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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 result. Voltage regulation is typically achieved by either the stopping the wind turbine by shorting the generators EMF or by diverting (dumping) the power into a resistive load (heater). A universal 4-stage dump-load charge controller circuit (with load) was designed and built for ~AU$140
Keywords: wind power, wind turbine charge controller, battery voltage conditioner, overcharge protection, wind turbine voltage regulator
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LIST OF FIGURES
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Figure |
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Page |
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1 |
12 Volt, 600 Watt dump-load charge controller circuit diagram |
2 |
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2 |
100 Watt 2 Ohm (dump-load) resistors mounted on a heatsink |
3 |
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3 |
Typical dump-load voltages in a 12 Volt system |
3 |
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4 |
Fully assembled 12 Volt four-stage 600 Watt dump load controller |
4 |
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5 |
Electronic components |
4 |
1. Design of the dump-load controller
Dump-load circuits are not complex, this one has been assembled on veroboard, 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.
Figure 1. 12 Volt, 600 Watt dump-load charge controller circuit diagram
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, 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.
2. Assembling the dump-load controller
Figure 2. 100 Watt 2 Ohm (dump-load) resistors mounted on a heatsink
Four separate loads (figure 3) 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.
Using the trimpots, the dump-voltages have been set between 13.75 volts to 14.4 volts as below
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relay |
on-voltage |
off-voltage |
resistance |
power |
total power |
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1 |
13.9v |
13.75v |
2 ohm |
100W |
100W |
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2 |
14.0v |
13.85v |
2 ohm |
100W |
200W |
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3 |
14.2v |
14.05v |
1 ohm |
200W |
400W |
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4 |
14.3v |
14.15v |
1 ohm |
200W |
600W |
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
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� Qty |
Part |
Description |
unit cost |
cost |
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4 |
LM311 |
Comparator |
$1.75 |
$7.00 |
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4 |
BC547 |
NPN Transistor |
$0.26 |
$1.04 |
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1 |
7808 |
Voltage Regulator � 8.0 Volts |
$1.65 |
$1.65 |
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4 |
5k |
10-turn trimpot resistor |
$1.75 |
$7.00 |
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9 |
1N4004 |
Diode |
$0.13 |
$1.17 |
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1 |
1N4752 |
Zener diode � 33 Volts |
$0.55 |
$0.55 |
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1 |
L8 |
25x15x10mm Toroid Core |
$1.75 |
$1.75 |
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28 |
- |
Resistors |
$0.06 |
$1.68 |
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15 |
- |
Capicators |
$0.35 |
$5.25 |
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1 |
- |
305mm veroboard |
$11.50 |
$11.50 |
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Total |
$38.59 |
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Figure 5. Electronic components
3. System cost (AUD)
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
4. Additional Notes
1 - The heatsink gets warm with only a single fan cooling it, adding a second fan would increase cooling and reliability.
