CHARGING METHODS FOR NICKEL-ZINC BATTERY PACKS
A temperature compensated constant voltage battery charging algorithm charges batteries quickly and safely. Charging algorithms also include methods to recondition batteries after storage and to correct cell imbalances in a battery pack. A battery charger able to perform these functions is also disclosed.
1 . A method of charging a nickel-zinc battery comprising:
measuring a temperature of the battery,
calculating a calculated voltage based on at least the temperature of the battery,
charging the battery at a constant current until a measured battery voltage reaches the calculated voltage,
charging the battery at the calculated voltage, and
stopping the battery charging at the calculated voltage when an end-of-charge condition is satisfied;
wherein the battery comprises one or more cells.
2 . The method of claim 1 , wherein the constant current is about 1-2 amps per 2 Amp hour of capacity in the battery.
3 . The method of claim 1 , wherein the constant current charging operation increases a capacity of the battery to about 80%.
4 . The method of claim 1 , further comprising:
charging the battery at a corrective current to correct cell imbalance after charging the battery at the calculated voltage.
5 . The method of claim 1 , further comprising:
charging the battery at a minimum current to maintain charge during period when the battery is not in use and the end-of-charge condition has been satisfied.
6 . The method of claim 1 , further comprising:
charging the battery at an initial current until a start-of-charge condition is satisfied.
7 . The method of claim 4 , wherein the corrective current is about 50-200 milliamps per 2 Amp hour of capacity in the battery.
8 . The method of claim 5 , wherein the minimum current is about 0-50 milliamps per 2 Amp hour of capacity in the battery.
9 . The method of claim 6 , wherein the initial current is about 0-50 milliamps per 2 Amp hour of capacity in the battery.
10 . The method of claim 1 , wherein the end-of-charge condition is selected from the group consisting of:
a charging current of less than a defined current associated with a specified state-of-charge;
a lapse of 1.5 hours of charging at the calculated voltage;
a battery temperature increase of 15 degrees Celsius;
a charging current of more than about a defined threshold associated with a short circuit in the battery; and,
combinations thereof.
11 . The method of claim 6 , wherein the start-of charge condition is selected from the group consisting of:
(a) a battery temperature of 15 degrees Celsius;
(b) a battery voltage of about 1 volt per cell; and,
(c) a lapse of about 20 hours or more without meeting either of conditions (a) or (b).
12 . The method of claim 1 , further comprising
repeating the measuring, and the calculating during the charging.
13 . A nickel-zinc battery charger comprising:
an enclosure for holding the nickel-zinc battery,
a thermistor configured to thermally couple to a battery during operation; and,
a controller configured to execute a set of instructions, the instructions comprising instructions to:
measure a temperature of the battery,
calculate a calculated voltage,
charge the battery at a constant current until a measured battery voltage equals the calculated voltage,
charge the battery at the calculated voltage, and
stop the charge at the calculated voltage when an end-of-charge condition is detected.
14 . The battery charger of claim 13 , further comprising:
a recondition button and wherein the instructions further comprises
charging the battery at an initial current when the recondition button is pressed.
15 . The battery charger of claim 13 , wherein the instructions further comprises instructions to
charge the battery at a corrective current.
16 . The battery charger of claim 13 , wherein the instructions further comprises instructions to
charge the battery at a minimum current.
17 . A method of correcting nickel-zinc battery cell imbalance comprising:
providing a battery pack at greater than about 90% state-of-charge in a charger, and
charging the battery at a corrective current for about 30 minutes to 2 hours without limiting the voltage.
18 . The method of claim 17 , wherein the corrective current is about 50-200 milliamps per 2 Amp hour of capacity in the battery.
19 . The method of claim 17 , further comprising:
charging the battery at a minimum current until the battery is removed from the charger.
20 . The method of claim 19 , wherein the minimum current is 0-50 milliamps per 2 Amp hour of capacity in the battery.
21 . A method of charging a battery comprising:
measuring a temperature of the battery,
measuring a voltage of the battery,
calculating a calculated voltage based on at least the temperature of the battery,
charging the battery at a charge current until the battery voltage equals the calculated voltage,
reducing the charging current by a defined factor,
charging the battery at the reduced charge current until the battery voltage equals the calculated voltage,
wherein the factor is about 2-10.
22 . The method of claim 21 , further comprising
repeating the reducing and charging the battery at the reduced charge operations to the same voltage level.
23 . A method of charging a nickel-zinc cell, the method comprising:
(a) charging the nickel-zinc battery at a constant current until reaching a point at which (i) the cell's state of charge is at least about 70%, (ii) a nickel electrode of the cell has not yet begun to evolve oxygen at a substantial level, and (iii) the cell voltage is between about 1.88 and 1.93 volts; and
(b) charging the nickel-zinc battery at a constant voltage in the range of 1.88-1.93 until an end-of-charge condition is satisfied.
24 . The method of claim 23 , wherein charging the battery at a constant current is conducted at a current of up to about 4 Amps per 2 Amp hour battery capacity, and wherein the nickel-zinc battery employs an electrolyte having a conductivity of at least about 0.5 cm −1 ohm −1 .
25 . The method of claim 24 , wherein charging the battery at a constant current is conducted until the cell voltage is between about 1.88 and 1.91 volts.