Using SunAir for Wind Power Control

December 12, 2014 Arduino, Project Curacao, Raspberry Pi, Solar Power, SunAir, SwitchDoc Dual WatchDog Timer, Wind Power

Using SunAir for Wind Power Control

Sun Air is now available here.

The latest SwitchDoc Labs Kickstarter project is SunAir, a board designed to charge LiPophoto-1024x768 batteries from Solar Panels (Solar Power) and power your Arduino as well as a Raspberry Pi.  SunAir, however, is a very flexible charge controller.  With a small amount of additional circuitry, SunAir can control a Wind Turbine.IMG_1223 copy

Second SunAir Kickstarter Update (with Video) (Dec 10, 2014) Published here.

In this design we are using a 50W Wind Turbine.  It’s not a very good Wind Turbine, but it was what we had.  The very minimal specifications say in perfect conditions we can get 2A at 25V which is 50W. However, if we aren’t taking 2A (which at 6V would be 8.3A!), the voltage goes up.  This means that you can generate far more than 25V in the worse case condition (we call this the “Open Loop” test condition – 50WWindTurbineOpentesting the turbine with no load connected).   To test this, we placed the 50W wind turbine in a car, drove at fixed speeds (on a windless night) and generated the curve to the right.  You can see that the voltage exceeds 40 Volts at 50 MPH.  This means we need to build a circuit that can handle a worst case of 40V at 8A.  In actuality, this is an overkill, but not by as much as you think.  If you have a fully charged battery, SunAir will stop taking current, which makes it look very much like an “Open Loop” no-load circuit.

 

SunAir Interface

Since SunAir is designed to take a maximum of 6V and a maximum charge current of 1A, we need to add two pieces of hardware.  We added an over voltage circuit on the Wind Turbine side of the DC/DC regulator (We used a DROK® 3A/18W DC Buck Converter Car Regulated Power SuppIies 9-22V 12V to 6V available on Amazon – this device has a maximum input voltage of 22V).  Below is our Block Diagram.

Wind Power
Wind Power to SunAir Block Diagram

Over Voltage Protection

The wind turbine is rated at 50W, but we aren’t going to trust the number. We built one using TVS diodes and made sure we sized it for about 4A@25V (100W) to cover hurricanes (although in a hurricane, that will be the least of our problems – We would expect the Turbine to be halfway to China by then). We did this by getting a 50W 5 Ohm resistor and putting 10-5W TVS diodes in parallel. TVS diodes operate by shunting excess current when the induced voltage exceeds the avalanche breakdown potential (about 20V in this case). It is a clamping device, suppressing all over voltages above its breakdown voltage.   This protects the 12V (22V maximum) to 6V voltage converter.  Like all diodes of this type, it automatically resets when the over voltage goes away.

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We set the over voltage protection at 20V to avoid this problem.

This is a good link for a diode based over voltage protection circuit.

Below is a picture of the hand wired voltage protection circuit in Project Curacao.

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We took this circuit and ran it for months on Project Curacao with the 2nd Generation SunAir Charger.  It survived 35 MPH winds, but never experienced a hurricane, luckily.