Parasitic Wind Turbine




Posted in WorkshopEnergy

Introduction: Parasitic Wind Turbine

About: Working my dream job in the Telecom industry, so chances are, i'll never have time to respond to comments or messages, nothing personal.

This was built as a lark, a whimsical attempt to recapture some of the hundreds of dollars I spend on air conditioning each year. It's a wind turbine powered by the compressor fan on my air conditioning unit.
But, It is a ponderable notion. And you could reverse the rotor, add a tail and yaw bearing and make a regular wind turbine.

Step 1: The Alternator

I started off by messing around with a stepper motor I had, it was rated 6 volts 0.4 Amps per phase and was a two phase motor, meaning max input would be 4.8 watts. So running it backwards could I get that much out?

I'm not really an electronics guy, so I stuck my meter in AC mode across the terminals, spun it with my fingers, and got a reading of 50 volts! On current it read .2 amps. Umm okay, never mind the meter, would it light LEDs?

So wanting to see if it would light LEDs I wired 5 red LEDs together, four as a full wave bridge rectifier and the fifth as the load. As you can see in the video and pics, it had no problem lighting those LEDs, nor the five super bright white LEDs arranged in the same manner.

Step 2: The Rotor

In the vein of keeping the design simple I wanted to have a simple rotor. My solution was to pull the blade assembly off of a cheap box fan that had reached the end of it's life. The rotor had been attached to the fan on a 1/2 inch shaft. To accommodate the 5mm shaft on my stepper motor, I press fitted a half inch dowel into the fan and then bored a 7/32nds hole through the dowel, and split the end of the dowel with a razor saw to allow the use of a hose clamp to secure the fan to the motor shaft.

Step 3: Housing and Mount

The housing and mount are made from PVC, the housing is made from two 2" end caps, a 2"ring to align the caps and hold the motor in place and a 1/2" elbow cut down to attach the housing to the mount. The two end caps are held together with aluminum tape.

Step 4: The Load

The load is a group of five LEDs per phase arranged as a full wave bridge with the fifth as the load. Instead of poorly drawn schematics, I suggest you read this wikipedia article. Here are some pix.

Step 5: All That's Left

Is to place the motor mount onto the stand and place it on top of the compressor. adjust for best RPM and you are good to go. You might note that contrary to expectations, ie, that you could just set it on top in line with the fan, the best RPM comes from an offset 45 degree placement.

Addendum, I constructed a diode bridge with diodes salvaged with from a CFL and replaced one of the LED loads and recorded an open circuit voltage of 10 volts. Now here's a question for smarter people. Could I put the two phases in series for an OCV of 20 and charge a 12 volt battery?

Step 6: Acknowledgements

These persons are directly or indirectly responsible for this project.

William Kwamba for his inspiration

Alan Parekh who provided the LEDs.


The Reuk website for the info on steppers.

Step 7: Addendum

Not as neat as I'd like, but I bodgered up the turbine in conventional form for those who might be interested, alas Code Enforcement would be all over me if I actually installed a wind turbine.

PVC fittings
broom stick boom
road spam tail
bamboo stake for yaw bearing.

All held together with screws.



    • Microcontroller Contest

      Microcontroller Contest
    • Spotless Contest

      Spotless Contest
    • Space Challenge

      Space Challenge

    We have a be nice policy.
    Please be positive and constructive.




    I'm sure the extra load on the AC is negligible since, with the turbine on top, in open air, it is not a closed system. Unlike the turbo which has a restricting conduit that does not give the exhaust an alternative path to spooling the turbine.

    1 reply

    I agree, I believe the unit is already loaded by " Sucking" air through the coils.. the fan appears high enough to not restrict the air flow out of the collar of the unit ( for lack of a better word, much like the back side of a house fan, at least on my ac unit it has a cone in which the fan sits slightly in front of)

    Soooo.... I dont know that much about steppers... Whats single phase vs. dual phase? Also with a stepper that i know has 2 dc power inputs, would those 2 dc inputs (when the stepper is used as a generator) output dc? or AC? if ac... HOW DO I MAKE A FULL WAVE BRIDGE RECTIFIER?

    1 reply

    you can check You tube or perhaps search here, a full wave Bridge will change AC into DC Current. I am sure Wikipedia has something on the subject also.

    It would be more efficient to just run the LEDs from a wall power supply because you are robbing Peter to pay Paul. You are making the A/C blower motor work a bit harder by putting that resistance over it. The A/C blower only runs when the A/C condenser coils reach a certain temperature. By putting resistance in the path of the cooling air, you are just delaying the blower motor from shutting off by some amount and make it run longer. You need to make the system do *less* work, not *more*, to get a savings. In dry climates, I've used a water mist on the intake air into the A/C outdoor condenser unit to make the heat exchange more efficient. This allowed the A/C to run more efficiently. At the cost of the water I was spraying anyway. There is no free lunch.

    2 replies

    My thought exactly on adding resistance to the condenser motor. Spraying water on the condenser coils will certainly improve the system, but at the risk of leaving hard water deposits fouling the coils.

    Hard water. Good point. Maybe I should have taken the condensate from the inside evaporator and sprayed that water instead as it should be much more scale free than tap water having lost the scale when it became humidity in the air.

    I stuck an old 140mm PC fan over my Trane unit and at best generated 4v at 20ma. Cool idea, I'm gonna build by own with a 200mm fan.

    I must admit to not knowing much of anything about this but wouldn't it be more efficient if the blades of the fan were parallel to the exaust fan of the ac?

    I got the idea for using a fan when, a few years ago, I bought a small electric fan and walking to the car I noticed the breeze I was generating by walking slowly was spinning the blades of the fan.

    What about adding two more at 1/3 of the angle? Like a PEACE sign

    I was mislead by the amount of torque you were applying to light the LED's, -and I want to know how hard the wind was blowing for this picture.
    I have some steppers laying-around, and your 'ible has got me thinkin'!!!

    All I can say comes from the fertile-mind of Robert Heinlein:

    To answer your question about phases. Two voltages are only 'summing' if their phases are the same. 180 degrees out of phase would be subtractive, so you would get less power out. 90 Degrees out of phase would give you no effect. You may be better to generate two DC outputs and put those in series (provided that the source resistance is high enough). The other alternative is to look up inductors and capacitors and their corresponding phaser math to offset your motor phases enough to make them additive. I hope that gets you started--doing the vector math isn't hard when you have the circuit in front of you... if my memory serves me right, capacitors are:

    Z = -[j]/ [(omega)*(Capacitance) or Z = 1/[(omega)*(Cap)] < -90 degrees
    and an inductor is

    Z = [j]*(omega)*(inductance) or Z = (omega)*(Ind) < +90 degrees

    if you want something to work on then try this take a mirrored satellite dish and put in the center of it a mirrored tube at the focal point must be a mirrored cone shape or small dish your choice sending the light down the mirrored tube into the basement straight into the mirrored box i am using a frig, solar panels are inside of frig i used rollers from a desk to slide solar panels back and forth for cleaning if they need it .small fan takes the hot air out cooling system will cause sweat sending the light into the mirrored box is a GOOD IDEA BUT NOT THE GREAT ONE I AM WORKING NOW.

    OK, I'm just a housewife, never studied thermodynamics or physics, so don't rake me over the coals. In NC, I use my heat pump AC from March (sparingly) to November (again sparingly), with the heaviest usages from last week of April to 3rd week of October. In the worst part of the year, the AC runs CONSTANTLY - not only heating, but pulling out humidity. My condenser unit is under my deck, on purpose, to eliminate freezing over when we get our wonderful ice storms. There is a six foot clearance vertically, and I can tell you when I walk across that part of the deck, especially in a skirt, there is still a strong wind current - certainly enough to power a turbine. I bought a unit a full 1/2 ton larger than my neighbors ( I have 3080 sq/ft heated space, so I got a 4 ton unit), which only cost me about $100 more, and my electric bill is always, year round, cheaper than my neighbors by 10% +/-; my EPP is $199/mo., and the 12th month they always owe me, most years I only pay 10 1/2 months of electricity. I haven't even thought about salvaging the heat loss, because it seems to me it would be complicated and expensive, but maybe that's just me being ignorant. But seriously, if you're wont to create a wind generator, in my climate, this would be an absolutely dependable source of 'wind' to power one, and you wouldn't have to worry about damage due to the HAWT or VAWT being too close to the unit - 6 feet will still 'get her done'! This instructable is the closest thing I've seen to date for someone thinking to salvage this unused energy. Get to work boys, I want to see something real - I'm closing in on retirement, and I still can't get rid of the kids and their electronics.

    where can i buy the generator thingy? ive been lookign around and cant find it.

    All the comment relate to the 2nd law of thermodynamics.  The resultant of any process will always be less that the amount of energy you put into it!

    You tap energy off a condensing unit, you'll get less energy out of your process, and increase the amount of energy the condenser uses.  There's just no way around it!  There's no such thing as 'free energy".

    2 replies

    'honeybees can't fly per law of aerodynamics'
    dm, the energy being tapped is the dump/waste heat energy. there is no strain on the condenserunit as it is designed to push air away from said unit to remove the excess temperature, aka cooling effect.
    if anything. the small fan blade assists in moving the air by deflecting it.

    I would have thought that the fan on top once it got going if it had no load or very little load, it would have helped to draw the air away from the AC unit's fan because it would be pulling air upwards to keep it spinning?