Solar Hot Water - Diversion Load Control

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Diversion Load Information

In most hydroelectric and wind-powered battery charging systems, the charging source cannot be disconnected from the batteries while running without the possibility of damaging them from over-voltage. With No Load on them, they also spin out of control, damaging parts.

The typical way to regulate battery charging voltage with this type of generating system is to use a “load diversion” type charge controller.

Example Charge Controllers with Diversion Mode:
· Morningstar TS45 and TS60
· Xantrex C-35, C-40 and C-60
· Outback Power MX60
· Plus Many Others

A diversion-type charge controller also may be used in a PV system. If the array is much larger than necessary to charge the battery, excess power can be used to heat water by using a water heating diversion load. In operation, when battery voltage reaches the full charge setting in the charge controller, it begins to divert power to the diversion load. The controller uses pulse width modulation to turn the load on just enough to keep the battery voltage from rising further. To determine wattage of these diversion loads at other voltages, use Ohm’s Law: voltage = amps x ohms. The critical requirements are that the diversion load can dissipate more watts than the charging source can deliver, and that the maximum amperage that the load can draw is smaller than the maximum diversion rating of the charge controller. Order one or more loads with a total current (amps) draw greater than your charging system’s maximum output, but no more than the maximum power rating of the charge controller in the diversion mode. We recommend that you do not use a load that draws more than 75 percent of the maximum rating of the charge controller. For example, if the charging source can deliver 20 amps at 24 volts, use a 30-amp diversion load with a 40-amp or larger charge controller.

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Trace Engineering Note TN09 on Diversion Loads

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