AC to DC step-up/step-down power transmission system.

Discussion in 'The Projects Forum' started by teneagles, Nov 29, 2009.

  1. teneagles

    Thread Starter New Member

    Nov 29, 2009
    First off, while I am a total newbie to the theory of electronics, I have however built many practical devices from the proper store bought components. So if you start talking inductance values or resistance or the like, my eyes are likely to glaze over. However, if you say "use this, solder it to that, in series or parallel to the other thing, bolt it there, adjust to three turns or 3 ft pounds of torque", Ill be just fine, especially if pictures accompany the advice.

    In this project, I want to take power from a windmill that uses a 110v treadmill motor to produce the juice, to a charge controller 300-400 feet away, that takes it in as 24v DC to the battery bank. The motor is permanent magnet, rated 8 amps, so when spinning backwards should produce 8 amps output.

    I envision doing this by placing a 4x wound AC transformer for the step-up at the windmill, using the smallest possible line for 440v between the two points, and then having a step-down from 440v to 24v, and then having a rectifier to DC.

    If this is incorrect, feel free to correct me. If I am not incorrect, then what I need to learn is how to build the transformers. The rectifier I figure I can scrounge out of an old alternator. If there are usefull inexpensive transformers that can be taken out of other junkyard electronic devices that would suit and save time, please, by all means tell me what devices to look for. I once used the magnets and the entire sttor out of old microwaves to get what I needed for a project, so I am not afraid to scavange.

    Otherwise, does anyone know of some good links that have SIMPLE to use and understand design formulas or even plug in the numbers modules, that can help me figure out magnet types I can use, wire sizes for the loads I am speaking of, formulas for the 440v-24v step-down wraps, etc...?

    Thank you in advance

  2. SgtWookie


    Jul 17, 2007
    It's a good basic idea, and very likely do-able.

    However I'm afraid that you will have to dig deep, and really start understanding electricity/electronic theory before taking on such an ambitious project.

    This is not a "solder tab A into slot B" kind of thing. We just can't go into that much detail.

    Rather than go from 110VDC to 440DC, you might consider going from 110VDC to 480VAC at moderately high frequency, perhaps 400 to 1KHz or so. 400Hz 3-phase 115vac is typically used on aircraft. Higher frequencies are OK for short distances. The higher the frequency, the smaller the size of transformer that you will need. It will have to be a custom-designed transformer if you are going to use other than 60Hz or 400Hz.

    You'll basically need a power inverter at the windmill side to convert the 110VDC to 480VAC. Then instead of your line current being 8A, it will be 1.83A.

    Then you'll need a step-down transformer and bridge rectifier circuit at your battery bank. Again, if you are using non-standard frequencies and voltages, you will need a custom-designed transformer.
  3. JDT

    Well-Known Member

    Feb 12, 2009
    I agree, interesting project. Something I have always wanted to get around to.

    Before you get too carried away with your electrical design I would do a simple experiment to see just how much power your motor produces when used as a generator. Some of these motors are not very efficient.

    If your motor/generator really did produce 110V 8A you would need a load of about 14 ohms. Get a resistor of this value, connect it to your motor and turn it by hand or with another motor (say an electric drill) and find out how many volts you actually get!

    Bear in mind that the wind will not always be blowing a gale. What happens when the turbine goes slower?

    Then do the battery charging design.