PM Generator drains battery???

Discussion in 'The Projects Forum' started by Tech Building, Feb 4, 2011.

  1. Tech Building

    Thread Starter New Member

    Feb 4, 2011
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    Hi, I'm a newbie and this is my first post and already asking help. Please forgive if I am used to metric measurement.

    I'm building a permanent magnet generator using 8 NdFeB magnets (500x200x10 cm), installed on 200mm in diameter iron disc (5mm thickness). The goal is to build a wind generator.
    For coils, I wound 8 coils, 220 wound each, 0.5mm in diameter. The dimension of each coils are 650x26x10 mm. Both magnets and coils are set to 45 deg.
    For testing, I'm using a 12v dc motor.

    When testing, each coils' reading 26vac. I then connect them in series and parallel (leading to 1 phase) and add full brigde 6A diodes. The reading then became 15.8vdc.

    I connected it to a 12V-35A lead acid battery to charge it and here lies the problem. The battery reading before connection was 12.6vdc. When connected, it drops to 11.9 and continues to drop roughly 0.1 volts/minute :eek::eek::eek: until I disconected them when it reads 10.6v.

    The question is of course :confused::confused::confused: why? What am I missing? Can anyone help?

    Some clues or pointers:
    - no heat coming from the coils.
    - almost no heat coming from the diodes.
    - the motor speed drops significantly when connected to the battery.
    - I don't have the gauge to read the motor speed.

    All ideas are utmost appreciated. Thanks.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    We really need to see a schematic of the circuit.
     
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    Are you powering the 12v motor from the same battery that you're trying to charge? If so, that would explain the battery getting discharged.
     
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  4. wayneh

    Expert

    Sep 9, 2010
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    Sarge's explanation is the simplest, but here's another: It sounds like you may have wired your coils and/or rectifier incorrectly, so that some of them are fighting others. I'd expect some winding or diode heat in that case, but I'm still suspicious. It's very easy to lose track of coil polarity (winding direction).
     
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  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Do you have + and - reversed?
     
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  6. Tech Building

    Thread Starter New Member

    Feb 4, 2011
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    Thank you all so much for responding.

    @beenthere: I have the drawing, but failed to upload it here, but it's prety basic though, following hugh piggot's book.

    @sarge: I powered the motor using 1 amps transformer. The motor uses 0.66 amps.

    @thatoneguy: I've double check it following your suspicion and I didn't have them in reverse.

    @wayneh: I suspect what you've suspected too. So I have the coils rewired just to make sure. The results are the wiring is more neat and surprisingly the vdc reading became 19.8v, while the vac reading is still the same.

    However, if hooked to the battery, the generator still draining it. The motor speed drops significantly. No heat coming out from both the coils and diodes. Basically same conditions.

    I'm thinking of hooking up a car power regulator. You guys think it'll help?

    Thanks again. Keep enlighting me.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    It would help a great deal if you would post a schematic on how you have this wired, as "connect them in series and parallel leading to 1 phase" does not paint a clear picture.

    Further, I wonder why you decided on 8 magnets and 8 coils? That configuration, if laid out in a symmetrical fashion, will result in varying amounts of torque required to turn the generators' shaft, which will place strain on the driving blades and cause vibration.

    If you changed to an 8 magnet and 9 coil configuration, the torque requirement will be nearly constant.

    Also, with 9 coils, you can group three coils into a wye configuration; each coil will then require just two diodes. With 8 coils, you will need a full bridge per coil. [eta] (actually, you could parallel a couple of coils that were exactly opposite in polarity, but that would lead to losses if the power generated in the paired coils is not identical.)
     
    Last edited: Feb 5, 2011
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  8. wayneh

    Expert

    Sep 9, 2010
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    Just as it's easy to confuse the coil direction, it's easy to get the poles of your magnets reversed. Worth a check. One thing you might try is unwiring all the coils, and then adding each one back. If it contributes, you've got it right.

    Is this thing designed to produce an identical pulse in all 8 coils at once? If so, any coil or magnet that is reversed will be exactly 180° out of phase and fighting directly with the others.

    Do you have the coils sandwiched between two magnet disks, or just face-to-face?

    Finally, check your rectifier bridge. Take a picture and post it if you can. If it's done properly, no current should ever be able to pass from the battery to your coils. I suspect you've got one or more in backwards, or possibly one has shorted.

    Oh wait, really finally, clarify the problem a bit more: When you hook up the battery, instead of charging, it drains? AND, a load slows the motor you're using to turn the generator? Both observations consistent with the battery powering the coils to act as a brake on the motor. Right?
     
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  9. Tech Building

    Thread Starter New Member

    Feb 4, 2011
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    Thank you all again for responding. This is how I wired everything up. Sorry if the picture is too large.

    [​IMG]

    The 8 magnets is arranged N-S-N-S. On his book, hugh piggot mentioned that for coils that face different poles simply reverse the winding direction and the coils will work together. That's why I had those arrangement.

    This is a pilot project for me, so I didn't sandwiched the coils with 2 magnet disc. Just face to face. Save cost, you know.. :p

    And, Sarge, this is for vertical axis wind turbine. Previously, I made 12 coils and arrange them in 3 phase. It was also running quite well, considering it was in drum model and the air gap was pretty big (8mm), and produced 40vac each phase. However, I dismatled it due to problem with the solid construction. Now, I'm trying to make the construction as simple as possible. I believe it is now pretty solid and shouldn't affect the blade construction later.

    I have found something interesting last night. Each time I turn off everything, there's still a reading of vdc for some zero point something volts, which takes a while to dissipate. As you can see, I haven't add up a capacitor after the bridge.

    Well, again do you think a car voltage regulator would help?

    Thanks.
     
  10. Tech Building

    Thread Starter New Member

    Feb 4, 2011
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    Yes! That is exactly what I think. But I dont know what went wrong. Is it possible that coils with air as cores if powered produces magnetic field that would fight the permanent magnets? If so, then maybe the diodes is the problem and I should buy another set?
     
  11. wayneh

    Expert

    Sep 9, 2010
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    No, you need to solve the problem at hand first.

    Thanks for the drawing. It "should" work, but I'd still bet something is wrong or you've got a bad or reversed diode. How about a picture?
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Yes, absolutely, and in fact it doesn't even need to be a magnet. Lookup "eddy current braking" and you'll see that moving a conductor through a magnetic field takes work. Try rubbing one of your magnets across a slab of aluminum some time. If you try to slide it quickly, you'll feel a strong "viscous" effect, even though there is no attraction.
     
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