Lead Acid Battery Pulse Charge Algorithm
This is an adaptation of Three Phase, Intermittent Charge and Interrupted Charge Control algorithms in an attempt to improve efficiency for chargers where there are a number of batteries under charge. As with those chargers, the gassing voltage is avoided as far as possible to reduce the effects of overcharging, particularly important for SLA batteries.
The algorithm is aimed at a battery bank in which each battery is charged individually. It keeps batteries always under charge until all have passed to the float stage. An Intermittent Charge mode is used to bring the batteries as close as possible to full charge, with the Three Phase algorithm absorption phase used at the final stage to complete the charging and bring each battery to float phase. Normally the charger is turned off in float phase and reconnected when the battery charge drops to a specified limit.
The algorithm is described as follows:
(Note that the term "float phase" is used although in reality the charger is removed from the battery until the terminal voltage falls below the fully charged value).
not known if this algorithm will fully charge the batteries, any more
that any other algorithm can guarantee. The termination condition is
similar to that of the three phase
algorithm and relies on
manufacturers' recommendations regarding the level of gassing that is
acceptable at the gassing voltage. The termination condition for
algorithm attempts to draw on that recommendation by measuring the
average current over each cycle. The battery is kept at the constant
gassing voltage by means of a first order heuristic control that simply
pulls the voltage back to the target voltage.
This algorithm will still have periods where the charger is idle, but the efficiency is expected to be better than the other algorithms, including the three phase charging algorithm where the charger is underutilised during the absorption phase.
Initial tests with the algorithm show promising results. For three 50AH car batteries charged from a solar panel the following voltage curves were obtained:
of the three lines shows the terminal voltage of a battery placed
on charge alternately. The yellow line shows a battery initially on
bulk charge. The blue line is a battery nearly at full charge that
passes through three absorption cycles until it reaches the float
phase. The red and yellow batteries alternate between rest and
absorption phases until the red battery reaches float phase. The yellow
battery which was at low charge initially continues on in the
absorption phase. Note the peaks well above the 14.6V gassing voltage
at the start of the absorption phase. These occur because the battery
is placed on bulk charge initially to bring it up to the gassing
voltage, however because the batteries are nearly fully charged the
process is very rapid and an overshoot occurs before the voltage can be
dragged back by the constant voltage tracking algorithm. The peaks
settle within about 10 seconds as the following trace of a closeup of
the early stages shows.
These curves show the batteries swapping between bulk charge and rest phases before moving into absorption phase. The minimum time in rest phase is 30 seconds and in absorption phase 90 seconds.