 contains tite results of those
tests. As can be seen, the capacity re-
moved anal charge time are somewhat inde-
pendant of the . cha7'ging wave obaape. In all
cases the capacity removed tars about 63% of
the rated capacity and the charging time
varied between 77 and $1 minutes. of sig-
nificance is the energy efficiency. pulse
charging rosulted in a h to lq percentage
point drop in efficiency when compared to
constant current chnraing.
Using as it
	
the Roumnov pulse
described in Fig. 2(c), the effects of free-
queney, duty cycle slid the size of the de-
polarization pulse was oteAsured. A ournmary
of toter data is presented in 'table 3. Fre-
quency had little effect on charge time,
capacity removed or energy efficiency,
Increasing Cho duty cycle to 941 from 502
did not significantly change the energy
efficiency (66 to 71%), bat allowed the
charging tints to he reduced by a factor of
two with s it 	 drop i ll 	 removed
(193 to 171 A-h), Tbw reduction in the
charging time and Lite capacity removed was
due to tit* increased time-averaged cur-
rent. Increasing the site of the depolar-
izotion pulse decreased the energy offi-
cioncy and slightly increased the charging
time with no change in the capacity removed.
From tile data presonted in Tables 2
sad 3, relationships are evident between
average charge current, capacity remtoved,
charging time and energy efficiency. pulse
charging, as investigatod, tends to have an
energy efficiency of 69 to 70%, tends to
deliver 63% of the rated capacity after
being charged ill 	 an hour and a half.
Constant current charging has a higher
e ►torgy efficiency at comparable delivered
capacity and charge time.
Overni g ht char n g. Charging current
waavelwrma anticipated from slow overnight
chargers were studied on a basis of their
effect on the cycle,• life of small nickel-
zinc cello (Hot. 5). These nickel-zinc
cells offered a means of quickly evaluating
the effect of overnight charger designs on
the cycle lifte, of an el'sctrochomical sys-
tern, 'Bite nickel-ainc cells were c:n-
otructed in-house at Lewis Heseareb Center
and were sized to meet the constraints of
the available chargers.
The study was aimed at measuring the
effect on battery cycle life of tour types
of charging waveforms conaidared viable
candidates for overnight chargers. Tito
wavefonno investigated were full wave rec-
tified sinusoidal, 120 liz phsae control
rectified, 1 kilt square wave and, as A
baseline, constant current.
'lice cells were discharged at 2 amperes
to 75% of rated capacity, and charged at an
Average current of 0.25 amperes with a 5%
coulombic overcharge. This discharg-
ing/charging cycle was repented until the
cello failed to deliver 50% of the initial
dischargo capacity.
Tito effect of tite four charging wave-
forms on the cycle life of the nickel-zinc
cells is shown in pig. 3. As can be seen,
the full wave•
 and I kliz waveforms have
minimal effects on the cycle life of the
nickel-zinc cells when compared to the
baseline constant current charging method.
Unfortunately, during the phase control
rectified warefottn charging toots, there
was an equipment problem which caused a
oustantial overcharge vhich may have led to
premature failure. Failure analysis of the
cells indicated that Enilurc was due co
internal cell allotting.
We conclude from these tests that
wavOlOrIns hnv, little effect on the cycle
life of nickel-zinc cells. Ittiaxpensivo
c.hnrgors which deliver full wave rectified
2
current have little detrimental affect on
cycle life when compared to the relatively
expensive constant current or 1 kHz square
wave chargers. Unfortunately, any conclu-
sion on the offset of phase control recti-
fied chargers would be inappropriate,
As yet unpublished data indicates
there are no subbtantial differences in the
energy efficiency of large load-acid trac-
tion cells when there calls are charged
using the four charging waveforms discussed
above (Ref. 6).
Discharaina
Chopper controlled die has e . Tile
speed and acceleration of many electric
vehicles are controlled by amature chop-
pers. When operating, these choppers im-
pose a chopped current demand on the elec-
tric vehicle battery. The peak current
demand during the short "on` time may be
several hundred amperes while the frequency
can be as high as 500 Uz.
To measure the affect of chopper type
discharges on the energy available from a
battery, a series of discharge experiments
were performed on several golf car bat-
teries rated at 132,5 A-h (Ref, 1). In
these experiments the energy available from
the lead-acid battery was measured for
chopped discharge currents having time-
averaged current values of 100 to 300 am-
peres, peak-to-average current ratios up to
4 to I and pulse repetition frequencies up
to 500 Hz. The battery energy removed
under the chopped conditions was then com-
pared to the energy removed from the same
battery under a constant current discharge
condition.
The results of these tests are shown
in Fig. 4. The data presented here are
corrected for electrolyte temperature. The
final temperature of the battery during
chopped discharge was 5 e to 1Do
 C high-
er than the constant current discharges,
As seen, the chopped discharges exhib-
ited a substantial reduction in available
energy at low specific powers. At high
specific powers, the chcpped energy ap-
proaches the constant current energy. In
some caacs, the energy removed during
chopped discharges exceeded that for con-
stint current discharges. This increase
were primarily due to the increased dia-
charge capacity which had been observed for
chopper discharges, The increased capacity
more than compensated for the increased
12R heating losses present during chapped
discharges,
Tnere are ongoing efforts in this
area. An in-house NASA Lewis effort on the
chopper discharge effects on nickel-zinc
cells is nearing completion (Ref, 8).
Also, a contractcd effort with TRW at
Redondo Beach is directed toward evaluating
the effects of chopper discharges on the
life expectancy of 'lead-acid batteries.
R	 e	 , t r, ativ ae^ki11Y The objectives
of tease testa are two- old. First, to
verify that electrical regenerative braking
can increase the range of an electric vehi-
cle in a mathematically predictable man-
ner. Though an increase in the range of an
electric vehicle with regenerative is a x-
pacted, we also are attempting to predict
this increase by the application of battery
performance models. The second objective
is to quantify any affect regeneration may
have on the cycle life of a battery -
Soon to be published test results show
that electrical regeneration does indeed
increase the rangy of an electric vehicle
(Ref. 9). Raferanco 10 describes a battery
model developed at NASA-Lewis which reason-
ably predicts the battery performance•
Table 4 shows the results of the
laboratory tests and model predictions for
a golf car Littery rated at 132.5 A-h.
During the laboratory tests the discharge
current was programmed to those values ex-
pected in electric vehicles following the
various SAS J227a driving schedules (B, C,
and D).
The laboratory experiments show a
range increase due to electrical regenera-
tion of 15% for the D schedule and 25% for
the A schedule, while the model predictions
show an increase of 10% for the D schedule
ar,d 16% for the B schedule. Also, as shown
in Table 4, the maximum deviation between
laboratory test data and mathematical pre-
dictions is 10%.
To complement the on-going in-house
effort at NASA-Lewis, a contracted effort
has recently been initiated with the Naval.
Weapons Support Center in Crane, Indiana.
Tile objective of this effort into deter-
mine the cycle life of lead-acid batteries
as a function of electric vehicle propul-
sion system design, The benefit of elec-
trical regeneration (i.e., increasing the
range of an electric vehicle), is well
docu:oented. The effect of electrical re-
generation on the cycle life of a battery
is not known. The possibility of electri-
cal regeneration reducing the cycle life to
an extent that it may overshadow an in-
crease in range needs to be clarified.
There is also a need to clarify the bene-
fits of a mechanical regenerative propul-
sion system (i,e,, flywheel) over an elec-
trical regenerative propulsion system, The
increased complexity of a mechenical re-
generative system muse be compensated for
by an increase in vehicle performance
(range) or an increase in battery cycle
life over that observed for an electrical
regenerative propulsion system. In our
contracted effort we will be investigating
the effect on three different types of
lead-acid batteries of three different
types of electric vehicle propulsion ays-
tems. The batteries are: (1) golf car
batteries, (2) thin plat y, high energy bat-
teries, and (3) long life tubular bat-
teries. The propulsion systems are: (1)
40	 -,.I
nonredenerative, (2) electrical regenera-
tive, and (3) mechanical regenerative.
SUMMARY
A bcttery can he recharged rapidly
(I.e., in less than an hour), but one pays
the price of lowered output capacity and
lowered energy efficiency. pulse charging
does not decrease charge time when compared
to constant current charging but does de-
cress^ the energy efficiency. Depolariza-
tion pulses do not red to charge times or
increase charging energy efficiency. A
relatively inexpensive, full wave recti-
fied, overnight charger is an good as an
expensive, complicated, constant aurrent
charger when both are compared on the basis
of cycle lift, and energy efficiency.
Chopper type discharging decrease@ the
energy available from a battery especially
at low power levels and may increase the
energy available at high discharge rates.
Electrical regeneration does improve the
range of so electric vehicle in a mathemat-
ically predictxb a manner.
On-going programs at NASA -Lewis will
help clarify the effects of Propulsion sys-
tem design concepts on the cycle life of
batteries.
REFERENCES
2. Vinal, 0. W., Rocfgs Ha t ri , 4th ad.,
Wiley, Now York, 195.3"
3, Soitis, D.G., Private Communication, NASA
Lewis Roaenreb Center.
4. Smithrick, J', J.,"Puloa Charging of Load-
Acid Traction Calla," NASA TN-81513,
1980.
5. Smithrick, J. J., "Effact of Positive
Pulse Charge Wavoforms on eyelo Life of
Nickel-2ittc Coils," DOE/NASA/1044-79/3,
NASA T4-79215, 1979.
G. Smithrick, J. J., NASA Lewis Research
Center, goon to be published,
7, Cataldo, K. L., "Response of Load-Acid
Batteries of Chopper-Controllod Dis-
charge," CONS/1044.1, NASA TN-73834
(Revised), 1978.
8, Cataldlo, K. L., NASA lAwis Research
Canter, seen to be published.
9. Ewaahinkn, J. G., NASA Lewis Research
Center, soon to he published.
10. Nowak, J. M., "An Averaging Battery Model
for n Losd^Acid flattery Operating in an
Electric Car," DOE/NASA/1044 -79/5, NASA
111-79321. 1979,
1. Smithrick, J. J., "Rap:id Efficient Charg-
ing of Land-Acid and Nickel-Zinc Trac-
tion Calls," DOE/NASA/loll-78/28, NASA
TM-78901, 1978.
TXB14E 1. - NIGN RATE TAPER DIRECT CURRENT CHARGE
Type of cell
	
Rated	 Charge	 Capacity	 Energy
	
capacity ,	 time,	 removed	 efficiency,
	A-11min	 %
A-h % rated
Nickel; zinc	 300	 53	 214	 71	 52
Lead-acid	 300	 46	 189	 63	 64
TABLE 2. - PULSE CHARGING OF 300 A-11 LEAD-ACID CELLS
Type of charge Time averaged Charge	 Capacity	 Energy
current,	 time,
	 removed,	 efficiency,
	
amp	 min	 %
A-h % rated
Constant current	 147	 80	 193	 64	 go
Positive pulse
	
149	 77	 191	 64	 71
Romanov pulse
	
147	 81	 193	 64	 66
McCulloch Pulse
	
147	 77	 187	 62	 61
A
4
TABLE 3. , PULSE CNARCINU VARIABLES 300 A-11 LMO-ACID CELL
Variable	 Time averaged Charge C4pacity Energy
current, rime, removr.i efficiency,
amp will
A-11 S rated
Frequency, H.-
8 140 66 100 67 67
60 147 63 198 00 65
200 149 s0 196 65 67
400 '48 80 193 64 67
Uuty cycle, %
50 06 di 193 64 66
75 225 49 183 61 69
94 268 U 171 57 71
Size of dopolariration
pulso, amps
0 lag 77 191 64 71
15 140 81 193 64 66
35 133 68 190 63 59
TABLE 4. - RKCKNKRATIVI DRAKINU TLST RESULTS WITH A132.5 A-11 LtAU^ACIu BATTERY
SAE J221a Laboratory measured range* Mathematically predicted rangk* 	 Daviotion of predicted
driving from muddurad
schedule Without	 With	 Regen Without With Resen
regen	 regen	 increase, regen regen increase, Without With
% % regen, regen,
W	 mi	 M	 mi kM	 mi kM mi % %
D 164	 104	 204	 127	 25 158	 98 183 114 16 x-3.9 -10
C 100	 62	 119	 74	 19 101	 63 114 71 13 +1.p -4.1
U 64	 40	 74	 46	 15 6b	 41 72 45 l0 +2,5 -22
*Ranses based on; 0. 23 W/B achodale p 0.60 AMA; schedule, 1.71 kM/la schedule.
5
.Y
i3x
U
307 A.
600 CELL TEMPERATURE 120
H 500 100
CHARGE CURRENT 80 Ur
300 60z v^
c'
°C
200 CELL
GASSING
RATE100 —"A AA
0	 10	 20	 30	 40	 50	 60
CHARGE TIME, MIN
Figure 1. High rate taper direct current
charge of 300 A-H nickel -zinc cell.
300
	 301 A.
147 A.
0
(a) CONSTANT CURRENT.	 (b) POSITIVE PULSE.
TIME, in.
(c) ROMANOV PULSE. ' 	 (d) McCULLOCH PULSE.
Figure 2. - Pulse charging waveforms 30OA-H lead-acid
cell.
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An electric vehicle propulsion system's impact on battery performance: An overview

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