Inverter (HF) technology
With inverter technology, the battery charging process is monitored throughout. The battery is charged with a constant current until a specific voltage is achieved. Following this, the charger switches over to constant-voltage charging. Furthermore, continuous comparison between target and actual charge voltage values mean that fluctuations in the mains voltage can also be eliminated. In chargers using inverter technology, the charge current has a very slight residual ripple, which ensures that the battery cannot heat up too much while being charged. The battery is charged gently, and over- and undercharging are avoided. This form of energy conversion, which is sometimes referred to as primary-switched technology, is more efficient and thus also results in lower energy consumption. These chargers can be recognised at a glance as they are roughly one-fifth smaller and considerably lighter.
Standard chargers operate with conventional 50 Hz transformers, and are the simplest and cheapest chargers on the market. They are usually supplied with unregulated charging characteristics (so-called W or Wa characteristics). Since the charging current is set depending on the battery voltage, and since the battery voltage increases the longer the battery has been on charge, the charge current is reduced as the charge state improves. Fluctuations in the mains voltage have a great influence on the progress of the charging curve. If the mains voltage is too low, the battery will not be fully charged. If, however, the mains voltage is too high, the result may be a very high charging voltage, which in turn can cause overcharging, gassing and damage to the battery. Not only are chargers of this type heavy, but the energy costs involved are also relatively high.
50 Hz battery chargers with a two-stage characteristic (WoWa chargers) differ from 50 Hz battery chargers with a single-stage characteristic in that they switch over during the charging process. The charging current and battery voltage initially increase rapidly. Following an interval with a high charging current, the capacity of the battery to accept charge drops, and the charging current is reduced accordingly. After a specific value has been reached, an electromagnetic switch (=contactor) comes into play and switches over to top-up charging. This phase is time-limited, and when it ends the charger automatically switches off and stops charging. This charger does not feature a separate conservation charging phase.
Since the 50 Hz charger system does not concern itself with either the age of the battery or its charge state, it has now been superseded. However, it continues to be widely used in the field of traction batteries.