Basic Classification Of Electric Vehicle Chargers

Negative Pulse Chargers
Lead-acid batteries have a history of over 100 years. Initially, the world generally followed old viewpoints and operating procedures: a charge/discharge rate of 0.1C (C is the battery capacity) resulted in a longer lifespan. In 1967, American Mr. Max published his research results to the world to solve the problem of fast charging, using a pulse current with a rate greater than 1C for charging, and discharging the battery during charging intervals. Discharging helps eliminate polarization, lower electrolyte temperature, and improve the ability of the plates to accept charge.

Around 1969, some Chinese scientists successfully developed various brands of fast chargers based on Mr. Max's three laws. The charging cycle is: high-current pulse charging → disconnecting the charging path → briefly discharging the battery → stopping discharging → connecting the charging path → high-current pulse charging…

Around 2000, this principle was applied to electric vehicle chargers. During charging, the charging path is not disconnected; a small resistor is used to short-circuit the battery momentarily to discharge it. Because the charging path is not disconnected during the short circuit, an inductor is connected in series in the charging path. A short circuit typically lasts 3-5 milliseconds (1 second = 1000 milliseconds) within 1 second. Because the current in the inductor cannot jump, the short circuit time is brief, protecting the charger's power conversion section. If the charging current is called positive, then discharging is naturally negative, leading to the term "negative pulse charger" in the electric vehicle industry, which is claimed to extend battery life, etc.

Three-stage chargers are commonly used in electric vehicles. The first stage is called the constant current stage, the second the constant voltage stage, and the third the trickle charge stage. From an electronic perspective regarding the battery: the first stage is more accurately described as the charging current limiting stage, the second as the high constant voltage stage, and the third as the low constant voltage stage. When transitioning between the second and third stages, the indicator light on the panel changes accordingly. Most chargers show a red light for the first and second stages and a green light for the third. The transition between the second and third stages is determined by the charging current; a current greater than a certain threshold enters the first or second stage, and a current less than a certain threshold enters the third stage. This current is called the transition current or inflection current.

Early chargers, including those for brand-name vehicles, while also displaying indicator lights, were actually constant voltage, current-limiting chargers, not three-stage chargers. These typically had a stable voltage value of around 44.2V, which was adequate for the high-density sulfuric acid batteries of the time.