Charge controller programming

Example of a programmable charge controller with an LCD screen and buttons.

The simplest of charge controllers - rely upon factory settings and do not permit any programming. A charge controller is vital to ensuring the longevity or cycle life of batteries, therefore a charge controller that cannot be programmed must be carefully selected to ensure that the factory settings are appropriate for the type, voltage, and size of energy storage that will be used with the system. Charge controllers for all but the smallest systems offer varying degrees of programming from basic settings (system voltage, battery type) to complex modifications to how the charge controller regulates charging. With charge controllers that permit programming, it is necessary to have the manuals for the charge controller, battery type, and any communications systems on hand.

Common settings

Charge controllers that allow programming will still often come with pre-programmed settings for different battery types and charging voltages, but it is recommended that all settings are examined and adjusted to the specifications of the specific system.

• Nominal voltage: The nominal voltage of the battery bank. Typically 12V, 24V or 48V.
• Energy storage capacity: The total energy storage capacity of the system. This will be in Amp-hours (Ah) for lead acid batteries.
• Charging set points: The voltages at which different charging phases start and stop vary depending on the battery type and manufacturer. Manufacturers of batteries will provide specific charging specifications in the product manual for bulk, absord, float, and equilization charging. These values will often be given as a range, it is recommended to program the charge controller to the upper end of the range for each of these values.
• Maximum charge rate: The maximum amount of charging current that a type of battery can handle varies based upon its size, type and manufacturer. Specifications for the maxmimum charge rate can be found in the manual for the battery and will typically be given as a percentage of the C-rate. Flooded lead acid (FLA) batteries and Gel batteries generally have a maximum charge rate of around 13% of the C/20 rate. Absorption glass mat (AGM) batteries are often able to accept higher charge currents, sometimes as high as 20% of their C/20 rate. It is important that the maximum charge rate is set taking into account all parallel strings in the battery bank.

Example 1: A 48V system has 2 parallel strings of batteries rated at 205Ah @ C/20 rate. The recommended charge rate for this type of battery is 12% of the C/20 rate. What is the maximum charge rate for this battery bank?

Maximum charge rate = C/20 rate × parallel strings × manufacturer maximum C/20 rate percentage

Maximum charge rate = 205Ah x 2 parallel strings x .12 (12%) = 49.2A