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Charge controllers are designed to withstand a specific maximum input voltage. Exceeding this can damage the charge controller and possibly void its warranty.

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Installation & Maintenance Considerations

Ambient temperature refers to the temperature of the air in the room or enclosure where the charge controller— and, usually, the inverter and other equipment— is located. Heat from a working charge controller is dissipated with cooling fins convectively, or is pushed out with a fan, adding heat to the space.

Systems with sizable arrays or with the equipment housed in small rooms require that the room be well ventilated, perhaps even actively with an exhaust fan. Too much heat can affect efficiency or damage the controller.

Equalization is a controlled overcharge of a battery bank. Battery cells are not precisely equal and will come to have different states of charge. The only way to bring them all back to an equal state is to periodically give the whole bank an overcharge.

Generally, flooded lead-acid batteries require this treatment every five to seven deep discharges (50% or more of capacity), or every two months, whichever comes first. The beginning of winter is a good time to do an equalization, as it will prepare a battery for the deeper cycles normally found at this time of year. Equalization also helps mix the electrolyte after watering the batteries, and helps remove old sulfate crystals from the plates. Some types of batteries (sealed) can be permanently harmed if they receive higher-voltage equalization.

Among the featured controllers, the C series products from Xantrex and all the controllers from Apollo, OutBack, and Morningstar offer both manual and automatic equalization. The other controllers offer only manual equalization.

Effective battery equalization requires a larger array than most systems have, so owners often equalize from an external charge source like a generator or the grid.

Morningstar's TriStar charge controller (left) and remote display (below).

increase the charge termination set point for a cold battery and decrease this set point for a warm battery—resulting in an appropriate charging regimen.

Warranty—Charge controller warranties range from two to five years. Although having a long warranty to back you up is great, there are other factors to consider, including down-time and service-related expenses. A product with a long history made by a reputable company may save you money (and time) in the long run, regardless of the warranty offered. All the controllers shown are produced by reputable companies that are known to stand by their products.

Manufacturer Suggested Retail Price (MSRP)—Each manufacturer lists a suggested retail price. This is typically the highest price distributors will list; some may choose to sell at a lower price.

Meters & Data Logging

All the units listed in this article include at least basic displays and metering. (If the meters are optional, the prices shown reflect their inclusion.) The displays provide basic voltage and amperage readings necessary for system checks during installation and, later, for monitoring the array for wiring, module, or even shading problems.

All the units listed display battery voltage, and some models (like Apollo) employ a separate wire to take this reading right at the battery bank. MPPT controllers show array voltage and current, as well as output (battery) voltage and current.

Some controllers show array power production in watts, and many have data-logging functions, which can be especially useful for off-grid systems. For example, data logging that includes "time in float mode" helps system owners know the batteries reached full charge for each day the controller dropped to float mode. A number of controllers can be connected to a computer for real-time monitoring and data collection.

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Justine Sanchez ([email protected]) is a NABCEP-certified PV installer, Home Power Technical Editor, and Solar Energy International instructor. Justine lives, works, and teaches from an on-grid, PV-powered home in Paonia, Colorado.

Brad Burritt ([email protected]) is a NABCEP-certified PV and wind installer, and renewable energy consultant. Brad lives on an off-grid PV- and wind-powered farm near Hotchkiss, Colorado.

This installation by Kent Osterberg of Blue Mountain Solar shows just what can be done in a small amount of space on a limited budget.

The MNE175ALPLUS combines the charge controller and inverter on the door for a truly compact and tidy installation. Price $639

"Professional looking installations require quality products," says Kent Osterberg

425-374-9060 "'^LJ^ www.midnitesolar.com 17722 67th Ave NE Unit C, Arlington, WA 98223

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