AN3971

Charging a lead acid battery

Doc ID 022119 Rev 2

11/28

So, to respect all the constraints mentioned above, the charging strategy used is a multi-

voltage battery charging profile with:

●

Constant current to perform a bulk charge, when the battery is charged using a current

regulation to I_batt_max, up to 70% SOC, in about 4 hours, and the battery voltage

slowly increases up to the nominal value (equal to 2 V per cell)

●

Constant voltage to perform a floating charge, when the battery is charged using a

voltage regulation to V_batt_max, up to the remaining 30% SOC, with a slow current

decrease down to C/10 or C/100 values. This stage lasts 6 hours and is essential for

the battery lifetime

●

Constant current to perform a trickle charge, which compensates the self-discharge of

the battery, even after it has been fully charged. Normally the charging current is less

than C/100, and even if the battery is not completely saturated, the SLA can eventually

lose its ability to accept a full charge and its performance is reduced.

3.1

Constant current – constant voltage control

In order to properly control the lead acid charging profile in terms of max. current during the

bulk charge, and the max. voltage during the floating charge, the SEA05 IC has been used.

The lead acid battery chemistry and physics behavior affect the charging strategy itself.

This occurs particularly during the last two steps of the lead acid charging profile:

●

During the floating charge, the sink current decreases slowly because of the battery

features keeping a constant voltage charge at the maximum value

●

During the trickle charge (which is normally necessary just after the natural battery

discharging), in order to keep the battery at a maximum SOC. In this case, no control

acts, just to allow the energy flow directly from the panel towards the battery, without

any constraints or voltage/current limitation.

3.2

SEA05 features

The SEA05 is a highly integrated solution for SMPS applications requiring a dual control

loop to perform CV (constant voltage) and CC (constant current) regulation, implemented by

two operational amplifiers, and a low-side current sensing circuit.

Figure 10.

SEA05 internal architecture