CHARGING METHODS - CONTINUED
(b) Rapid charging When rapidly charging the battery, a large charge current is required in a short time for replenishing the energy which has been discharged. Therefore, some adequate measures such as the Control of charge current is required to prevent overcharging when the rapid charging is complete. Basic requirements for rapid charging are as follows:
Sufficient charging should be made in a short time for fully replenishing the amount discharged.
Charge current should be automatically controlled to avoid overcharge even on prolonged charging.
The battery should be charged adequately in the ambient temperature range of 0C to 40C.
Reasonable cycle life of charge/discharge should be secured.
Typical methods to control charging so as to satisfy the above requirements follow.
Two-step constant voltage charge control method Two-step constant voltage charge control method uses two constant-voltage devices. At the initial stage, the battery is charged by the first constant- voltage device SW(1) of high setup voltage (set- up for cycle charge voltage). When the charge current, the value of which is detected by the current-detection circuit, has reduced to the preset value, the device is switched over to the second SW(2) of low set-up voltage (setup for trickle charge voltage). This method has the advantage that the battery in trickle use can be charged in a comparatively short time for the next discharge.
Charging characteristics of the two-step constant voltage control charger
Battery voltage / Charge current
Block diagram of the two-step constant voltage control charger
Current detection circuit
Charging power supply
Sealed Lead-Acid Handbook, Page 21