Charge Controllers/Regulators - Why you need a controller

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 compromised.

Simple controllers contain a relay that opens the charging circuit, terminating the charge at a pre-set high voltage and, once a pre-set 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 being fully charged. The first 70% to 80% of battery capacity is easily replaced. It is the last 20% to 30% that requires more attention and therefore more complexity. Almost all newer grid intertie inverters have a built in charge controller.

How Controllers Work and Available Options

The circuitry in a controller reads the voltage of the batteries to determine the state of charge. Designs 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 include:

  • Reverse current leakage protection- by disconnecting the array or using a blocking diode to prevent current loss into the solar modules at night.
  • Low-voltage load disconnect (LVD)- to reduce damage to batteries by avoiding deep discharge.
  • System monitoring- analog or digital meters, indicator lights and/or warning alarms.
  • Overcurrent protection- with fuses and/or circuit breakers
  • Mounting options- flush mounting, wall mounting, indoor or outdoor enclosures
  • 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.
  • Load control- automatic control of secondary loads, or control of lights, water pumps or other loads with timers or switches
  • 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.
  • Central wiring- providing terminals to interconnect system wiring.

Some systems require all of these functions, others require only one or a certain combination.

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 of 25% bringing our minimum controller amperage to 18.7. Looking through the products we find a 20 amp controller, as close a match as possible. There is no problem with going to a 30 amp or larger controller, besides possible additional cost. If you think the system may increase in size, additional amperage capacity at this time should be considered.

On small systems where a 10 watt or smaller module charges 100 amp hour battery or larger, no regulator is required. Typically this module to battery ratio cannot overcharge the battery.

Will a controller be included in my powercenter or grid tied inverter?

Yes, all powercenters include a solar charge controller. In fact, if you are building a system that utilizes an inverter, we recommend looking strongly at utilizing a powercenter. Why? Simply because they are typically more reliable, save time and money.

The controller, array and battery disconnects, monitoring and central wiring can all be handled with one enclosure instead of five or more.

Some owners prefer to purchase their system component by component, and others would rather buy the carburetor with the rest of the vehicle.


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