Battery Chargers : Which One’s For You?

There are many kinds and capacities of battery chargers. However, there are three major types – One-stage, two-stage and three-stage chargers.The ordinary one-stage charger you buy from the local auto-parts store is inexpensive, but it charges slowly and cannot completely re-charge a battery to its rated capacity. There are no automatic voltage or current shifts during the charge cycle and without monitoring, overvoltage and water loss can cause premature battery failure.

Samlex does not make nor recommend one-stage chargers because they easily damage the battery by warping its plates or boiling it dry, effectively destroying it. A two or three-stage charger is recommended because both adjust current and voltage according to the battery's requirements.

The choice is between a two or three-stage charger, depending upon its use:

If there are permanent or transient loads on the battery during charging, a two-stage charger has the advantage because its circuits cannot be “fooled” into pushing a higher “absorption" voltage than required for charging.

Without loads during charging, the three-stage charger has the advantage because it provides a more complete recharge. A two-stage charger provides a constant current until the battery reaches its rated capacity and then switches to a “float” voltage. The current then reduces as necessary to maintain the battery at the float voltage. The charger can be connected to the battery indefinitely. A two-stage charger is recommended in most instances since it is the most versatile and can be permanently connected to attenuate the characteristic discharge of unused batteries. A load can be put on the battery or batteries without altering its ability to keep the battery at optimal charge.

A three-stage charger is the most complete charger. It charges the battery at a constant current until the battery voltage reaches a slightly elevated level. The battery is maintained at this voltage while the charging current diminishes to a low value, and then the battery is switched to the float voltage where it can be maintained indefinitely. However, the charger cannot differentiate between a current going to a load on the battery, or being absorbed by the battery, so it can overcharge a battery supplying current to a load. A two-stage charger is preferred for “loaded” batteries and a three-stage for idle or “unloaded” batteries during recharging. Samlex chargers which offer 3 stage charging can be switched to 2 stage if required by simply Adjusting a dip switch.

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