Line losses A/C vs. D/C

Discussion in 'The Projects Forum' started by floomdoggle, Dec 31, 2008.

  1. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
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    Hi all,
    I finally got my first real windmill built. What I am wondering is, where should I put the rectifier. Right off the motor? Or right before the battery I am charging? I know about wire size, (even though more info would be appreciated), so I will be running 12 ga from the windmill to the battery.
    I had heard that A/C is better to run longer distances. I am talking only about 100'. But the more efficient the better. Figure about 30V max.
    Dan
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Right before the battery.
     
  3. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
    217
    2
    Thanks Wookmeister,
    As always, you are one of the best.
    Dan
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Yes, it is better to use AC for long distances because electrons do not travel around the circuit but they vibrate around a point. In DC electrons travel around the circuit.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here's a voltage drop calculator page:
    http://www.stealth316.com/2-wire-resistance.htm

    If you have a 100' run from the alternator to where the battery is, you'll actually have a 200' loop.

    10A through a 200' loop of AWG 12 will get you a drop of around 3.243 volts.

    If you're using a standard full-wave bridge rectifier, you'll have an additional voltage drop of somewhere between 1.3v to 3v, depending upon your load current and the rectifier's rating. If you want to reduce the loss in the bridge, you might consider using Shottky diodes or a synchronous rectifier.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    The advantage of AC is the ease of transforming voltages/currents. The main disadvantage of AC is skin effect, but that only comes into play for large diameter wire that has to carry high currents.
     
  7. leftyretro

    Active Member

    Nov 25, 2008
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    The advantage of using DC vs AC vs given wire gauge size has to do with 'skin effect' of AC current that tends to travel on the outside of the wire rather then being able to take advantage of the whole wire diameter. This is frequency dependent and may have no particular disadvantage in your case.

    You would have to search for the applicable formula to see if the effective resistance differences is worth the effort. All things being equal, there would I think be an advantage to having the rectifier down at ground level for easier access.

    Lefty
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Skin depth at 60Hz is about 8.5mm. The radius of AWG 12 wire is ≈1mm, so AC vs DC is a toss-up as far as losses are concerned.
     
  9. leftyretro

    Active Member

    Nov 25, 2008
    394
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    I figured 60hz would not be significant, however for a wind powered AC generator I have no clue as to it's frequency. Would vary if it's direct drive or gear driven and of course would vary with the wind speed. So I left the calculations for the OP. ;)
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Good point.
     
  11. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
    217
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    Ron, Lefty, Mik, Wookie,
    Thank you al.
    Dan
     
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