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12v ac 300w wind turbine.

Discussion in 'Renewable Energy' started by Steve K, Mar 8, 2016.

  1. Steve K

    Steve K New Member

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    I have been given a 12v ac 300w wind turbine and would like to charge a 12v dc battery in my caravan with it. I realise that I have to change the ac current to dc then control and dump the excess to prevent overcharging.

    Where do I get a big enough ac to dc converter and controller from. Could someone point me in the right direction please
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Welcome to ETO!
    Does the turbine already have an output controller? Normally the output voltage would rise with wind speed.
     
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  3. Steve K

    Steve K New Member

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    Hi alec_t
    Thanks for coming back so quickly. No controller that I am aware of just 3 (red,blue, green) .wires coming from the underside of the turbine . All I have done is unpack and assemble the unit . My next step will be to put a multimeter on it and see what is being produced. The markings on it are 12v ac 300w.
     
    Last edited: Mar 8, 2016
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    If it really is only 12Vac, by the time you subtract two forward drops of rectifiers (about 2.4V for a full-wave-bridge) you will not have enough to charge a 12V battery, which requires up to 14.6Vdc during charging...

    The open-circuit AC voltage out of the dynamo should be 15 to 20Vac to make this work...

    Check to see if the third wire is a field winding that controls the AC output...
     
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Um what?
    12 x √2 = 16.98
    16.9 - 2.4 = 14.68

    BTW those must be some pretty crappy diodes to have a forward drop of 1.2 volt each. :(
     
  7. Colin

    Colin Member

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    12v AC may be just enough to charge a 12v battery.
     
  8. Prismseed

    Prismseed New Member

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    Newb question,

    Even if it isn't enough voltage could a capacitor store up current over time and intermitently release pulses of volts to charge the battery?
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    With 12Vac out of the generator, the charging current only flows during about 10% of the AC wave, only during the peaks. The average charging current will be less than 2A, far from the 300W the generator is supposedly rated for.

    This 25A FWB rectifier has a forward drop of 1.1V per leg at only 12.5A.
     
    Last edited: Mar 8, 2016
  10. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Yes as I said pretty crappy rectifier choice. Especially so for a higher powered application. :(

    http://www.digikey.com/product-detail/en/diodes-incorporated/SBRT60U50CT/SBRT60U50CTDI-ND/5149285 520 mV @ 30 amps. $1.57 :troll:

    Have you ever tried hooking up a honest 12 VAC high current capable power source through a basic full wave bridge rectifier with modern specs into a 12 volt battery? :rolleyes:

    Believe me under voltage and low current supply are not a problem. Overvoltage overcurrent and a cooked battery are. :facepalm:

     
  11. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Is not a full wave bridge. You would have to use three of those devices to make a FWB. I cannot find a ready-made 200V 25A Schottky FWB on Digikey.


    Yes, and it takes a transformer with a minimum or 14Vrms secondary to make a useful battery charger. 12Vrms wont hack it.

    Isn't that what regulators are for? If you hook a windpower AC generator to a battery with only a rectifier in between, you are guaranteed a spoiled battery.
     
  12. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Yes I am aware they are single diodes and to make a three phase full wave bridge would require 6 not three. Three would still be a half wave system on three phase. Even at that with two in series to make a full wave bridge they are still under the 1.2 volt per diode value of the unit you referenced.

    Have you ever built a battery charger or 12 volt higher current capable power supply with a 14 volt AC transformer and tried to charge a battery with it? :rolleyes:

    Believe me I have been rebuilding battery chargers since I was in my teens 25 + years ago and I know full well what is required to make a basic reliable battery charger and a 14 volt transformer is not it. It will cook a battery every time unless you are using ancient selenium plate rectifiers or something similar with huge forward drop values when loaded up.

    For a normal safe continuous charging capable system a ~11 volt transformer with diodes that have less than a 1 volt forward drop works very well being it puts the peak voltage right in the 14 - 15 volt sweet spot for getting a common 12 volt LA battery charged up without over charging it.

    The only time I would go up to 14 volts AC is for a high current fast charge/booster function that only runs for a short period of time.

    I don't know where you got your theory of alternators and AC to DC conversion from but every time it gets covered here and you comment on some part of it you leave me scratching my head as to how you came to believe what you do.
    I got mine from hands on practical application and basic analysis while working with design repair and redesign of 100's of such systems over the years and anm well known in my parts for my expertize on battery charging systems whether they be generator, alternator, single or three phase AC power based.
    If it charges a battery I have dissected and studied it in detail and Frankensteined it into working for something else probably more than once. ;)
     
  13. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    It sounds like tcmtech is stuck in the world of obsolete buzz-box lead-acid battery chargers, while the world has moved on to automatic, microprocessor-controlled regulated charging systems that implement complex charging algorithms rather than rely only on the transformer design to simultaneously limit max charging current and end-of-charge final voltage. I know I have :smug:

    Back to the TS's original problem. He has a three wire wind machine, the control of which is nothing like a line-powered battery charger. We need to know what the three wires do? Do the three wires come from a three-phase stator winding like an automotive alternator? If so, is the field supplied with a rotating permanent magnet?

    If yes, then because of the large AC voltage fluctuation as the wind speed varies, there will have to be a dual circuit between the wind machine and the battery bank: one to provide charge control for the batteries, the other is a dynamic braking system to keep the wind machine from over-speeding if the batteries are charged and not drawing current.
     
  14. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    And that relates to anything here how being we were discussing the basics of AC to DC conversion to charge a battery and up to now nothing was said about secondary control such as microprocessor controlled systems? :rolleyes:
    Which BTW still have to rely on the physics behind the transformer and the rectifiers plus a pile of other components now at the very heart of their power system regardless of whether they are buzz box transformer or SMPS based. :facepalm:

    And whats with the third person speak now too? :troll:
    Also surprised you didn't go after my spelling and grammar as a way to change the topic in defence of yourself as well. :rolleyes::troll::troll:

    Oh yea and I too have smart chargers as well. I also have numerous dumb chargers as well.
    A few in my collection that are pushing 80+ years old , two of them even use vacuum tubes for rectification!:wideyed:, and still able to their job when called upon.
    Old dumb and inefficient as they may be they still charge batteries to where they need to be because some engineer did his homework and calculations on what transformer voltage he needed to match his forward drops in the rectifiers he used so that in the end the batteries would reach that standard 2.3 - 2.5 volts per cell point that LA batteries like and no higher just like what a smart charger does before backing off into a different charge mode. :p


    So with that yes until the OP gives us some more info on what he has we can only speculate on what is what and how it works.
     
    Last edited: Mar 10, 2016

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