Determining State of charge of a 12 Volt Battery

Nov 23
2009
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If batteries have been receiving a charge current within the previous few hours, the open-circuit voltage may read misleadingly high. If the open-circuit voltage reads much lower than the values given in the table corresponding to the measured specific gravities, then the battery will almost certainly be suffering an internal failure. Odd cells which show specific gravity readings .050 lower than other cells are probably internally short-circuited. Such batteries should be replaced.

Batteries which are at less than 75% state-of-charge need recharging before proceeding with any further tests. Observe that the battery does accept a charging current, even though it may be small in amperes, when the charger is switched on.

If the state-of-charge is 75% or higher, the battery should be given a high-rate load test. Typically, the high-rate load tester will discharge a battery through an adjustable carbon-pile resistance and indicate the terminal voltage as the discharge proceeds. After 15 seconds the battery voltage will not drop below a specified value if the battery is in good condition and if the current is set at about 50% of the Cold Cranking Amps (CCA). The minimum acceptable voltage reading will vary as battery temperature decreases. Read and follow the manufactures instructions for the tester.

Batteries which have a low but uniform specific gravities in each cell and which clearly require an extended recharge may have become deeply discharged through accidentally leaving a car door open overnight. It may also be the result of undercharging caused by regular driving in heavy traffic patterns or by a fault in the vehicle charging system. This may be nothing more than a slack alternator/generator drive belt, but system should be checked out before the battery is returned to service.

Batteries which have suffered as a result of considerable overcharging may show extremely low electrolyte levels, black deposits on the underside of the vent plugs or black “tide-marks” on the inside walls of the container from about one inch below the cover. If these signs are present, the voltage regulator/generator setting must be checked and reset according to the manufacturer’s instructions before a battery is returned to service, modern car batteries in which electrolyte levels have to be adjusted frequently are clearly receiving too much charging current.

Below is a batteries state of charge when hooking a volt-meter to the battery.

  • 12.75 & Above      100% Charged
  • 12.60 to 12.74      85 to 100% charged
  • 12.40 to 12.59      75 to 85% Charged
  • 12.20 to12.39        50 to75% Charged
  • 12.00 to12.19        25 to 50% Charged
  • 12.00 & Below       Fully Discharged

Over Charged Battery

Over Charged Battery

Helpful Resource: Exide Technologies

Superior Battery Manufacturing Company Inc.

Written by Kip in: Battery Condition | Tags: , , , ,

Battery Charging Techniques(Battery Charging)

Nov 20
2009
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Battery Charger

Charging Your Battery

The room or compartment in which the battery is being charged should be well ventilated. Do not put a battery on charge unless you are wearing safety goggles and a face shield. It must be assumed that explosive mixtures of hydrogen gas are present within the battery cells at all times. Even a battery standing idle generates small quantities of hydrogen due to the self-discharge action. This gas collects in the cells and can be exploded by a torch, match flame, lighted cigarette, sparks from loose connections or metal tools making contact between the terminals and the ungrounded terminal and adjacent metal parts which are grounded.

Since vent cap designs having flame barrier features are not easily distinguished from other style vent caps, it is recommended that vent caps be left on the battery during charging. As a further precaution, place a wet cloth over the battery vent caps. sense flame arresters are used in most modern vent cap designs to reduce the possibility of the battery being exploded by an external spark, this safety feature could be bypassed by removal of the vent caps. Whether such vent caps are present or not, always shield eyes when working around the battery and follow the precautions covered here.

Do not charge a battery unless you are thoroughly familiar with the step-by-step procedure to use. Follow the manufacturer’s instructions on the charger. If the instructions are no longer legible and you do not have the literature containing the instructions, obtain them from the manufacturer of the charger. Never use a charger without instructions.

Turn the charge rate switch and timer to the “OFF” position before connecting the leads to the battery. Next, connect the charger leads to the battery terminals, red positive(+) lead to positive terminal and black negative (-) lead to negative terminal. If the battery is in the car, connect the negative lead to the engine block if the car has a negative ground(negative battery terminal is connected to the ground). Connect the positive lead to ground if the car has a “positive ground”(now rarely occurs). “Rock” the charger lead clamps to make certain a good connection has been made. Set the electric timer to the desired charging time. Now, turn on the charger and slowly increase the charging rate until the desired ampere value is reached. Do not charge in the red zone. If smoke or dense vapor comes from the battery, shut off the charger and reject the battery. If violent gassing or spewing of electrolyte occurs, reduce or temporarily halt charging.

Never touch the charger leads when the charger is “ON”. This could break a connection at the battery terminal, creating a spark which could ignite the explosive gases in the battery. Never break a “LIVE” circuit at the battery terminals for the same reason. Always turn the charger “OFF” before removing a charger lead from the battery.

When charging or testing a side terminal battery out of a vehicle, always use the side terminal charging and testing posts which have been designed for this purpose.

Written by Kip in: Charging Your Batteries | Tags: , , , , , ,