Charge regulator
A charge controller or a charging circuit has the task of technically implementing the charging process for charging accumulators . Some of these procedures are standardized.
Installation
The electronic assembly of the charge controller can be accommodated in the following locations:
- in a charger
- external charger for battery-operated devices
- Charger for inserting or connecting the accumulators
- in a battery-operated device (e.g. mobile phone, laptop)
- on the battery itself (e.g. external USB battery)
- on the accumulator and an energy management system for systems for self-supply with electricity and heat
Layout and function
The different types of accumulators also require different charging methods . In current concepts, this is achieved through power electronics , while older charge controllers in motor vehicles with DC alternators also worked electromechanically. They had switching coils, similar to relays, as well as switching contacts, one of which disconnected the battery when the alternator was stationary (reverse current switch) and the other controlled the excitation current of the alternator by continuously switching it on and off.
The tasks of the charge controller or a charging circuit are:
- Preventing overcharging, for example with lead-acid batteries and lithium-ion batteries, by limiting the charging voltage
- Limitation of the charging current, partly depending on the state of charge and / or the temperature
More complex charge controllers sometimes use several parameters for charge control:
- temperature
- tension
- capacity
- time
- Charging current
Complex charge controllers can be implemented with a microprocessor or a special charging IC . These charging circuits contain all the control and protection functions that are required for the respective battery type, in some cases they do not require any external power electronic components. Some of them have inputs for evaluating temperature sensors built into lithium batteries, for example. Such controllers are partially able to recognize the connected battery, to diagnose possible errors and to adjust the charging parameters accordingly. For example, after the end of the actual charging process, you can switch to a trickle charge mode to compensate for the self-discharge of the connected battery and thus enable storage without loss of charge.
In some lithium-ion batteries , electronic circuits are integrated that monitor their end-of-charge voltage and total discharge voltage. They are usually not referred to as charge controllers and should not be used as the sole control elements. They serve to protect the battery from being destroyed.
Charge controllers in motor vehicles with internal combustion engines
Motor vehicles with internal combustion engines usually have a lead-acid battery ( starter battery ) which is charged using the constant voltage method. The output voltage of the generator depends heavily on its drive speed and the connected load; therefore it is necessary to use a charge regulator to avoid voltage that is too high or too low . The controller uses the excitation voltage to control the current and thus the magnetic field strength in the excitation winding in such a way that, for example, when the load increases or the speed decreases, the excitation current increases and the output voltage is thus kept constant.
The charge controller thus has the following tasks:
- Regulation of the voltage generated by the alternator
- Protection against overload due to excessive output current (for direct current alternators)
- Protection against reverse current
Regulation of the excitation magnetic field
In generators with electromagnetic excitation, the output current depends not only on the speed and the connected load, but also directly on the current in the field winding. With this type of generator, the charge control can be implemented by influencing the excitation current. This version is the most common.
Electromechanical charge controller
The regulation is carried out by an electromagnetic generator regulator. The excitation current is influenced by constantly opening and closing a contact that feeds the excitation coil. As with a switching regulator, the excitation coil smooths the excitation current due to its inductance . If the DC generator generates a lower voltage than that of the vehicle battery due to insufficient speed, the reverse current switch disconnects the connection of the generator output to the battery through a switching contact. Sufficiently resilient semiconductor diodes to replace the reverse current switch were not yet available in the age of the direct current generator. Mechanical controllers cause interference by switching sparks, are prone to failure and react slowly, which is why electronic controllers have been installed in new vehicles since the early 1970s.
Electronic charge regulator
In three-phase alternators, the electrically generated excitation field of the alternator rotor is influenced by an attached electronic charge regulator. This forms a unit with the holder of the carbon brushes , which transmit the excitation current to the slip rings of the rotor.
The controller compares the rectified actual voltage of the generator with a stable reference voltage inside the controller and adjusts the strength of the excitation field (excitation current) by means of a more or less strong current flow ( PWM , switching regulator ) so that the actual voltage of the generator is constant regardless of load and speed remains. Only the voltage of the rotor electromagnet is regulated, the associated generator current results directly from the construction-related internal resistance of the stator coils according to Ohm's law . Thermal monitoring limits the current in the event of insufficient cooling.
Due to the material and construction, the magnetic flux density of the rotor is limited. Therefore, the level of the permissible magnetizing voltage is stored in the controller as a parameter during manufacture. The purpose is not to exceed the saturation magnetization of the rotor electromagnet, which otherwise would only lead to unnecessary heating of the electromagnet without additional power.
Regulation of the induced current
With AC or three-phase generators with permanent magnet excitation, the output voltage of the generator must be limited in order not to exceed the end-of-charge voltage of the battery. This is usually done by thyristors , which, depending on the charge controller concept, either temporarily interrupt the charging current or temporarily short-circuit the generator in order to regulate the (average) charging current to the battery.
In the former case , the thyristors are also part of the rectifier , which ensures the necessary conversion of the alternating or three-phase current at the output of the generator into direct current. This version is found more often on motorcycles.
The stator coils are connected in three phases and in the latter case lead out of the housing. The controller is external. The rectified voltage is short-circuited by the regulator when it has reached the charging voltage of the lead-acid battery. This short circuit of the excess power is partly converted into heat in the controller, but mainly in the stator coils themselves. In order to dissipate the heat, they are usually operated in an oil bath. Nevertheless, coils can fail due to overheating because the insulating varnish is destroyed. In terms of energy, this type of construction is unfavorable, as the full power is constantly generated and - if not consumed - it is burned. There are versions up to 400 watts. The "regulators" used here are - from a technical point of view - surge short-circuiters.
Charge regulators in battery-operated devices and chargers
Charge regulators in mobile devices or in chargers have very different technical levels; see also loading procedure . Accumulators are differently sensitive to treatment errors depending on the type. Accordingly, charge controllers take into account a different number of parameters (end-of-charge voltage, total discharge, max. Charging current, temperature, battery type). The technical design ranges from a current-limiting series resistor and a time limit via the measurement of the battery parameters (differential internal resistance, original voltage , temperature) during charging to the detection of the battery status / type, in particular to avoid overcharging and exceeding the charging current / temperature.
Charge controllers for this purpose are available as electronic assemblies, which often contain a special integrated circuit or even a microcontroller .
Some devices / assemblies for battery management are also able to discharge batteries in a monitored manner in order to determine their capacity or to condition them (see memory effect ).
Charge controller with energy management system for self-supply with electricity and heat
This type of charge controller combines the principle of island and feed-in systems. The main difference, however, is that the energy generated is not fed into the public network, but is made available for direct and also via accumulators for later self-supply. The integrated energy management system ensures a distribution in the own power grid, as well as the possibility of storage in thermal energy. This system is to be considered in particular from a tax point of view, as no financial resources flow. So this type is tax-exempt in Germany.
See also
Web links
literature
- Reference books
- Norbert Adolph: Car electronics: Basics and building proposals. Schulfernsehen publishing company, Cologne 1979, ISBN 3-8025-1128-X .
- Jürgen Kasedorf, Richard Koch: Service primer for vehicle electrics. 14th edition, Vogel, Würzburg 2001, ISBN 3-8023-1881-1 .
- Technical brochures
- Bosch technical briefing on generators. Robert Bosch GmbH Stuttgart, VDT-UBE 301/1 De (1.80)