Wind generator breaking circuit

Discussion in 'The Projects Forum' started by ocelot28374, Apr 16, 2012.

  1. ocelot28374

    ocelot28374 Thread Starter Member

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    I am having a problem with my off grid wind generators. The "moderately" high winds in wyoming are wreaking havock on my turbines. I have burned up 12 turbines from the built in breaking action of commercial controllers and over speed.

    I have a background in troubleshooting but not design. I am a technician not an engineer.

    My system is 24 volts DC, 27 volts float, 28.4 volts Bulk charge. I would like to use this voltage variable to control an electromagnetic breaking device on the turbine rotor. with no application at 27.0 volts and adjustable application at 28 volts and higher to reduce turbine output and prevent over speed when the battery system has reached full charge.

    This would have immediate commercial applications to which I have no interest. I would just like access to test and use the design.

    The circuit should have adjustable input variables and adjustable output current.

    I hope someone can help me with this challenge. Contact me with questions, I can provide pictures of the turbines i will use for testing and help with physical design. I can also help with concept.

    Thank You
  2. Felo

    Felo Member

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    Hi, I am just thinking out loud here but I find this very interesting, tell us how does the built in break woks, (or pictures of it) is it a mechanical device like a motorcycle break? (I have no idea I'm just telling something).

    But then a vehicle break with hydraulic pump action may be just what you need, it should be easy to build a "electric push rod" with threads and nuts and control it by monitoring the voltage output of your turbines.

    Another thought is to attach a dc motor with a "upper H" PWM drive as to control not the speed of the motor but PWM control it's breaking action.

    Does these turbines have a "high side" spining speed limit? are the winds there so strong as to destroy the turbine if left spining free with no breaking action? the excess energy can be dealt with by making a SMPS wich can take a huge voltage and then regulate it for you at desired levels.

    Just a few ideas
  3. #12

    #12 AAC Fanatic!

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    Is the basic concept to redirect the excess energy so it works against the velocity of the blades?
  4. wayneh

    wayneh AAC Fanatic!

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    Search on wind BRAKING. This is at least the second thread on this topic in the last month.
  5. ocelot28374

    ocelot28374 Thread Starter Member

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    most common small wind turbine controllers brake the turbine by shorting out the coils in the stator, other controllers accomplish loading the turbine by applying a diversion load in place of the battery bank or in parallel to the battery bank. what I would like to accomplish is physical braking of the turbine with a current controlled device such as an electromagnet with spring loaded rollers to apply resistive force to the rotation of the rotor without stopping it. this would effect a change in output current from the turbine that would limit the applied charge current automaticaly allowing the turbine to opperate in high wind conditions at much lower RPMs than the diversion load would allow as well as preventing the turbine from burning up from an exess of current from the stator coils or burning it up by trying to stop or slow the turbine by shorting out the coils. both situations I have encountered already. Also, brake pads applied by mechanical force wear out quickly and must be applied by hand. by using a device such as described the turbine would be prevented from overspeeding by physical force but not applied by manual means.
  6. ocelot28374

    ocelot28374 Thread Starter Member

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    wayneh, Thank you for the search topic. I found a few threads but they seem to deal with shorting the turbine. in high winds this has always resulted in terminal damage to the stator. I am always looking for way to make improvements to my system, any advice would be greatly appreciated
  7. ocelot28374

    ocelot28374 Thread Starter Member

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    #12, in short yes..
  8. ocelot28374

    ocelot28374 Thread Starter Member

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    Felo, "attach a dc motor with a "upper H" PWM drive as to control not the speed of the motor but PWM control it's breaking action."

    Please forgive my ignorance but I dont understand what you are saying.

    as for the turbine control it is fairly simple, on my system the controller uses a diversion load in parallel to the batteries when the voltage has exceeded a set point. the turbines in high winds can "over run" the load and continue to provide current to the batteries, over speeding and the burning up in the process. a larger diversion load does provide for more current absorbtion but has the side effect of drastically effecting battery bank voltage and switching between over run and under voltage conditions. damaging the controller and the turbine in the process
  9. wayneh

    wayneh AAC Fanatic!

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    The hard part is the mechanical braking system. The electronic control stuff happens at very low power and voltage. Even the translation of the control signal to higher power to drive a brake is relatively straightforward. But then what?

    I know a recent thread on this topic was definitely about a mechanical brake, not electrical. Can't say it will help.
  10. Ron H

    Ron H E-book Developer

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    Do your blades have pitch control?
  11. ocelot28374

    ocelot28374 Thread Starter Member

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    Ron H, No.. 1600 watt small turbine fixed prop.
  12. ocelot28374

    ocelot28374 Thread Starter Member

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    wayneh, once the output current drops battery bank voltage drops releasing the braking effect. to cycle again when voltage rises to the preset braking level. lead acid batteries above nominal ie, 2.1 to 2.16 volts per cell fully charged or in this case, 25.2 to 25.92 lose the excess voltage quickly. my idea is to keep the battery bank in between float voltage 27.0 and absorbtion voltage 28.4. after 28.4 volts the internal resistance of the batteries presents a situation that to the turbine looks almost like an open circuit (just observational not actual). allowing more over speed and more current to be generated which results in large amounts of heat in the turbine causing cascade failure of the coil shorting the stator.
  13. Ron H

    Ron H E-book Developer

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    I don't see how rollers can effect braking unless there is friction (e.g., brake pads). Braking has to dissipate power somewhere, and it will show up as heat, no matter how you do it (in the absence of a gearing mechanism such as prop feathering).
  14. ocelot28374

    ocelot28374 Thread Starter Member

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    By providing rolling resistance. at some point if the electromagnetic force overcomes the spring tension the face of the braking assembly would come into contact with the rotors breaking plate, simular to a disk brake. that would stop the rotor completely. the rotors force would be overcome by the pressure from the rollers until it slowed gently. maybe rollers with inertial resistance. a wear pad could be placed on the face of the assembly to avoid damage to the magnet.
  15. ocelot28374

    ocelot28374 Thread Starter Member

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    wayneh, Could you please elaborate on the electronic control circuits?
  16. ocelot28374

    ocelot28374 Thread Starter Member

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    Ron H, I dont have the machining skills to make a variable pitch rotor.
  17. wayneh

    wayneh AAC Fanatic!

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    To define the controls, you need to specify the input conditions that lead to the output conditions, all in terms of voltage, current, rpm, whatever details you can provide. Since the output will depend on the needs of the mechanical braking system, that needs to be figured out before that final stage of the electronics can be designed.

    Your control points will probably be in terms of voltage, and that's fine. Even a current flow can be converted to voltage by looking at the drop across a resistor.

    The folks here are pros at figuring out how to turn your voltages into actions.
  18. ocelot28374

    ocelot28374 Thread Starter Member

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    The control signal as it where would be the voltage differential from 27 volts to 28.4 volts or higher depending on battery state of charge and turbine output. that differential should drive a circuit that would drive the electromagnetic device. an off the shelf device from the hardware store used in wheel brakes on a trailer. it can handle varying currents and provides a small foot print for mounting on a plate for the mechanical system. the control circuit could then control a varialble current driver getting its supply from the battery bank (950 Ah) at regulated voltage between 25.9 to 28.4 volts.
  19. williamj

    williamj Member

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    ocelot28374,

    What comes to my mind is a seperate wind speed indicator controlling a magnetic brake. Magnetic brakes are used in industry all the time. They are, however, very expensive. But if you built your own windgen you can build one of these.

    Physically attach the wind speed indicator(wi) to you wind turbine(wt), the wsi will controll a Pulse Width Modulator(PWM), the PWM will control coil voltage to the magnetic brake thus varying the magnetic field strength of the brake directly proportional to the speed of the wind.

    The faster the wind the higher the magnet field the slower the turbine is allowed to rotate.

    I am not very good with intergrated circuitry but the fine folks here are and they are more than happy to help you like they've helped me and many others.

    williamj
  20. shortbus

    shortbus Well-Known Member

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    A problem with a mechanical brake that may come up is, instead of burning out stator coils you will then start breaking blades. Using permanent magnet generators is a cheap solution but one with a problem with regulation. Because you can't easily regulate the out-put.

    Not knowing what type of generator your using, either a radial or axial style, can you tell us? There is a way of regulating that isn't well known but seems to work pretty well called "field regulation". This is where you add a coil around the stator and put a current through it to counter act the current made in the stator. In effect it counter acts the fields of the rotating permanent magnets. Their using it in some PMDC motors for EVs to create 'field weakening' to get more speed from the motor at light load.
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