Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
2000-12-15
2001-12-11
Toatley, Jr., Gregory J. (Department: 2838)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C320S136000, C702S063000
Reexamination Certificate
active
06329823
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This Application claims the priority of German Application No. 199 60 761.3, filed Dec. 16, 1999, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention concerns a process in accordance with a process for monitoring the residual charge and the capacity of a load-carrying battery system with a limiting voltage level and a minimum current.
Battery monitoring systems that determine the state of charge of the battery in the current-free condition of the battery are well-known. Systems of this type utilise the largely linear dependency of the open-circuit voltage on the acid density of the electrolyte. This acid density changes in proportion to the amount of charge that has already been drawn from the battery. These systems can determine the charging condition of the battery when the battery has been current-free for a number of hours and the internal diffusion processes have calmed down.
Furthermore, it is known from the dissertation on a process to estimate the internal values of starter batteries by Steffens,W. (“Verfahren zur Schätzung der Inneren GröBcn von Starterbatterien”), RWTIH Aachen 1987, how to estimate the values of battery condition from examining a model. These values of battery condition also cover the open-circuit voltage of the battery. Although this model operates in the current carrying condition of the battery, no information is available on the remaining energy content of the battery. Also, the formation of the model is extremely complex and in practice, therefore, it has not won recognition.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a process to monitor a battery, that firstly allows the battery to be monitored without enforcing rest periods and secondly and simultaneously allows the remaining energy content of the battery to be determined.
According to the invention, this task is solved by the characterising features of the independent claim. Additional advantageous embodiments are contained in the sub-claims.
According to the invention, this is achieved by carrying out at least two current-voltage measurements on the load-carrying battery. The current load of the battery selected here should be greater than 30% of the nominal capacity per hour, e.g. for a 100 Ah battery, at least 30 amperes. The initial current-voltage measurement will be measured at an initial time for an initial load condition of the battery. A second current-voltage measurement will be carried out at a second time for a second load condition of the battery. It is essential here that the load condition of the battery has changed because of the current that has been drawn. The current-voltage measurements produce an initial measuring point and a second measuring point. The two measuring points set an interpolation line and determine the point of intersection with a limiting voltage level (U
Gr
). This point of intersection is marked by a so-called limiting current (I
Gr
). The limiting voltage level is decided from the minimum voltage required by the connected consumers in order for them to operate fault-free. The limiting voltage level is therefore stipulated for the technical layout of the battery system and is known. Furthermore, fault-free operation of the connected consumers requires a minimum operating current (I
min
), which is also specified and known as a design parameter of the battery system. The difference between the determined limiting current I
Gr
and the minimum operating current I
min
is determined and recorded. This difference is a dimension for the residual charge of the battery that is still available and in accordance with the invention, is here designated as the limiting current reserve.
Primarily, the invention achieves the following advantages:
The limiting current reserve can be determined from a battery that is carrying current. This means that battery monitoring can also be carried out on systems that are operated continuously and thus do not allow open-circuit measurement of battery voltage. A typical example of this type of system in a vehicle is a taxi that is in use 24 hours a day. With a taxi of this type, conventional battery monitoring systems cannot function. The taxi driver does not receive any information on the imminent collapse of his vehicle electrical system and thus the failure of a number of relevant safety devices, such as anti-lock systems, airbags, electronic stabilisation programs, seatbelt pretensioning systems, level control systems, etc. The conventional charging current indicator lamp only gives information about the direction of current between the generator and the battery. However, with the charging current indicator lamp, it is not possible to make a diagnosis of the battery condition to anticipate the imminent collapse of the vehicle electrical system or whether there is still sufficient energy available for the systems relevant to safety. This will only become possible with the process according to the invention.
The limiting current reserve takes into consideration in a single dimension the influences relevant for battery diagnosis, such as the battery temperature, the average discharge current of the battery and the battery ageing condition.
The limiting current reserve is not affected by the diffusion processes or by other non-linearities of the battery, which in the case of small discharge currents, have a drastic effect on the battery voltage situation, and thus make it possible to obtain reliable and quantifiable information about the residual charge of the battery.
Determining, the limiting current reserve by means of the limiting current (I
Gr
) evaluates the battery capacity in the fringe range of operability of the connected consumer system. The limiting current reserve thus allows a safety estimation, that the connected consumer system will not fail even in critical load conditions. This is a great advantage, particularly with regard to the aforementioned devices in a vehicle that are relevant to safety, as their presumably perfect function can be reliably forecast with the limiting current reserve.
Furthermore, the process according to the invention allows a maximum output to be specified that can still be drawn from the battery without falling below the limiting voltage level, by adding the limiting voltage level (U
Gr
) and the limiting current (I
Gr
).
REFERENCES:
patent: 5596260 (1997-01-01), Moravec et al.
patent: 29 52 853 A1 (1981-05-01), None
Blessing Alf
Schoner Hans-Peter
Daimler-Chrysler AG
Kunitz Norman N.
Toatley , Jr. Gregory J.
Venable
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