Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
1994-02-03
2001-03-27
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C320S118000, C370S455000, C370S902000
Reexamination Certificate
active
06208148
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a battery charger, and particularly to an end of charge detection technique for use in a battery charger.
BACKGROUND TO THE INVENTION
Charging characteristics for nickel cadmium (NICD) batteries are shown in curve b of FIG.
5
. The battery voltage increases slowly for 90% of the battery capacity during charging, but then starts to climb steeply after that, from point P
1
onwards. At point P
3
the voltage levels off and starts to decline from point P
3
to point P
4
. It is known to attempt to determine the end of charge point by detecting this voltage drop (−dV) at the end of charging.
Due to increasing usage of ultra-fast or fast charging rates (one hour or less than one hour charging time) in present day high end chargers, switch mode power supply technology is employed for the design of chargers due to reasons of size and efficiency. However, these designs have high switching noise.
These switching noises can take the form as shown in
FIG. 8
a
. They can be spikes or glitches S on an otherwise calm and slowly changing battery voltage level V
batt
. False detection by a conventional charger monitor using a −dv method can occur in cases like that depicted in
FIGS. 8
b
and
8
c
. In
FIG. 8
b
, a noise spike S reaches a voltage level v
1
. If one voltage measurement is made at v
1
and another at v
2
, a −dV detection will be indicated if the measurement at v
2
is lower than that at v
1
by more than the preset threshold, e.g. 50 mV. The same false detection will occur if, as in
FIG. 8
c
, the measurement at noise spike v
4
is lower than that at v
3
by more than the same threshold value (
FIG. 8
c
).
Due to the fact that amplitudes of switching noises S are generally in the range of hundreds of mV, whereas the detection threshold of −dV detection is only tens of mV, to avoid false detection due to these noise signals, extensive filtering has to be used. Very often, too much filtering causes a slow response and the result is that the battery is overcharged before the −dv point is detected and charging terminated. The avoidance of noise by filtering is also very dependent on the particular design of charger. Optimum filtering for one charger may be insufficient for another. It also increases the cost of implementation.
Another known method to avoid false detection in −dV detection techniques is to interrupt charging and to measure the battery voltage before resuming charging. This is done because during the interval when charging is stopped, switching noises are minimal and it is thus an optimum time to take a measurement of battery voltage. The drawback of this approach is that charging times are considerably longer due to the interruptions and also delays are caused due to the waiting times during voltage measurements. The waiting times are necessary for the battery voltage to settle down just after charge interruptions to ensure accurate readings.
The aim of the present invention is to enable the −dV point to be detected accurately at the end of charge when charging on an NICD battery in a noisy environment.
SUMMARY OF THE INVENTION
According to the present invention there is provided a battery charging including:
a voltage detection circuit for monitoring the voltage of a battery being charged and for providing sequentially a plurality of voltage values;
a comparator connected to compare each voltage value with the preceding voltage value thereby to determine when there is a difference exceeding a theshold value; and
a detector arranged to output an end of charge detection signal when said difference has been determined and when the last preceding voltage value has not exceeded the last but one preceding value.
Preferably, a further voltage value is generated after the voltage value at which said difference is determined, said further voltage value being compared with the last voltage value.
By taking measurements before the moment when a voltage drop is suspected and also taking measurements after that moment, it is possible to eliminate the effect of switching noises and only act on a genuine voltage drop.
The voltage detection circuit can be enabled in response to a signal from a pre-measurement circuit which identifies the time when a voltage drop is suspected. This pre-measurement circuit can take the form of a dV/dt circuit (voltage gradient measurement) or a dT/dt circuit (temperature gradient measurement) as described herein.
The present invention also provides a method of detecting a voltage drop when charging a battery, the method including monitoring the voltage of a battery being charged and providing sequentially a plurality of voltage values; comparing each voltage value with a preceding voltage value thereby to determine when there is a difference exceeding a theshold value; and producing an end of charge detection signal when said difference has been determined and when the last preceding voltage value has not exceeded the last but one preceding value.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings.
REFERENCES:
patent: 4388582 (1983-06-01), Saar
patent: 4503378 (1985-03-01), Jones
patent: 4629965 (1986-12-01), Fallon et al.
patent: 4792743 (1988-12-01), Tsujino
patent: 5180961 (1993-01-01), Tsujino
patent: 5206579 (1993-04-01), Kawate et al.
patent: 90 04 061 U (1990-09-01), None
patent: 0 147 241 A2 (1985-07-01), None
patent: 0368353 (1990-05-01), None
patent: 0522691 (1993-01-01), None
patent: 0 580 300 A1 (1994-01-01), None
patent: 63-234844 (1988-09-01), None
patent: 2-74127 (1990-03-01), None
patent: 2-133039 (1990-05-01), None
patent: 2-266835 (1990-10-01), None
patent: 4-093452 (1992-08-01), None
patent: 4-118745 (1992-10-01), None
patent: 5-49183 (1993-02-01), None
Mobers, A., “Versatile Battery-Management IC for NiCd and NiMH Charging Systems”, International Conference on Consumer Electronics Digest of Technical Papers., Jun. 2, 1992. pp. 414-415.
Goodenough, Frank, “Battery-Based Systems Demand Unique ICs”, Electronic Design, Jul. 8, 1993, No. 14, pp. 47-61.
Metjahic Safet
SGS-Thomson Microelectronics Pte Ltd
Solis Jose M.
Venglarik Daniel E.
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