CS241355B1 - A method of experimentally determining the capacity of nickel-cadmium batteries with pocket electrodes - Google Patents

Abstract

The problem of determining the capacity of nickel-cadmium batteries during their charging is solved. The essence of the solution lies in the possibility of determining the capacity of nickel-cadmium batteries during their charging. When charging Ni-Cd batteries, the cadmium electrode is first effectively charged. After the cadmium electrode is charged, the voltage of the Ni-Cd battery increases sharply, which is associated with the transition to ineffective overcharging of the cadmium electrode, which is associated with significant hydrogen evolution. The capacity of Ni-Cd batteries corresponds to the time when the evaluated battery reaches the charging voltage value, which ranges from 1.45 to 1.80 V. The value of the capacity of the measured Ni-Cd cells is then determined from the product of this time and the current with which the battery is charged. The method can be used to determine the capacity of all types of pocket-sized nickel-cadmium batteries.

Description

batteries with pocket electrodes

The problem of determining the capacity of nickel-cadmium batteries during charging is being solved.

The essence of the solution lies in the possibility of determining the capacity of nickel-cadmium batteries during their charging. When charging Ni-Cd batteries, the cadmium electrode is first effectively charged. After the cadmium electrode is charged, the voltage of the Ni-Cd battery increases sharply, which is associated with the transition to ineffective overcharging of the cadmium electrode, which is associated with significant hydrogen evolution. The capacity of Ni-Cd batteries corresponds to the time when the evaluated battery reaches the charging voltage value, which ranges from 1.45 to 1.80 V. The value of the capacity of the measured Ni-Cd cells is then determined from the product of this time and the current with which the battery is charged.

The method can be used to determine the capacity of all types of nickel-cadmium batteries of pocket design.

The invention relates to a method for experimentally determining the capacity of nickel-cadmium batteries with pocket electrodes.

The capacity of nickel-cadmium batteries with pocket electrodes, usually expressed in θ/ο of the nominal capacity stated by the manufacturer, means the Ah capacity of these batteries obtained during a capacity test carried out in accordance with CSN 354»350 ST SEV.

Users of nickel-cadmium batteries or organizations providing, as part of routine, medium or general repairs of equipment containing these batteries, also check the capacity of the batteries, associated with the replacement of their electrolytes, mostly in a different way, primarily with regard to determining the end of the discharge curve and the resulting capacity of the evaluated batteries.

According to ČSN 364 350 ST SEV, the capacity of nickel-cadmium batteries with pocket electrodes is determined from the product of the constant discharge current value I and the time t corresponding to the time when the battery reaches the final voltage value of 1.0 V or even lower depending on the size of the discharge current, the type of battery being evaluated and the ambient temperature at which the battery capacity is measured.

However, during capacity measurement of a large number of nickel-cadmium batteries connected in series, due to the rapid decrease in voltage of the batteries being evaluated towards the end of discharge, i.e. from voltage values of 1.15 V, most users terminate the capacity control measurement when the voltage reaches 1.10 V/battery. The main reason is the increased instability of the discharge current during part of the discharge curve and the difficulty of quickly performing the required disconnection of those batteries that have reached the final discharge voltage value, which leads to a significant decrease in the accuracy of determining the battery capacity.

These inaccuracies could be partially eliminated by gradually automatically switching off the discharge of batteries that have reached the required end of discharge voltage, but this is not feasible for most users of nickel-cadmium batteries, as such demanding equipment is not manufactured in our country.

For the above reasons, most users of nickel-cadmium batteries with pocket electrodes measure their capacity during practical operation in two ways:

They either use 1.10 V as the final discharge voltage for evaluating the capacity of nickel-cadmium batteries, or they evaluate the capacity of the batteries from the voltage reached after 3.5 hours of discharge with a discharge current of the required value, i.e. after delivering 70% of the specified capacity, which is the criterion for the practical use of nickel-cadmium batteries with pocket electrodes.

In both cases, although higher stability of the discharge current is ensured during the discharge of a larger number of measured batteries with different capacities, the error resulting from the necessity of interrupting the discharge when disconnecting batteries that have reached the final discharge voltage value is not eliminated.

In addition, both described methods do not allow to determine the exact values of the capacity of the measured batteries or the batteries are not discharged down to a voltage of 1.0 V (or lower), as required by ČSN 36 4350 ST SEV. This fact does not allow to reassemble the battery pack from batteries of the same capacity, which must always be done after the test in order to prevent a rapid decrease in the capacity of those batteries of the battery system during the further course of the battery life, which show significantly lower capacity values during the capacity test compared to other batteries of this system.

The above-mentioned inaccuracies and existing difficulties for users are eliminated by the method of experimentally determining the capacity of nickel-cadmium batteries with pocket electrodes according to the invention, the essence of which is that the nickel-cadmium batteries are first discharged to a voltage of 1.0 V, then the measured batteries are charged with a given charging current in stages until the voltage of the nickel-cadmium batteries reaches a value of 1.45 V to 1.80 V, depending on the type of batteries, while the value of the capacity of the measured nickel-cadmium batteries is then determined as the product of the determined time and the current with which the battery is charged.

This method is based on the existence of a direct relationship between the capacity value of nickel-cadmium batteries determined from the discharge curve after reaching the final discharge voltage of 1.0 V and the capacity value determined when charging this battery to the steep part of the charging curve, in which the efficient charging of these batteries changes to inefficient charging, which is associated with a significant increase in voltage of 200 to 300 mV depending on the type of battery and its service life.

The capacity value of nickel-cadmium batteries obtained from the charging curve corresponds to the charging voltage values, which range from 1.50 to 1.73 V and depend on the type of battery being measured.

The method of experimentally determining the capacity of nickel-cadmium batteries from the charging curve according to the invention provides the following advantages for users of these batteries:

It brings significant savings in electrical energy, which amounts to 150% of the nominal capacity of each of the measured batteries, leads to a reduction in the laboriousness of the capacity test by eliminating 1 discharge and charge cycle and further leads to ensuring greater current stability and thus the accuracy of the capacity test by eliminating current interruptions during the current method of performing the capacity test due to the need to disconnect cells with a completed capacity test when measuring the entire battery system consisting of up to 50 batteries connected in series.

To ensure the accuracy of determining the capacity of individual types of nickel-cadmium batteries listed in the examples of embodiments of the invention below, an Ah counter of our own design was used, enabling direct measurement of the supplied and withdrawn capacity of the measured batteries in Ah.

The discharge of all evaluated nickel-cadmium batteries was carried out with a current of 0.2 Cs JA], since, in particular, users of KPH type batteries [formerly NKS) cannot meet the current CSN 36 4350 ST SEV by using a discharge current of 1 Ci [A], due to the significantly higher complexity of the discharge process, both in terms of the discharge current level and in terms of the complexity of the entire capacity test, compared to the previously used discharge current of 0.2 Cs [Al used within the previously valid CSN.

Charging of these batteries was carried out with both a current of 0.2 Cs [A] and a current of 0.25 Ci [A].

With regard to the generalization of the appropriate charging voltage value for determining the capacity of a given type of nickel-cadmium battery, the charging voltage value was determined in a wide range of the service life of these batteries cycled both according to the relevant ČSN and in the operating conditions of their function.

Examples of implementation:

Example

Nickel-cadmium batteries of the KPH 80 type [formerly NKS 80] after various numbers of cycles according to ČSN were subjected to equalization cycles during charging with a current of 0.25 C4 [A] and discharging with a current of 0.2 Cs [A] to a final voltage of 1.0 V. These cycles were followed by the actual capacity test of the evaluated batteries, i.e. charging with a current of 0.2 Cs [A] for 7.5 hours, i.e. when delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 Ci [A] to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 1 for one of the evaluated batteries, type KPH 80.

The discharge capacities of the evaluated batteries together with the corresponding charging voltage values are given in Table 1. Table 2 lists the errors incurred when measuring the capacity of the evaluated batteries using the method currently used by their users when discharging to 1.10 V, along with the error in determining the capacity of these batteries using our proposed method of determining it from the charging curve.

Table No. 1 battery cycle according to ČSN charging current 0.2 Cs (A] type number- capacity during discharge corresponding charging [Ah] voltage (V)

KPH 80 2,630 936 84.7 1.62 KPH 80 831 936 82.3 1.62 KPH 80 371 936 83.9 1.62 KPH 80 371 3 97.6 1.62 KPH 80 1112 3 98.4 1.62 KPH 80 1489 436 93.6 1.62 KPH 80 2,630 537 92.0 1.62 KPH 80 average — —. 1.62 Table No. 2 type measurement errors battery existing ways new way and b c % Cj charging 0.2 Cs (A) KPH 80 +12.5 —2.2 —5.0 +12.5 ±1.3/0.01V

- 7.2 a — error caused by discharging batteries only up to 1.10 V b — error caused by current instability c — error caused by interruption of current when discharging e.g. 50 batteries due to gradual disconnection of cells with final discharge (time required to disconnect 1 battery including reconnecting the discharge — 15 sec)

Example 2

Nickel-cadmium batteries of the KPH 80 type (formerly NKS 80) after various numbers of cycles according to ČSN were subjected to equalization cycles during charging with a current of 0.25 C4 [A] and discharging with a current of 0.2 Cs [A] to a final voltage of 1.0 V. These cycles were followed by the actual capacity test of the evaluated batteries, i.e. charging with a current of 0.25 C4 [A] for 6 hours, i.e. when delivering 150 % of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 Cs [A] to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 1 for one of the evaluated batteries, type KPH 80.

The discharge capacities of the evaluated batteries together with the corresponding charging voltage values are listed in Table 3. Table 4 lists the errors incurred when measuring the capacity of the evaluated batteries using the method currently used by their users when discharging to 1.10 V, along with the error in determining the capacity of these batteries using our proposed method of determining it from the charging curve.

Table No. 3 Battery Cycle according to CSN

type number KPH 80 2,630 937 KPH 80 831 937 KPH 80 371 . 937 KPH 80 371 3 KPH 80 1112 3 KPH 80 1489 436 KPH 80 2,630 537 KPH 80 average —

Charging current 0.25 C4 [A] capacity during discharge corresponding to charging [Ah] voltage [V]

81.5 1.69 81.0 1.69 82.4 1.68 — — — — — — — —

battery type

Table 4: Measurement errors of existing methods b c

2J [% Cj] new charging method 0.25 C4 [A]

KPH 80 +12.5 —2.2 —5.0 +12.5 +2.1/0.01 V

- 7.2 a— error caused by discharging batteries only up to 1.10 V b — error caused by current instability c — error caused by current interruption when discharging e.g. 50 batteries due to gradual disconnection of cells with completed discharge (time required to disconnect 1 battery, including reconnecting the discharge — 15 sec)

Example 3

Nickel-cadmium batteries of the KPM 160 type (formerly NKT 160) after 2 to 5 years of operation in battery trucks were subjected to equalization cycles during discharge with a current of 0.2 Cs [A] to a final discharge voltage of 1.0 V: After these cycles, the batteries were subjected to charging with a current of 0.2 Cs [A] for 7.5 hours, i.e. by delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 Cs [A] to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 2 for one of the evaluated batteries KPM 160.

The discharge capacities of the evaluated batteries together with the corresponding charging voltage value are listed in Table 5. Table 6 lists the errors incurred when measuring the evaluated batteries using current methods used by their users, along with the error in determining the capacity of these batteries using the proposed method from the charging curve.

T a b l e 1 k a n. 5 Battery type number operating time charging current 0.2 Cs [A] capacity during discharge corresponding charging [Ah] voltage [V]

KPM 160 29297 2 years 139.4 KPM 160 26540 2 years 142.6 KPM 160 32855 5 years 110.5 KPM 160 26355 3rd cycle 173.9 KPM 160 24261 3rd cycle 160.0 KPM 160 22559 3rd cycle 164.3 KPM 160 28398 3rd cycle 162.7 KPM 160 average

Table No. 6

1.67

1.68 1.68 1.65

1.65

1.66 1.68 1.67 battery type and

measurement errors existing methods b c

Σ [% Cj] new charging method 0.2 Cs [A]

KPM 160 +4.2 +0.8 —5.0 +5.0 +1.9/0.01 {V] —5.0 a — error caused by discharging batteries only up to 1.10 V b — error caused by current instability c — error caused by interruption of current when discharging e.g. 50 batteries due to gradual disconnection of cells with completed discharge (time required to disconnect 1 battery including reconnecting the discharge — 15 sec).

Example 4

Nickel-cadmium batteries of the KPM 160 type (formerly NKT 160) after 2 to 5 years of operation in battery trucks were subjected to equalization cycles during discharge with a current of 0.2 Cs [A] to a final discharge voltage of 1.0 V. After these cycles, the batteries were subjected to charging with a current of 0.25 Cl [A] for 6 hours, i.e. by delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 Cs (Aj to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 2 for one of the evaluated batteries KPM 160.

The discharge capacities of the evaluated batteries together with the corresponding charging voltage value are given in Table 7. Table 8 lists the errors arising when measuring the evaluated batteries using current methods used by their users, together with the error in determining the capacity of these batteries using the proposed method from the charging curve.

Table No. 7 Battery operating time charging current 0.25 C4 [A] type number capacity during discharge corresponding charging [Ah] voltage [V]

KPM 160 29297 2 years 137.1 1.69 KPM 160 26540 2 years 142.6 1.70 KPM 160 32855 5 years 106.3 1.71 KPM 160 26355 3rd cycle — — KPM 160 24261 3rd cycle — — KPM 160 22559 3rd cycle — — KPM 160 28398 3rd cycle — — KPM 160 average 1.70

battery type

Table No. 8 11 measurement errors existing ways Σ [% Cj] new way b c charging 0.25 C4 [A]

KPM160 +4.2 +0.8 —5.0 +5.0 +1.78/0.10 V —5.0 a — error caused by discharging the battery only up to 1.10 V b — error caused by current instability c — error caused by current interruption when measuring 50 batteries due to gradual disconnection of cells with completed discharge (time required to disconnect 1 battery including reconnecting the discharge — 15 sec).

Example 5

Nickel-cadmium batteries of the KPL 118 type (formerly NKO 118) after 3/4 years of operation as emergency lighting sources for residential buildings were subjected to equalization cycles during charging with a current of 0.25 Ci [A] and discharging with a current of 0.2 Cs [A] to a final discharge voltage of 1.0 V. After these cycles, the batteries were subjected to their own capacity test, i.e. charged with a current of 0.2 Cs [A] for 7.5 hours while delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 Cs [A] to a final voltage of 1.0 V/battery.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 3 for one of the evaluated batteries of the KPL 118 type.

The discharge capacities of the evaluated batteries together with the corresponding values of the charging voltages of all measured batteries are listed in Table 9. Table 10 lists the errors that occurred when measuring the capacity of the evaluated batteries using the current methods used by their users, and also lists the errors in determining the capacity of these batteries that occurred when using our proposed method of determining it from the charging curve.

Table No. 9 battery charging current 0.2 Cs [A] type number discharge capacity [Ah] corresponding charging voltage [V] KPL 118 3515 114.4 1.69 KPL 118 3566 119.4 1.70 KPL 118 3604 123.8 1.71 KPL 118 average Table No. 10 1.70 type existing ways 2J [% Cj] new way battery measurement errors and b c charging 0.2 Cs [A]

KPL 118 +3.4 —1.9 —5.0 +3.4 +3.8/0.01 —6.9 a— error caused by discharging the battery only up to 1.10 V b — error caused by current instability c — error caused by current interruption when measuring 50 batteries due to gradual disconnection of cells with completed charging (time required to disconnect 1 battery including reconnecting the discharge — 15 sec).

Example 6

Nickel-cadmium batteries of the KPL 118 type (formerly NKO 118) after 3/4 years of operation as emergency lighting sources for residential buildings were subjected to equalization cycles during charging with a current of 0.25 C4 [A] and discharging with a current of 0.2 C5 [A] to a final discharge voltage of 1.0 V. After these cycles, the batteries were subjected to their own capacity test, i.e. charged with a current of 0.25 Ch [A] for 6 hsdin, i.e. when delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 C5 [A] to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 3 for one of the evaluated batteries of the KPL 118 type.

The discharge capacities of the batteries together with the corresponding values of the charging voltages of all measured batteries are listed in Table 11. Table 12 lists the errors that occurred when measuring the capacity of the evaluated batteries using the current methods used by their users, and at the same time lists the errors in determining the capacity of these batteries that occurred when using the method we proposed for determining it from the charging curve.

battery Table No. 11 charging current 0.25 Č4 [A] capacity during discharge corresponding charging type number [Ah] voltage [V] KPL 118 3515 111.5 1.74 KPL 118 3566 115.2 1.72 KPL 118 3604 117.7 1.73 KPL 118 average 1.73 Table No. 12 type measurement errors battery existing methods L [% Cj] new way and b c charging 0.25 Ci[Al KPL 118 +3.4 —1.9 —5.0 '+3.4 +3.1/0.01V

—6.9 a — error caused by discharging the battery only to 1.10 V b — error caused by current instability c — error caused by current interruption when measuring 50 batteries due to gradual disconnection of cells with completed discharge (time required to disconnect 1 battery including reconnecting the discharge — sec).

Example 7

Nickel-cadmium batteries of the KPL 60 type (formerly NKN 60) after various numbers of cycles according to ČSN 36 4350 ST SEV were subjected to equalization cycles during charging with a current of 0.25 Cd [Aj and discharging with a current of 0.2 C5 [AJ to a final discharge voltage of 1.0 V. After these cycles, these batteries were subjected to charging with a current of 0.2 Čs [A] for 7.5 hours, i.e. by delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 C5 [A] to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 4 for one of the evaluated KPL 60 batteries.

The discharge capacities of the evaluated batteries together with the corresponding charging voltage value are listed in Table 13. Table 14 lists the errors incurred when measuring the capacity of the evaluated batteries using the current methods used by their users, along with the error in the capacity of these batteries using our proposed method of determining it from the charging curve.

From the results given, it is clear that even after 1,440 cycles, i.e. after three times the service life of Ni-Cd batteries of the KPL 60 type, than required by the relevant ČSN, batteries that no longer meet the required nominal capacity according to ČSN achieve the same charging voltage values corresponding to their capacity during discharge as at the beginning of their service life.

Table No. 13 battery cycle charging current 0.2 Č6 [A] type number capacity during discharge corresponding charging [Ah] voltage [V]

KPL 60 15496 1440 and 1441 25.1 1.55 KPL 60 14612 1,440 and 1441 29.8 1.57 KPL 60 16177 1440 and 1441 36.9 1.56 KPL 60 15496 3 66.0 1.55 KPL 60 14612 3 61.2 1.57 KPL 60 16177 3 62.4 1.56 KPL 60 15496 593 56.8 1.55 KPL 60 14612 593 55.6 1.57 KPL 60 16177 593 53.6 1.57 KPL 60 diameter type of battery T a b u t 1 k a n. 14 measurement errors existing methods L [% Cj] 1.56 new way and b c charging 0.2 Cs [Aj KPL 60 +4.2 —0.7 —5.0 +4.2 +1.0/0.01 [V] a — error b — error originated originated when discharging batteries only up to 1.10 V due to current instability -5.7 c — error originated by interrupting the current during discharge, e.g. 50 batteries under the influence of

gradual disconnection of batteries with complete discharge (time required to disconnect 1 battery including reconnecting the discharge — 15 sec).

Example 8

Nickel-cadmium batteries of type KPL 60 (formerly NKN 60) after different numbers of cycles of charging with a current of 0.25 Cl [A] and discharging with a current of 0.2 Cs [A] to a final discharge voltage of 1.0 V. After these cycles, these batteries were subjected to charging with a current of 0.2 Cs [A] for 6 hours, i.e. by delivering 150% of the nominal capacity. This was followed by discharging these batteries with a current of 0.2 Cs [Aj to a final voltage of 1.0 V.

The corresponding charging and discharging curves for both types of charging modes are shown in Fig. 4 for one of the evaluated KPL 60 batteries.

The discharge capacities of the evaluated batteries together with the corresponding charging voltage value are listed in Table 15. Table 16 lists the errors incurred when measuring the capacity of the evaluated batteries using current methods used by their users, along with the error in determining these batteries using our proposed method of determining it from the charging curve.

From the results given, it is clear that even after 1,440 cycles, i.e. after three times the service life of Ni-Cd batteries of the KPL 60 type, than required by the relevant ČSN, these batteries, which no longer meet the required nominal capacity according to ČSN, achieve the same charging voltage values corresponding to their capacity during discharge as at the beginning of their service life.

battery type number

Table No. 15 cycle charging current 0.25 Ci [Al capacity during discharge corresponding charging [Ah] voltage [VJ

KPL 60 15496 1,440 and 1,441 24.8 1.58 KPL 60 14612 1,440 and 1,441 29.5 1.60 KPL 60 16177 1,440 and 1,441 36.4 1.59 KPL 60 15496 3 — — KPL 60 14612 3 — — KPL 60 16177 3 — — KPL 60 15496 593 — — KPL 60 14612 593 — — KPL 60 16177 593 — — KPL 60 average 1.59

T a b l e 1 a n o. 16 type of battery and measurement errors existing methods b c £ [% Cjj new charging method 0.25 C4 [A] KPL 60 +4.2 —0.7 —5.0 +4.2 +0.7/0.01V

a — error caused by battery discharge pause to 1.10 V b — error caused by current instability c — error caused by current interruption when discharging, for example, 50 batteries due to gradual disconnection of cells with completed discharge (time required to disconnect 1 battery including reconnecting the discharge — 15 sec].

The method for determining the capacity of Ni-Cd batteries according to the aforementioned patent can be used to determine the capacity of Ni-Cd batteries for a number of users, such as railway repair shops and engine rooms, workshops for repairing mechanisms and individual railway stations in the field of railway transport, transport enterprises of individual places in the field of urban transport, individual plants with intra-company transport, local economy enterprises and others.

Claims (1)

SUBJECT Method for experimentally determining the capacity of nickel-cadmium accumulators with pocket electrodes, characterized by first discharging nickel-cadmium accumulators to a voltage of 1.0 V, followed by charging the measured accumulators with a given charging current for a time before the voltage OF THE INVENTION The nickel-cadmium accumulators reach a value of 1.45 V to 1.80 V, depending on the type of accumulators, and the value of the capacity of the measured nickel-cadmium accumulators is then determined as the product of the determined time and current with which the accumulator is charged. 4 sheets of drawings