The post explains a simple yet effective MPPT lead acid battery charger circuit using the IC bq2031 from TEXAS INSTRUMENTS.
This practical application article is for the individuals who may be developing an MPPT-based lead acid battery charger with the aid of bq2031 battery charger.
This article includes a structural format for charging a 12-A-hr lead acid battery employing MPPT (maximum power point tracking) for improving charging efficiency for photovoltaic applications.
The easiest procedure for charging a battery from a solar panel systems could be to hook up the battery straight to the solar panel, however this may not the most effective technique.
Presume a solar panel bears a rating of 75 W and generates a current of 4.65 A with a voltage of 16 V at normal test environment of 25 ° C temperature and 1000 W/m2 of insolation.
The lead acid battery is rated with a voltage of 12 V; directly hooking up the solar panel to this battery would decrease the panel voltage to 12 V and only 55.8 W (12 V and 4.65 A) could be produced from the panel for charging.
A DC/DC converter may be most suitably needed for economical charging here.
This practical application document explains a model, making use of the bq2031 for effective charging.
I-V Characteristics of Solar Panel
Figure 1 displays the standard aspects of a solar panel systems. Isc is a short-circuit current that streams through the panel in case the solar panel is short circuited.
It happens to be the optimum current that may be extracted from the solar panel.
Voc is the open-circuit voltage at the terminals of the solar panel.
Vmp and Imp are the voltage and current levels where maximum power can be purchased from the solar panel.
While the sunshine decreases the optimum current (Isc) which may be attained, the highest current from the solar panel also suppresses. Figure 2 indicates variation of I-V characteristics with sun light.
The blue curve links the details of the maximum power at various values of insolation
The reason for the MPPT circuit is to try to sustain the working level of the solar panel at the maximum power point in several sunshine conditions.
As observed from Figure 2, the voltage where maximum power is delivered does not alter greatly with sunshine.
The circuit constructed with the bq2031 makes use of this character to put into practice MPPT.
An additional current control loop is included with decrease the charge current as the daylight decreases as well as to sustain solar panel voltage around the maximum power point voltage.
bq2031-Based MPPT Charger
Figure 3 displays the schematic of a DV2031S2 board with an added current control loop added to carry out the MPPT making use of the operational amplifier TLC27L2.
The bq2031 keeps the charging current by retaining a voltage of 250 mV at sense resistance R 20. A reference voltage of 1.565 V is created by using 5 V from U2.
The input voltage is compared with the reference voltage to produce an error voltage that could be implemented at the SNS pin of bq2031 to decrease the charge current.
The voltage (V mp) where maximum power can be acquired from the solar panel is conditioned employing resistors R26 and R27. V mp = 1.565(R 26 +R 27)/R 27.
With R 27 = 1 k Ω and R 26 = 9.2 k Ω, V mp = 16 V is achieved. TLC27L2 is internally adjusted with a bandwidth of 6 kHz at V dd = 5 V. Mainly because the bandwidth of TLC27L2 is significantly below the switching frequency of bq2031, the added current control loop continues to be constant.
The bq2031 in the earlier circuit (Figure 3) offers an optimum current of 1 A.
In case the solar power panel can furnish adequate power to charge the battery at 1 A, the outer control loop does not proceed into action.
However if the insulation reduces and the solar power panel struggles to deliver sufficient energy to charge the battery at 1 A, the outer control loop decreases the charge current to preserve input voltage at V mp.
The outcomes demonstrated in Table 1 confirm the functioning of the circuit. The voltage readings in bold type signify the issue whenever the secondary control loop is minimizing the charge current to preserve input at V mp