Methods for charging batteries

Abstract

Method for charging batteries, in particular traction batteries in industrial trucks, wherein - before a charging process, the battery's degree of discharge is determined and compared with a predetermined minimum degree of discharge, where the degree of discharge corresponds to the amount of charge by which the battery was discharged, - where the charging process is initiated when the current discharge level is greater than the minimum discharge level, and no charging process takes place when the battery has discharged less than the minimum discharge level or not at all, - where the value of the minimum discharge level depends on the frequency of battery use, with a more frequently used battery having a lower minimum discharge level than a less frequently used battery.

Description

[0001] The present invention relates to a method for charging batteries, in particular for charging traction batteries in industrial trucks.

[0002] The lifespan of rechargeable batteries is limited even when not in use. Battery life is typically expressed in charge cycles. A cycle, in this context, refers to the charging process followed by the discharge process. The battery's lifespan and the number of usable charge cycles depend on a variety of parameters, including its design and usage.

[0003] When using traction batteries in industrial trucks, it is common practice to connect all traction batteries for a fleet of vehicles to chargers at the end of each shift. This is done regardless of whether and how heavily the vehicle was used during the shift, the battery's charge capacity, or any other factors.

[0004] From DE 10 2004 041 722 A1 a method for charging batteries has become known which detects the state of charge of the battery and in which charging starts automatically when a discharged battery is connected.

[0005] German patent application DE 10 2009 035 472 A1 discloses a method for reading the state of charge of a battery in a disconnected state. This makes it possible to monitor the state of charge of a battery during its journey from manufacturing to installation and to connect the battery if deep discharge is imminent.

[0006] US Patent 8,497,686 B2 discloses a method and a device for assessing the condition and residual value of rechargeable batteries. By applying defined charge and discharge patterns, the usable charge-discharge-able range (CRV) is determined and compared with a required charge-discharge-able range (RCRV), which indicates the minimum capacity necessary to reliably fulfill a specific usage scenario (motive). Based on this, the remaining service life, residual value, leasing fees, and reuse potential of a battery can be objectively determined, thereby supporting the establishment of a secondary market for used batteries.

[0007] German patent DE 102007 031 568 A1 discloses a charging device for accumulators with several charging modes, including a storage charging mode in which the battery is brought to a partial charge state suitable for long-term storage. This is intended to reduce aging during prolonged storage, particularly for lithium-ion batteries.

[0008] The invention is based on the objective of providing a method for charging batteries, in particular traction batteries for industrial trucks, which increases the number of usable charging cycles for the battery over its lifetime.

[0009] According to the invention, the problem is solved by a method with the features of claim 1. Further advantageous embodiments are contained in the dependent claims.

[0010] In the inventive method for charging batteries, particularly traction batteries for industrial trucks, the battery's state of charge is determined before a charging process and compared with a predetermined minimum state of charge. The charging process is initiated when the current state of discharge is greater than the minimum state of discharge, i.e., when the current state of discharge is below the minimum state of discharge. Checking the current state of charge ensures that the battery has been discharged by at least a predetermined amount of charge before it is recharged. If the battery has been discharged less than the minimum state of discharge or not at all, no charging process takes place. This ensures that the battery always undergoes a minimum charging cycle, as defined by the minimum state of discharge.This minimum cycle increases the battery's lifespan and, especially in the case of batteries that are only slightly discharged, prevents premature recharging from reducing the battery's capacity and thus the total number of usable charging cycles.

[0011] In a preferred embodiment, the minimum discharge level is stored in a battery controller and read from the battery controller by a charger. Storing the minimum discharge level in the battery controller allows it to be configured individually for different battery types and / or depending on other factors, even battery-specific factors.

[0012] According to the invention, the value for the minimum discharge level depends on the frequency of battery use, with a lower minimum discharge level being provided for frequently used batteries. This approach to usage-dependent parameterization of the minimum discharge level is based on the understanding that frequently used batteries are at lower risk of being prematurely recharged. The low minimum discharge level allows such frequently used batteries to be recharged for the next use even if they were not discharged particularly deeply on one occasion.

[0013] In a further preferred embodiment, a discharge process is additionally provided for the batteries. This forces a cycle of the battery if the current state of discharge exceeds the minimum state of discharge at least once or several times. In this case, the discharge process ensures that a sufficiently large charge cycle with sufficient charge transfer takes place. This discharge process also takes into account the fact that even unused batteries have a limited lifespan.

[0014] In a preferred embodiment, the current state of discharge of the battery is measured before a charging process. This measurement can be performed in the charger itself, or a value for the current state of discharge measured by the battery controller can be used.

[0015] A preferred embodiment of the method according to the invention is described below using an example. In this embodiment, the method is carried out by a controller in an external charger for a traction battery of a forklift truck. In a first step, a battery controller or the charger determines the battery's degree of discharge. Alternatively, measuring devices can be used, which are, for example, connected to the charger. If the measuring device detects that the degree of discharge is above a parameterized minimum degree of discharge, i.e., that the battery has not been sufficiently discharged, then no charging process takes place, and a discharge process is initiated, for example, in a manner known per se. If, on the other hand, the measured degree of discharge is below the parameterized minimum degree of discharge, then the charging process is carried out.

[0016] Particularly when using traction batteries for industrial trucks, it is common practice to connect the traction battery to the charger at the end of each shift without further inspection and regardless of its use during the shift. In the method according to the invention, only those batteries from which sufficient charge has been drawn are recharged. Preferably, the minimum discharge level is defined as 30% to 50%. This means that the battery must be discharged by at least 30% or at least 50%, respectively, to be recharged by the charger.

[0017] If the discharger detects that a battery has not been charged once or several times because it was not used sufficiently for a charging cycle, the discharger can initiate a discharge process. This discharge process continues until the battery reaches a discharge level below its minimum discharge level, meaning the battery will continue to discharge until it reaches a minimum discharge level that prevents recharging. Once the discharge process is complete, the battery can be recharged by the charger.

Claims

[1] Method for charging batteries, in particular traction batteries in industrial trucks, wherein - before a charging process, the battery's degree of discharge is determined and compared with a predetermined minimum degree of discharge, where the degree of discharge corresponds to the amount of charge by which the battery was discharged, - where the charging process is initiated when the current discharge level is greater than the minimum discharge level, and no charging process takes place when the battery has discharged less than the minimum discharge level or not at all, - where the value of the minimum discharge level depends on the frequency of battery use, with a more frequently used battery having a lower minimum discharge level than a less frequently used battery. [2] Method according to claim 1, characterized by that the minimum discharge level is stored in a battery control unit and read out by a charger. [3] Method according to claim 1 or 2, characterized by , that if the current value of the discharge level is at least one or more times above the minimum discharge level, a discharge process is initiated up to a predetermined discharge level. [4] Method according to any one of claims 1 to 3, characterized by that the current discharge level of the battery is measured by a battery controller.