Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Patent
1981-09-04
1984-06-05
Tokar, Michael J.
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
324426, G01N 2746
Patent
active
044531290
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for measuring the charge state of an accumulator subjected to heavy transitory consumptions by measuring a temporary voltage drop at the terminals thereof, and a device for implementing such method.
It is current practice, when using accumulators for example electric storage batteries, to try to get to know their charge or discharge state so as to determine the time during which they may still operate. Different methods are known for determining this charge state more or less rapidly and more or less accurately : one precise method consists in determining the density of the electrolyte contained in the accumulator. This method is however difficult to implement and inconvenient in use. Generally a second method is used which consists in measuring by means of a voltmeter the voltage of the terminals of the accumulator in the absence of charge or discharge current. FIG. 1 is a diagram showing the variation of this off-load voltage at the terminals of the accumulator depending on the discharge state of this accumulator. Such voltage decreases first of all rapidly, then levels off and finally decreases rapidly at the end of discharge. It has been noticed that the ability of an accumulator to restore the maximum energy stored up depends on the discharge mode. A discharge in a short time restores a smaller amount of energy than a slow discharge. There is shown in the Figure a first curve reaching point A to illustrate a slow discharge and a second curve reaching point A' to illustrate a rapid discharge. Conventional voltmeters showing the off-load voltage are limited to giving the moment when this latter reaches point A or A' shown in the diagram, indicating that the voltage drops rapidly and that the accumulator must be recharged. A third method consists in measuring the dynamic resistance of the accumulator : this method is used when the accumulator feeds into a useful load which cannot be disconnected ; the dynamic resistance of the accumulator is assessed by connecting for a short time an additional auxiliary load, producing an additional current flow and a voltage drop at the terminals of the accumulator the measurement of which allows this resistance to be calculated. The auxiliary load is connected for a short time so as to avoid unnecessary discharge of the accumulator. Experimental studies have enabled a limit value of this resistance to be determined from which the accumulator should be recharged. These last two methods have the advantage of being relatively simple and rapid to put into use, but do not give sufficient indication when it is desired to know sufficiently long in advance that the accumulator is reaching the end of discharge. Thus, when this accumulator is used for delivering a heavy transitory consumption device at start-up such as an electric motor driving a load with great inertia and/or with high friction on start, particularly when starting up an internal combustion engine, it is necessary to know if the accumulator will be able to start up the engine at least once. Now, when the voltmeter of the second method indicates that point A or A' on the diagram has been reached, it is already too late and there is every chance that the engine cannot be started.
Similarly, the substantial variation of the dynamic resistance of the accumulator only occurs when the vicinity of point A or A' on the diagram has been reached and the method does not allow the end of discharge of the accumulator to be forecast sufficiently long in advance in the case of application thereof to starting up an electric motor. In fact, in the case of heavy transitory drains from the accumulator, the discharge is sometimes slow, sometimes rapid and passes gradually from the first curve to the second curve of FIG. 1. These phenomena are not linear, so that forecasting them is not possible by simply measuring linear effects such as the dynamic resistance. The non-linear phenomena accompanying the high value transitory discharges must on the contrary be integrated.
It will be noted in
REFERENCES:
patent: 4021718 (1977-05-01), Konrad
patent: 4321541 (1982-03-01), Nishizuka
M. B. Weinstein et al., "Guard Your Battery with PM's Charge Checker", Popular Mechanics, vol. 151, No. 5, May 1979, pp. 84, 86 and 264.
Esteve Jacques
Lissalde Francois-Claude
Cristec Industries
Plottel Roland
Tokar Michael J.
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