Automotive Battery Chargers - Auto Parts

Automotive Battery chargers range from 1-amp-output promotional models to commercial units with amp ratings in excess of 100. For normal home auto use, a 3- to 10- amp rating is sufficient for slow charges and 60 to 100 amps for fast charges. The amp rating is the output of the charger and controls the length of time required for the battery to charge. Most car batteries are rated around 50 to 70 amp/hours. A constant amp output multiplied by the number of hours would indicate the charge in the battery.

Ten amps output for five hours would equal 50 amp hours. Most battery chargers, however, have tapered charges, meaning that the output is not constant. As the charge builds up in the battery, the battery voltage retards the output  of the charger to as much as 50 percent capacity. A 10-amp charger, then, might be putting out only 5 amps as the battery nears its full charge. Constant-output chargers are available but have limited applications.

Another element found on some chargers is the “booster charge.” This is a device that converts household alternating current to direct current, allowing the automobile engine to start directly from the outside current supplied. This eliminates having to wait for the battery to charge before the engine can be started.

Booster capacities are available in ratings as high as 300 amps, but most cars require from 90 to 110 amps of cranking power. A 100- amp booster element is usually sufficient for normal home use.

Battery Voltage

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Battery chargers specify the voltage of the battery on which they can be used. Some can be used only on 6V or 12V batteries while others can be used on both types. Manufacturers’ specifications should indicate output at specific voltages.

Automatic Chargers

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If a charge is applied to a battery after the battery is fully charged, the amperage converts to heat energy, causing the electrolyte to evaporate. Automatic chargers eliminate this problem by automatically switching off when the battery is charged and back on again if the charge decreases.

This is useful for people who own boats, electric golf carts and other items used occasionally. The charger can be attached to the battery to keep it fully charged for months at a time. Virtually all batteries will lose their charge during a long period of inactivity; an automatic charger keeps them at peak efficiency.

A quality automatic charger should be capable of keeping a battery fully charged over a long period without causing electrolyte evaporation or any noticeable increase in the electrolyte temperature.