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Charge Controllers

Photovoltaic charge controllers are devices used to protect batteries from damage due to overcharging. They limit the voltage and current delivered to a battery. Some have additional features such as a low voltage disconnect to prevent your batteries from being over discharged.

Choosing a Charge Controller
When choosing a charge controller for your system keep in mind that you may want to expand your charging capability. A larger controller may be a wise investment.

Wire Size
Wires from a DC charging source, such as a PV array, can be large so ensure that the wire connections on the controller can handle the wires you plan to use. Small PV systems may require #12 - #8 AWG wire while larger systems can require #6 AWG or even #4 AWG wire.

Electrical Connection
Poor connections are often made when the controller has its own wires that must be connected using a wire connector (Marr type), or where the wires are held in place by a screw which requires a crimped terminal connector. Soldering may be the only way to ensure a reliable electrical connection. The best method of connecting wires to the controller is a box type pressure connector where the wires are compressed by a screw.

Electrical Codes
Most electrical codes (including the Canadian and the American Codes) require that all electrical connections are done inside an enclosure to prevent the possibility of accidental shorts. Ensure that the controller you purchase does not have any exposed connections and that it can be easily mounted into an enclosure.

Voltage Set Point
A battery¼s full state of charge voltage is dependent on the charge rate and the temperature of the battery. While achieving an exact voltage setting is not critical for small systems (under 15A) we recommend controllers that have adjustable voltage set points. Some controllers feature automatic temperature compensation to adjust the voltage set points based on battery temperature.

Indicator Lights
Many controllers have LED indicator lights. Indicator lights are good for showing the stage the charge controller is in and the approximate battery state of charge. LEDs are an inexpensive means of monitoring a small PV system. However, the use of a good charge source ammeter and a battery voltmeter is more valuable and larger systems should have accurate meters.

If your power system has no means of equalizing other than the renewable energy source it is important that you can bypass the charge control function so that an equalization charge can occur. If the controller does not have a bypass then it will be necessary to disconnect the controller when you equalize your battery.

Temperature Compensation
If the battery bank is exposed to temperatures of greater than 30fC or less than 0fC then the controller should be temperature compensated. A temperature probe is attached to the side of the battery and the controller will automatically adjust the voltage setpoints based on the temperature. Some controllers attempt temperature compensation without a remote temperature probe. This is not recommended since the controller may be at a different temperature from the battery.

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