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Charge Controllers

Charge Controllers tame the charging current from the solar panels as it flows to the batteries. They have three basic functions:
1) To properly charge the batteries while preventing them from being overcharged.
2) To prevent power from draining back through the solar panels at night.
3) To boost the useable power sent to the batteries. (MPPT)

While there are over a hundred controllers available, we have tested and sold the following controllers for years.These are the most reliable and each have outstanding performance for their price. We reccommend oversizing the controller, to improve reliability in cold, sunny weather when solar modules can exceed their rated output. A failed charge controller can leave you in the dark, ruin your batteries, or both; don't skimp.

Link to Catalog for Current Listings.

BATTERY (output) VOLTAGE is the nominal voltage of the battery bank. The voltage of a 12V battery bank may actually vary from 10Vto 16V.

ARRAY (input) VOLTAGE is also listed as a nominal voltage. A 12V solar module may actually vary from 0 to 22 volts. So a controller that can handle a 60V array (5 modules in series) needs to be able to handle up to 140V.

MAX AMPS is the maximum rated current the controller can deliver to the batteries. We recommend oversizing the controller by at least 25% more than the total amperage of the solar modules. This allows for intense sun during cold temperatures, when the modules can make more than their rated power.

CHARGING PROFILE:The earliest controllers were considered single stage, and simply turned the charge current off when the batteries reached a certain "fully charged" voltage, then turned it back on once the battery voltage dropped to another preset voltage. Newer 3-stage controllers can charge a battery much more fully. Basically, in stage 1: bulk charge allows full amps to flow until the battery voltage reaches a bulk voltage setting.Then in stage 2: absorption charge, current is gradually reduced while holding the batteries at the same voltage. After a certain time in absorption mode, the battery is considered to be fully charged. In the third stage: float charge the voltage is held indefinitely at a slightly lower voltage. The Outback MX-60 has a refloat setting, which after float charging for a time, recharges the batteries to a voltage higher than the regular float voltage, but lower than the bulk charge voltage.

EQUALIZATION (EQ): In order to keep the individual battery cells in a battery bank at the same voltage, the batteries must be periodically overcharged ("equalized"). This controlled overcharge mixes the electrolyte through bubbling, removes harder crystals from the battery plates, and brings all cells to the same charge.
We do NOT recommend equalizing every month since this process uses extra water and can cause overheating in the batteries. Instead, we reccomend equalizing whenever the batteries have not come to full charge for more than 2 weeks. This way you may not equalize for several months in the summer, but you may actually equalize once a month in periods of bad weather.

TEMPERATURE COMPENSATION modifies charging voltage according to battery temperature. Batteries need higher voltage to fully charge when it is colder than 50º F, they also need lower voltage when hotter than 85º F. If your batteries will not be indoors, they'll last longer if your controller has temperature compensation.

PWM: Pulse Width Modulation means the controller turns the current to the batteries on and off very rapidly, so that overall a lower current flows as the battery reaches full charge. It allows the batteries to reach a fuller charge, and it can pulse sulfation off the battery plates so they last longer.

MPPT: Maximum Power Point Tracking allows solar modules to operate at higher voltage (Their Max Power Point), which is where they produce their highest amount of power, and then it lowers the voltage and boosts the current to charge the batteries. Typically it boosts charging current from the same modules by 10 to 25%. It boosts the most when it is cold outside and the batteries are low. The extra cost of the controller can be worth the gain in power for arrays 400 watts and larger.
MPPT controllers also allow higher voltage arrays to charge lower voltage battery banks, thus reducing the wire losses. (You can move double the power at double the voltage.)
More about MPPT

METER: Shows battery voltage and solar charging current--some also show load current (the amount of amps being used). some show total power and energy produced. For small systems the SCI controller's meter is adequate, but for larger systems we recommend the Trimetric Meter.
More about Meters

Link to Catalog for Current Listings.