The main function of a controller or regulator is to fully charge a battery without permitting overcharge. If a solar array is connected to lead acid batteries with no overcharge protection, battery life will be shortened. Simple controllers contain a relay that opens the charging circuit, terminating the charge at a preset voltage and, once a preset low voltage is reached, closes the circuit, allowing charging to continue. More sophisticated controllers have several stages and charging sequences to assure the battery is fully charged. The first 70 to 80 percent of battery capacity is easily replaced. It is the last 20 to 30 percent that requires more attention and therefore more complexity.

How controllers work and available options
The circuitry in a controller reads the voltage of the batteries to determine the state of charge. Desig ns and circuits vary, but most controllers read voltage to reduce the amount of power flowing into the battery as the battery nears full charge.

Features that can be included with controllers:
  • Reverse current leakage protection by disconnecting the array or using a blocking diode to prevent current loss into the modules at night
  • Low-voltage load disconnect to reduce damage to batteries by avoiding deep discharge.
  • System monitoring analog of digital meters, indicator lights and/or warning alarms.
  • Overcurrent protection with fuses and/or circuit breakers.
  • System control control of other components in the system; standby generator or auxiliary charging system, diverting array power once batteries are charged, transfer to secondary batteries.
  • Temperature compensation utilized whenever batteries are placed in a non-climate controlled space. The charging voltage is adjusted to the temperature. Recommended on most systems.

Sizing a Controller
Charge controllers are rated and sized to the systems they protect by the array current and voltage. Most common are 12, 24, and 48 volt controllers. Amperage ratings run from 1 amp to over 100.
For example, if one module in your 12 volt system produces 3.5 amps and four modules are utilized, we produce 14 amps of current at 12 volts. Because of light reflection and the edge of cloud effect, sporadically increased current levels are not uncommon. For this reason we increase the controller amperage by a minimum 25 percent bringing our minimum controller amperage to 18.7. Looking through the products available, we find a 20 amp controller. There will be no problem using a 30 amp or larger controller, aside from the additional cost. If you think you may increase the system size, a larger than needed controller may be the best idea.




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