Choosing A Charge Controller
Charge controllers regulate the output of solar modules, wind generators and hydroelectric generators to prevent overcharging of the battery. For off grid solar power systems, when battery voltage rises to a preset maximum, where the battery is completely charged, the control automatically reduces or stops the solar charge. Some charge controllers are that simple, but most include some other features like volt & amp meters, voltage conversion, low battery load disconnect or night light timer.
Volt and Ampere Rating of the Charge Controller
Select a control able to handle a little more than the amperes your solar modules are rated to generate. Though solar modules don’t usually produce more than their rated amperes, they can momentarily produce 15% more on cold bright days.
The electric code recommends leaving a 25% margin, that is, for a 47 amp solar array use a 60 amp control rather than a 50 amp control. And if you plan future expansion of your solar array, allow a lot more headroom to accommodate the added solar panels.
Be sure the model you choose is designed for your battery voltage: 12, 24 or 48 volts. A given control will handle twice as many solar modules watts in a 24 volt system as in a 12 volt. Maximum power point tracking “Boost” and voltage converting controllers are rated for the boosted output to the battery, not the slightly lower solar input amperes.
Since a battery voltmeter and solar amp meter are needed to show that the battery is really getting charged, most controllers have those meters built in or optional. We always recommend a control with built-in amp meters and volt meters. User-adjustable battery voltage set points is a feature of most controllers, so voltage can be set exactly for your battery type, temperature and age.
Battery Temperature Sensor is available for some to automatically adjust charge voltage for batteries exposed to large temperature changes. Automatic or Manual equalization, used on flooded batteries gives an occasional overcharge to restore all cells to 100%. The equalization feature is not used on sealed AGM and Gel batteries.
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