Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-06-08
2001-05-08
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06229284
ABSTRACT:
The present invention concerns method for controlling an accumulator charge as well as a device for implementing this method. It concerns in particular accumulators intended for wireless applications such as watches, portable telephones, video cameras etc.
For a conventional electronic watch to operate properly, a simple low voltage battery is sufficient. The movements which are fitted to this type of watch consume very low currents of the order of several microamperes at voltages usually not exceeding 1.5volts. Low voltage batteries generally give these watches autonomy for approximately two years.
However it is currently sought to integrate in the watch additional auxiliary devices such as, for example, a transceiver device associated with an antenna allowing the watch to be used like a telephone. Such a device requires much higher currents and voltages than those required for the simple horological function. By way of example, when the radio-frequency link is in service, the electric consumption is established at values higher than 50mA for voltages which exceed 2.5volts. Confronted with such high power requirements, the batteries cannot assure a suitable power supply since they would run down very quickly, which would oblige the watch wearer to replace them frequently. In order to overcome this drawback, it has thus been decided to use rechargeable accumulators to power the auxiliary functions. For reasons of cost and compactness, the battery has been omitted and the horological function, whose power consumption is minimal, is also powered by the accumulators.
In order to charge an accumulator, various methods are known. Among these methods, the most commonly used is that known under the name of the quick charging method which consists in injecting into the accumulator, within limits fixed by the manufacturer, a constant current which is the higher the quicker one wishes the charge to be. The difficulty of such a method consists in determining when to stop charging, knowing that several minutes of overcharge reduce, by overheating, the lifetime of the accumulator, and that several tens of minutes in excess can put it out of use or destroy it.
Numerous methods exist for determining the end of the quick charge of an accumulator when it has reached its nominal charge. These methods are characterized by their reaction time after the end of charging. This reaction time has to be as short as possible in order to protect the accumulator against any overheating. These methods are also characterized by their reliability, able to be repeated and their cost.
The most conventional method uses the characteristic accumulator charge voltage curve. When the accumulator is full, and even slightly overcharged, the voltage decreases slightly after having increased continually during charging. This voltage drop is detected by an electronic control circuit which then decides to stop the charging.
This method has two drawbacks. First of all, when the voltage decreases, the accumulator is already slightly overcharged and its temperature has already started to increase. It is thus already a little late, since it is overheating which is the primary cause of accumulator ageing. This is all the more true the quicker the charging. The higher the charge current, the greater the overcharge and overheating. Secondly, certain accumulators have a less pronounced voltage drop which is thus much more difficult to detect.
A more recent method consists in measuring, not only the charge voltage, but also the temperature of the accumulator and deciding to stop the charge when the temperature increase rate exceeds a certain threshold. The temperature remains constant during almost the entire charging and begins to increase more and more strongly towards the end thereof. With this temperature measuring method, the charge is stopped when the temperature increases at a greater speed than a certain rate fixed in advance.
One drawback of this method is that it requires a temperature sensor on each accumulator, as well as one or two additional contacts at the accumulator-charger connection. This is sometimes a very high cost. A second drawback of this method is that the temperature propagates slowly from the core of the battery to its periphery and then to the sensor. In other words, when the charge is stopped, the accumulator has already had time to be overheated.
Contrary to the quick charge methods described above, so-called slow charge methods can also be used, which consist in injecting into the accumulator a current whose intensity is low compared to its capacity. For example, a constant current of 10 mA can be permanently applied to an accumulator of 100mAh without any risk of damaging it. For higher charge currents, of the order of 20mA to 30mA, it is possible to define the end of the accumulator charge as a function of the time during which the latter has been on the charger.
This latter solution has however a significant drawback. If one takes account solely of the time which has elapsed since the moment when the accumulator was put onto the charger, the fact of removing it then immediately putting the accumulator back onto the charger completely resets the charge time limit. The same problem is posed in the event of a micro-interruption in the electric power network or when the charger undergoes a shock which momentarily interrupts the electric connection between the latter and the accumulator.
The object of the present invention is to overcome the above problems and drawbacks by providing an accumulator charge control method which allows the accumulator charge to be stopped prior to the occurrence of overheating, and thus prior to overcharging, without requiring a complex and costly device.
The present invention therefore concerns a method for controlling the charge of an accumulator as a function of the time during which said accumulator has been on a charger said accumulator being intended to power an horological function and one or more auxiliary functions, this method being characterized in that it includes the steps of:
incrementing a step counting signal during the charge time during which the accumulator is on the charger;
causing the accumulator charge to stop when the counting signal has reached a previously defined maximum value corresponding to the nominal charge of said accumulator; and
decrementing the step counting signal during the discharge time during which the accumulator is not on the charger, the counting signal being decremented with a first step when only the horological function is used, and with a second step which differs from the first and which depends on the auxiliary function or functions used so that, if the counting signal reaches zero, the next charge will be made until said counting signal has again reached its maximum value, whereas if the accumulator is replaced on the charger before the counting signal has reached zero, the next charge will be made for a shorter period of time.
As a result of these features, the present invention provides a method for controlling the charge of an accumulator which allows the accumulator charge to be interrupted sufficiently early so that, whatever the circumstances, said accumulator does not have time to overheat, which significantly increases its lifetime. Further, contrary to the prior art, the present invention does not require a complex and expensive electronic device, for example to monitor the evolution of the charge voltage or to measure the accumulator temperature, which allows substantial savings to be made.
According to one advantage of the invention, not only the accumulator charge time is counted, but also the time during which the latter is not on the charger, only authorising a completely new charge of the accumulator if the counter reaches zero. Thus, if for example, a micro-interruption occurs in the power supply network, the charge limit time is not completely reset, which allows any damaging overcharge of the accumulator to be avoided.
According to another feature of the invention, whatever interruption occurs to the a
Guanter Jean-Charles
Martin Jean-Claude
Asulab S.A.
Griffin & Szipl, P.C.
Tso Edward H.
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