Method for determining deterioration of accumulator battery, method for measuring internal impedance of secondary battery, equipment for measuring internal impedance of secondary battery, equipment for determining deterioration of secondary battery, and power supply system

• US 20060186890A1
• Filed: 12/27/2005
• Published: 08/24/2006
• Est. Priority Date: 06/27/2003
• Status: Active Grant

• Current Assignee: Furukawa Electric Company Limited
• Original Assignee: Furukawa Electric Company Limited
• Inventors: Watanabe, Yuichi, Kimura, Atsushi, Iwane, Noriyasu, Kanou, Tetsuya, Sugimura, Takezo, Iwahana, Fumikazu, Satoh, Toshiyuki, Inaniwa, Katsumi
• Granted Patent: US 7,362,074 B2
• Time in Patent Office: Days
• US Class Current: 324/426
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health

Abstract

A method for determining deterioration of accumulator battery hooked up with loads in a system based on results of measuring internal resistances of an accumulator battery, the method comprising the steps of; predetermining as a specified temperature a temperature at which the deterioration of the accumulator battery is determined; calculating in advance temperature correction coefficients of the internal resistances from changes of the internal resistances depending on temperatures; predetermining resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and terminal discharge voltages of the accumulator battery which are obtained at the specified temperature under a condition of flowing predetermined discharge currents from the accumulator battery; measuring the internal resistances of the accumulator battery and temperature of the accumulator battery at an internal resistance measurement; converting the measured internal resistance values into the internal resistance values at the specified temperature with use of the temperature correction coefficients of the internal resistances; converting the internal resistance values at the specified temperature into the terminal discharge voltage values of the accumulator battery at the specified temperature with use of the resistance-voltage conversion factors; and determining whether the accumulator battery is deteriorated or not by means of comparison of the terminal discharge voltage values of the accumulator battery at the specified temperature and a predetermined threshold value as a deterioration judgment standard.

Claims

1. A method for determining deterioration of accumulator battery hooked up with loads in a system based on results of measuring internal resistances of an accumulator battery, the method comprising the steps of;

predetermining as a specified temperature a temperature at which the deterioration of the accumulator battery is determined;

calculating in advance temperature correction coefficients of the internal resistances from changes of the internal resistances depending on temperatures;

predetermining resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and terminal discharge voltages of the accumulator battery which are obtained at the specified temperature under a condition of flowing predetermined discharge currents from the accumulator battery;

measuring the internal resistances of the accumulator battery and temperature of the accumulator battery at an internal resistance measurement;

converting the measured internal resistance values into the internal resistance values at the specified temperature with use of the temperature correction coefficients of the internal resistances;

converting the internal resistance values at the specified temperature into the terminal discharge voltage values of the accumulator battery at the specified temperature with use of the resistance-voltage conversion factors; and

determining whether the accumulator battery is deteriorated or not by means of comparison of the terminal discharge voltage values of the accumulator battery at the specified temperature and a predetermined threshold value as a deterioration judgment standard.

4. The method for determining deterioration of accumulator battery according to claim 1,

wherein the specified temperature is within an operating temperature range of the accumulator battery, and is set to a temperature at which the terminal discharge voltage get lowest when predetermined discharge currents are flowed from the accumulator battery.

5. The method for determining deterioration of accumulator battery according to claim 4,

wherein waveforms of the predetermined discharge currents are substantively equal to waveforms of discharge currents required to put the loads in operation.

6. The method for determining deterioration of accumulator battery according to claim 1,

wherein the predetermined threshold value as the deterioration judgment standard is a voltage value equal to or more than a minimum voltage required to put the loads in operation.

9. The method for determining deterioration of accumulator battery according to claim 1,

wherein in the process of predetermining the resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and the terminal discharge voltages of the accumulator battery which are obtained at the specified temperature under the condition of flowing predetermined discharge currents from the accumulator battery, the terminal discharge voltages of the accumulator battery is a minimum voltage in discharge of the accumulator battery.

10. The method for determining deterioration of accumulator battery according to claim 1,

wherein in the process of predetermining the resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and the terminal discharge voltages of the accumulator battery which are obtained at the specified temperature under the condition of flowing predetermined discharge currents from the accumulator battery, the terminal discharge voltages of the accumulator battery is a voltage after the accumulator battery is discharged for predetermined period of time.

11. The method for determining deterioration of accumulator battery according to claim 1,

wherein the deterioration can be identified in the case that the one or more accumulator batteries are deteriorated or threaten to be deteriorated as the result of determination of deterioration of one or more of plural accumulator batteries.

12. The method for determining deterioration of accumulator battery according to claim 1,

wherein there are equipped a display part which indicates information as for handling-needing accumulator batteries needing to be discharged or replaced, and

as for ongoingly-usable accumulator batteries possible to be ongoingly used in the case that the one or more accumulator batteries are deteriorated or threaten to be deteriorated as the result of determination of deterioration of one or more of plural accumulator batteries, a storage part in which the records of the accumulator batteries are stored, and controlling, and

a determining part which has the programs to store the records of at least the accumulator batteries which are used after charge or are possible to be ongoingly used, and/or to ongoingly determine deterioration of the accumulator batteries.

2. A method for determining deterioration of accumulator battery hooked up with loads in a system based on results of measuring internal resistances of the accumulator battery, the method comprising the steps of:

predetermining as a specified temperature a temperature at which the deterioration of the accumulator battery is determined;

calculating in advance temperature correction coefficients of the internal resistances from changes of the internal resistances depending on temperatures;

predetermining resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and discharge drop voltages of the accumulator battery which are obtained at the specified temperature under condition of flowing predetermined discharge currents from the accumulator battery;

measuring internal resistances of the accumulator battery and a temperature of the accumulator battery at an internal resistance measurement;

converting measured internal resistance values into the internal resistance values at the specified temperature with use of the temperature correction coefficients of the internal resistances;

converting the internal resistance values at the specified temperature into the discharge drop voltage values of the accumulator battery at the specified temperature with use of the resistance-voltage conversion factors; and

determining whether the accumulator battery is deteriorated or not by means of comparison of the discharge drop voltage values of the accumulator battery at the specified temperature and a predetermined threshold value as a deterioration judgment standard.

7. The method for determining deterioration of accumulator battery according to claim 2,

wherein the predetermined threshold value as the deterioration judgment standard is a voltage value equal to or less than a falling voltage value minimally required to put the loads in operation.

3. A method for determining deterioration of accumulator battery hooked up with loads in a system based on results of measuring internal resistances of the accumulator battery, the method comprising the steps of;

predetermining as a specified temperature a temperature at which the deterioration of the accumulator battery is determined;

calculating in advance temperature correction coefficients of the internal resistances from changes of the internal resistances depending on temperatures;

predetermining resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and discharge drop voltages of the accumulator battery which are obtained at the specified temperature under condition of flowing predetermined discharge currents from the accumulator battery;

measuring internal resistances of the accumulator battery and temperature of the accumulator battery at an internal resistance measurement;

converting the measured internal resistance values into the internal resistance values at the specified temperature with use of the temperature correction coefficients of the internal resistances; and

determining whether the accumulator battery is deteriorated or not by means of comparison of the internal resistance values at the specified temperature and predetermined threshold value as a deterioration judgment standard.

8. The method for determining deterioration of accumulator battery according to claim 3,

wherein the predetermined threshold value as a deterioration judgment standard is a resistance value equal to or less than an internal resistance which enables the loads to minimally operate.

13. A method for determining deterioration of accumulator battery hooked up with loads in the system based on discharge performance of the accumulator battery, the method comprising the steps of;

picking up plural specified temperatures depending on the measured temperature in determination deterioration of the accumulator battery;

presetting the selected specified temperatures as a specified temperature at which deterioration of the accumulator battery is determined;

measuring correlation values correlative with the discharge performance at a desired temperature;

converting the correlation values into correlation values at the specified temperature based upon the temperature correcting formula obtained in advance, the desired temperature in the measurement of the correlation values and the correlation values;

calculating the discharge performance from the converted correlation values by means of a relational formula between correlation values and the discharge performance; and

determining the deterioration of the accumulator battery by means of comparison between the calculated discharge performance values respectively at the plural specified temperatures or judgment of correlation between the calculated discharge performance values.

14. The method for determining deterioration of accumulator battery according to claim 13,

wherein the correlation values are such electric conduction values as direct-current resistances of the internal resistance values, alternating-current impedance values or alternating-current conductance values, which are inverses of the alternating-current impedance values.

15. The method for determining deterioration of accumulator battery according to claim 13,

wherein the predetermined relational formula indicates a relation between the discharge performance and the terminal voltage of the accumulator battery which occurs at flowing electric currents which have a time fluctuation pattern corresponding to or similar to a time fluctuation pattern of consumption current in the loads.

16. The method for determining deterioration of accumulator battery according to claim 13,

wherein the specified temperature is set to a temperature at which the discharge performance gets lowest in the predetermined operating temperature range of the accumulator battery.

17. The method for determining deterioration of accumulator battery according to claim 13,

wherein the specified temperature is set to a temperature which is lower than the desired temperature by a predetermined degree.

18. The method for determining deterioration of accumulator battery according to claim 13,

wherein the specified temperature is set to a predetermined temperature in the temperature range including the desired temperature of the predetermined temperature ranges.

19. An equipment for determining deterioration of accumulator battery hooked up with loads in a system based upon results of measuring internal resistances of the accumulator battery,

which predetermines a specified temperature as a temperature at which the deterioration of the accumulator battery is determined,

calculates in advance temperature correction coefficients of the internal resistances from changes of the internal resistances depending on temperatures,

predetermines resistance-voltage conversion factors to convert between the internal resistances at the specified temperature and the terminal discharge voltages of the accumulator battery which are obtained at the specified temperature under the condition of flowing predetermined discharge currents from the accumulator battery;

the equipment including;

a battery temperature measuring part which measures internal resistances of the accumulator battery and temperature of the accumulator battery at the internal resistance measurement;

an internal resistance converting part which converts the measured internal resistance values into the internal resistance values at the specified temperature with use of the temperature correction coefficients of the internal resistances;

a terminal voltage converting part which converts the internal resistance values at the specified temperature into the terminal discharge voltage values of the accumulator battery at the specified temperature with use of the resistance-voltage conversion factors; and

a deterioration determining part which determines whether the accumulator battery is deteriorated or not by means of comparison of the terminal discharge voltage values of the accumulator battery at the specified temperature and predetermined threshold value as a deterioration judgment standard.

20. The equipment for determining deterioration of accumulator battery according to claim 19, which includes

a display part which makes it possible to identify the deterioration in the case that the one or more accumulator batteries are deteriorated or threaten to be deteriorated as the result of determination of deterioration of one or more of plural accumulator batteries.

21. The equipment for determining deterioration of accumulator battery according to claim 19, which includes;

a display part which indicates information as for handling-needing accumulator batteries needing to be discharged or replaced, and as for ongoingly-usable accumulator batteries possible to be ongoingly used in the case that the one or more accumulator batteries are deteriorated or threaten to be deteriorated as the result of determination of deterioration of one or more of plural accumulator batteries;

a storage part in which the records of the accumulator batteries are stored; and

a controlling and determining part which has the programs to store the records of at least the accumulator batteries which are used after charge or are possible to be ongoingly used, and/or to ongoingly determine deterioration of the accumulator batteries.

22. A method for measuring internal impedance of secondary battery, which comprising the steps of:

measuring the input currents and the responsive voltages to the input currents at charge or discharge;

acquiring plural of current measurement values and voltage measurement values on time axis;

calculating amplitude of the input currents and amplitude of the responsive voltages at a predetermined frequency from the acquired plural current measurement values and the acquired plural voltage measurement values by means of Fourier transformation; and

calculating internal impedances at the predetermined frequency as the result of dividing the amplitude of the responsive voltages at the predetermined frequency by the amplitude of the input currents at the predetermined frequency.

23. The method for measuring internal impedance of secondary battery according to claim 22,

wherein the plural current measurement values and the plural voltage measurement values are respectively N measurement values with sampling intervals of a predetermined time interval Δ

t, and the amplitude of the input currents and the amplitude of the responsive voltages at the predetermined frequency are calculated by means of dispersion Fourier transformation.

24. The method for measuring internal impedance of secondary battery according to claim 23,

wherein when F denotes the predetermined frequency, i(n·

Δ

t) denotes N pieces of the input current measurement values, and v(n·

Δ

t) denotes N pieces of the voltage measurement values, herein n is an integer from zero to N−

1, the amplitude of the input currents I(ω

)and the amplitude of the responsive voltages V(ω

) are calculated with use of the following formulas;

$I<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{\omega <br><br>}\right)=\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t<br><br>\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(n·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)·<br><br>\exp <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(j<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\omega <br><br>}·<br><br>n·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{dt}$$V<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{\omega <br><br>}\right)=\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t<br><br>\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>v<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(n·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)·<br><br>\exp <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(j<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\omega <br><br>}·<br><br>n·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{dt},$

herein ω

denotes 2π

F,

and the internal impedance Z(ω

) is calculated with use of the following formula.

$Z<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{\omega <br><br>}\right)=\frac{V<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{\omega <br><br>}\right)}{I<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{\omega <br><br>}\right)}$

25. The method for measuring internal impedance of secondary battery according to claim 22,

wherein at least M internal impedances are calculated correspondent to at least M different frequencies, and M circuit constants included in the equivalent circuit of the secondary battery are calculated with use of a simultaneous equation which includes the M circuit constants as a unknown quantity, based upon the internal impedances at the plural frequencies.

26. An equipment for measuring internal impedance of secondary battery comprises:

charge circuits which supply the secondary battery with charge currents when the secondary battery is charged;

discharge circuits which supply the secondary battery with discharge currents when the secondary battery is discharged;

detection means which measure input currents of the secondary battery and responsive voltages when the input currents are the charge currents or the discharge currents; and

control means which obtain the plural current measurement values and the plural voltage measurement values respectively on time axis from the measurement result of the detection means, calculate amplitudes of the input currents and the responsive voltage at a determined frequency from the plural current measurement values and the plural voltage measurement values with use of Fourier transformation, and calculate internal impedances of the secondary battery as the result of dividing the amplitude of the responsive voltages at the predetermined frequency by the amplitude of the input currents at the predetermined frequency.

27. The equipment for measuring internal impedance of secondary battery according to claim 26,

wherein the control means compose both of the current measurement values and the voltage measurement values of N measurement values with sampling intervals of a predetermined time interval Δ

t, and calculate the amplitude of the input currents and the amplitude of the responsive voltages at the predetermined frequency by means of dispersion Fourier transformation.

28. The equipment for determining deterioration of secondary battery in which the deterioration of the secondary battery is determined based upon the internal impedances calculated with use of the equipment for measuring internal impedance of secondary battery according to claim 27.

29. The power supply system including the equipment for measuring internal impedance of secondary battery according to claim 27.

30. A method for measuring internal impedance of secondary battery, which comprises the steps of:

determining which polarization due to charging or polarization due to discharging occurs in a secondary battery to supply electric power with some loads;

applying discharge current pulses with a constant time cycle to the secondary battery with polarization due to charging, and applying charge current pulses with a constant time cycle to the secondary battery with polarization due to discharging;

measuring the input currents and the responsive voltage of the secondary battery after a predetermined number of the constant time cycles from start of applying the discharge current pulses or the charge current pulses; and

calculating internal impedances of the secondary battery from the measured input currents and the measured responsive voltage.

31. The method for measuring internal impedance of secondary battery according to claim 30,

wherein the discharge current pulses or the charge current pulses are rectangular pulses which have predetermined time cycle and predetermined amplitude.

32. The method for measuring internal impedance of secondary battery according to claim 30,

wherein the measured input currents and the measured responsive voltage from which the internal impedances are calculated, start to be measured after a predetermined number of the time cycles in the range of 10 to 50 cycles from start of applying the discharge current pulses or the charge current pulses.

33. A method for measuring internal impedance of secondary battery, which comprises the steps of;

determining which polarization due to charging or polarization due to discharging occurs in a secondary battery to supply electric power with some loads;

applying discharge current pulses with a constant time cycle to the secondary battery with polarization due to charging, and applying charge current pulses with a constant time cycle to the secondary battery with polarization due to discharging;

measuring the input currents and the responsive voltage of the secondary battery within a predetermined time after the discharge current pulses or the charge current pulses start to be applied;

calculating plural internal impedances of the secondary battery on time axis from the measured input currents and the measured responsive voltage;

determining coefficients of a quadratic or more exponential damping function which approximates the time characteristics of the internal impedance by means of recursive calculation with use of the plural internal impedances; and

obtaining convergent values of the internal impedance from at least the determined coefficients.

34. The method for measuring internal impedance of secondary battery according to claim 33, wherein the exponential damping function expressed as the following function F(T), herein T is time, is used to determine five coefficients of A1 to A5.

F(T)=A1 exp(A3·

T)+A2 exp(A4·

T)+A5

35. The method for measuring internal impedance of secondary battery according to claim 33,

wherein the discharge current pulses or the charge current pulses are rectangular pulses which have a predetermined time cycle and a predetermined amplitude.

36. The method for measuring internal impedance of secondary battery according to claim 35,

wherein the measured input currents and the measured responsive voltage from which the internal impedances are calculated, start to be measured after a predetermined number of the time cycles in the range of 10 to 50 cycles from start of applying the discharge current pulses or the charge current pulses.

37. An equipment for measuring internal impedance of secondary battery including;

detection means which measure input currents of the secondary battery and responsive voltages when the input currents are the charge currents or the discharge currents;

charge and discharge circuits which make it possible to apply charge or discharge current pulses with a constant time cycle to the secondary battery; and

control means determining which polarization due to charging or polarization due to discharging occurs in a secondary battery supplying some loads with electric power, applying discharge current pulses with a constant time cycle to the secondary battery in the former case, and charge current pulses with a constant time cycle are applied to the secondary battery in the former case, measuring the input currents and the responsive voltage of the secondary battery after a predetermined number of the constant time cycles from start of applying the discharge current pulses or the charge current pulses, and calculating internal impedances of the secondary battery from the measured input currents and the measured responsive voltage.

38. The power supply system includes the equipment for measuring internal impedance of secondary battery according to claim 37.

39. A method for determining deterioration of secondary battery based upon internal resistances of the secondary battery, which comprises the steps of:

calculating the internal impedances from currents and voltages of the secondary battery measured in the condition that predetermined currents are applied to the secondary battery;

determining coefficients of respective terms of an approximate function which comprises a cubic or more polynomial expression and approximates the temperature characteristics of the secondary battery, based upon the calculated internal impedances and the measured temperature of the secondary battery;

calculating a specified internal impedance, which is a presumed internal impedance value at a predetermined specified temperature, with use of the cubic or more polynomial expression based upon the determined coefficients; and

determining deterioration of the secondary battery based upon the specified internal impedance.

40. The method for determining deterioration of secondary battery according to claim 39,

wherein the coefficients of respective terms of the cubic or more polynomial expression are set in reference to a common specified factor, the common specified factor is calculated from the calculated internal impedance and the measured temperature, and the coefficients of respective terms is determined base upon the specified factor.

41. The method for determining deterioration of secondary battery according to claim 40,

wherein the approximate function including the cubic or more polynomial expression is

Z=C+f1(C)·

Tp+f2(C)·

Tp²+ . . . +fn(C)·

Tpⁿ,

where Tp, Z and C respectively indicate temperature, the internal impedance and the specified factor, n indicates a integer of more than or equal to 3, and f1 to fn indicate predetermined function.

42. The method for determining deterioration of secondary battery according to claim 41,

wherein the function f1(C) to fn(C) included in the respective terms of the cubic or more polynomial expression are expressed in a linear expression of the specified factor C.

43. The method for determining deterioration of secondary battery according to claim 39,

wherein a judging threshold is predetermined depending on the specified temperature, and deterioration of the secondary battery is determined depending on the magnitude relation between the calculated specified internal impedance and the judging threshold.

44. A method for measuring internal impedance of secondary battery, which comprises the steps of:

obtaining respective amplitudes of the discharge currents at the various frequencies by means of applying Fourier transformation to the discharge current waveform when the frequency of the discharge current pulse is set up to various frequencies while the discharge currents are flowed;

obtaining respective amplitudes of the responsive voltages at the various frequencies by means of applying Fourier transformation to the responsive voltage waveform;

comparing internal impedances at the various frequencies each other after the internal impedances are obtained respectively at the various frequencies by means of dividing the amplitudes of the responsive voltages by the amplitudes of the discharge currents; and

determining the noise level in the measurement of the currents and the voltages as low when proportion of the data spread of the internal impedances is less than or equal to a predetermined value, and determining the noise level in the measurement of the currents and the voltages as high when proportion of the data spread of the internal impedances is more than the predetermined value.

45. The method for measuring internal impedance of secondary battery according to claim 44,

wherein a set of discharges having at least three different time cycles is carried out repeatedly, internal impedances are calculated at not less than three different cycles, and desired internal impedance are calculated from at least the three impedances.

46. An equipment for determining deterioration of secondary battery based upon the internal resistances of the secondary battery supplying electric power with loads includes:

circuits which can apply current pulses to the secondary battery;

detection means which measures currents and voltages of the secondary battery;

temperature sensors which measure the temperature of the secondary battery; and

control means which calculates the internal impedances from the measurement results of the detection means in condition that the circuits apply current pulses to the secondary battery,

determines coefficients of the respective terms of an approximate function which comprises a cubic or more polynomial expression and approximates the temperature characteristics of the secondary battery,

calculates a specified internal impedance, which is a presumed internal impedance value at a predetermined specified temperature, with use of the cubic or more polynomial expression based upon the determined coefficients, and

determines deterioration of the secondary battery based upon the calculated specified internal impedance.

47. The equipment for determining deterioration of secondary battery according to claim 46, which further includes

nonvolatile storage means which stores in advance the configuration information about coefficients of the respective terms of the cubic or more polynomial expression, and wherein the control means calculates the coefficients of the terms from the configuration information to be read out from the nonvolatile storage means.

48. The equipment for determining deterioration of secondary battery according to claim 47,

wherein the nonvolatile storage means stores the plural configuration information about plural combinations of the coefficients of the respective terms of the cubic or more polynomial expression, and the control means can selectively read out from the plural configuration information.

49. The equipment for determining deterioration of secondary battery according to claim 47,

wherein the nonvolatile storage means stores judging threshold values predetermined depending on the specified temperature, and the control means determines deterioration of the secondary battery depending on the magnitude relation between the calculated specified internal impedance and the judging threshold to be read out from the nonvolatile storage means.

50. The equipment for determining deterioration of secondary battery according to claim 49,

wherein the nonvolatile storage means stores the plural judging threshold values, and the control means can selectively read out from the plural judging threshold values

52. A power supply system including the power supply system with the equipment for determining deterioration of secondary battery according to claim 46.

51. An equipment for determining deterioration of secondary battery includes determining parts which

calculates respective amplitudes of the discharge currents at the various frequencies from the discharge current waveforms by means of Fourier transformation when discharge currents are flowed at various frequencies by means of discharging continuously at various frequencies,

calculates respective amplitudes of responsive voltages at the various frequencies from the responsive voltage waveforms by means of Fourier transformation,

compares internal impedances at the various frequencies each other after the internal impedances are obtained respectively at the various frequencies as a result of dividing the magnitudes of responsive voltages by the magnitudes of the discharge currents respectively at the various frequencies, and

determines the noise level in the measurement of the currents and the voltages as low when proportion of the data spread of the internal impedances is less than or equal to a predetermined value, and

determines the noise level in the measurement of the currents and the voltages as high when proportion of the data spread of the internal impedances is more than the predetermined value.