MPPT Lead Acid Battery Charger Circuit

The article clarifies a highly effective MPPT lead acid battery charger circuit applying the IC bq2031 from TEXAS INSTRUMENTS.

Abstract

This useful application article was written just for the individuals who could possibly be generating an MPPT-based lead acid battery charger with the assistance of bq2031 battery charger.

This content consists of a structural format for charging a 12-A-hr lead acid battery utilizing MPPT (maximum power point tracking) for boosting charging capability for photovoltaic applications.

Development

The most convenient method of charging a battery from a solar panel systems would be to link up the battery right to the solar panel, still this may well not be the recommended procedure.

Believe a solar panel possesses a rating of 75 W and creates a current of 4.65 A with a voltage of 16 V at regular test environment of 25 ° C temperature and 1000 W/m2 of insolation.

The lead acid battery is graded with a voltage of 12 V; perfectly hooking up the solar panel to this battery would lessen the panel voltage to 12 V and only 55.8 W (12 V and 4.65 A) may very well be manufactured from the panel for charging.

A DC/DC converter may be most sufficiently essential for affordable charging here.

This effective application document clarifies a model, implementing the bq2031 for beneficial charging.

I-V Qualities of Solar Panel

I/V characteristic curve of solar panel

I/V quality curve of solar panel

Figure 1 shows the regular elements of a solar panel systems. Isc is a short-circuit current that options by way of the panel for instance the solar panel is short circuited.

It is always the most effective current which may be acquired 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 utmost power is available from the solar panel.

While the sunshine lowers the optimum current (Isc) which might be obtained, the highest current from the solar panel also suppresses. Figure 2 signifies variation of I-V qualities with sun light.

The blue curve links the particulars of the optimum power at various values of insolation

 

I-V variation characteristics with regard to sunlight

I-V variation qualities concerning to sunlight

The purpose of the MPPT circuit is to attempt to keep up the operating level of the solar panel at the optimum power point in a number of sunshine circumstances.

As realized from Figure 2, the voltage where maximum power is provided is not going to alter considerably with sunshine.

The circuit designed with the bq2031 employs this character to perform MPPT.

An additional current control loop provides the decrease the charge current as the daylight reduces in addition to take care of solar panel voltage around the maximum power point voltage.

 

MPPT circuit for charging lead acid batteries

MPPT circuit for charging lead acid batteries

bq2031-Based MPPT Charger

Figure 3 shows the schematic of a DV2031S2 board with an extra current control loop included onto undertake the MPPT utilizing the working amplifier TLC27L2.

The bq2031 continues the charging current by maintaining a voltage of 250 mV at sense resistance R 20. A reference voltage of 1.565 V is produced through the use of 5 V from U2.

The input voltage is in comparison with the reference voltage to deliver an error voltage which may be applied at the SNS pin of bq2031 to lessen the charge current.

The voltage (V mp) wherein maximum power can be obtained 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 attained. TLC27L2 is internally altered with a bandwidth of 6 kHz at V dd = 5 V. Considering the bandwidth of TLC27L2 is far below the switching frequency of bq2031, the added current control loop happens to be regular.

The bq2031 in the earlier circuit (Figure 3) delivers an optimum current of 1 A.

If perhaps the solar power panel can produce enough power to charge the battery at 1 A, the outer control loop is not going to continue into action.

In spite of this if the insulation lessens and the solar power panel challenges to provide satisfactory energy to charge the battery at 1 A, the outer control loop reduces the charge current to conserve input voltage at V mp.

The outcomes exhibited in Table 1 reveal the performing of the circuit. The voltage readings in daring sort suggest the difficulty the moment the secondary control loop is lessening the charge current to conserve input at V mp