JP2004159379A - Charging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the charging time of a battery and lengthen its cycle life by selecting an appropriate charging current corresponding to the cooling of a battery pack with a cooling fan. <P>SOLUTION: When a battery temperature gradient is smaller than a first predetermined value in which a battery temperature decreases and which may be regarded as having a cooling effect after a predetermined time has passed since charging start, this charging device increases the charging current. When the battery temperature gradient is larger than the first predetermined value and is a second predetermined value or more in which the battery temperature increases and which may not be regarded as having the cooling effect, the charging device decreases the charging current. When the battery temperature gradient exists between the first predetermined value and the second predetermined value, in other words, a variation in the battery temperature is small, the charging current value is taken as appropriate for the battery life of the battery pack, thus preventing the charging current from being switched. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging device for charging a secondary battery such as a nickel cadmium battery or a nickel hydride battery.
[0002]
[Prior art]
When charging nickel cadmium batteries or nickel-metal hydride batteries used as power supplies for cordless tools, etc., charging with a large charging current can charge the battery in a short time, but the battery generates more heat during charging, and the cycle life of the battery Therefore, a charging device that charges over a long time with a small charging current so as to suppress heat generation of a battery has been proposed.
[0003]
On the other hand, there has also been proposed a charging device that performs charging while cooling a battery pack by a cooling fan provided in the charging device, suppresses heat generation of the battery during charging, and charges the battery pack with a large charging current in a short time.
[0004]
The charging methods of the above two charging devices differ depending on whether or not the battery pack can cope with forced cooling, that is, whether or not the battery pack has a structure such as an air hole for blowing air from a cooling fan.
[0005]
In consideration of the fact that the charging method is different between the cooling-capable battery and the non-cooling-compatible battery in this way, by determining whether the battery temperature gradient at the start of charging is equal to or greater than a predetermined value, the charging device Judgment of the presence or absence of the cooling effect by the air blow to the battery pack by the installed cooling fan, and according to the result, increase the average charging current when there is a cooling effect and decrease the average charging current when there is no cooling effect. A charging method for charging has been proposed (for example, see Patent Document 1).
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-31440 (Claim 1)
[0007]
[Problems to be solved by the invention]
However, in such a charging device, an alternative charging control of selecting a current depending on the presence or absence of a cooling effect is performed, and for example, an intermediate between a case where it is determined that there is a cooling effect and a case where it is determined that it is not. It is difficult to say that charging control that makes the most of the degree of cooling can be performed with respect to the degree of cooling.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned disadvantages of the prior art and to select an appropriate charging current depending on the degree of cooling of a battery by a cooling fan, thereby shortening the charging time and extending the cycle life of the battery.
[0009]
[Means for Solving the Problems]
The object is to provide a control means for controlling a charging current, a cooling fan for cooling a battery pack, a battery temperature detecting means for detecting a battery temperature, and a battery temperature storage for storing a battery temperature based on an output of the battery temperature detecting means. Means, and battery temperature gradient calculating means for calculating a battery temperature gradient based on the outputs of the battery temperature detecting means and the battery temperature storing means. If the cooling effect is smaller than the first predetermined value, the charging current is increased, and the battery temperature rises and is equal to or greater than the second predetermined value larger than the first predetermined value, which is not considered to have the cooling effect. Reduces the charging current, and when it is between the first predetermined value and the second predetermined value, that is, when the change in the battery temperature is small, it is determined that the current value is appropriate for the battery life of the battery pack to be charged. , And technical features that no switching the charging current.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a circuit diagram showing one embodiment of the present invention. 1 is an AC power supply, 2 is a battery pack, and is equipped with a battery pack 2a in which a plurality of battery cells are connected in series, and a temperature-sensitive element 2b made of, for example, a thermistor or the like that detects or detects a battery temperature in contact with or close to the battery pack 2a. Have been. Reference numeral 3 denotes current detecting means for detecting a charging current flowing through the battery pack 2, 4 denotes a charging control signal transmitting means for transmitting a signal for controlling start and stop of charging, and 5 denotes charging for returning a signal of the charging current to the PWM control IC 23. It is a current signal transmission means. The charging control transmission signal means 4 and the charging current signal transmission means 5 comprise a photocoupler or the like. Reference numeral 6 denotes a cooling fan for cooling the battery pack 2, and reference numeral 7 denotes driving means for driving the cooling fan 6. The driving means 6 includes transistors 7a, resistors 7b, and 7c. Control the drive. Reference numeral 10 denotes a rectifying / smoothing circuit including a full-wave rectifying circuit 11 and a smoothing capacitor 12, and reference numeral 20 denotes a switching circuit including a high-frequency transformer 21, a MOSFET 22, and a PWM control IC 23. The PWM control IC 23 is a switching power supply IC that adjusts the output voltage of the rectifying and smoothing circuit 30 by changing the drive pulse width of the MOSFET 22. Reference numeral 30 denotes a rectifying / smoothing circuit including diodes 31 and 32, a choke coil 33, and a smoothing capacitor 34. Reference numeral 40 denotes a battery voltage detecting unit including resistors 41 and 42, which divides the terminal voltage of the battery pack 2. Reference numeral 50 denotes a microcomputer including an arithmetic unit (CPU) 51, a ROM 52, a RAM 53, a timer 54, an A / D converter 55, output ports 56a and 56b, and a reset input port 57. The CPU 51 calculates a battery temperature gradient from the latest battery temperature and the battery temperature sampled before the predetermined sampling time stored in the RAM 53. Reference numeral 60 denotes a charging current control unit including operational amplifiers 61 and 62 and resistors 63 to 66. Reference numeral 70 denotes a constant voltage including a power transformer 71, a full-wave rectifier circuit 72, three-terminal regulators 73 and 74, smoothing capacitors 75 to 77, and a reset IC 78. The power supply serves as a power supply for the cooling fan 6, the microcomputer 50, the charging current control means 60, and the like. The reset IC 78 outputs a reset signal to a reset input port 57 to bring the microcomputer 50 into an initial state. Reference numeral 80 denotes charging current setting means for setting a charging current, which changes a voltage value applied to the inverting input terminal of the operational amplifier 62 in accordance with a signal from the output port 56a. Reference numeral 90 denotes a battery temperature detecting means including resistors 91 and 92. The microcomputer 90 converts the voltage divided by the resistor 91 connected to a constant voltage source of 5V, the resistor 92 and the temperature sensing element 2b in the battery pack 2 into the microcomputer. The A / D converter 50 is configured to detect the battery temperature and control charging.
[0011]
When the power is turned on, the microcomputer 50 initially sets the output ports 56a and 56b and enters a connection standby state of the battery pack 2 (step 201). When the battery pack 2 is connected, the microcomputer 50 determines the battery connection based on a signal from the battery voltage detecting means 40. Next, the cooling fan 6 is operated from the output port 56b via the drive means 7 (step 202), and a charge start signal is transmitted from the output port 56a to the PWM control IC 23 via the charge control signal transmission means 4 and the output port 56a. The charging current setting reference voltage value Vi0 is applied to the operational amplifier 62 via the charging current setting means 80, and charging is started with the charging current I0 (step 203). The charging current flowing to the battery pack 2 is detected by the current detecting means 3 simultaneously with the start of charging, and the difference between the voltage corresponding to this charging current and the charging current setting reference value Vi0 is transmitted from the charging current control means 60 via the signal transmission means 5. To the PWM control IC 23. That is, when the charging current is large, a pulse with a narrowed pulse width is supplied to the high frequency transformer 21 when the pulse width is widened, and the pulse is widened to the high frequency transformer 21 to be smoothed to a direct current by the rectifying and smoothing circuit 30 to keep the charging current constant. That is, the charging current is controlled to the predetermined current value I0 via the current detecting means 3, the charging current control means 60, the signal transmitting means 5, the switching circuit 20, and the rectifying / smoothing circuit 30.
[0012]
Next, the battery temperatures Ti-36, Ti-35,..., Ti-01 up to 36 samples before the storage data in the RAM 53 and the cooling effect determination end flag are initially reset (step 204), and the battery temperature sampling timer is started. (Step 205). When the sampling timer time has exceeded Δt (step 206), the sampling timer is started again (step 207). In the present embodiment, Δt is 5 seconds.
[0013]
Next, the voltage from the temperature sensing element 2a is divided by the resistors 91 and 92 of the battery temperature detecting means 90, and the divided voltage value is A / D-converted by the A / D converter 55 and taken in as the battery temperature Tin (step 208). . Then, the CPU 51 calculates dT / dt (in) = Tin-Ti-36 as the latest battery temperature gradient from the difference between Tin and the data Ti-36 before sampling 36 (step 209). It is determined whether or not it is (step 210). If Ti-36 is not ∞ in step 210, a predetermined time (in this case, time for sampling the battery temperature for 36 samplings) has elapsed, so it is determined whether the cooling determination end flag is 1 or not. Is performed (step 211). If T-36 is ∞ in step 210, the predetermined time (in this case, the time required to sample the battery temperature for 36 samplings, ie, 3 minutes) has not elapsed, and in step 217, the detection of full charge is performed. I do. If the cooling determination end flag is not 1 in step 211, it is determined whether or not the current battery temperature gradient dT / dt (in) is less than a predetermined value P (step 212). If the cooling determination end flag is 1 in step 211, the switching of the charging current based on the determination of the cooling effect has been completed, and therefore, in step 217, full charge is detected. In step 212, when the current battery temperature gradient dT / dt (in) is less than the predetermined value P, it is determined that there is a cooling effect, and the charging current I0 at the start of charging is set to the charging current I1 (I1> I0). Increase it (step 213). In step 212, if the current battery temperature gradient dT / dt (in) is equal to or larger than the predetermined value P, it is determined whether the current battery temperature gradient dT / dt (in) is larger than a predetermined value Q (> P). A determination is made (step 214). In step 214, if the current battery temperature gradient dT / dt (in) is larger than the predetermined value Q, it is determined that there is no cooling effect, and the charging current I0 at the start of charging is reduced to the charging current I2 (I0> I2). (Step 215). In step 214, when the current battery temperature gradient dT / dt (in) is equal to or less than the predetermined value Q, it is determined that the change in the battery temperature is small, the charging current value is appropriate for the battery life of the battery pack 2, and the charging current is determined. Does not switch.
[0014]
Next, when the switching of the charging current due to the battery temperature gradient ends, the cooling determination end flag is set to 1 (step 216). Thereafter, full charge is detected (step 217). As is well known, there are various detection methods for determining the full charge in step 217. For example, based on the output of the battery voltage detecting means 40, the charging is controlled by detecting that a predetermined amount has dropped from the peak voltage at the end of charging. The purpose of ΔV detection and to stop overcharging before the battery voltage reaches a peak is to reduce overcharge and improve the cycle life of the battery. And a second-order differential detection method for controlling charging by detecting the battery temperature, and controlling the charging by detecting that the temperature rise value of the battery from the start of charging becomes equal to or more than a predetermined temperature rise value based on the output of the battery temperature detecting means 90. The ΔT detection method described in Japanese Patent Application Laid-Open Nos. Sho 62-193518, Hei 2-24639, and Hei 3-34638 discloses a battery temperature rise rate (temperature gradient) per predetermined time during charging. It may be performed using one or a plurality of full charge detection methods such as a dT / dt detection method of controlling charging by detecting that the charge becomes equal to or more than a predetermined value.
[0015]
If the battery pack 2 is fully charged in step 217, the microcomputer 50 transmits a charge stop signal to the PWM control IC 23 from the output port 56b via the charge control signal transmitting means 4, and stops charging (step 219). Next, it is determined that the battery pack 2 is taken out (step 220). When the removal of the battery pack 2 is determined, the cooling fan 6 is stopped from the output port 56b via the driving means 7 (Step 221), and the process returns to Step 201 to be in a standby state for the next charging.
[0016]
If it is determined in step 217 that the battery pack 2 is not fully charged, the battery temperatures Ti-36, Ti-35,... → Ti-36, Ti-34 → Ti-35,..., Tin → Ti-01, transfer the respective storage data to the storage area one sample before (step 218), and perform the processing from step 206 again. .
[0017]
In the above-described embodiment, the predetermined time until the cooling effect is determined is the time for the microcomputer 50 to sample the battery temperature for 36 samplings. However, the present invention is not limited to this. For example, the battery may be three minutes after the start of charging. The cooling effect may be determined from the temperature gradient.
[0018]
【The invention's effect】
As described above, according to the present invention, it is possible to select an appropriate charging current depending on the degree of cooling of the battery by the cooling fan, thereby shortening the charging time and extending the cycle life of the battery.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the charging device of the present invention.
FIG. 2 is an example of a flowchart for explaining the operation of the charging device of the present invention.
Reference numeral 2 denotes a battery pack, 2a denotes a battery pack, 6 denotes a cooling fan, 50 denotes a microcomputer which is a control means having functions of an arithmetic means 51, a storage means 53, an A / D converter 55 and the like, and 90 denotes a battery temperature detecting means.

Claims (1)

Control means for controlling the charging current; a cooling fan for cooling the battery pack; battery temperature detecting means for detecting the battery temperature; battery temperature storing means for storing the battery temperature detected by the battery temperature detecting means; A battery temperature gradient calculating means for calculating a battery temperature gradient based on the output of the detecting means and the battery temperature storing means,
If the battery temperature gradient after a lapse of a predetermined time from the start of charging is smaller than a first predetermined value that can be regarded as having a cooling effect when the battery temperature decreases, the charging current is increased, and when the battery temperature increases and a cooling effect is obtained. When the charge current is smaller than the second predetermined value that is larger than the first predetermined value that cannot be considered, the charging current is reduced, and when it is between the first predetermined value and the second predetermined value, that is, when the change in the battery temperature is small, A charging device characterized in that the charging current is not switched.

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