Car Battery Monitor. Beginner’s Trial 14


Monitor your Car battery or Inverter battery with this simple circuit. It always follows the terminal voltage of the battery and gives corresponding LED indications. A 12 volt Lead-Acid battery attains 13.85 volts in full charged condition and Inverter Tubular battery 14.85 volts. So it is necessary to have an idea about the charge status of the battery. If the battery discharges below 10 volts, it needs immediate charging to prevent the deep discharge. The circuit gives three LED indications. If the terminal voltage of the battery rises above 13.5 volts, Red LED lights. If the voltage drops below 10 volts, Green LED lights. If the voltage is normal around 12 volts, both the LEDs remain off.

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What causes premature battery breakdown? Fact File 32


So many factors. Battery needs care to maintain its chemistry and its energy efficiency. The aging process starts at the moment the battery leaves the manufacturing factory. Self discharge ,sulphation, capacity loss, overcharging, dendrite growth, grid corrosion, excessive heat and water loss etc are some common reasons for the premature battery failure.

If the battery is not cycling for long period, self discharge takes place @ 4 % per week at 27 degree. For example, a 125 Ah battery shows self discharge @ 5 Amps current per week if it is not discharging through the Inverter. Sulphation is another important factor affecting battery efficiency. The lead sulphate accumulating on the plates prevents charge release/ acceptance cycles. Usually the lead sulphate crystals will be removed during water filling and charging. So it is better to charge the battery as soon as possible to prevent sulphation.

Another important reason is overcharging. The battery used in backup systems should have a charger cut off facility, otherwise the battery will get over charged due to float charging. When the battery is overcharged, the charge voltage increases above the Gassing voltage. This causes formation of excess hydrogen. The Gassing voltage of a 12 V lead acid battery is 14.3 at room temperature. The battery voltage crosses the gassing voltage level if one or more cells are damaged or weaker. The weaker cell will charge last since its resistance is lower than the good cells. So higher voltage appears across the good cells and may increase the voltage above the gassing voltage level.

By using the battery equalization method, it is easy to make the battery fully charged. All the cells in the battery will not be equally good due to aging. Some cells accept charge very fast and some in a slow rate. If this happens, the battery will not hold sufficient charge and will discharge very fast through the load. Equalization is done by giving slight overcharge to the battery even after the terminal voltage rises to maximum. Due to this overcharging, the weaker cells also get time to accept full charge. A fully charged 12 volt lead acid battery will show 13.8 V terminal voltage and a 12 V tubular battery will show 14.8 V in the fully charged state.

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Trick to Save Battery


Save your spare batteries from self discharge due to improper charge- discharge cycles. If you forget to charge the sealed lead acid battery for long period, it will not accept full charge during charging and its performance deteriorates. A solar panel can solve the problem and since it charges only during day time, over charging can be prevented .
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Battery monitor


Most of the Emergency lamps do not have low battery indicator which is essential to indicate the deep discharge of battery. So if the Emergency lamp is switched on continuously, battery will discharge deeply and causes 2 problems. 1. Ends of the fluorescent tube will turns black and fails. 2. If the battery is discharged fully, it may develop memory effect and will not accept full charge. To avoid these problems, the battery should not be allowed to discharge below its 50% efficiency. This simple add on circuit will give a visual indication when the battery enters in to the deep discharge stage.

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Battery Level Meter


With this circuit, you can assess the voltage level in Lead Acid Car battery or Inverter battery. It gives LED indications in Dot Mode display to show the level of voltage in the battery. A Lead Acid battery attains 13.8 volts and tubular battery 14.8 volts in the fully charged state. If the battery voltage level drops below 10 volts, it needs immediate charging, and if it is not attaining full charge, it cannot be used to drive the load.

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