Electric Car Energy Management System Based on DS2438

1. Features of DS2438
The battery monitoring chip DS2438 produced by American DALLAS company has rich functions, which can easily realize the monitoring of the operating status of the battery pack of electric cars. DS2438 can provide the following parameter information:
(1) Battery temperature value. DS2438 can measure the temperature value through the integrated temperature sensor on the chip, the temperature range of measurement is -55℃~+125℃, and the resolution is 0.03125℃.
(2) Battery voltage. DS2438 integrates a 10-bit A/D converter on-chip, which can detect the current battery voltage. The measurement range is 0-10v, and the resolution is 10mV.
(3) Battery current. DS2438 measures the current flowing through the battery by measuring the voltage on the external resistor. The voltage value on the reference resistor is sampled into the current register. The battery current is equal to the value in the current register and a compensation register is specially set to eliminate conversion errors.
(4) Tracking of remaining power. DS2438 can use the integrated current accumulator (ICA) to track the remaining power of the battery. The total current flowing through the battery is stored in the ICA, which can reflect the power of the battery.
D52438 is a single-bus working mode, data input/output is completed by a data line, and each DS2438 has a unique 64-bit serial number, which can be communicated by querying the serial number in order to achieve a single bus Connect multiple DS2438s.

2. Application of DS2438
DS2438 can be used to monitor various storage batteries. The power source for electric cars is a battery pack composed of multiple batteries in series and parallel. The performance of each battery directly affects the characteristics of the entire battery pack. Therefore, in practical applications, each battery should be tested online in real time. Each battery should be equipped with a piece of DS2438, and their data terminals can be connected to a bus. The power supply of the DS2438 can come from the battery under test. The potential of the DS2438 signal terminal DQ is for the ground of the DS2438. Due to the inconsistency of the reference ground potential of each DS2438, it is bound to cause the signal terminals of the DS2438 to the same reference point. The DQ potential is different, so it cannot be connected to the same bus, so when it is used to measure the battery pack, it needs to be improved appropriately. This design is based on DS2438 as the core to form a monitoring module. By adding isolation measures, the data line is changed from a single-wire system to a two-wire system for receiving and sending, and the data lines of all modules are respectively connected to the two lines of REC and TRA. ,As shown in Figure 1.

Electric Car Energy Management System Based on DS2438
Figure 1 Wiring diagram when DS2438 is used to measure battery pack

3. Matters needing attention in system design
(1) DS2438 communication protocol is changed to signal negation, “0” and “1” are interchanged. When the machine number, the machine receiving line REC should be high; when the host receives the signal, the host signal line TRA must be kept low, and the sending and receiving cannot be carried out at the same time.
2) During communication, the host sends signals to all modules connected to the bus, and each module needs a certain drive current, so the signal sent by the host must be amplified.
(3) In the module, the signal ground GND1 of the DS2438 should be higher than the ground GND of the battery under test, because the maximum value of the DQ effective low level is 0.5V. Properly raise the ground of the DS2438 to ensure that under various operating conditions Reliability of data transmission.