Device Ascertaining the Time Required to Charge a Battery and Timing the Charge

1. Field of the Invention

Relates to a timing device which indicates the charged condition of a battery.

2. Brief Description of the Prior Art

Presently known battery chargers read open circuit voltage and the percent of charge in a battery.

Known also are battery chargers having meters which provide a reading requiring reference to a chart or the use of an equation to determine the time required to charge a battery.

In U.S. Pat. No. 3,118,137 to Long, a disclosure is made to indicate when the terminal voltage of a battery falls below a predetermined value as a warning indicator.

In U.S. Pat. No. 2,991,413 to Taylor, a battery voltage indicator is disclosed to show the general level of the battery charge, such as "high", "medium" and "low".

In U.S. Pat. No. 3,383,580 to Wallace, Jr., a device is disclosed indicating when a drop in battery potential is below a useful level.

In U.S. Pat. No. 2,654,865 to Klug, a termally actuated voltage indicator shows the relative charge of a storage battery.

It is desired to provide a more exact determination of the charge condition of a lead acid storage battery.

It is the main object of this invention to provide an exact determination of the time interval required to charge a battery, such as an automobile battery, and to automatically control the timing of the charge.

It is a further object of the invention herein to provide a battery charger which measures the open circuit voltage of a battery for conversion into the interval of time that would be required to fully charge the battery and further automatically time the interval required to charge the battery.

These and other objects and advantages of the invention will be set forth in the following description made in connection with the accompanying drawings in which like reference characters refer to similar parts throughout the several views.

FIG. 1 is a view in elevation showing the face of the battery charger herein;

FIG. 2 is an enlarged view in elevation of a meter of said battery charger; and

FIG. 3 is a schematic diagram relating particularly to the charging meter.

Referring to FIG. 1, a 10 amp/12 volt battery charger 10 is shown comprising a housing 12 having a front wall 14 upon which are shown a switch 15 having "Off", "Read" and "Charge" positions and also thereon is a conventional timer 17. Further included on said front wall is a standard commercial milliamp meter 19 having a dial 20 thereon with a percentage scale 21 showing the percent of charge in the battery indicated by a pointer 22. In addition to said percent figures on said dial and corresponding therewith are the hour readings 23 giving the time interval required to charge the battery in hours according to the percent of charge figure. Said scales here shown are for 100 AH, 90 AH and 80 AH batteries, AH indicating ampere hours. Thus the pointer 22 will indicate the percentage of charge condition of a battery and the corresponding time required to fully charge the battery which will be the hour time on the appropriate battery scale most closely related to the indication of the pointer. Reference is had to a lead acid storage battery.

In connection with said battery charger, for a hook up with a battery, are conventional cables 26 having battery clamps 27.

In connection with said charger is the schematic wiring diagram of FIG. 3 by means of which the charge condition of a battery is ascertained.

The circuit of FIG. 3 in the present embodiment consists of a 200 ohm potentiometer R1, a 150 ohm resistor R2, a IN4007 diode D1 a 1N5232 zener diode D3 and a 1N751 zener diode D2. The circuit connects to said meter 19, a 35 ohm milliamp meter. The meter deflection is a linear function of the amount of current which passes through it. Said meter 19, in the present embodiment, is calibrated to have zero milliamps cause no scale deflection and to have twenty-five milliamps cause a full scale deflection. The diode D1 protects the circuit and meter against a reverse or incorrect connection of a battery clamp. It also provides a 0.6 voltage drop thereacross. The zener diodes D2 and D3 block the current flow through the circuit until their breakover voltage is reached. The diode D3 requires 5.6 volts across it before it conducts. The diode D2 requires 5.1 across it before it conducts. It takes a voltage greater than 11.3 (5.6+5.1+0.6) before current will flow in the circuit. The potentiometer adjusts the amount of current flowing through the circuit. It is used to calibrate the circuit in designing the same. If the battery were fully charged its output voltage would be 12.72. This has reference to a 100 AH battery. With this voltage across the circuit, the three diodes would conduct dropping 11.3 volts. This leaves 1.42 volts across the potentiometer and the meter. L With the potentiometer adjusted to 21.8 ohms, for purposes herein, 25 milliamps are flowing through the meter causing a full scale deflection of the meter. This is indicated on the meter as a fully charged condition.

The formula which relates open circuit voltage to current flowing through the meter is ##EQU1##

The range of time for charging a battery is from zero to 12.5 hours for a 100 AH battery. This is obtained from the formula: ##EQU2##

Both equations are linear functions so that they can be represented using a linear circuit.

In view of the described circuitry, to carry out the operation, the switch 19 is set on its "Read" position. The cable clamps 27 are attached to the battery terminals. The meter 19 responsive to the open circuit voltage of the battery provides the reading of the hours of time required to charge the battery. The timer 17 is then set for the number of hours required for charging the battery. The switch 15 position is changed from "Read" to "Charge". At the expiration of the time set for charging the battery, the timer shuts off the charging circuit.

The relationship between open circuit voltage and percent of charge in the battery and the relationship between the percent of charge figure and hours required to charge the battery are linear. Hence it is possible to use a linear circuit to indicate the hours required to charge a battery as a function of open circuit voltage. Any non-linearity can be corrected by adjusting the meter artwork.

As above described, a battery is readily charged by hooking up the battery charger cable clamps to the battery terminal, positioning the switch, reading on the meter dial the time required to charge the battery, setting the timer for the required time to charge after setting the switch to the "Charge" position and then you may leave. The charging will be terminated by the timer at the time set.

As above described, a situation was indicated wherein the battery was fully charged. Now if the battery is not fully charged, there will be a voltage differential across the test circuit between zero and 1.42 as the charger is presently calibrated and the zero voltage indication will require a full maximum charge period.

If the open circuit voltage, in the present embodiment, is less than 11.3 volts, the diodes will not conduct and the indicator 22 will make no indication. This means that the battery requires to be charged for the maximum time on the appropriate scale and the times will be set accordingly.

The significant contribution of the meter 19 and the timer 17 is that an inexperienced person can safely charge an automotive battery with no risk of overcharging and with the knowledge that when charged, the battery will be fully charged. It is seen that the charge condition of the battery may be tested immediately.

The circuit of FIG. 3 is included on a circuit board positioned within the housing 12 of a conventional battery charger equipped with a timer.

The timer in a conventional manner is placed in circuit with the "Charge" position top of the switch 15 and the output lines 35 and 37 of the circuit are in circuit with the positive and negative battery charger cable clamps. This wiring is all well known in the art and deemed not to be required to be shown.

It will of course be understood that various changes may be made in form, details, arrangement and proportions of the product without departing from the scope of the invention which, generally stated, consists in a product capable of carrying out the objects above set forth, in the parts and combination of parts disclosed and defined in the appended claims.