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Battery Charger Control Basics

Written by William C. Shumay Jr. for Arcon Equipment Inc., published in the Material Handling Wholesaler
copyright © William C. Shumay Jr.
For more articles, please visit http://www.arconequipment.com

Chargers for electric lift truck batteries range from the fairly simple to quite complex, but their purpose is the same: charge a battery of a specific size in an 8-hour shift. The 8-hour charging cycle is a universal standard, but many chargers will accommodate a larger ampere-hour capacity than their nominal rating if allowed to operate longer.

It is important to understand that a lead-acid battery is an electrochemical system, not an electrical storage fuel tank that can be filled with energy at any rate over an arbitrary time period. The 8-hour charging cycle, at minimum, is necessary to properly restore an industrial deep-cycle lead-acid cell to its original chemical balance.

The battery charging cycle starts with a high initial current (start rate) of approximately 18 amperes for each 100 ampere-hour of battery capacity rating. This rate begins to taper off as the battery reaches its gassing voltage of 2.37 volts per cell. For the last third of the charging cycle, the charger current settles into a finish rate of approximately 4 amperes per 100 ampere hour of capacity. Each phase of the charging cycle is important, and the charger controls are designed to ensure that this sequence takes place each time a battery is hooked up for a charge.

A large number of new chargers on the market come equipped with computerized auto-start controls that keep track of battery status and properly manage the charging cycle. Most chargers in service today, however, use a gappy mechanical timer, or a timer combined with an electromechanical relay, to time the charging cycle.

As a charger ages, the timer (and electromechanical relay that activates it) may wear out and become unreliable. The charger may still seem to operate properly when first turned on, but may shut off at unpredictable times or never shut off at all. This is a natural consequence of the fact that mechanical parts wear out, and the timer and relay found on many older (as well as some new) solid-state chargers happen to be the only moving parts in the system.

Fortunately, it is now possible to quickly convert an older timer/relay style charger to a computerized auto-control. Not only are there strong customer sales advantages to retrofitting a charger with a new control kit, but this is certainly the easiest way to eliminate the headache of repairing timer switches and adjusting balky electromechanical calibrated-voltage relays.

There are dozens of different charger models that lend themselves to direct conversion to auto-control. The easiest are those chargers that have an AC line contactor (solenoid breaker). If the charger’s AC current draw is very low, a line contactor may not be necessary. But, in most cases, a charger will require the installation of a line contactor if one is not present in the AC circuit.

An auto-control conversion kit consists of an encased microprocessor charger control circuit that is readily installed by connecting four wires: two to sense battery voltage and two to operate the AC line contactor. The microprocessor charger control keeps track of the battery voltage over time and matches the rate of change against the known ideal charge curve. Unacceptable deviation from this curve will trigger an abnormal shutdown and the control unit will display a fault code.

Because a computer is keeping track of charger performance, and human interference with charger adjustments is kept to a minimum, battery overcharging is virtually eliminated.

Low-cost auto-start controls simply replace the mechanical timer with an electronic timer. This does not provide the versatility and advantages of a true computerized control. Before purchasing, check to see that you are getting a microprocessor charger control, one that shuts off within minutes, rather than hours, if plugged into an already fully charged battery. Programming options such as adjustable start delay and automatic equalizing cycle are important features of such a unit.

Microprocessor Charger Control Advantages:

  • An old charger is given new life through replacement of a worn timer, mechanical relays, and outdated circuitry with a single, precise computerized control
  • Charger starts automatically after battery is plugged in
  • Charger starts automatically after battery is plugged in
  • Battery receives only as much charge as it needs
  • Periodic equalizing charges are automatically handled by the control unit
  • Battery or charger damage caused by plugging wrong voltage battery into charger is eliminated by control voltage sensing

For more information, contact Arcon Equipment Inc. (440) 232-1422.

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