MOTHER's MICROHYDROELECTRIC PLANT REVISITED

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The variable-pulley arrangement used a drive belt roughly four inches wide, and an impressive amount of heat was released by the hardware during operation. Heat means friction, and it was obvious that our watts were being used to warm the generator shack (as it turned out, about 300 watts were going to friction). On top of the inefficiency of the mechanical control, its response lagged behind drastic changes in load, allowing transient changes of cycling to as low as 52 and as high as 68 hertz. The final blow, though, was the cost of the system: roughly $3,000, custom-made.

When we substituted the Winpower alternator for the Kato, we changed the speed control to an electronic load diverter, which we bought for $575 from Hydro-Watt, Inc. This device maintains a constant output from the generator by switching the load between the demand circuit and a water heater (or other resistive load). Now, when we call for lights in the log cabin woodworking shop, the electronic panel automatically diverts power from the water heater and delivers it to the shop.

Building an Electronic Speed Control

George Ruppert's electronic speed control can be built almost entirely from parts available at a local Radio Shack. The triac and its heat sink, however, will have to be obtained through an electronics supply house. Bear in mind that these components will have to be sized according to your system's output. Because the maximum current our generator can produce is a little less than 20 amps, and the peak voltage could be about 230 in a severe overspeed condition, George picked a 40-amp, 400-volt triac to allow a generous margin of safety. (Also, the model George used doesn't require insulated mounting screws, which reduces the chance of failure and shock.) The triac you choose should have a control current of 50 milliamps or less.
Very briefly, the device is a voltage sensor that controls the portion of each cycle in which power is delivered to a resistive load (a water heater). The power supply transforms 120 VAC to 12 VAC, and a bridge rectifier dips the alternating current pulses. The power supply has three outputs: a line pulse to control the two-part timer, an 18-volt output that varies with generator voltage, and regulated 5 VDC. A comparator circuit supplies a variable current, the level of which depends on the deviation from 18 volts, to the front half of the LM 556 timer. A potentiometer on one side of the comparator allows the voltage to be adjusted. The length of time that the first timer stays on determines when the second timer sends a signal (of about 85 milliamps) to the triac. Only when activated by the second timer does the triac send power to the water heater. And, because the triac resets each time voltage crosses zero, the amount of current delivered to the water heater is in proportion to the point in the sine wave where the second timer tells it to kick on.
A few precautions about the device: The 120-VAC neutral ties from the transformer across to the triac, so the circuit board of the controller could deliver a dangerous shock. Bear this in mind when you're fiddling with the board or adjusting the voltage. A protective cover, with an access hole for the voltage-adjustment potentiometer, would offer worthwhile protection. Also, the heat sink for the triac must be large enough to dissipate heat adequately, or the triac will fail to switch. Be sure to use a large heat sink (Fair Radio Sales Co., P.O. Box 1105, Lima, OH 45802, is one low-cost source), and apply the triac to it with heat-sink compound. Finally, the load that the triac supplies should be resistive (as is our water heater), because a reactive load may require phase correction.

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