Method and apparatus for charging sealed nickel-cadmium batteries

• US 5,659,239 A
• Filed: 10/06/1995
• Issued: 08/19/1997
• Est. Priority Date: 10/05/1995
• Status: Expired due to Fees

• Current Assignee: SAFT SA (Totalenergies Se)
• Original Assignee: SAFT SA (Totalenergies Se)
• Inventors: Liska, Jean-Louis, Sanchez, Patrick
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/539,756
• Time in Patent Office: 683 Days
• Field of Search: 320/21, 320/22, 320/23, 320/24, 320/29, 320/30, 320/35, 320/36, 320/39, 320/48
• US Class Current: 320/150
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

A method of charging a sealed nickel-cadmium battery, in which the battery first is charged for a duration t₁ at current I₁, such that: I_min ≦I₁ ≦I_max with 0≦I_min ≦C₁ and 0.2 C₁ ≦I_max ≦5 C₁, and I₁ 32 αC₁ (1+aT) where 0.2≦α≦5 and 0≦α≦0.1, where T is the temperature and C₁ is the nominal current. The battery then is charged at a voltage U₂, such that: U_min ≦U₂ ≦U_max where 1.45 V≦U_min ≦1.75 V and 1.50 V≦U_max ≦1.80 V, and U₂ =U_i +bT, and a duration t₂ =βt₁ +c where 0.2≦β≦5 and 5≦c≦60. Current I₁ and voltages U₁ and U₂ are readjusted as the temperature in the battery changes. Apparatus for performing the inventive method also is provided.

Claims

1. A method of charging a battery of sealed nickel-cadmium cells defined by a nominal capacity, said battery having a variable temperature, the method comprising the following steps:

a first step of charging said battery at applied current I₁, in amps, wherein said applied current I₁ falls between a minimum value I_min and a maximum value I_max in accordance with the conditions 0≦

I_min ≦

C₁ and 0.2 C₁ ≦

I_max ≦

5 C₁, where C₁ is the current in amps corresponding to discharge of said nominal capacity in one hour, and I₁ satisfies the formula;

I₁ =α

C₁ (1+aT) where α

is a number such that 0.2≦

α

≦

5 and a is a coefficient, in units of 1/°

C., such that 0≦

a≦

0.1 where T is said temperature in degrees Celsius, the product aT being dimensionless, said first charging step being stopped at the first-satisfied stop criterion selected from a first criterion which is a voltage U₁, in volts, which falls between a minimum value U_min and a maximum value U_max in accordance with the conditions 1.45 V≦

U_min ≦

1.75 V and 1.50 V≦

U_max ≦

1.80 V and the formula U₁ =U_i +bT where b is a coefficient such that -0.005≦

b≦

0, and where U_i is a voltage coefficient defined by 1.45 V≦

U_i ≦

1.75 V, and a second criterion which is the rate of change dT/dt of said temperature which is 0.3°

C./min±

0.2°

C./min, said current I₁ and said voltage U₁ being calculated and readjusted during said first step depending on the change in the temperature of said battery,

a second step of charging said battery at a voltage U₂, in volts, where U₂ falls between said minimum value U_min and said maximum value U_max in accordance with the conditions 1.45 V≦

U_min ≦

1.75 V and 1.50 V≦

U_max ≦

1.80 V and has the formula;

U₂ =U_i +bt where -0.005≦

b≦

0, and at a current I₂ in amps which is not greater than 0.2C₁, the duration of said second period t₂, in minutes, being determined by the formula;

space="preserve" listing-type="equation">t.sub.2 =β

t.sub.1 +c where 0.2≦

β

≦

5 and

5 min≦

c≦

60 min, where t₁ is the duration of said first step, said voltage U₂ being calculated and readjusted during said second step depending on the change in the temperature of said battery.

2. A method according to claim 1, further comprising, before said first step, a step for stabilizing said temperature which finishes at a stop criterion which is the rate of change dT/dt of said temperature which is 0.3°

C./min±

0.2°

C./min.

3. Apparatus for charging according to claim 1, comprising:

a current and voltage supply;

memory means for memorizing data constituted by the values which the charging parameters must take at said temperature;

measuring means for measuring said temperature and said charging parameters;

comparing means for comparing said charging parameters with said data;

applying means for applying the values which said charging parameters must take.

4. Apparatus for charging according to claim 1, comprising:

a current and voltage supply;

memory means for storing data relating to variation of the charging parameters as a function of said temperature;

calculating means for calculating the values which said charging parameters must take as a function of said temperature;

measuring means for measuring said temperature and said charging parameters;

comparing means for comparing said charging parameters with the value which said charge parameters must take;

applying means for applying the values which said charge parameters must take.

5. Apparatus according to claim 3, in which said measuring means, said comparing means and said applying means are capable of measuring, comparing and permanently readjusting said charging parameters.