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Design and construction of a
wind turbine dump-load charge controller

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Abstract
Overcharging lead-acid batteries shortens life and capacity. If the battery voltage is not kept below 14.4 Volts, permanent capacity loss will occur. Voltage regulation is typically achieved by either stopping the wind turbine by shorting the generators EMF or by diverting (dumping) the power into a resistive load (heater).  A universal 4-stage wind turbine charge controller circuit (with load) was designed and built for ~AU$140
Keywords: Wind Power, Dump-Load Charge Controller, Battery Voltage Conditioner, Overcharge Protection, Wind Turbine Voltage Regulator
Figure Page
1 12 Volt, 600 Watt dump-load charge controller circuit diagram 2
2 100 Watt 2 Ohm (dump-load) resistors mounted on a heatsink 3
3 Typical dump-load voltages in a 12 Volt system 3
4 Fully assembled 12 Volt four-stage 600 Watt dump load controller 4
5 Electronic components 4
LIST OF FIGURES

1. Design of the dump-load controller

4 Stage Automatic Dumpload Controller. Circuit Diagram
Dump-load circuits are not complex, this one has been assembled on veroboard and it uses a single IC (voltage comparator) to switch on an automotive relay when the voltage exceeds the pre-set threshold (5k trimpot). Each relay can divert a maximum of 40 Amps through the dump-load resistor, the maximum power per relay is 576 Watts (40A x 14.4V) or 1.2 kW in a 24 Volt system.
The voltage at the battery has significant noise due to the rectification of 3-phase AC-power. The input LC filter removes most of this noise and the Zener diode protects the circuit from any inductively induced voltage spikes. The 7808 voltage regulator supplies power to the comparator and is also the voltage reference for the trimpot. The circuit has 0.15 volts of hysteresis, set by the *500k resistor. Hysteresis can be increased by decreasing the value of this resistor.
Using the trimpots, the dump-voltages have been set between 13.75 volts to 14.4 volts as in Figure 3.
relay on-voltage off-voltage resistance power total-power
1 13.90 V 13.75 V 2 Ohm 100 W 100 W
2 14.00 V 13.85 V 2 Ohm 100 W 200 W
3 14.20 V 14.05 V 1 Ohm 200 W 400 W
4 14.30 V 14.15 V 1 Ohm 200 W 600 W
Figure 3.

Typical dump-load voltages in a 12 Volt system

Figure 4.

Fully assembled 12 Volt four-stage 600 Watt dump load controller

Two pairs of wires (load and sense) connect the dump-load controller to the battery.

5. Comments

Frequently asked questions about plan orders, blade design, electrical work and generator matching can be found on our Q&A pages.
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Figure 1.

12 Volt, 600 Watt dump-load charge controller circuit diagram

Qty Part Description Unit cost Cost
4 LM311      Comparator $1.75 $7.00
4 BC547      NPN Transistor $0.26 $1.04
1 7808      Voltage Regulator, 8.0 Volts $1.65 $1.65
4 5k      10-turn trimpot resistor $1.75 $7.00
9 1N4004      Diode $0.13 $1.17
1 1N4752      Zener diode , 33 Volts $0.55 $0.55
1 L8      25x15x10mm Toroid Core $1.75 $1.75
28 -      Resistors $0.06 $1.68
15 -      Capicators $0.35 $5.25
1 -      305mm veroboard $11.50 $11.50
      Total $38.95
Figure 5.

Electronic components

3. System cost (AUD)

4. Additional Notes

 
1 - The heatsink gets warm with only a single fan cooling it, adding a second fan would increase cooling and reliability.

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Figure 2.

100 Watt, 2 Ohm (dump-load) resistors mounted on a heatsink

Four separate loads (Figure 2) are made from six 100 Watt power resistors. Multiple loads increase reliability. They dissipate low watts in low wind and high watts in high wind, minimising battery discharge. They also have the advantage of requiring a lower hysteresis for reliable operation.

2. Assembling the dump-load controller

Heatsink $20
12 Volt Fan $12
electronic components $38.59
40 Amp automotive relays  (x4)  $24
  2 Ohm  (100 Watt)  Resistors  (x6)  $48

Total cost $142.59
100 Watt 2 Ohm (dump-load) resistors mounted on a heatsink
Fully assembled 12 Volt four-stage 600 Watt dump load controller
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