SOhlE TESTS OF THE EDISON STORAGE BATTERY BY C. W. BESSETT AiYD H. N . GILBERT
The Edison battery, as developed by the Edison Company, is an extremelyimportantaddition toelectrochemical apparatus. This is realized when it is remembered that the equivalent of about 300,000, 150 ampere-hour cells are being used to-day. The performance and properties of this battery have been studied exhaustively by the Edison Company only. A few of the papers' which have appeared in the literature on this subject may be referred to. These have dealt with the manufacture, details of construction, and performance of cells operating at normal rates. In view of the fact t h a t this information is meagre, it was thought that measurements from a different standpoint, made by different workers, would be of value. For these measurements, a battery of four cells was loaned the departmexlt of physical chemistry by Dr. E. W. Brown, P A . Surgeon, U. S. K. The battery being available only for a short time, it was decided t o run a few efficiency tests a t different rates of discharge, study the effects of charging a t different rates, check the measurements of capacity, and study the cell operating a t a low temperature. The cells used were the standard type, A8, 300 amperehour cells, normal charging and discharging rates, 60 amperes. The cells were connected in series. Kennelly: Trans. Am. Inst. Elec. Eng., 18, 219 (1901). Roebcr: Elec. Il-orld and Eng., 37, 367 (1900); 38, 931 (1901). Marsh: Elec. World, 39, 996 (1902). Hospitalier: L'Industrie Electrique, 12, 493 (1903). Jungner: Electrochem. Ind., I , 2j8, 46j, jo8 (1903). Schoop: Ibid., 2, z j z , 310 (1904). Silg: Ibid., 3, 2 3 7 (1903). Jououst: L'Eclairage Electrique, 38, 2 0 1 (1904). Hibbert: Jour. Inst. Elec. Eng., 33, 203 (1904). Joly: Ibid., 33, 226 (1904). Kennelly and Whiting: Trans. ilm. Electrochem. SOC.,6 , 13j (1904). Thompson and Richardson. Ibid., 7, 9 j (190j). Elbs: Zeit. Elektrochemie, 11, 734 (190j). Zedner: Ibid., 11, 809 ( 1 9 0 j ) ; 1 2 , 463 (1906). Faust: Ibid., 13, 161 (1907). Foerster: Ibid., 13, 414 (1907). Holland: Electrician, 68, 165 (1911). Montpellier: Lum'isre klec., 16, 244 (1911). Lyon: Jour. Ind. and Eng. Chem., 3, 922 (1911). Schneckenberg: Elektrochem. Zeit., 19, I (1912).
Some Tests o j the Edison Storage Batterji
323
In order to obtain these data in the course of the short time which the cells were a t our command, i t was decided to charge the cells until the voltage had remained practically constant on the highest part of the curve, for one hour. This was, therefore, called a complete charge, instead of the seven hours’ run a t 60 amperes, as recommended by the Edison Company. The battery \vas, therefore, completely charged, and then discharged a t the desired rate until the \-oltage on closed circuit was 0.7 volt per cell. The amount of energy necessary to bring the battery back to the original voltage was taken as the proper input for the calculation of efficiency. Recording meters were used and the mean voltage obtained from the equation I
=
v,;
-
where I = mean radius measured on a chart, which of course corresponds to the mean 7-oltage, n =- area of the sector
Fig.
I
bounded by the voltage time cur\-e, and the radii extended to the center of the chart, and a = the angle in radians, which was subtended b y the time-voltage curve. The area was ob-
C . 11.. Bennett a n d H . S.Gilbel-t
324
tained by a planimeter, the angle being measured in degrees. The current of course was constant. The meters were carefully calibrated, and the errors introduced minimized as much as possible. For comparison, Fig. I shows curves for charge and discharge a t 60 amperes and one discharge a t 1 2 0 amperes. For the normal charge it is seen that the average voltage is about j volts for the battery, the average discharge voltage being 4.5 volts, or 1 . 1 2 per cell. It is seen that the voltage continuously decreases, upon discharge. The actual figures for curves and B are as follom-s: ~.
~
Percent
Ampere-hours input Smpere-hours output Xmpere-hour efficiency TVatt-hour input
2874 I589
II'att-hours output I\-att-hour efficiency
It has been stated that the Edison battery is capable of operating a t high rates. S o actual figures horn-ever are available as to n h a t energy efficiencies or capacities are obtained under these conditions. The figures given below are not extremely accurate for they only represent one measurement each. They do, however, give an idea of what may be expected from these cells. Belon- are given efficiencies for four rates of discharge, the charge being normal. The output of the four cells is also given. TABLE2 Discharge rate in amperes ~
,
1
'IT-att-hour efficiency Percent
-~ ~-~ ~-
~~
60
I
I20 200
270
1
4 4 3 3
55 30
I
80
I
50
55 53 38 32
output Ampere-hours
'
3 50 2 60 225
1
1
IVatt-hours
I__---
~-
I80
~
1
I593 I118 8.55 630
Soinr Tests
o j tlie Edisoti S t o m g e Battery
325
The decrease in eficiency as well as capacity is seen from curves in Figs. 2 and 3. From these figures it may be concluded
Fig.
2
Fig. 3
that the battery is capable of operating a t high rates with a remarkably small decrease in efficiency and capacity. An astonishingly small decrease in the average voltage is also noted a t the higher rates of discharge. It is stated that “booster” charges can be given these
C. IT*. Bentiett arid H .-I-.Gilbest
326
cells practically. It was therefore decided to try some abnormal charging rates, discharging a t the normal rate, calculating efficiency. Below are given some of these tests.
T.\BLE3 IYatt-hours
Charge
~
~~
Input 2
hours at 1 2 0 . balance a t 60 amperes., . . . . . . . . . .
I
hour a t zoo, balance a t Go amperes.. . . . . . . . . . .
I
hour at 300, balance at Go a m p e r e s . . . . . . . . . .
output
IYatt-hour efficiencj Percent
’IVith the “booster ’ charqe of 2 0 0 amperes the charge was complete in about four hours and tn enty-five minutes, the battery giving considerably over its rated output on discharge, the efficiency being about the same as for the normal charge. The Bdison cell is said to lose about I O percent of its charge upon standing 24 hours, after nhich there is practically no loss. I t was therefore decided to allow the charged battery t o stand 30 hours and then measure the output upon discharge. It was found that the voltage of the battery had dropped to about 6 1-olts, and upon discharge the follon ing was obtained : T.WLE -1 Discharge after standing j o hours normal rate ~
output Initial voltage
.1\erage vr)ltagc \Vatt-hours -
j
9s
-1 54
1354
.Impere- hour> -
305
The loss in capacity is about I O percent of the normal output. I n order to see if this loss could not be avoided in
S o m e Tests o j the Edisoii Storage Battery
327
cases \\-here a battery is not t o be used for some time after charging, it was decided to charge the battery to a definite voltage and discharge from this, taking the output. This arbitrarily selected voltage should be higher than the open circuit voltage of the battery after standing 30 hours. The drop across the battery on charge, upon momentarily closing the circuit, 11-asfound to be about 16 percent higher than the cell voltage upon open circuit. It n-as therefore decided to charge the battery until the drop across it n-as 16 percent higher than the voltage of the battery after standing 30 hours. The charge was therefore maintained until the voltage n-as ; . I volts. The following n-as obtained :
TABLE5 Battery charged t o 7.1 Yolts and discharged a t normal rate Input ___ ~ _IVatt-hours Ampere-hours
-.
-7101
315
output
_ ~ 11-att-hours .4mpere-hours I --~ _ _ _ _
I343
Energy efficiency
290
From this it may be seen that the output is practically the same as that for the discharge after standing 30 hours. The efficiency is very good under these conditions, and on the basis of a charge of this nature it seems as if the battery can approach favorable comparison with the lead cell in regard t o efficiency. -1 measurement should have been made by charging up to this voltage, allowing t o stand for 30 hours, to show that under these conditions there is practically no loss of the charge. On account of limited time, however, this could not be done. In reference to the effect of lon- temperatures, it may be said that one charge and one discharge was obtained in a n ice water bath, the temperature of the battery being kept a t 4' C. The results of a charge a t 4 O C of the previously completely discharged battery a t ordinary temperatures, and the
C. T I ' . Be?z?zett n?zd H . S .Gilbert
328
corresponding discharge are given. properly be calculated from these. Charge and discharge at 4 ' C. -
~~
X\erage voltage .hipere-hour Charge charge Dis- Input O u t p u t
7 36
4 46
396
233
The efficiency cannot
Kormal rate
~
n'att-hours
Duration
Input
Output
2920
1037
Charge
6-2
j
Hours Discharge
3-7 S
very marked effect is obtained here The voltage diuerence betn een charge and discharge is abnormally high. The battery n a s later charged a t the normal rate under ordinary conditions This charge gives data for calculating efticiency comparable with that given above This is the normal u5e of the cell in cold climates In cars, of course, the battery would receive discharqe a t low temperatures on the road, and be charged a t room temperature, in the garage. The results follonT ~ B L 7E Charge after discharge at 4 ' C __
Input oltage
Xrnpcrc-hours
n'att-hours
Efficiency calculated on pre\ ious discharge Percent
6 94
460
3190
33
i\\ erage \
The fact that more energy \?as required for this charge than for the previous one probably means that nickel peroxide n a s not formed a t 4' C, probably because the charge was not maintained long enough. If not accurately, the tests show, however, that there is a larger voltage difference between charge and discharge a t low temperatures than under normal conditions. The efficiency must, therefore, be lower than normal. From what has been said and from experience with the Edison cell i t may be concluded, that
Some T e s t s of the Edison Storage Batter]'
329
I . The energy eficiency, a t the normal rate of operation. is about j \ j percent, the ampere-hour efficiency being about 85 percent. 2 . The cell is capable of operating contintiously a t high rates. 3. -At the 4o-mitiute discharge rate, irith charge a1 the riornial rate the energy efficiency is about 3' per cent, the ampere-hour output being about 60 percent of the rated output. 4. The cell can be charged a t high rates, the efficiency being about normal n-hen a "booster" charge a t 3',,< times the normal rate, for one hour, icas given the cell. There is no reason if-hy the cell should not be charged a t j times the normal rate for a feiv minutes. 5 . If the cell is to be charged the day before i t is to be used. energy is comer\-ed if the charge is maintained until the \-oltage reaches about I . Y volts, instead of carrying it to completion. In other \\-or&, no nickel peroxide should be formed on charging, the loss of energy on standing being due. presumably, to the spontaneous decomposition of this conipound. 6 . If the charge is stopped before the higher oxidation products of nickel are formed, the efficiency is higher than normal, being about ti.+ percent. ;. -At 4' C the battery is capable of delivering more than ', its normal output, when charged a t the same temperature. The voltage, of course, is lon-er than normal, for the internal resistance of the cell is higher a t the lon-er temperatures. The efficiency also is low. 8. The cell may unquestionably be allowed to stand a n indefinite length of time without injury. 9 . The flexibility is so great that the cell can be used under, the most adverse circumstances. I O . The method of charging until the voltage has remained constant for one hour gives satisfactory results, but requires watching or the use of a recording voltmeter. 1 1 . The continuous drop in voltage on discharge (about
330
C . W . Bennett and H . S.Gilbert
I O percent per hour) is a disadvantage against this cell, over the lead cell. 1 2 . When referred to equal amounts of power, delivered, the Edison battery weighs about 25 percent less and costs about 25 percent more than the iron-clad Exide battery.
Electrochemical Laboratory, Cornell Lniversity
