Smart Battery Charger Operation

These Smart Battery Chargers have three distinct operating modes: BULK, ABSORPTION and MAINTENANCE.

In the BULK mode, the charger limits the maximum charging current to a preset Imax value while monitoring the battery voltage.

In the ABSORPTION mode, the charger elevates the voltage to Voc while monitoring the current. When the current decreases (tapers down) to a preset value (Ioct), the charger enters the MAINTENANCE mode.

In the MAINTENANCE mode the charger will issue from ZERO to Imax current while maintaining the battery at Vf.

Please note that the MAINTENANCE mode IS NOT a trickle mode, the charger will issue ZERO current if the battery accepts proper charge during the first two modes. This feature allows the charger to be connected indefinitely.

There are two LED's on the front panel. One labeled CHARGING and the other labeled FINAL CHARGE.

Although we commonly refer to a battery as a 12V battery, meaning a battery having 6 cells at 2.0V per cell (12.0V). The actual Lead-Acid battery voltage is closer to 2.3V per cell (13.8V).

Below we will discuss the operation of a 12V @ 1 Amp Smart Battery Charger. The 12V @ 5 Amp Smart Battery Charger operation is similar, the voltage and current values change per the table below.

Operation is as follows:

1. With the AC off, connect the charger to a 12V battery that has at least 6V terminal voltage. This charger has a CHARGE ENABLE function. If you connect a battery that has less than 6V, the charger assumes there is a defect in the battery and it will not attempt to charge. Likewise if you turn the charger on without a battery connected, the charger will not output any voltage/current. This is a safety feature which prevents output short circuits.
2. Next turn on the AC via the front panel, lighted rocker switch. The switch should light signifying that the input AC voltage is present and the charger is now turned on.
3. The charger will enter the BULK mode and the CHARGING (GREEN) LED will light. The current will be limited to the Imax (1 A) value which is set by the circuit. Depending on the battery and state of charge, the current could be less than Imax.
4. When the battery voltage reaches about 95% of Voc (about 13.68 VDC), the charger will enter the ABSORPTION mode and the FINAL CHARGE (RED) LED will also light. In this mode, both LED's are lit. The charger then elevates the voltage to Voc (14.4V for the 1 A charger) and begins monitoring the current.
5. When the current tapers down to Ioct (0.1 A for the 1 A charger), the charger will enter the MAINTENANCE mode and both LED's will go out. This signals the end of the three mode charge cycle. The charger will then issue from 0 to Imax (1 A for the 1 A charger) to maintain the battery at Vf (13.8 V for the 1 A charger).
6. You may leave the charger connected indefinitely. It will not overcharge (or trickle charge) your battery. If you apply a load in excess of Imax (1 Amp for the 1 A charger), the charger will simply contribute Imax to the load. If the load is removed, the 1 Amp will then flow into the battery. If the load draws the battery down sufficiently, the three mode charging sequence will repeat again.

All voltage values stated are typical at 77°F. The charger compensates for temperature variations. At elevated temperatures, all voltages are lower. Likewise at colder temperatures, all voltages are higher. Normal operation assumes the battery and charger are in the same environment.

The Smart Battery Charger does not have any timers. All decisions are based on the battery voltage/current. The charger may stay in either of the first two states as long as necessary to achieve a proper battery charge. Very large battery banks may require BULK or ABSORPTION cycles of 100+ hours (days) or longer.

If you would like to see the Smart Charger being used with the Elecraft K2 internal battery,
see the write up by Don Wihelm, W3FPR

go to W3FPR WebPage