System and method for battery charging
A method for charging a lead acid storage battery to advantageously extend its life is described. The termination of a charging process is based upon an evaluation of the first derivative (dv/dt) and second derivative (d2v/dt2) of the applied charging voltage. By utilizing the first derivative (dv/dt) and second derivative (d2v/dt2) as charging criteria, an amount of overcharge is applied to the battery that takes into account the precise amount of amp-hours previously removed from the battery. A charger arrangement for performing a charging process of the invention also is described.
1. A method for charging flooded deep cycle lead acid batteries comprising the steps of:
applying charging energy to such a battery;
monitoring the charging energy as to quantity delivered to the battery and its dv/dt and d 2 v/dt 2 aspects; by use of information about a first amount of charging energy delivered to the battery to a point in the process when dv/dt is a maximum and d 2 v/dt 2 =0, determining at that point and delivering to the battery beyond that point a defined quantity of charging energy additive to said first amount adequate to overcharge the battery to a predetermined extent related to said first amount.
2. A method for charging flooded deep cycle lead acid batteries comprising the steps of:
applying to such a battery a first amount of charging energy adequate, in combination with an initial charge condition of the battery, to cause the battery to attain a detectable charge state which is less than a full charge condition and which has a known relation to a full charge condition, and
applying to the battery a further second increment of charging energy which is adequate, in combination with the initial charge condition and the first amount of charging energy, to overcharge the battery to a selected extent and the quantity of which is determined as a selected percentage of the first amount of charging energy when the detectable charge state is attained.
3. The method as claimed in claim 2 in which the detectable charge state is the state at which the battery is at substantially 98% of full charge.
4. The method as claimed in claim 3 in which the step of determining the amount of the further second increment of charging energy includes:
dividing a) the product of (i) first amount of charging energy and (ii) the sum of unity (one) and the decimal equivalent of the percent of overcharge by b) 0.98.
5. The method as claimed in claim 4 in which the step of determining the amount of the second increment of charging energy further includes determining the difference between a) the result of the division operation described in claim 4 and b) the first amount of charging energy.
6. The method as claimed in claim 2 in which the detectable charge state is detected by:
determining when the rate of change of an applied charging voltage with respect to time (dv/dt) is a maximum; and
determining when the acceleration of the applied charging voltage with respect to time (d 2 v/dt 2 ) is zero.
7. A method for charging deep cycle lead acid batteries comprising:
applying charging energy to such a battery;
detecting a point of 98% of full charge in the charging process;
monitoring the charging energy provided in amp hours to attain the 98% full charge point;
determining the remaining charging energy to be applied to fully charge the battery and to overcharge the battery by an amount substantially equal to a predetermined percentage of the quantity of energy applied to the battery from the commencement of charging to the 98% full charge point of the battery; and
applying the remaining charging energy to the battery.
8. The method of claim 7 for charging a deep cycle lead acid battery wherein the step of detecting the 98% full charge point comprises:
determining when the rate of change of an applied charging voltage with respect to time (dv/dt) is a maximum; and
determining when the acceleration of the applied charging voltage with respect to time (d 2 v/dt 2 ) is zero.
9. Apparatus for charging flooded deep cycle lead acid batteries which includes a DC source, a mechanism operable to measure the amount of charging energy delivered to a battery from the beginning of a battery charging event, and a mechanism operative for detecting when a battery being charged by the apparatus is at a detectable point in a charging event at which the battery has a certain state of charge less than full charge and for determining at that point and controlling the application to the battery beyond that point of a further quantity of charging energy effective to overcharge the battery by a selected percentage of the amount of charging energy delivered to the battery to that detectable point in that charging event.
10. Apparatus as claimed in claim 9 further including:
a dv/dt measurement circuit, a
d 2 v/dt 2 measurement circuit, and
a controller coupled to the dv/dt and d 2 v/dt 2 measurement circuits, the controller being configured for detecting the point in a battery recharge event at which dv/dt is a maximum and d 2 v/dt 2 =0, and at which the battery is at substantially a certain percentage of full charge, and for determining the value of Q D from the relation Q S /p =Q D /(1+x) in which Q S is the ampere-hours of charging energy delivered to the battery in the interval from the beginning of the recharge event to the detected point, p is the decimal equivalent of the certain percentage, x is the decimal equivalent of a desired percentage amount of replenishment charge to be delivered to the battery as an overcharge amount, and Q D is the total amount of charging energy to be delivered to the battery from the beginning of the recharge event to the end of that event.
11. Apparatus according to claim 10 in which the value of p is substantially 0.98.
12. Apparatus according to claim 10 in which x is in the range of from about 0.08 to about 0.12.